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Electron Pair Density (electron + pair_density)
Selected AbstractsNecessary conditions for the N -representability of pair distribution functionsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2006Paul W. Ayers Abstract A necessary condition for the N -representability of the electron pair density proposed by one of the authors (E. R. D.) is generalized. This shows a link between this necessary condition and other, more widely known, N -representability conditions for the second-order density matrix. The extension to spin-resolved electron pair densities is considered, as is the extension to higher-order distribution functions. Although quantum mechanical systems are our primary focus, the results are also applicable to classical systems, where they reduce to an inequality originally derived by Garrod and Percus. As a simple application, bounds to the average angle between an electron pair are derived. It is shown that computational methods based on variational minimization of the energy with respect to the electron pair density can give extremely poor results unless robust N -representability constraints are considered. For reference, constraints for the N -representability of the pair density are summarized. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Electron localizability indicators ELI and ELIA: The case of highly correlated wavefunctions for the argon atomJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2008Viktor Bezugly Abstract Electron localizability indicators based on the same-spin electron pair density and the opposite-spin electron pair density are studied for correlated wavefunctions of the argon atom. Different basis sets and reference spaces are used for the multireference configuration interaction method following the complete active space calculations aiming at the understanding of the effect of local electron correlation when approaching the exact wavefunction. The populations of the three atomic shells of Ar atom in real space are calculated for each case. © 2007 Wiley Periodicals, Inc. J Comput Chem 29: 1198,1207, 2008 [source] Chemical bonding: From Lewis to atoms in moleculesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2007R. F. W. Bader Abstract The Lewis electron pair concept and its role in bonding are recovered in the properties of the electron pair density and in the topology of the Laplacian of the electron density. These properties provide a bridge with the quantum mechanical description of bonding determined by the Feynman, Ehrenfest, and virial theorems, bonding being a consequence of the electrostatic forces acting within a molecular system. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Charge-Shift Bonding,A Class of Electron-Pair Bonds That Emerges from Valence Bond Theory and Is Supported by the Electron Localization Function ApproachCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005Sason Shaik Prof. Abstract This paper deals with a central paradigm of chemistry, the electron-pair bond. Valence bond (VB) theory and electron-localization function (ELF) calculations of 21 single bonds demonstrate that along the two classical bond families of covalent and ionic bonds, there exists a class of charge-shift bonds (CS bonds) in which the fluctuation of the electron pair density plays a dominant role. In VB theory, CS bonding manifests by way of a large covalent-ionic resonance energy, RECS, and in ELF by a depleted basin population with large variances (fluctuations). CS bonding is shown to be a fundamental mechanism that is necessary to satisfy the equilibrium condition, namely the virial ratio of the kinetic and potential energy contributions to the bond energy. The paper defines the atomic propensity and territory for CS bonding: Atoms (fragments) that are prone to CS bonding are compact electronegative and/or lone-pair-rich species. As such, the territory of CS bonding transcends considerations of static charge distribution, and involves: a) homopolar bonds of heteroatoms with zero static ionicity, b) heteropolar , and , bonds of the electronegative and/or electron-pair-rich elements among themselves and to other atoms (e.g., the higher metalloids, Si, Ge, Sn, etc), c) all hypercoordinate molecules. Several experimental manifestations of charge-shift bonding are discussed, such as depleted bonding density, the rarity of ionic chemistry of silicon in condensed phases, and the high barriers of halogen-transfer reactions as compared to hydrogen-transfers. [source] | ||||||||||