Electron group functions for the analysis of the electronic structures of molecules

Abstract

The electronic structure of a vast majority of molecular systems can be understood in terms of electron groups and their wave functions. They serve as a natural basis for bringing intuitive chemical and physical concepts into quantum chemical calculations. This article considers the general electron group functions formalism as well as its simple geminal version. We try to characterize the wave function with the group structure and its capabilities in actual calculations. For this purpose we implement a variational method based on the wave function in the form of an antisymmetrized product of strongly orthogonal group functions and perform a series of electronic structure calculations for small molecules and model systems. The most important point studied is the relation between the choice of electron groups and the results obtained. We consider energetic characteristics as well as optimal geometry parameters. In view of practical importance, the structure of variationally optimized local one-electron states is considered in detail as well as intuitive characteristics of chemical bonds.

The electronic mean field configuration interaction method: III – the p-orthogonality constraint

“…In the second class, one finds methods based on valence-bond wave functions, such as those implemented in the code TURTLE [12], and XMVB [13], or on more general group function products as implemented in the code VB2000 [14]. A fairly extensive bibiliography on early works using group function product wave functions has been given in a previous article of this series [3], a few other relevant references are [15][16][17][18][19][20][21][22]. More references on non-orthogonal methods can be found in Ref.…”

Strongly separated pairs of core electrons in computed ground states of small molecules

“…If Ψ has the form (2), then there exist orthogonal subspaces G and H of the 1-electron space such that g is a superposition of 2-particle Slater determinants of spin-orbitals from G while h is a superposition of Slater determinants of N − 2 spin-orbitals from H. The subspace G belonging to the separated electron pair has been called the pair's "orbital domain" [3], "Arai subspace" [2], and "carrier space" [25].…”

MNDO parameterized hybrid SLG/SCF method as used for molecular modeling of Zn(II) complexes

“…The quantum chemical scheme 8–11 is implemented with use of semi‐empirical Hamiltonians. (There are also methods employing optimized carrier spaces in the ab initio context 13–15.) The MINDO/3 16, MNDO 17, AM1 18, and PM3 19 parameterizations for the molecular Hamiltonian were used.…”