The Experts below are selected from a list of 174 Experts worldwide ranked by ideXlab platform
Uğur Bozkaya - One of the best experts on this subject based on the ideXlab platform.
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Orbital-Optimized MP3 and MP2.5 with Density-Fitting and Cholesky Decomposition Approximations
Journal of Chemical Theory and Computation, 2016Co-Authors: Uğur BozkayaAbstract:Efficient implementations of the orbital-optimized MP3 and MP2.5 methods with the density-fitting (DF-OMP3 and DF-OMP2.5) and Cholesky decomposition (CD-OMP3 and CD-OMP2.5) approaches are presented. The DF/CD-OMP3 and DF/CD-OMP2.5 methods are applied to a set of alkanes to compare the computational cost with the conventional orbital-optimized MP3 (OMP3) [Bozkaya J. Chem. Phys. 2011, 135, 224103] and the orbital-optimized MP2.5 (OMP2.5) [Bozkaya and Sherrill J. Chem. Phys. 2014, 141, 204105]. Our results demonstrate that the DF-OMP3 and DF-OMP2.5 methods provide considerably lower computational costs than OMP3 and OMP2.5. Further application results show that the orbital-optimized methods are very helpful for the study of open-shell noncovalent interactions, Aromatic Bond dissociation energies, and hydrogen transfer reactions. We conclude that the DF-OMP3 and DF-OMP2.5 methods are very promising for molecular systems with challenging electronic structures.
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Assessment of Orbital-Optimized MP2.5 for Thermochemistry and Kinetics: Dramatic Failures of Standard Perturbation Theory Approaches for Aromatic Bond Dissociation Energies and Barrier Heights of Radical Reactions.
Journal of Chemical Theory and Computation, 2015Co-Authors: Emine Soydaş, Uğur BozkayaAbstract:An assessment of orbital-optimized MP2.5 (OMP2.5) [Bozkaya, U.; Sherrill, C. D. J. Chem. Phys. 2014, 141, 204105] for thermochemistry and kinetics is presented. The OMP2.5 method is applied to closed- and open-shell reaction energies, barrier heights, and Aromatic Bond dissociation energies. The performance of OMP2.5 is compared with that of the MP2, OMP2, MP2.5, MP3, OMP3, CCSD, and CCSD(T) methods. For most of the test sets, the OMP2.5 method performs better than MP2.5 and CCSD, and provides accurate results. For barrier heights of radical reactions and Aromatic Bond dissociation energies OMP2.5–MP2.5, OMP2–MP2, and OMP3–MP3 differences become obvious. Especially, for Aromatic Bond dissociation energies, standard perturbation theory (MP) approaches dramatically fail, providing mean absolute errors (MAEs) of 22.5 (MP2), 17.7 (MP2.5), and 12.8 (MP3) kcal mol–1, while the MAE values of the orbital-optimized counterparts are 2.7, 2.4, and 2.4 kcal mol–1, respectively. Hence, there are 5–8-folds reductions i...
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Analytic Energy Gradients and Spin Multiplicities for Orbital-Optimized Second-Order Perturbation Theory with Density-Fitting Approximation: An Efficient Implementation.
Journal of Chemical Theory and Computation, 2014Co-Authors: Uğur BozkayaAbstract:An efficient implementation of analytic energy gradients and spin multiplicities for the density-fitted orbital-optimized second-order perturbation theory (DF-OMP2) [Bozkaya, U. J. Chem. Theory Comput. 2014, 10, 2371–2378] is presented. The DF-OMP2 method is applied to a set of alkanes, conjugated dienes, and noncovalent interaction complexes to compare the cost of single point analytic gradient computations with the orbital-optimized MP2 with the resolution of the identity approach (OO-RI-MP2) [Neese, F.; Schwabe, T.; Kossmann, S.; Schirmer, B.; Grimme, S. J. Chem. Theory Comput. 2009, 5, 3060–3073]. Our results demonstrate that the DF-OMP2 method provides substantially lower computational costs for analytic gradients than OO-RI-MP2. On average, the cost of DF-OMP2 analytic gradients is 9–11 times lower than that of OO-RI-MP2 for systems considered. We also consider Aromatic Bond dissociation energies, for which MP2 provides poor reaction energies. The DF-OMP2 method exhibits a substantially better perfo...
Jay K. Kochi - One of the best experts on this subject based on the ideXlab platform.
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Novel Synthesis and Structures of Tris-Annelated Benzene Donors for the Electron-Density Elucidation of the Classical Mills−Nixon Effect
Journal of the American Chemical Society, 1998Co-Authors: Rajendra Rathore, Sergey V. Lindeman, Arvind Kumar, Jay K. KochiAbstract:A versatile method for the high-yield synthesis of various tris-, bis-, and mono-annelated benzenes (as well as cyclooctatetraene) is based on the Pd-catalyzed coupling of three (or four) ethylenic units comprised of α,β-dibromoalkenes and α‘-alkenyl Grignard reagentsall carried out in a single pot. The particular application to tris(bicyclopentyl)-annelated benzene yields the syn isomer 1s in high purity; X-ray diffraction analysis confirms the Aromatic Bond alternation relevant to the Mills−Nixon effect. Most importantly, the efficient synthesis of 1s crystals of extraordinary quality allows us (for the first time) to make precise electron-density measurements of the “banana-type” distortion and the ellipticity (π-character) of the various Aromatic C−C Bondssufficient to identify the electronic origin of the classical Mills−Nixon effect. The unique electron-donor properties of tris-annelated benzenes also relate to their highly reversible one-electron oxidation potentials even in nonpolar solvents.
Volodymyr Bezverkhniy - One of the best experts on this subject based on the ideXlab platform.
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Structure of the Benzene Molecule on the Basis of the Three-Electron Bond
viXra, 2017Co-Authors: Volodymyr BezverkhniyAbstract:Using the concept of three-electron Bond one can represent the actual electron structure of benzene, explain specificity of the Aromatic Bond and calculate the delocalization energy. It was shown, that functional relation y = a + b/x + c/x^2 fully describes dependence of energy and multiplicity of chemical Bond on Bond distance. In this article carbon-to-carbon Bonds are reviewed. Using these dependences it is possible to calculate chemical bound energy by different Bond distance or different multiplicity of chemical Bond, that makes possible to calculate delocalization energy of benzene molecule.
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Review. Benzene on the Basis of the Three-Electron Bond. Theory of Three-Electron Bond in the Four Works with Brief Comments
viXra, 2017Co-Authors: Volodymyr BezverkhniyAbstract:Using the concept of three-electron Bond we can represent the actual electron structure of benzene and other molecules, explain specificity of the Aromatic Bond and calculate the delocalization energy. Gives theoretical justification and experimental confirmation of existence of the three-electron Bond. It was shown, that functional relation y = a + b/x + c/x^2 fully describes dependence of energy and multiplicity of chemical Bond from Bond distance.
Bezverkhniy Volodymyr Dmytrovych - One of the best experts on this subject based on the ideXlab platform.
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Review. Benzene on the Basis of the Three-Electron Bond. (The Pauli Exclusion Principle, Heisenberg's Uncertainty Principle and Chemical Bond).
viXra, 2017Co-Authors: Bezverkhniy Volodymyr Dmytrovych, Bezverkhniy Vitaliy Volodymyrovich.Abstract:The present work shows the inapplicability of the Pauli principle to chemical Bond, and a new theoretical model of the chemical Bond is proposed based on the Heisenberg uncertainty principle. See pp. 88 - 104. Using the concept of three-electron Bond we can represent the actual electron structure of benzene and other molecules, explain specificity of the Aromatic Bond and calculate the delocalization energy. Gives theoretical justification and experimental confirmation of existence of the three-electron Bond. It was shown, that functional relation y = a + b/x + c/x^2 fully describes dependence of energy and multiplicity of chemical Bond from Bond distance.
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Theory of Three-Electron Bond in the Four Works with Brief Comments
Organic Chemistry: Current Research, 2017Co-Authors: Bezverkhniy Volodymyr DmytrovychAbstract:Using the concept of three-electron Bond we can represent the actual electron structure of benzene and other molecules, explain specificity of the Aromatic Bond and calculate the delocalization energy. Gives theoretical justification and experimental confirmation of existence of the three-electron Bond. It was shown, that functional relation y=a+b/x+c/ x2 fully describes dependence of energy and multiplicity of chemical Bond from Bond distance.
Ivan Bernal - One of the best experts on this subject based on the ideXlab platform.
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Structural properties of dicyclopentenobenzo-cyclobutene, a small ring tris-annelated benzene
Tetrahedron, 2001Co-Authors: James D. Korp, Randolph P. Thummel, Ivan BernalAbstract:Abstract The synthesis of dicyclopententobenzocyclobutene from 1,1-dicyclopentenyl and dimethyl cyclobutene-1,2-dicarboxylate is described. Current theories regarding sterically induced Aromatic Bond alternation would predict that both the σ and π frameworks should show more double Bond character exocyclic to the small fused rings. The structural parameters of dicyclopentenobenzocyclobutene have been determined by single crystal X-ray analysis. No significant Bond alternation is observed in the central ring. The thermal ellipsoids for the cyclopentene rings show the non-benzylic methylene groups to be moving perpendicularly through the plane of the molecule while the adjacent benzylic methylenes compensate by lateral movement in the plane.
