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Letteratura scientifica selezionata sul tema "Pseudopotential model"

Autore: Grafiati

Pubblicato: 19 ottobre 2024

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Articoli di riviste sul tema "Pseudopotential model"

Liu, Fu-Min, An-Lin Wang, Ruo-Fan Qiu e Tao Jiang. "Improved lattice Boltzmann model for multi-component diffusion flow with large pressure difference". International Journal of Modern Physics C 27, n. 11 (29 agosto 2016): 1650130. http://dx.doi.org/10.1142/s0129183116501308.

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The pseudopotential lattice Boltzmann model has been widely used to solve multi-phase and multi-component flow problems. However, original pseudopotential model cannot be used in simulating diffusion flow with large pressure difference because of its limitation. In this paper, we incorporate pseudopotential model with a new form of effective mass to solve this problem based on the relationship between pressure difference and effective mass. The improved model is verified through Laplace’s law and binary immiscible Poiseuille flow. By simulating pipeline binary diffusion flow and two-inlet binary cavity jet flow, we show that the improved model can achieve larger pressure difference than pseudopotential model with traditional effective mass forms.

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Evseevichev, N. I. "Pseudopotential model of glassy semiconductors". Journal of Non-Crystalline Solids 90, n. 1-3 (febbraio 1987): 57–60. http://dx.doi.org/10.1016/s0022-3093(87)80383-6.

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M. Vora, Aditya. "STUDY OF SUPERCONDUCTING EFFECTS IN TRANSITION METALS BASED BINARY ALLOYS USING PSEUDOPOTENTIAL THEORY". Latvian Journal of Physics and Technical Sciences 48, n. 1 (1 gennaio 2011): 42–54. http://dx.doi.org/10.2478/v10047-011-0004-y.

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STUDY OF SUPERCONDUCTING EFFECTS IN TRANSITION METALS BASED BINARY ALLOYS USING PSEUDOPOTENTIAL THEORYSuperconducting state parameters (SSP) (viz., electron-phonon coupling strength λ, Coulomb pseudopotentialμ*transition temperatureTC, isotope effect exponent α and effective interaction strengthNOV) of transition metals based binary alloys are studied using - for the first time - a potential formalism with a pseudoatom-alloy model. In the study, noticeable influence of various exchange and correlation functions on λ andμ*has been revealed. The SSP results are found to be in a qualitative agreement with the available experimental data.

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Wang, Dongmin, Gaoshuai Lin, Yugang Zhao e Ming Gao. "Effects of Numerical Schemes of Contact Angle on Simulating Condensation Heat Transfer in a Subcooled Microcavity by Pseudopotential Lattice Boltzmann Model". Energies 16, n. 6 (10 marzo 2023): 2622. http://dx.doi.org/10.3390/en16062622.

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Various numerical schemes of contact angle are widely used in pseudopotential lattice Boltzmann model to simulate substrate contact angle in condensation. In this study, effects of numerical schemes of contact angle on condensation nucleation and heat transfer simulation are clarified for the first time. The three numerical schemes are pseudopotential-based contact angle scheme, pseudopotential-based contact angle scheme with a ghost fluid layer constructed on the substrate with weighted average density of surrounding fluid nodes, and the geometric formulation scheme. It is found that the subcooling condition destabilizes algorithm of pseudopotential-based contact angle scheme. However, with a ghost fluid layer constructed on the substrate or using geometric formulation scheme, the algorithm becomes stable. The subcooling condition also decreases the simulated contact angle magnitude compared with that under an isothermal condition. The fluid density variation near a microcavity wall simulated by pseudopotential-based contact angle scheme plays the role of the condensation nucleus and triggers “condensation nucleation”. However, with a ghost fluid layer constructed on the substrate or using geometric formulation scheme, the simulated fluid density distribution near the wall is uniform so that no condensation nucleus appears in the microcavity. Thus, “condensation nucleation” cannot occur spontaneously in the microcavity unless a thin liquid film is initialized as a nucleus in the microcavity. The heat flux at the microcavity wall is unphysical during the “condensation nucleation” process, but it becomes reasonable with a liquid film formed in the microcavity. As a whole, it is recommended to use pseudopotential-based contact angle scheme with a ghost fluid layer constructed on the substrate or use the geometric formulation scheme to simulate condensation under subcooling conditions. This study provides guidelines for choosing the desirable numerical schemes of contact angle in condensation simulation by pseudopotential lattice Boltzmann model so that more efficient strategies for condensation heat transfer enhancement can be obtained from numerical simulations.

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Koptsev, A. P., A. V. Nyavro e V. N. Cherepanov. "A power-law model of the pseudopotential". Russian Physics Journal 54, n. 4 (settembre 2011): 430–34. http://dx.doi.org/10.1007/s11182-011-9635-y.

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Tsirkin, S. S., S. V. Eremeev e E. V. Chulkov. "Model pseudopotential for the Cu(110) surface". Physics of the Solid State 52, n. 1 (gennaio 2010): 188–94. http://dx.doi.org/10.1134/s1063783410010324.

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Gao, Shangwen, Chengbin Zhang, Yingjuan Zhang, Qiang Chen, Bo Li e Suchen Wu. "Revisiting a class of modified pseudopotential lattice Boltzmann models for single-component multiphase flows". Physics of Fluids 34, n. 5 (maggio 2022): 057103. http://dx.doi.org/10.1063/5.0088246.

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Since its emergence, the pseudopotential lattice Boltzmann (LB) method has been regarded as a straightforward and practical approach for simulating single-component multiphase flows. However, its original form always results in a thermodynamic inconsistency, which, thus, impedes its further application. Several strategies for modifying the force term have been proposed to eliminate this limitation. In this study, four typical and widely used improved schemes—Li's single-relaxation-time (SRT) scheme [Li et al., “Forcing scheme in pseudopotential lattice Boltzmann model for multiphase flows,” Phys. Rev. E 86, 016709 (2012)] and multiple-relaxation-times (MRT) scheme [Li et al., “Lattice Boltzmann modeling of multiphase flows at large density ratio with an improved pseudopotential model,” Phys. Rev. E 87, 053301 (2013)], Kupershtokh's SRT scheme [Kupershtokh et al., “On equations of state in a lattice Boltzmann method,” Comput. Math. Appl. 58, 965 (2009)], and Huang's MRT scheme [Huang and Wu, “Third-order analysis of pseudopotential lattice Boltzmann model for multiphase flow,” J. Comput. Phys. 327, 121 (2016)]—are systematically analyzed and intuitively compared after an extension of the MRT framework. The theoretical and numerical results both indicate that the former three schemes are specific forms of the last one, which thus help further understand the improvements of these pseudopotential LB models for achieving thermodynamic consistency. In addition, we modified the calculation of the additional source term in the LB evolution equation. Numerical results for stationary and moving droplets confirm the higher accuracy.

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Ghillino, Enrico, Carlo Garetto, Michele Goano, Giovanni Ghione, Enrico Bellotti e Kevin F. Brennan. "Simplex Algorithm for Band Structure Calculation of Noncubic Symmetry Semiconductors: Application to III-nitride Binaries and Alloys". VLSI Design 13, n. 1-4 (1 gennaio 2001): 63–68. http://dx.doi.org/10.1155/2001/74207.

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A set of software tools for the determination of the band structure of zinc-blende, wurtzite, 4H, and 6H semiconductors is presented. A state of the art implementation of the nonlocal empirical pseudopotential method has been coupled with a robust simplex algorithm for the optimization of the adjustable parameters of the model potentials. This computational core has been integrated with an array of Matlab functions, providing interactive functionalities for defining the initial guess of the atomic pseudopotentials, checking the convergence of the optimization process, plotting the resulting band structure, and computing detailed information about any local minimum. The results obtained for wurtzite-phase III-nitrides (ALN, GaN, InN) are presented as a relevant case study.

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Al-Douri, Y. "Electronic and Positron Properties of Zinc-Blende MgTe, CdTe and their Alloy Mg_1-XCd_XTe". Advanced Materials Research 264-265 (giugno 2011): 580–85. http://dx.doi.org/10.4028/www.scientific.net/amr.264-265.580.

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Based on the pseudopotential scheme, the electronic and positron properties of zinc-blende compounds MgTe, CdTe and their alloy MgxCd1-xTe alloy have been studied. The agreement between our calculated electronic band parameters and the available experimental data is reasonable. For the ternary alloy MgxCd1-xTe, the virtual crystal approximation is coupled with the pseudopotential method. The energies at Γ, X and L points of MgxCd1-xTe alloy as a function of the alloy concentration are calculated. The electronic and positron band structures derived from pseudopotential calculations are also reported. Other quantity such as ionicity factor by means of our model with respect to the alloy concentration is discussed.

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Rudavskii, Ponedilok e Klapchuk. "MODEL PSEUDOPOTENTIAL OF THE ELECTRON - NEGATIVE ION INTERACTION". Condensed Matter Physics 6, n. 4 (2003): 611. http://dx.doi.org/10.5488/cmp.6.4.611.

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Più fonti

Tesi sul tema "Pseudopotential model"

Koyeerath, Graham Danny. "Topology optimization in interfacial flows using the pseudopotential model". Electronic Thesis or Diss., Nantes Université, 2024. http://www.theses.fr/2024NANU4008.

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L'optimisation des systèmes et des processus est un exercice qui s'effectue en tenant compte de l'expérience et des connaissances de chacun. Nous explorons ici une approche mathématique pour optimiser les problèmes physiques en utilisant divers algorithmes d'optimisation. Dans cette thèse, l'objectif préliminaire de l'optimiseur est de modifier les caractéristiques d'écoulement du système en ajustant les forces capillaires. Cet objectif peut être atteint en modifiant l'un des deux ensembles de paramètres : (a) en introduisant un matériau solide mouillant (paramètre de niveau) ou (b) en changeant la mouillabilité des surfaces solides existantes (paramètre de mouillabilité). Nous proposons que le premier ensemble de paramètres soit modifié à l'aide de l'algorithme d'optimisation topologique, où le gradient de la fonction de coût est obtenu en résolvant un modèle d'état adjoint pour le modèle monocomposant multiphase de Shan et Chen (SCMP-SC). De même, nous proposons que ce dernier ensemble de paramètres soit modifié à l'aide de l'algorithme d'optimisation de la mouillabilité, où nous dérivons à nouveau un modèle d'état adjoint pour le modèle SCMPSC. Enfin, nous utilisons un algorithme d'optimisation multi-échelle, dans lequel nous calculons le gradient de la fonction de coût à l'aide de la différence finie. Nous avons réussi à démontrer la compétence de cet optimiseur pour maximiser la vitesse moyenne d'une gouttelette 2D jusqu'à 69%
The optimization of systems and processes is an exercise that is carried out taking into account one’s experience and knowledge. Here we explore a mathematical approach to optimize physical problems by utilizing various optimization algorithms. In this thesis, the preliminary objective of the optimizer is to modify the flow characteristics of the system by tweaking the capillary forces. This could be accomplished by modifying either of the two sets of parameters: (a) by introducing a wetting solid material i.e. the level-set parameter or (b) by changing the wettability of the existing solid surfaces i.e. the wettability parameter. We propose that the former set of parameters could be modified using the topology optimization algorithm, where the gradient of the cost function is obtained by solving an adjointstate state model for the single component multiphase Shan and Chen (SCMP-SC) model. Similarly, we propose that the latter set of parameters are modified using the wettability optimization algorithm where we again derive an adjoint-state model for the SCMP-SC. Lastly, we utilize a multiscale optimization algorithm, where we compute the gradient of the cost function using the finite difference. We have succeeded in demonstrating the competence of this optimizer for maximizing the mean velocity of a 2D droplet by up to 69%

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Mason, Colin Raymond. "An evaluation of model potential and pseudopotential methods for the calculation of interatomic potentials". Thesis, University College London (University of London), 1991. http://discovery.ucl.ac.uk/1363642/.

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This thesis presents an evaluation of the model potential and pseudopotential methods for the calculation of atom-atom interaction curves. At University College London, Peach has computed interatomic potential curves for several alkali-rare gas pairs using both the model potential and pseudopotential methods in a completely self-consistent manner. The value of these calculations is that any differences between the interatomic potential curves obtained from the model potential and pseudopotential methods can be attributed unambiguously to the theoretical representations of the Pauli exclusion principle which differentiate the two methods. The work of Peach thus allows the utility of these two representations to be compared directly and their effect on the quality of the resulting interatomic potentials to be assessed. The present study has developed a suite of computer programs designed to calculate observable quantities which are sensitive to the interatomic potentials. Calculations of the profiles, widths and shifts of the alkali resonance line when perturbed by rare gases, together with cross sections for fine structure state changing transitions within the alkali excited state multiplet, are reported and comparisons are made with experimental measurements of these observables. It is demonstrated that the theoretical representation of the Pauli exclusion principle has a significant effect on the quality of the resulting interatomic potentials. Observables calculated on the basis of interatomic potentials obtained via the model potential method are in better agreement with the available experimental data than those calculated on the basis of pseudopotential interaction curves. From this it may be inferred that the interatomic potentials obtained by the model potential method represent the actual interaction between alkali and rare gas atoms more accurately than do interatomic potentials obtained by the pseudopotential method. The results of this study provide strong evidence for the superiority of the model potential method for the calculation of interatomic potentials.

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Punter, Alexander. "Développement de pseudopotentiels moléculaires adaptés à l'étude de propriétés moléculaires". Electronic Thesis or Diss., Aix-Marseille, 2019. http://theses.univ-amu.fr.lama.univ-amu.fr/191016_PUNTER_557rbnbaz334eufx966nnztk692fxvgiy_TH.pdf.

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Les pseudopotentiels permettent de simplifier les calculs moléculaires en remplaçant des atomes ou des groupements chimiques par des pseudosystèmes simples associés à des fonctions mathématiques rapides à évaluer. Dans ce travail, de nouveaux pseudopotentiels ont été créés pour la reproduction des propriétés électroniques de fragments carbonés. Initialement j’ai travaillé sur des systèmes contenant des carbones hybridés sp2 et j’ai pu reproduire plusieurs propriétés de base (énergie de la HOMO, énergie de 1ère ionisation, énergie d’excitation) de ces systèmes (polyènes et hydrocarbures polycycliques aromatiques) avec une précision satisfaisante. La procédure d’optimisation des paramètres des pseudopotentiels a été généralisée grâce à l’écriture d’un programme en Python, qui m’a permis d’obtenir des pseudopotentiels pour d’autres types de fragments carbonés : un pseudo sp3 à 1 électron, un pseudo sp3 à 2 électrons et un pseudo sp2 supplémentaire à 2 électrons. J’ai aussi réoptimisé les potentiels originaux (sp2 à 1 électron) spécifiquement pour le calcul des spectres UV et ECD. Enfin, j’ai expérimenté les pseudopotentiels sur des systèmes moléculaires variés tels que des systèmes organométalliques et des systèmes PI enchevêtrés. Leurs spectres UV ont pu être reproduits correctement en respectant les conditions suivantes : 1) le pseudopotentiel n’est pas lié à un hétéroatome, 2) les cycles PI ne sont pas tordus de plus de quelques degrés. J’ai aussi participé à une étude théorique de réactivité originale de cycloaddition intramoléculaire (2+2+3) dirigée par le cobalt
A pseudopotential method for replacing small hydrocarbon fragments in molecular quantum chemistry calculations is derived and tested. These fragments contain only one or two explicitly-treated electrons. The first is an sp2 carbon atom fragment optimised on ethylene. This potential is found to transfer well to all-trans-polyene and PAH systems, reproducing the HOMO and 1st ionisation and excitation energies to within around 20 % of all-electron DFT calculations. Additional pseudopotentials are created for other sp2 and sp3 hybridised carbon-based fragments. They are able to form bonds with all-electron atoms, and are also found to transfer well to larger systems, provided the systems with which they interact are similar enough to those on which they were optimised. The pseudopotentials are found to be able accurately to reproduce molecular UV and ECD spectra, and are tested on a variety of larger and more complex systems including helicenes, nanotubes and a metallocomplex. A program for the optimisation of these pseudopotentials is developed in Python, which is able to extract pseudopotentials from a variety of all-electron reference criteria.Unrelated to the above, the effects of a lactone group on a particular cobalt-mediated cycloaddition are also examined

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Silva, Maurício Chagas da. "Estudo teórico de efeitos de solvatação do tetraidrofurano sobre um mecanismo modelo de Suzuki-Miyaura". [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/248953.

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Orientador: Nelson Henrique Morgon
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química
Made available in DSpace on 2018-08-18T09:48:03Z (GMT). No. of bitstreams: 1 Silva_MauricioChagasda_D.pdf: 1640271 bytes, checksum: 4dc0aa6f7b350fe3e8808a9095aba5fe (MD5) Previous issue date: 2011
Resumo: Utilizando a implementação do método da coordenada geradora discretizada nos orbitais atômicos, conjuntos de bases adaptados ao pseudopotencial de caroço SBKJC (conjuntos GBSMCS) foram desenvolvidos, validados e utilizados no estudo de possíveis efeitos de solvatação do tetraidrofurano sobre um mecanismo modelo de Suzuki-Miyaura. As metodologias de validação adotadas para os conjuntos GBSMCS foram os cálculos teóricos da afinidade por próton de sistemas atômicos e moleculares, iônicos e neutros, das entalpias de liquefação de alguns solventes orgânicos rotineiros e das entalpias de hidratação de 29 compostos orgânicos diversos. Nas etapas de validação, observou-se de uma maneira geral, uma boa relação entre custo e benefício na utilização dos conjuntos de bases GBSMCS, obteveram-se desvios médios por volta de 0 até 20 kJ.mol, nas propriedades estudadas. Com as metodologias propostas neste trabalho e com a utilização dos conjuntos GBSMCS, determinou-se o perfil potencial da reação modelo de Suzuki-Miyaura tanto em fase gasosa como em fase solvatada de tetraidrofurano. Não se observou efeitos significativos nas estruturas dos estados estacionários caracterizados e nem nas DrG para as etapas de adição-oxidativa, transmetalação, eliminação-redutiva e isomerização. Contudo, observou-se que há efeitos consideráveis de solvatação para as espécies individuais. As etapas de adição-oxidativa e de eliminação-redutiva apresentaram-se como sendo etapas exergônicas e a etapa de transmetalação como sendo uma etapa endergônica tanto em fase gasosa como em tetraidrofurano. Abordou-se um mecanismo associativo em todas as etapas principais reacionais, contudo inferiu-se que a etapa de transmetalação tenha possíveis rotas mecanísticas dissociativas iônicas que serão estudadas em trabalhos futuros
Abstract: Using the implementation of the discretized generator coordinate method in atomic orbitals, atomic basis sets adapted to the pseudopotential core SBKJC were developed ( GBSMCS ), validated and used to study possible effects of tetrahydrofuran¿s solvation over a model Suzuki-Miyaura¿s mechanism. The methodologies adopted for the validation of GBSMCS basis sets were the theoretical calculations of proton affinities of atomic and molecular, ionic and neutral, systems, the liquefaction enthalpies of some common organic solvents and the hydration enthalpies of 29 organic compounds. In the validation steps a good relationship was abserved between cost and benefit in the use of GBSMCS basis set, average deviations around 0 to 20 kJ.mol for the properties studied. Applying the methodologies proposed in this research and using the GBSMCS atomic basis sets, the potential profile of the Suzuki- Miyaura¿s model mechanism was determinated in the gas and tetrahydrofuran phases. No significant tetrahydronfuran¿s solvation effects were observed for molecular stationarys state structures, neither for DrG for oxidative- addition, transmetallation, reductive-elimination and isomerization reaction steps. However, some strong solvation effects were observed for individual species. The oxidative-addition and reductive-elimination reaction steps were characterized as exergonic steps, but transmetallation reaction step was presented as an endergonic step, both in the gas and tetrahydrofuran phases. This work approaches an associative mechanism for all main reaction steps; however, we inferred that the transmetallation reaction step could have some ionic pathways and should be studied in future works
Doutorado
Físico-Química
Doutor em Ciências

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Forler, Nina. "A multinuclear solid-state NMR approach to the weathering of model phosphate glasses". Thesis, Lille 1, 2011. http://www.theses.fr/2011LIL10003/document.

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Les travaux de cette thèse portent sur la compréhension du processus du vieillissement des verres de phosphate à la base des études de résonance magnétique nucléaire (RMN) des solides. Le terme vieillissement se traduit dans ce cas par l’attaque aqueuse du verre sous atmosphère humide. Ce processus est d’un intérêt particulier dans tous les domaines où une haute résistance des verres de phosphate contre cette attaque constitue une propriété essentielle. Notamment c’est le cas pour la vitrification des déchets nucléaires. Dans le cadre de cette étude des systèmes modèles ont été étudiés (Na2O-P2O5 et Na2O-Al2O3-P2O5) pour obtenir une idée des changements structuraux qui ont lieu pendant l’attaque aqueuse. La résonance magnétique multinucléaire des solides (1H, 27Al, 31P et 17O) étant l’outil principal, des expériences en 1D et en 2D permettent de caractériser l’environnement proche des noyaux ainsi que leur environnement intermédiaire (connectivité hétéro- et homonucléaire). L’interprétation des données RMN de l’oxygène-17 est accompagnée d’une approche complémentaire. Des paramètres RMN calculés de l’oxygène-17 (DFT / GIPAW) des hydrogénophosphates cristallines ont été vérifiés et validés expérimentalement. Des corrélations entre les paramètres RMN de l’oxygène-17 (δCS, δiso, CQ, ηQ) et l’environnement structural du noyau ont été obtenu. Ces dernières permettent de caractériser les environnements du noyau oxygène-17 qui sont générés pendant le vieillissement d’un verre Na2O-P2O5 (NaPO3)
The present manuscript focuses on the investigation of phosphate glass weathering by multinuclear solid-state magnetic resonance. Weathering, that is aqueous attack and aging of the phosphate glass under humid atmosphere, becomes important in application domains where high resistance against aqueous attack is an essential property. In particular, this is the case for phosphate glass matrices for the immobilization of nuclear waste. In the frame of this work, binary (Na2O-P2O5) and ternary (Na2O-Al2O3-P2O5) model glass systems are considered. The aim is to obtain further insight into fundamental processes and structural changes that are taking place upon weathering attack on the glass. Solid-state nuclear magnetic resonance is used as the main tool for structural characterization. 1H, 27Al, 31P and 17O are employed as probe nuclei. A number of one- and two-dimensional techniques allows for insight into the glass structure on the low and intermediate range. The interpretation of 17O NMR data is accompanied by a complementary approach. Therefore, the reliability of calculated 17O NMR parameters of protonated crystalline phosphate phases has been validated for the first time. Relationships between 17O NMR parameters and the structural environment of the nucleus could be drawn. Those relationships prove to be helpful for the characterization of oxygen environments emerging in weathered NaPO3 glass based on the chemical shift (δCS, δiso) and the quadrupolar parameters (CQ, ηQ)

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Hliwa, Mohamed. "Traitement simplifie des interactions moleculaires en chimie quantique". Toulouse 3, 1988. http://www.theses.fr/1988TOU30038.

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Calculs ab initio sur le systeme hautement degenere cr h: mise en evidence d'un fort couplage entre etats ioniques et neutres et analyse des fonctions d'onde dans une description diabatique. Proposition d'une methode perturbative pour calcul des energies de dispersion entre un systeme versatil a (decrit dans une grande base) et un systeme quasi passif b (traite a l'approximation en coeur gele et caracterise par sa polarisabilite); calcul scf + ci de (a + b gele), du champ electrique exerce par a sur b, et de ses fluctuations, a l'aide d'un hamiltonien effectif; application a l'etude des courbes de potentiel des premiers etats excites des molecules diatomiques de ar avec na, k ou mg. Emploi de la theorie des pseudopotentiels et des potentiels modeles pour le calcul de potentiels impulsifs d'atomes inertes transferables a des systemes moleculaires; a partir de ces potentiels, calcul d'energies de dispersion applicable a la spectroscopie d'atomes alcalins en matiere de gaz rare

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Haldar, S., A. Ghorai e D. Sen. "Vacancy formation energy of simple metals using reliable model and ab initio pseudopotentials". 2017. https://ul.qucosa.de/id/qucosa%3A31555.

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We present a self-consistent calculation of the mono vacancy formation energy for seven simple metals Li, Na, K, Rb, Cs (all bcc), Al (fcc) and Mg (hcp) using both model and ab initio pseudopotential used in earlier unified studies. The local model pseudopotential calculations show small variations with respect to different exchange-correlation functions and the results are in fair agreement with other similar calculations and the available experimental data. The comparisons show that reliable model (pseudo) potential for simple metals can indeed be obtained for explaining a host of properties. Also, considering the importance of third order term in ab initio calculations, the results of our second order calculation appear fairly reasonable and are comparable with other first principle calculations. The perturbation series being an oscillating one, we hope to improve the calculational results using suitable series convergence acceleration method in the next part of our study.

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Libri sul tema "Pseudopotential model"

Dyall, Kenneth G., e Knut Faegri. Introduction to Relativistic Quantum Chemistry. Oxford University Press, 2007. http://dx.doi.org/10.1093/oso/9780195140866.001.0001.

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This book provides an introduction to the essentials of relativistic effects in quantum chemistry, and a reference work that collects all the major developments in this field. It is designed for the graduate student and the computational chemist with a good background in nonrelativistic theory. In addition to explaining the necessary theory in detail, at a level that the non-expert and the student should readily be able to follow, the book discusses the implementation of the theory and practicalities of its use in calculations. After a brief introduction to classical relativity and electromagnetism, the Dirac equation is presented, and its symmetry, atomic solutions, and interpretation are explored. Four-component molecular methods are then developed: self-consistent field theory and the use of basis sets, double-group and time-reversal symmetry, correlation methods, molecular properties, and an overview of relativistic density functional theory. The emphases in this section are on the basics of relativistic theory and how relativistic theory differs from nonrelativistic theory. Approximate methods are treated next, starting with spin separation in the Dirac equation, and proceeding to the Foldy-Wouthuysen, Douglas-Kroll, and related transformations, Breit-Pauli and direct perturbation theory, regular approximations, matrix approximations, and pseudopotential and model potential methods. For each of these approximations, one-electron operators and many-electron methods are developed, spin-free and spin-orbit operators are presented, and the calculation of electric and magnetic properties is discussed. The treatment of spin-orbit effects with correlation rounds off the presentation of approximate methods. The book concludes with a discussion of the qualitative changes in the picture of structure and bonding that arise from the inclusion of relativity.

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Capitoli di libri sul tema "Pseudopotential model"

Saritha Reddy, Gaddam, e R. Banerjee. "Evaluation of Forcing Schemes in Pseudopotential Based Multiphase Lattice Boltzmann Model". In Fluid Mechanics and Fluid Power – Contemporary Research, 1003–10. New Delhi: Springer India, 2016. http://dx.doi.org/10.1007/978-81-322-2743-4_94.

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Lopez, J. M., A. Ayuela e J. A. Alonso. "Electronic and Atomic Structure of NanZn Clusters in the Spherically Averaged Pseudopotential Model". In Density Functional Methods in Chemistry, 373–86. New York, NY: Springer New York, 1991. http://dx.doi.org/10.1007/978-1-4612-3136-3_24.

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Srichaikul, P., A. B. Chen e W. J. Choyke. "Electronic Band Structures of SiC Calculated from a Hybrid Pseudopotential and Tight-Binding Model". In Springer Proceedings in Physics, 170–75. Berlin, Heidelberg: Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/978-3-642-84804-9_24.

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Moriarty, John A. "Interatomic Potentials in Simple Metals". In Theory and Application of Quantum-Based Interatomic Potentials in Metals and Alloys, 91–134. Oxford University PressOxford, 2023. http://dx.doi.org/10.1093/oso/9780198822172.003.0003.

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Abstract In this chapter, quantum-based interatomic potentials for simple metals are derived starting from the corresponding cohesive-energy functional established in Chapter 2 via density functional theory and pseudopotential perturbation theory. This functional is expressed in reciprocal space for a general nonlocal pseudopotential and then transformed to the desired real-space representation in terms of a volume term and a volume-dependent pair potential. To allow full evaluation of the pseudopotential and the pair potential from first principles, a self-consistent electron screening calculation is also made. Accurate pair potentials so calculated have been obtained for a number of simple metals, including Na, Mg and Al prototypes, using two different optimized forms of nonlocal pseudopotential: the basic Austin, Heine and Sham form employed in generalized pseudopotential theory, and the norm conserving model potential form of Dagens, Rasolt and Taylor. Efficient practical methods to deal with the long-range Friedel oscillations in the pair potential arising from the self-consistent screening are also discussed.

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Schrader, D. M., T. Yoshida e K. Iguchi. "Binding energies of positronium fluoride and positronium bromide by the model potential quantum Monte Carlo method". In Quantum Monte Carlo, 88. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.0091.

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Abstract This paper and a companion paper0 describe three pseudopotential QMC calculations for the positronium halides PsF, PsCl, and PsBr with accuracies and reliabilities not previously available. These three compounds have a fleeting lifetime sufficiently long that time-independent nonrelativistic quantum mechanics should give good estimates of their energies but too short to allow direct measurements of those energies. Earlier estimates of several types and calculations at the Hartree-Fock level had given a wide spread in predictions of the binding energies of positronium to the halide ions, mostly in the range of 1 to 3 eV for the three molecules. The calculations were fixed-node diffusion QMC calculations for the eight valence electrons and the positron with a model potential expression replacing the core electrons and halide nucleus. The model or pseudopotential used was a simplified version without valence-core correlation and with several lesser terms eliminated in order to make it a local pseudopotential. This modelb had been used previously in successful predictions of the electron affinity of the Cl atom. An importance sampling trial wavefunction was constructed of Hartree-Fock orbitals for the halide ion and a 2s orbital for the positron, along with an electron-positron term but no electron-electron correlation terms. Checks of the consistency of the calculations with independent estimates of the correlation energies were entirely satisfactory. The results, in terms of binding energies, were obtained in the range of 1-2 eV (with uncertainties of 0.1-0.2 eV) in an order consistent with competitive formation experiments.

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Srivastava, P. K., e O. P. Kulshrestha. "Lattice Dynamics of Lanthanum by Using a Model Pseudopotential Approach". In July 1, 425–28. De Gruyter, 1985. http://dx.doi.org/10.1515/9783112495407-046.

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Igor, Vurgaftman. "Methods for Computing the States of Quantum Structures". In Bands and Photons in III-V Semiconductor Quantum Structures, 271–302. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198767275.003.0009.

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This chapter presents a detailed development of several numerical methods for calculating the band structure of semiconductor quantum wells and superlattices. These include the transfer-matrix method, the finite-difference method, and the reciprocal-space approach. The relative merits and drawbacks of each approach are briefly considered. It is pointed out that real-space methods often introduce spurious states for the most common forms of the Hamiltonian. The chapter also discusses how the tight-binding and pseudopotential methods can be applied to model quantum structures.

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Schautz, F., e H. J. Flad. "Selective correlation scheme within diffusion quantum Monte Carlo". In Quantum Monte Carlo, 135. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.00138.

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Abstract This paper describes the development of a new scheme for using an effective model potential to reduce the number of electrons explicitly treated in a QMC calculation for a molecular system. Like other pseudopotential and model-potential approaches it is based on differing treatments of core and valence (or frozen and explicitly correlated) electrons. It differs from the earlier schemes of Yoshida and co-workers0 in that it is adapted to multicenter systems and includes a projectionlike operator to enforce orthogonality between orbitals for the two sets of electrons. The model potential includes Coulomb and exchange terms and the projectionlike operator. The latter two are nonlocal. For these a localization procedure, similar to those used in pseudopotential calculations, was derived. In implementing the scheme the authors had to explore a number of questions, such as those related to nonequivalent nodal domains, and to devise a number of approximations to simplify the calculations. The triple-bonded nitrogen molecule N2, with correlation for the electrons of the bonding orgitals and with the nonbonding orbitals frozen, was used as a test case. A coupled cluster [CCSD(T)] calculation with a large basis set provided a benchmark with a correlation energy of 228 mhartree for the triple bond estimated to be accurate within a few mhartree. The corresponding result for the QMC calculation using the best approximations differed by 2-6 mhartree. Thus, quantitative agreement was obtained within the limits of statistical error. The authors indicated a “good chance” for further development to enable efficient treatment of problems involving solids and surfaces.

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Moriarty, John A. "Structural Phase Stability and High-Pressure Phase Transitions". In Theory and Application of Quantum-Based Interatomic Potentials in Metals and Alloys, 253–81. Oxford University PressOxford, 2023. http://dx.doi.org/10.1093/oso/9780198822172.003.0006.

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Abstract In this chapter, we address the subject of structural phase stability in both nontransition and transition metals, including as a fundamental test of prototype quantum-based interatomic potentials, calculation of the ground-state crystal structure amongst various competing alternate structures. In this process, we also discuss: (i) the basic separation of cohesion and structure in generalized pseudopotential theory (GPT); (ii) total-energy variations along important deformation paths connecting different higher-energy structures, including the Bain path linking the bcc and fcc structures; and (iii) structural phase stability in metals across the Periodic Table; and (iv) the prediction of pressure-induced solid-solid phase transitions, including a number of noteworthy GPT and model-GPT predictions that were subsequently confirmed by experiment.

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BALLE, S., F. LOPEZ-AGUILAR e J. COSTA-QUINTANA. "f–f AND f–d PSEUDOPOTENTIAL MODEL APPLIED TO THE BAND STRUCTURES OF Ce-SYSTEMS". In Anomalous Rare Earths and Actinides, 652–54. Elsevier, 1987. http://dx.doi.org/10.1016/b978-1-4832-2948-5.50193-3.

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Atti di convegni sul tema "Pseudopotential model"

Nabavizadeh, Seyed Amin, Mohsen Eshraghi e Sergio D. Felicelli. "Feasibility Study of Different Pseudopotential Multiphase Lattice Boltzmann Methods for Dendritic Solidification". In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71019.

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The formation of porosity and bubbles during solidification in manufacturing processes like casting or welding of metals has a negative effect on the mechanical properties of the manufactured components. Numerical simulation of this problem is important since the direct observation of the interaction of bubbles with dendrites is limited by the opacity of metals. Therefore, developing a reliable numerical model is essential to predict the mechanical properties of materials after solidification. The pseudopotential multiphase model is a popular method for simulating multiphase flow using the lattice Boltzmann method. This model and its variations have been used to simulate a variety of problems successfully. However, the original pseudopotential model has some deficiencies, including large spurious current and restriction to model low density and viscosity ratios. Several schemes have been proposed to improve the pseudopotential multiphase model and overcome the limitations, including using a realistic equation of state, introducing a force with higher order of isotropy, introducing a middle-range repulsion force, and implementing the force similarly to the Exact Difference Method (EDM). The aim of this article is to investigate these various enhancements available for the pseudopotential multiphase model in order to come up with a reliable scheme to simulate motion and interaction of bubbles during dendritic solidification in binary alloys. The proposed model is validated against published literature.

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Márk, Géza I. "Atomic pseudopotential model for wave packet tunneling through a carbon nanotube". In ELECTRIC PROPERTIES OF SYNTHETIC NANOSTRUCTURES: XVII International Winterschool/Euroconference on Electronic Properties of Novel Materials. AIP, 2004. http://dx.doi.org/10.1063/1.1812114.

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Arkhipov, Yu V., F. B. Baimbetov e A. E. Davletov. "Generalized pseudopotential model for description of thermodynamic and transport properties of plasmas". In 2009 IEEE 36th International Conference on Plasma Science (ICOPS). IEEE, 2009. http://dx.doi.org/10.1109/plasma.2009.5227738.

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Zunger, Alex. "Pseudopotential Theory of Semiconductor Quantum Dots, Wires and Films". In Chemistry and Physics of Small-Scale Structures. Washington, D.C.: Optica Publishing Group, 1997. http://dx.doi.org/10.1364/cps.1997.ctua.4.

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The electronic structure of nanostructures has been almost universally addressed by the “standard model” of effective-mass k·p envelope function approach. While eminently successful for quantum wells, this model breaks down for small structures, in particular, for small dots and wires[l]. Until recently, it was impractical to test the “standard model” against more general approaches that allow many-band (Γ-X-L) coupling. However, it is now possible, due to special tricks[2], to apply the all-band pseudopotential method to 103 - 104 atom nanostructures. This shows (i) how the “standard model” fails, for thin superlattices, [3], (ii) how size effect lead to a reduction in dielectric constants[3] and to band gaps that differ from what is expected in effective-mass theory, (iii) the emergence of a “zero-confinement state” in 2D films [4], (iv) that small dots of III-V materials have an indirect gap that converts to direct above a critical size[5], (v) how the spectra of CdSe dots evolve from the bulk[6] and (vi) how the spectra of dots of Si, GaAs, InP and CdSe compare with experiment, and (vii) how the use of pseudopotential wavefunctions leads to very different electron-hole coulomb and exchange energies relative to the “standard model”.

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Tang, Jun, Shengyuan Zhang e Huiying Wu. "Three-Dimensional Weighted Multiple-Relaxation-Time Pseudopotential Lattice Boltzmann Method for Multiphase Flow". In ASME 2021 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/fedsm2021-65506.

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Abstract The pseudopotential lattice Boltzmann (LB) method has been widely used for simulating multiphase flow due to its concise concept and computational simplicity. In this paper, based on the weighted orthogonal transformation matrix, a three-dimensional (3D) weighted multiple-relaxation-time pseudopotential lattice Boltzmann method (WRMT-LBM) is developed, in which the standard lattice stencil D3Q19 is adopted. Compared with the classical multiple-relaxation-time pseudopotential lattice Boltzmann method (CMRT-LBM) based on the orthogonal transformation matrix, the expressions of the equilibrium density distribution function and discrete force term in moment space are simplified in the present model, which contributes to simplifying the program implementation and improving the computational efficiency. Moreover, an additional discrete source term in moment space compatible with the proposed model is introduced to achieve tunable surface tension. A series of numerical tests are then implemented to investigate the performance of the proposed model. Compared with the CMRT-LBM, the results of the present model can achieve lower spurious velocity and higher computational efficiency while keeping comparable accuracy. Furthermore, using the present model, three benchmark cases, including droplet oscillation, droplet impacting on wall and droplet impact on thin film, are performed to investigate the performance of this model. The numerical results are in good agreement with the analytical solutions or the empirical correlations in the literature, which demonstrates that the present model can simulate the multiphase flow with large density ratio.

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Zhao, Wandong, Ben Xu e Ying Zhang. "Three-Dimensional Multiple-Relaxation-Time Lattice Boltzmann Simulation of Vapor Condensation on Subcooled Wall". In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-88490.

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Oscillating flows and multiphase heat transfer processes frequently occur in many engineering and scientific applications and systems, as is the case in enhanced geothermal energy, CO2 sequestration and storage, and in evaporation in soil, to name a few. Nevertheless, modeling of such flows is a rather challenging task due to the complex interfacial dynamics among different phases and solid porous structures. Over the decades, several types of Lattice Boltzmann (LB) models for multiphase flows have been developed under different physical pictures, for example the color-gradient model, Single-Relaxation-Time (SRT) pseudopotential model, and the HSD model. In this study, a pseudopotential Multiple-Relaxation-Time (MRT) LBM simulation will be utilized to simulate incompressible oscillating flow and condensation in 2D porous media. Initially, the model will be used to optimize the porous structure in order to have the maximum condensation rate of water vapor. Subsequently, the effects of contacting angle, wettability, oscillating frequency and phase angle to the heat flux, the temperature field of porous media, and the condensation rate will be discussed. Moreover, a multiscale approach will be considered in order to couple the heat transfer in macroscale applications. It is expected that such an approach will provide a different perspective regarding the engineering applications involved with oscillating flow and multiphase heat transfer processes.

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Zhang, Lei, Yunlong Zhu e Xiaoding Cheng. "Numerical study of successive droplets impingement on a solid surface with a pseudopotential based lattice Boltzmann model". In 2017 IEEE 7th Annual International Conference on CYBER Technology in Automation, Control, and Intelligent Systems (CYBER). IEEE, 2017. http://dx.doi.org/10.1109/cyber.2017.8446231.

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Li, Xi, Huixiong Li e Xiaoyi Wu. "Numerical Study of Pool Boiling Heat Transfer on a Heated Cylinder by Lattice Boltzmann Method". In ASME 2024 7th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2024. http://dx.doi.org/10.1115/mnhmt2024-131778.

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Abstract Pool boiling is widely utilized in various industrial applications due to the high heat transfer performance. In the numerical simulations, the pseudopotential LB model is capable of simulating the entire boiling processes, including the bubble nucleation. Under the effect of gravity and surface tension, the distribution of phase fields on the circle surface is nonuniform. The bubble dynamics, and the heat transfer characteristics during the pool boiling processes on the circular surfaces would be unique compared to those on the heated plate. In this study, the bubble dynamics and heat transfer during pool boiling processes at a heated cylinder with different wall superheats were simulated using the MRT pseudopotential model coupled with phase-change model. The bubble dynamics and heat transfer with various orientations of the heated cylinder during pool boiling processes were investigated. In addition, the influence of surface tension and saturated temperature on pool boiling heat transfer was studied. It was found that increasing surface tension could enhance the heat transfer performance for the nucleate boiling with high wall superheat, and CHF is proportional to 0.254 power of surface tension. When Ja is low, the saturated temperature has little influence on heat transfer performance. However, in the nucleate boiling regime with large Ja, heat transfer performance as well as CHF decrease with the increasing saturated temperature.

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Rakhecha, Shalu, N. K. Bhatt, P. R. Vyas e V. B. Gohel. "The study of structural phase transitions and static properties using transition metal model pseudopotential (TMMP) for Ca and Sr". In INTERNATIONAL CONFERENCE ON CONDENSED MATTER AND APPLIED PHYSICS (ICC 2015): Proceeding of International Conference on Condensed Matter and Applied Physics. Author(s), 2016. http://dx.doi.org/10.1063/1.4946286.

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Channouf, Salaheddine, Jaouad Benhamou e Mohammed Jami. "Condensation Behaviors of Droplet under the Gravity Effect on Hydrophobic Surface by Using the Hybrid Thermal Pseudopotential LBM Model". In 2022 2nd International Conference on Innovative Research in Applied Science, Engineering and Technology (IRASET). IEEE, 2022. http://dx.doi.org/10.1109/iraset52964.2022.9737978.

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