Journal articles on the topic 'Open Shell Molecular Systems'

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1

Nakano, Masayoshi, and Benoît Champagne. "Nonlinear optical properties in open-shell molecular systems." Wiley Interdisciplinary Reviews: Computational Molecular Science 6, no. 2 (February 25, 2016): 198–210. http://dx.doi.org/10.1002/wcms.1242.

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2

Zhang, Yu, Linqiu Li, Sergei Tretiak, and Tammie Nelson. "Nonadiabatic Excited-State Molecular Dynamics for Open-Shell Systems." Journal of Chemical Theory and Computation 16, no. 4 (March 2, 2020): 2053–64. http://dx.doi.org/10.1021/acs.jctc.9b00928.

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3

Feldt, Milica, and Ricardo A. Mata. "Hybrid Local Molecular Orbital: Molecular Orbital Calculations for Open Shell Systems." Journal of Chemical Theory and Computation 14, no. 10 (August 28, 2018): 5192–202. http://dx.doi.org/10.1021/acs.jctc.8b00727.

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4

Nakano, Masayoshi, Kotaro Fukuda, Soichi Ito, Hiroshi Matsui, Takanori Nagami, Shota Takamuku, Yasutaka Kitagawa, and Benoît Champagne. "Diradical and Ionic Characters of Open-Shell Singlet Molecular Systems." Journal of Physical Chemistry A 121, no. 4 (January 20, 2017): 861–73. http://dx.doi.org/10.1021/acs.jpca.6b11647.

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5

Nakano, Masayoshi, and Benoît Champagne. "Theoretical Design of Open-Shell Singlet Molecular Systems for Nonlinear Optics." Journal of Physical Chemistry Letters 6, no. 16 (August 7, 2015): 3236–56. http://dx.doi.org/10.1021/acs.jpclett.5b00956.

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6

Haque, Azizul, and Uzi Kaldor. "Open-shell coupled-cluster theory applied to atomic and molecular systems." Chemical Physics Letters 117, no. 4 (June 1985): 347–51. http://dx.doi.org/10.1016/0009-2614(85)85242-8.

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7

Perlt, Eva, Christina Apostolidou, Melanie Eggers, and Barbara Kirchner. "Unrestricted Floating Orbitals for the Investigation of Open Shell Systems." International Journal of Chemistry 8, no. 1 (January 26, 2016): 194. http://dx.doi.org/10.5539/ijc.v8n1p194.

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<p>The floating orbital molecular dynamics approach treats the basis functions' centers in ab initio molecular dynamics simulations variationally optimized in space rather than keeping them strictly fixed on nuclear positions. An implementation of the restricted theory for closed shell systems is already available (Perlt et al., Phys. Chem. Chem. Phys., 2014, 16, 6997–7005). In this article, the extension of the methodology to the unrestricted theory in order to cover open shell systems is introduced. The methyl radical serves as a test system to prove the correctness of the implementation and to demonstrate the scope of this method. The available spin density plots and vibrational spectra are compared to those obtained from atom-centered bases. Finally, more complex systems as well as further properties to be studied in future investigations by floating orbitals are suggested.</p>
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8

Cheng, Lixue, Jiace Sun, J. Emiliano Deustua, Vignesh C. Bhethanabotla, and Thomas F. Miller. "Molecular-orbital-based machine learning for open-shell and multi-reference systems with kernel addition Gaussian process regression." Journal of Chemical Physics 157, no. 15 (October 21, 2022): 154105. http://dx.doi.org/10.1063/5.0110886.

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We introduce a novel machine learning strategy, kernel addition Gaussian process regression (KA-GPR), in molecular-orbital-based machine learning (MOB-ML) to learn the total correlation energies of general electronic structure theories for closed- and open-shell systems by introducing a machine learning strategy. The learning efficiency of MOB-ML(KA-GPR) is the same as the original MOB-ML method for the smallest criegee molecule, which is a closed-shell molecule with multi-reference characters. In addition, the prediction accuracies of different small free radicals could reach the chemical accuracy of 1 kcal/mol by training on one example structure. Accurate potential energy surfaces for the H10 chain (closed-shell) and water OH bond dissociation (open-shell) could also be generated by MOB-ML(KA-GPR). To explore the breadth of chemical systems that KA-GPR can describe, we further apply MOB-ML to accurately predict the large benchmark datasets for closed- (QM9, QM7b-T, and GDB-13-T) and open-shell (QMSpin) molecules.
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9

Frishberg, C., L. Cohen, and P. Blumenau. "Hartree-fock density matrix equation: Open-shell systems." International Journal of Quantum Chemistry 18, S14 (June 19, 2009): 161–65. http://dx.doi.org/10.1002/qua.560180820.

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10

Pruitt, Spencer R., Dmitri G. Fedorov, and Mark S. Gordon. "Geometry Optimizations of Open-Shell Systems with the Fragment Molecular Orbital Method." Journal of Physical Chemistry A 116, no. 20 (May 11, 2012): 4965–74. http://dx.doi.org/10.1021/jp302448z.

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11

Guseinov, I. I. "Combined Open Shell Hartree–Fock Theory of Atomic–Molecular and Nuclear Systems." Journal of Mathematical Chemistry 42, no. 2 (May 17, 2006): 177–89. http://dx.doi.org/10.1007/s10910-006-9090-0.

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12

Martínez Araya, Jorge Ignacio. "The dual descriptor: Working equations applied on electronic open-shell molecular systems." Chemical Physics Letters 506, no. 1-3 (April 2011): 104–11. http://dx.doi.org/10.1016/j.cplett.2011.02.051.

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13

Jonas, R., and V. Staemmler. "CEPA calculations of potential energy surfaces for open-shell systems." Zeitschrift f�r Physik D Atoms, Molecules and Clusters 14, no. 2 (June 1989): 143–48. http://dx.doi.org/10.1007/bf01399036.

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14

Teixeira Filho, RM, LAC Malbouisson, and JDM Vianna. "An algebraic method for solving Hartree-Fock equations. II. Open-shell molecular systems." Journal de Chimie Physique 90 (1993): 1999–2005. http://dx.doi.org/10.1051/jcp/1993901999.

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15

Gupta, Tulika, and Gopalan Rajaraman. "Modelling spin Hamiltonian parameters of molecular nanomagnets." Chemical Communications 52, no. 58 (2016): 8972–9008. http://dx.doi.org/10.1039/c6cc01251e.

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With significant development in the computational methods applied to open-shell systems and tremendous improvements in computing resources, molecular modelling has become an integral part of the study of molecular magnetism. In this feature study, we have attempted to provide a bird's-eye view of the modelling of various spin Hamiltonian parameters of molecular nanomagnets.
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16

NAKANO, MASAYOSHI, RYOHEI KISHI, HITOSHI FUKUI, TAKUYA MINAMI, HIROSHI NAGAI, KYOHEI YONEDA, SEAN BONNESS, and HIDEAKI TAKAHASHI. "THEORETICAL STUDY ON OPEN-SHELL NONLINEAR OPTICAL MOLECULAR SYSTEMS AND A DEVELOPMENT OF A NOVEL COMPUTATIONAL SCHEME OF EXCITON DYNAMICS." International Journal of Nanoscience 08, no. 01n02 (February 2009): 123–29. http://dx.doi.org/10.1142/s0219581x09005803.

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This contribution firstly elucidates a structure–property relationship in third-order nonlinear optical molecular systems with singlet diradical characters. It turns out that the second hyperpolarizabilities (γ) of the singlet open-shell molecules with intermediate diradical characters are significantly enhanced as compared with those of closed-shell and pure diradical molecules. The hybrid density functional theory method, i.e. UBHandHLYP, is applied to the calculations of γ of dimer models composed of singlet diradical diphenalenyl molecules, which show a remarkable enhancement of γ per monomer as decreasing the intermolecular distance. The second contribution is concerned with a development of ab initio molecular orbital configuration-interaction-based quantum master equation (QME) approach. This is found to provide both coherent processes, e.g. dynamic polarization and exciton (electron–hole pair) recurrence motion, and incoherent processes, e.g. exciton migration, in molecular systems. Using this approach, the electron/hole dynamics for dynamic polarizabilities α(ω) are examined for several π-conjugated linear chain systems, and the structural dependences of α(ω) are elucidated.
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17

Nakata, Hiroya, Dmitri G. Fedorov, Kazuo Kitaura, and Shinichiro Nakamura. "Extension of the fragment molecular orbital method to treat large open-shell systems in solution." Chemical Physics Letters 635 (August 2015): 86–92. http://dx.doi.org/10.1016/j.cplett.2015.06.040.

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18

Ponec, Robert, Alicia Torre, Luis Lain, and Roberto C. Bochicchio. "Multicenter bonding in open-shell systems. A nonlinear population analysis approach." International Journal of Quantum Chemistry 77, no. 4 (2000): 710–15. http://dx.doi.org/10.1002/(sici)1097-461x(2000)77:4<710::aid-qua3>3.0.co;2-x.

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19

Räsänen, E., and S. Pittalis. "Exchange and correlation energy functionals for two-dimensional open-shell systems." Physica E: Low-dimensional Systems and Nanostructures 42, no. 4 (February 2010): 1232–35. http://dx.doi.org/10.1016/j.physe.2009.11.128.

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20

Lee, Mu-Tao, M. M. Fujimoto, S. E. Michelin, I. E. Machado, and L. M. Brescansin. "Elastic electron scattering by open-shell systems: an application to e--NO." Journal of Physics B: Atomic, Molecular and Optical Physics 25, no. 20 (October 28, 1992): L505—L510. http://dx.doi.org/10.1088/0953-4075/25/20/002.

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21

Guseinov, I. I. "Combined open shell Hartree-Fock theory of atomic and molecular systems constructed from noncharged scalar particles." Physics Essays 27, no. 3 (September 9, 2014): 351–55. http://dx.doi.org/10.4006/0836-1398-27.3.351.

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22

Nakano, Masayoshi, Hitoshi Fukui, Takuya Minami, Kyohei Yoneda, Yasuteru Shigeta, Ryohei Kishi, Benoît Champagne, et al. "(Hyper)polarizability density analysis for open-shell molecular systems based on natural orbitals and occupation numbers." Theoretical Chemistry Accounts 130, no. 4-6 (January 13, 2011): 711–24. http://dx.doi.org/10.1007/s00214-010-0871-y.

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23

Bacchus-Montabonel, M. C., and K. Amezian. "Theoretical treatment of electron capture processes for closed- and open- shell systems." International Journal of Quantum Chemistry 45, no. 6 (1993): 709–17. http://dx.doi.org/10.1002/qua.560450618.

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24

TOPOL, I. A., and V. I. POLYAKOV. "Method for Molecular Electronic State Multiplet Structure Calculation in the Space of Xα-SW-Orbitals." International Journal of Modern Physics C 02, no. 01 (March 1991): 510–14. http://dx.doi.org/10.1142/s0129183191000792.

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The SCF-Xα-scattered wave method (Xα-SW) as well as other versions of the density function approach cannot give a proper description of the open-shell many-electron energy levels and thus it is not always possible to reproduce electron spectra adequately by this method. We propose the following way to overcome this drawback of the X α-SW method. First one- and two-particle molecular integrals with Xα-SW molecular orbitals (MO) are calculated numerically. Then these integrals are used to evaluate Hamiltonian matrix elements (both diagonal and off-diagonal) in the basis of configuration state functions. The present scheme allows us to describe molecular electronic spectra in various approximations: a) one-configurational frozen orbitals approach; b) ΔSCF; c) configuration interaction (CI). Our method gives an opportunity to go beyond the muffin-tin (MT) approximation for a potential; inherent in the X α-SW method. In the X α-SW-MO basis it is simple enough to construct the full electron Hamiltonian matrix elements for various open-shell systems.
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25

Poon, Clement, and Paul M. Mayer. "Electron-spin conservation and methyl-substitution effects on bonds in closed- and open-shell systems — A G3 ab initio study of small boron-containing molecules and radicals." Canadian Journal of Chemistry 80, no. 1 (January 1, 2002): 25–30. http://dx.doi.org/10.1139/v01-185.

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High level ab initio molecular orbital theory calculations have been used to study the geometries and thermochemistry of molecules and free radicals substituted by BH2, BHCH3, and B(CH3)2. The heats of formation and RR'B—X bond strengths (RR' = H, H; H, CH3; CH3, CH3 and X = CH3, NH2, OH, F, SiH3, PH2, SH, and Cl) together with those for the open-shell systems RR'B—Y· (RR' = H, H; H, CH3; CH3, CH3 and Y = CH2, NH, O, SiH2, PH, and S) have been calculated at the G3 level of theory. The trends observed for the homolytic bond strengths in the closed-shell systems are those expected from electronegativity arguments, i.e., as the difference in electronegativity between the two atoms in the B—X bond increases, the bond strength increases. Methyl substitution on B in the closed- and open-shell species increases the ionic contribution to the bond thereby decreasing the bond strength. The lowest possible homolytic dissociation energy for the free radicals RR'BY· is lower than those of their closed-shell counterparts, yet the B—Y· bonds are shorter. This is due to the demands of spin conservation in the dissociation of the radicals favouring the formation of higher energy products.Key words: ab initio calculations, bond dissociation energy, organoboron compounds, thermochemistry.
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26

Vaara, Juha. "Quantum-Chemical Approach to Nuclear Magnetic Resonance of Paramagnetic Systems." Annales Academiae Scientiarum Fennicae, no. 1 (May 30, 2023): 96–115. http://dx.doi.org/10.57048/aasf.130117.

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Nuclear magnetic resonance (NMR) is a central method for investigating the microscopic structure and dynamics of molecules and materials, with numerous applications in science, technology, and medicine. Computational modelling is indispensable in NMR research due to the indirect nature of NMR information and the rich physical phenomenology behind its observables. While NMR is conventionally used to study diamagnetic systems, paramagnetic NMR (pNMR) of electronically open-shell systems is rapidly gaining importance. This inaugural article concerns the methodology and application of computational molecular science to the observables pNMR, including current challenges and outlook for the future.
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27

Mackenzie, Campbell F., Peter R. Spackman, Dylan Jayatilaka, and Mark A. Spackman. "CrystalExplorermodel energies and energy frameworks: extension to metal coordination compounds, organic salts, solvates and open-shell systems." IUCrJ 4, no. 5 (July 4, 2017): 575–87. http://dx.doi.org/10.1107/s205225251700848x.

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The application domain of accurate and efficient CE-B3LYP and CE-HF model energies for intermolecular interactions in molecular crystals is extended by calibration against density functional results for 1794 molecule/ion pairs extracted from 171 crystal structures. The mean absolute deviation of CE-B3LYP model energies from DFT values is a modest 2.4 kJ mol−1for pairwise energies that span a range of 3.75 MJ mol−1. The new sets of scale factors determined by fitting to counterpoise-corrected DFT calculations result in minimal changes from previous energy values. Coupled with the use of separate polarizabilities for interactions involving monatomic ions, these model energies can now be applied with confidence to a vast number of molecular crystals. Energy frameworks have been enhanced to represent the destabilizing interactions that are important for molecules with large dipole moments and organic salts. Applications to a variety of molecular crystals are presented in detail to highlight the utility and promise of these tools.
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28

Wilcox, Daniel A., Varad Agarkar, Sanjoy Mukherjee, and Bryan W. Boudouris. "Stable Radical Materials for Energy Applications." Annual Review of Chemical and Biomolecular Engineering 9, no. 1 (June 7, 2018): 83–103. http://dx.doi.org/10.1146/annurev-chembioeng-060817-083945.

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Although less studied than their closed-shell counterparts, materials containing stable open-shell chemistries have played a key role in many energy storage and energy conversion devices. In particular, the oxidation-reduction (redox) properties of these stable radicals have made them a substantial contributor to the progress of organic batteries. Moreover, the use of radical-based materials in photovoltaic devices and thermoelectric systems has allowed for these emerging molecules to have impacts in the energy conversion realm. Additionally, the unique doublet states of radical-based materials provide access to otherwise inaccessible spin states in optoelectronic devices, offering many new opportunities for efficient usage of energy in light-emitting devices. Here, we review the current state of the art regarding the molecular design, synthesis, and application of stable radicals in these energy-related applications. Finally, we point to fundamental and applied arenas of future promise for these designer open-shell molecules, which have only just begun to be evaluated in full.
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29

Argaez, C., and M. Melgaard. "Minimizers for open-shell, spin-polarised Kohn–Sham equations for non-relativistic and quasi-relativistic molecular systems." Methods and Applications of Analysis 23, no. 3 (2016): 269–92. http://dx.doi.org/10.4310/maa.2016.v23.n3.a4.

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30

Yamaguchi, K., M. Okumura, K. Takada, and S. Yamanaka. "Instability in chemical bonds. II. Theoretical studies of exchange-coupled open-shell systems." International Journal of Quantum Chemistry 48, S27 (March 13, 1993): 501–15. http://dx.doi.org/10.1002/qua.560480848.

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31

NAKANO, MASAYOSHI, SATORU YAMADA, RYOHEI KISHI, MASAHIRO TAKAHATA, TOMOSHIGE NITTA, and KIZASHI YAMAGUCHI. "THEORETICAL STUDY ON THE SECOND HYPERPOLARIZABILITY (γ) OF A HOMOGENEOUS MOLECULE IN THE BOND DISSOCIATION PROCESS: ENHANCEMENT OF γ IN THE INTERMEDIATE CORRELATION REGIME." Journal of Nonlinear Optical Physics & Materials 13, no. 03n04 (December 2004): 411–16. http://dx.doi.org/10.1142/s0218863504002031.

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The variation in the longitudinal second hyperpolarizability (γ) in the bond-dissociation process of a homogeneous molecule ( H 2) is investigated by the finite-field (FF) approach using several ab initio molecular orbital (MO) and density functional (DF) methods. The most accurate methods (UCCSD or RCCSD) employed in this study show that the magnitude of γ value is remarkably enhanced in the intermediate dissociation region, which corresponds to the intermediate correlation regime. Such behavior suggests that the magnitudes of γ values for open-shell neutral compounds in the intermediate correlation regime are remarkably enhanced as compared to the usual closed-shell neutral systems.
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32

Willitsch, Stefan, Frédéric Merkt, Mihály Kállay, and Jürgen Gauss. "Thermochemical properties of small open-shell systems: experimental and high-levelab initioresults for NH2and." Molecular Physics 104, no. 9 (May 10, 2006): 1457–61. http://dx.doi.org/10.1080/13895260500518551.

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33

Aquilanti, V., R. Candori, E. Luzzatti, F. Pirani, and G. G. Volpi. "Molecular beam studies of open‐shell systems: The van der Waals interaction between O(3P) and He(1S)." Journal of Chemical Physics 85, no. 9 (November 1986): 5377–78. http://dx.doi.org/10.1063/1.451159.

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34

Nakano, Masayoshi, Hitoshi Fukui, Takuya Minami, Kyohei Yoneda, Yasuteru Shigeta, Ryohei Kishi, Benoît Champagne, et al. "Erratum to: (Hyper)polarizability density analysis for open-shell molecular systems based on natural orbitals and occupation numbers." Theoretical Chemistry Accounts 130, no. 4-6 (November 2, 2011): 725–26. http://dx.doi.org/10.1007/s00214-011-1064-z.

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35

Aquilanti, Vincenzo, Simonetta Cavalli, Lev Yu Rusin, and Mikhail B. Sevryuk. "Post-adiabatic approach to atomic and molecular processes: The van der Waals interactions of some open shell systems." Theoretica Chimica Acta 90, no. 4 (February 1995): 225–56. http://dx.doi.org/10.1007/bf01113470.

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36

Kitakawa, Colin, Tomohiro Maruyama, Jinta Oonari, Yuki Mitsuta, Takashi Kawakami, Mitsutaka Okumura, Kizashi Yamaguchi, and Shusuke Yamanaka. "Linear Response Functions of Densities and Spin Densities for Systematic Modeling of the QM/MM Approach for Mono- and Poly-Nuclear Transition Metal Systems." Molecules 24, no. 4 (February 25, 2019): 821. http://dx.doi.org/10.3390/molecules24040821.

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We applied our analysis, based on a linear response function of density and spin density, to two typical transition metal complex systems-the reaction centers of P450, and oxygen evolving center in Photosystem II, both of which contain open-shell transition metal ions. We discuss the relationship between LRF of electron density and spin density and the types of units and interactions of the systems. The computational results are discussed in relation to quantum mechanics (QM) cluster and quantum mechanics/molecular mechanics (QM/MM) modeling that are employed to compute the reaction centers of enzymes.
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37

Hal�sz, G., �. Vib�k, and S. Suhai. "A BSSE-free SCF algorithm for intermolecular interactions. IV. Generalization for open-shell systems." International Journal of Quantum Chemistry 68, no. 3 (1998): 151–58. http://dx.doi.org/10.1002/(sici)1097-461x(1998)68:3<151::aid-qua2>3.0.co;2-u.

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38

Lindgren, Ingvar. "A coupled-cluster approach to the many-body perturbation theory for open-shell systems." International Journal of Quantum Chemistry 14, S12 (June 18, 2009): 33–58. http://dx.doi.org/10.1002/qua.560140804.

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39

Szymczak, J. J., R. W. Gora, S. Roszak, D. Majumdar, J. Wang, S. J. Grabowski, and J. Leszczynski. "Proton bound open shell systems – theoretical studies on O2H+(O2)n(n = 1–6) complexes." Molecular Physics 104, no. 13-14 (July 10, 2006): 2327–36. http://dx.doi.org/10.1080/00268970600654876.

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40

Altun, Ahmet, Masaaki Saitow, Frank Neese, and Giovanni Bistoni. "Local Energy Decomposition of Open-Shell Molecular Systems in the Domain-Based Local Pair Natural Orbital Coupled Cluster Framework." Journal of Chemical Theory and Computation 15, no. 3 (January 31, 2019): 1616–32. http://dx.doi.org/10.1021/acs.jctc.8b01145.

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41

Aquilanti, Vincenzo, Roberto Candori, and Fernando Pirani. "Molecular beam studies of weak interactions for open‐shell systems: The ground and lowest excited states of rare gas oxides." Journal of Chemical Physics 89, no. 10 (November 15, 1988): 6157–64. http://dx.doi.org/10.1063/1.455432.

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42

Plakhutin, Boris N., and Ernest R. Davidson. "Comment on “Combined open shell Hartree–Fock theory of atomic-molecular and nuclear systems” [J. Math. Chem. 42 (2007) 177]." Journal of Mathematical Chemistry 45, no. 3 (July 8, 2008): 859–66. http://dx.doi.org/10.1007/s10910-008-9396-1.

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43

Glushkov, V. N., and S. Wilson. "Distributed Gaussian basis sets: Variationally optimizeds-type sets for the open-shell systems HeH and BeH." International Journal of Quantum Chemistry 99, no. 6 (2004): 903–13. http://dx.doi.org/10.1002/qua.20143.

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44

Pamuk, H. Önder, and Carl Trindle. "Semiempirical estimation of correlation energy corrections to ionization potentials and dissociation energies for open-shell systems." International Journal of Quantum Chemistry 14, S12 (June 18, 2009): 271–82. http://dx.doi.org/10.1002/qua.560140821.

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45

Aquilanti, Vincenzo, Emilio Luzzatti, Fernando Pirani, and Gian Gualberto Volpi. "Molecular beam studies of weak interactions for open‐shell systems: The ground and lowest excited states of ArF, KrF, and XeF." Journal of Chemical Physics 89, no. 10 (November 15, 1988): 6165–75. http://dx.doi.org/10.1063/1.455433.

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46

Peirs, K., D. Van Neck, and M. Waroquier. "Self-consistent solution of Dyson's equation up to second order for closed- and open-shell atomic systems." International Journal of Quantum Chemistry 91, no. 2 (2002): 113–18. http://dx.doi.org/10.1002/qua.10405.

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47

Puzzarini, Cristina, and Vincenzo Barone. "Toward spectroscopic accuracy for open-shell systems: Molecular structure and hyperfine coupling constants of H2CN, H2CP, NH2, and PH2 as test cases." Journal of Chemical Physics 133, no. 18 (November 14, 2010): 184301. http://dx.doi.org/10.1063/1.3503763.

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48

Neogrády, Pavel, and Miroslav Urban. "Spin-Adapted restricted Hartree-Fock reference coupled-cluster theory for open-shell systems: Noniterative triples for noncanonical orbitals." International Journal of Quantum Chemistry 55, no. 2 (July 15, 1995): 187–203. http://dx.doi.org/10.1002/qua.560550214.

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49

Pavlov, R. L., J. Maruani, Ya I. Delchev, and R. McWeeny. "Density functional theory for open-shell systems using a local-scaling transformation scheme. I. Single-density energy functional." International Journal of Quantum Chemistry 65, no. 3 (1997): 241–56. http://dx.doi.org/10.1002/(sici)1097-461x(1997)65:3<241::aid-qua5>3.0.co;2-w.

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50

LIU, MIN-HSIEN, KEN-FA CHENG, CHENG CHEN, and YAW-SUN HONG. "SOLVENT EFFECT ON ELECTROPHILIC AND RADICAL SUBSTITUTION OF TOLUENE MONONITRATION REACTIONS." Journal of Theoretical and Computational Chemistry 07, no. 05 (October 2008): 965–76. http://dx.doi.org/10.1142/s0219633608004222.

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Abstract:
Two kinds of nitrating reagents, a nitronium cation [Formula: see text] and a nitro radical (· NO 2), were used in the gaseous phase toluene mononitration reaction. The closed shell calculation for electrophilic substitution and open shell calculation for radical substitution were both performed in solventless, H 2 O -solvated, and CH 3 OH -solvated molecular reaction systems. In the series of electrophilic toluene nitration reactions, both ortho-nitro toluene (o-MNT) and para-nitro toluene (p-MNT) are more abundant products than meta-nitro toluene (m-MNT), no matter what solvent is used in the reaction system. The reaction energy barrier for obtaining each kind of mononitro toluene follows a stepwise decreasing trend when the reaction is carried out in the solventless, H 2 O -solvated, and CH 3 OH -solvated systems. In all radical toluene nitration reactions, solventless or solvated, m-MNT is the most abundant product. The energy barrier data also show that the nitration reaction is more feasible in a solvated than in a solventless system. H 2 O has a more obvious solvent effect than CH 3 OH in the · NO 2 radical substitution reaction, and the H 2 O -solvated system provides a lower activation energy reaction path.
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