Academic literature on the topic 'Ground-state atomic-charge distributions'
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Journal articles on the topic "Ground-state atomic-charge distributions"
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Marahatta, Anant Babu. "Chemical Energetics and Atomic Charges Distribution of Variably Sized Hydrated Sulfate Clusters in the light of Density Functional Theory." International Journal of Progressive Sciences and Technologies 25, no. 1 (February 28, 2021): 595. http://dx.doi.org/10.52155/ijpsat.v25.1.2690.
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Among the ions classified in the Hofmeister series, the firstly ranked divalent sulfate anion has the strongest hydrating and water-structure making propensity. This unique characteristic actually makes it kosmotropic which causes water molecules to interact each other and contributes to gain structural stability of its hydrated clusters [SO42−(H2O)n]n = 1−40. In this study, few variably sized microhydrated sulfate clusters [SO42−(H2O)n]n = 1−4, 16 are considered separately, and inquired their chemical energetics and atomic charge distributions through ab initio based theoretical model. The main objective of this insight is to specify and interpret their thermodynamic stabilities, binding energies, and specific bonding and electronic interactions quantum mechanically. An in-depth analysis of their change in relative ground state electronic energy with respect to hydration number indicates stronger affinity of the sulfate ion towards water molecules while attaining structural stability in any aqueous type solutions. The mathematically determined values of their binding energy (DE) almost holds up the same with this structural stability order: [SO42−(H2O)16] > [SO42−(H2O)4] > [SO42−(H2O)3] > [SO42−(H2O)2] > [SO42−(H2O)], as reliable as experimentally and molecular dynamics simulation predicted trend. Moreover, the Mulliken derived partial atomic charges feature qualitative charge distribution in them which not only depicts electronic interactions between the specific atoms but also exemplifies the involvement of central sulfate units in hydrogen bond formation with surrounding water molecules.
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Schott, Wolfgang, Erwin Gutsmiedl, Karina Bernert, Ralf Engels, Roman Gernhäuser, Stefan Huber, Igor Konorov, et al. "Towards a first measurement of the free neutron bound beta decay detecting hydrogen atoms at a throughgoing beamtube in a high flux reactor." EPJ Web of Conferences 219 (2019): 04006. http://dx.doi.org/10.1051/epjconf/201921904006.
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In addition to the common 3-body decay of the neutron n → pe-ν̅e there should exist an effective 2-body subset with the electron and proton forming a Hydrogen bound state with well defined total momentum, total spin and magnetic quantum numbers. The atomic spectroscopic analysis of this bound system can reveal details about the underlying weak interaction as it mirrors the helicity distributions of all outgoing particles. Thus, it is unique in the information it carries, and an experiment unravelling this information is an analogue to the Goldhaber experiment performed more than 60 years ago. The proposed experiment will search for monoenergetic metastable BoB H atoms with 326 eV kinetic energy, which are generated at the center of a throughgoing beamtube of a high-flux reactor (e.g., at the PIK reactor, Gatchina). Although full spectroscopic information is needed to possibly reveal new physics our first aim is to prove the occurrence of this decay and learn about backgrounds. Key to the detection is the identification of a monoerergtic line of hydrogen atoms occurring at a rate of about 1 s−1 in the environment of many hydrogen atoms, however having a thermal distribution of about room temperature. Two scenarios for velocity (energy) filtering are discussed in this paper. The first builds on an purely electric chopper system, in which metastable hydrogen atoms are quenched to their ground state and thus remain mostly undetectable. This chopper system employs fast switchable Bradbury Nielsen gates. The second method exploits a strongly energy dependent charge exchange process of metastable hydrogen picking up an electron while traversing an argon filled gas cell, turning it into manipulable charged hydrogen. The final detection of hydrogen occurs through multichannel plate (MCP) detector. The paper describes the various methods and gives an outlook on rates and feasibility at the PIK reactor in Gatchina.
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Poirier, Raymond A., Arpita Yadav, and Péter R. Surján. "Effect of protonation on the ground state properties of retinal analogs: an ab-initio study." Canadian Journal of Chemistry 65, no. 4 (April 1, 1987): 892–97. http://dx.doi.org/10.1139/v87-150.
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The ground state properties (bond lengths, bond orders, net atomic charge distribution) of various cis and trans isomers of retinal analogs have been studied at abinitio SCF and correlated levels. The effect of protonation on the properties of the retinal Schiff base analogs has also been studied. Convergence in various properties has been observed with increasing chain length justifying the use of smaller analogs mimicking retinal. Convergence is, however, slower for the protonated retinal Schiff base analogs. The protonated retinal Schiff base analogs show an increased conjugation reflected in the bond orders, bond lengths, and in the decrease in the HOMO–LUMO gap. The nodal characteristics of the HOMO of the protonated retinal Schiff base analog also indicate a strong conjugation in the vicinity of the protonated nitrogen. Based on the results of calculations at the correlated level, the sudden polarization charge transfer mechanism is shown to be an artifact of HF-based methods used in the calculations.
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NOGUERA, CLAUDINE. "INSULATING OXIDES IN LOW DIMENSIONALITY: A THEORETICAL REVIEW." Surface Review and Letters 08, no. 01n02 (February 2001): 121–67. http://dx.doi.org/10.1142/s0218625x01000847.
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In the light of recent studies, we summarize our present theoretical understanding of insulating oxides in low dimensionality, including unsupported clusters, planar or stepped surfaces and ultrathin films. We review the various theoretical approaches, their efficiency in calculating ground and excited state properties, and their applications to the present systems. We discuss the forces at work which determine the atomic structure around under-coordinated atoms (equilibrium geometries of very small clusters, bond lengths, relaxation and rumpling at surfaces), the energetics associated with low dimensionality (surface energies and mean cohesion energy in clusters), the electronic properties, such as electron distribution, magnetic interactions and ordering, and electronic excitations (ionization potentials, electron affinity, quasiparticle spectra, d → d and charge transfer excitations).
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Kars Durukan, İlknur, and Yasemin Oztekin Ciftci. "First-principles study on B2 based XAl(X = Rh, Ru)compounds." Physica Scripta 96, no. 12 (November 30, 2021): 125726. http://dx.doi.org/10.1088/1402-4896/ac3b6d.
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Abstract In this study, to see pressure effects on optical, thermodynamic, structural, elastic, electronic properties, charge density, and phonon frequencies of the XAl (X:Rh, Ru) compounds in B2 structure, the first-principles methods were used. The ground-state properties of these compounds were determined and compared with experimental and theoretical data. High Young’s and shear modulus showed these compounds to be hard materials. The investigated compounds have ductile property according to the Paugh criterion and Poisson’s ratio calculated from elastic constants. The electronic band structure showed that these compounds have a metallic nature. Dynamic stability using phonon distribution curves was determined under pressure. The bond properties between Rh-Al and Ru-Al atoms were evaluated in detail by Mulliken Atomic Populations and charge density analysis. Also, the optical properties are examined in detail. We think that this theoretical work contributes greatly to engineering applications due to the electronic, thermodynamic, and optical behavior of XAl (X: Rh, Ru) compounds.
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Gieseking, Rebecca L., Mark A. Ratner, and George C. Schatz. "Semiempirical modeling of electrochemical charge transfer." Faraday Discussions 199 (2017): 547–63. http://dx.doi.org/10.1039/c6fd00234j.
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Nanoelectrochemical experiments using detection based on tip enhanced Raman spectroscopy (TERS) show a broad distribution of single-molecule formal potentials E°′ for large π-conjugated molecules; theoretical studies are needed to understand the origins of this distribution. In this paper, we present a theoretical approach to determine E°′ for electrochemical reactions involving a single molecule interacting with an electrode represented as a metal nanocluster and apply this method to the Ag20–pyridine system. The theory is based on the semiempirical INDO electronic structure approach, together with the COSMO solvation model and an approach for tuning the Fermi energy, in which the silver atomic orbital energies are varied until the ground singlet state of Ag20–pyridine matches the lowest triplet energy, corresponding to electron transfer from the metal cluster to pyridine. Based on this theory, we find that the variation of E°′ with the structure of the Ag20–pyridine system is only weakly correlated with changes in either the ground-state interaction energy or the charge-transfer excited-state energies at zero applied potential, which shows the importance of calculations that include an applied potential in determining the variation of formal potential with geometry. Factors which determine E°′ include wavefunction overlap for geometries when pyridine is close to the surface, and electrostatics when the molecule-cluster separation is large.
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Zhong, Quanjie, Jian Zheng, Lin Zhang, and Xuan Luo. "Theoretical study on nonlinear optical properties of N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole." Journal of Nonlinear Optical Physics & Materials 27, no. 04 (December 2018): 1850036. http://dx.doi.org/10.1142/s0218863518500364.
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The first-, second- and third-order nonlinear optical properties of N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole in gas phase employing sum-over-states (SOS) method have been calculated for the first time. The ground state molecular structure of N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole was obtained by the geometrical optimizations based on the B3LYP/6-31[Formula: see text]G(d) level. The energy of excited states and transition dipole moments between different excited states were obtained by using the time-dependent density functional theory (TDDFT) based on the CAM-B3LYP/Sadlej POL level. Charge transfer during electron excitation was analyzed based on hole and electron distributions. Our calculations showed that the N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole has good nonlinear optical properties and its nonlinear optical properties arise from charge-transfer excitation and local excitation but charge transfer plays the leading role.
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Dufresne, R. P., and G. Del Zanna. "Modelling ion populations in astrophysical plasmas: carbon in the solar transition region." Astronomy & Astrophysics 626 (June 2019): A123. http://dx.doi.org/10.1051/0004-6361/201935133.
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The aim of this work is to improve the modelling of ion populations in higher density, lower temperature astrophysical plasmas, of the type commonly found in lower solar and stellar atmospheres. Ion population models for these regions frequently employ the coronal approximation, which assumes conditions more suitable to the upper solar atmosphere, where high temperatures and lower densities prevail. The assumed conditions include all ions being in the ground state and steady-state equilibrium, where there is sufficient time for ionisation and recombination to take place. Using the coronal approximation for modelling the solar transition region gives theoretical lines intensities for the Li-like and Na-like isoelectronic sequences which are often factors of two to five times lower than observed. The works of Burgess & Summers (1969, ApJ, 157, 1007) and Nussbaumer & Storey (1975, A&A, 44, 321) show the important part ions in excited levels play when included in the modelling. As density increases metastable levels become populated and ionisation rates increase, whereas dielectronic recombination through highly excited levels is suppressed. Photo-ionisation is also shown by Nussbaumer & Storey to have an effect on the charge-state distribution of carbon in these regions. Their models, however, use approximations for the atomic rates to determine the ion balance. Presented here is the first stage in updating these earlier models of carbon by using rates from up-to-date atomic calculations and more recent photo-ionising radiances. Where atomic rates were not readily available, in the case of electron impact direct ionisation and excitation–auto-ionisation, new calculations were made using the Flexible Atomic Code and Autostructure, and compared to theoretical and experimental studies. The effects each atomic process has on the ion populations as density changes is illustrated, and final results from the modelling are compared to the earlier works. Lastly, the new results for ion populations were used to predict line intensities for the solar transition region in the quiet Sun. In comparison to coronal approximation modelling the new results show significantly improved agreement with observations.
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Oks, Eugene. "Analysis of Experimental Cross-Sections of Charge Exchange between Hydrogen Atoms and Protons Yields More Evidence of the Existence of the Second Flavor of Hydrogen Atoms." Foundations 1, no. 2 (November 19, 2021): 265–70. http://dx.doi.org/10.3390/foundations1020019.
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Measurements of cross-sections of charge exchange between hydrogen atoms and low energy protons (down to the energy ~10 eV) revealed a noticeable discrepancy with previous theories. The experimental cross-sections were systematically slightly higher—beyond the error margins—than the theoretical predictions. In the present paper, we study whether this discrepancy can be eliminated or at least reduced by using the Second Flavor of Hydrogen Atoms (SFHA) in calculations. We show that for the SFHA, the corresponding cross-section is noticeably larger than for the usual hydrogen atoms. We demonstrate that the allowance for the SFHA does bring the theoretical cross-sections in a noticeably better agreement with the corresponding experiments within the experimental error margins. This seems to constitute yet another evidence from atomic experiments that the SFHA is present within the mixture of hydrogen atoms. In combination with the first corresponding piece of evidence from the analysis of atomic experiments (concerning the distribution of the linear momentum in the ground state of hydrogen atoms), as well as with the astrophysical evidence from two different kinds of observations (the anomalous absorption of the redshifted 21 cm radio line from the early universe and the smoother distribution of dark matter than that predicted by the standard cosmology), the results of the present paper reinforce the status of the SFHA as the candidate for dark matter, or at least for a part of it.
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Oks, Eugene. "Distinctive Features of Charge Exchange Involving the Second Flavor of Hydrogen Atoms—The Candidates for Dark Matter." Physics 4, no. 1 (February 23, 2022): 286–93. http://dx.doi.org/10.3390/physics4010019.
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The second flavor of hydrogen atoms (SFHA) refers to the kind of hydrogen atoms that have only the states of the zero orbital angular momentum (the S-states), both in the discrete and continuous spectra. They were first discovered theoretically in one of my earlier papers, where a proof of their existence was also provided by analyzing atomic experiments concerning the high-energy tail of the linear momentum distribution in the ground state of hydrogen atoms. From a theoretical point of view, the discovery was based on the standard Dirac equation for hydrogen atoms without changing the existing physical laws. Recently, the existence of the SFHA was seemingly also confirmed by two types of astrophysical observations: the allowance for the SFHA explained the puzzling results concerning both the anomalous absorption of the redshifted 21 cm spectral line from the early Universe, and the observations by the Dark Energy Survey (DES) team where it was found that the distribution of dark matter in the Universe is noticeably smoother than predictions employing Einstein’s relativity. In the present review, we exhibit results from two recent papers where attention was brought to a visible difference in the cross-sections of the resonant charge exchange for collisions of the SFHA with incoming protons, compared to collisions of the usual hydrogen atoms with incoming protons. It was shown that, after taking into account the SFHA, there is a better agreement with the corresponding experimental cross-section. Coupled with the previous evidence of the existence of the SFHA, deduced from the analysis of the other kind of atomic experiments, and evidenced by two different kinds of astrophysical observations, this strengthens the standing of the SFHA as the most probable candidate for all or a part of dark matter.
Book chapters on the topic "Ground-state atomic-charge distributions"
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Coppens, Philip. "Space Partitioning and Topological Analysis of the Total Charge Density." In X-Ray Charge Densities and Chemical Bonding. Oxford University Press, 1997. http://dx.doi.org/10.1093/oso/9780195098235.003.0008.
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In partitioning space in the analysis of a continuous charge distribution, the requirement of locality, formulated by Kurki-Suonio (Kurki-Suonio 1968, 1971; Kurki-Suonio and Salmo 1971), should be preserved. It states that density at a point should be assigned to a center in the proximity of that point. In discrete boundary partitioning schemes, the density at each point is assigned to a specific basin, while in fuzzy boundary partitioning, the density at the point may be assigned to overlapping functions centered at different locations. The least-squares formalisms described in chapter 3 implicitly define a space partitioning scheme, based on the density functions used in the refinement that are each centered on a specific nucleus. Since the density functions are continuous, they overlap, so the fragments interpenetrate rather than meet at a discrete boundary. Such fuzzy boundaries correspond to smoothly varying functions, both in real and reciprocal space, and therefore to well-behaved fragment scattering factors, and reasonable fragment electrostatic moments. The interpenetratingfragment partitioning schemes are related to the Mulliken and Løwdin population analyses of theoretical chemistry. The topological analysis of the total density, developed by Bader and coworkers, leads to a scheme of natural partitioning into atomic basins which each obey the virial theorem. The sum of the energies of the individual atoms defined in this way equals the total energy of the system. While the Bader partitioning was initially developed for the analysis of theoretical densities, it is equally applicable to model densities based on the experimental data. The density obtained from the Fourier transform of the structure factors is generally not suitable for this purpose, because of experimental noise, truncation effects, and thermal smearing. The topological analysis of the density leads to a powerful classification of bonding based on the electron density. It is discussed in the final sections of this chapter. The stockholder partitioning concept is one of the important contributions to charge density analysis made by Hirshfeld (1977b). It defines a continuous sampling function wi(r), which assigns the density among the constituent atoms. The sampling function is based on the spherical-atom promolecule density—the sum of the spherically averaged ground-state atom densities.