Quantum chemical valence indices from the one-determinantal difference approach

Abstract

The recently introduced quadratic (two-electron) valence indices, ionic and covalent, derived from the HartreeFock finite-difference approach, are applied to selected organic and inorganic molecules to demonstrate their utility in monitoring chemical bonding patterns in molecular systems. The indices are defined in terms of differerences between simultaneous probabilities of finding two electrons on specified atoms, calculated from the molecular and separated-atomlimit (SAL) wave functions, respectively, in the UHF approximation. The total quadratic valence number represents the overall number of chemical bonds in the system under consideration; it is interpreted as the molecular expectation value of the difference operator of the molecular and SAL density operators. This interpretation leads to a new set of ionic atomic and diatomic valence components; these modified valence numbers are discussed using the two-orbital model in the UHF scheme. A new procedure is proposed for dividing the one-center contributions to the bond valences; it generates effective bond orders in qood agreement with chemical expectations. The new valence quantities are tested on selected typical molecules and prototype hydrogen-bonded dimers. A more extensive study has been canied out on small-ring propellanes, to examine changes in bond valences between bridgehead atoms in selected systems.

On the asymmetry in molybdenum–oxygen bonding in the MoO3 structure: ETS–NOCV analysis

“…The NOCV have been derived from the NalewajskiMrozek valence theory [40][41][42][43][44][45] as eigenvectors that diagonalize the deformation density matrix. It was shown that the pairs of the natural orbitals for chemical valence (w -k , w k , corresponding to eigenvalues -v k and v k ) decompose the differential density Dq into NOCV-contributions (Dq k ):…”

Chemical bonds from through-bridge orbital communications in prototype molecular systems

“…A similar description follows [1][2][3] from the Wiberg-type bond-multiplicities formulated in the MO theory [4,[14][15][16][17][18][19][20][21][22][23]. In MO description the chemical interaction between, say, two (valence) AO or general basis functions originating from different atoms is strongly influenced by their direct overlap and interaction, which both condition the bonding effect experienced by electrons occupying their bonding combination in the molecule, compared to the non-bonding reference of electrons on separated AO.…”

“…This quadratic bond-multiplicity concept has been subsequently extended [14][15][16] and generalized in terms of the bond-orders from the two-electron difference approach [17][18][19][20][21][22][23]. It follows from Eq.…”

Communications in molecules: local and multi-configuration channels and their entropic descriptors of bond multiplicity and composition

“…It vanishes for the lone-pair configurations, when P = (0 or 1), This simple model thus properly accounts for the competition between the bond covalency and ionicity, while preserving the single bond-order measure reflected by the conserved single IT multiplicity of the chemical bond. Similar effects transpire from the quadratic bond indices formulated in the MO theory [87][88][89][90][91][92][93][94][95][96][97]. For example, the plot of Wiberg bond-order [87] for this model (see Fig.…”