Valence bond theory for chemical dynamics

Abstract

This essay provides a perspective on several issues in valence bond theory: the physical significance of semilocal bonding orbitals, the capability of valence bond concepts to explain systems with multireferences character, the use of valence bond theory to provide analytical representations of potential energy surfaces for chemical dynamics by the method of semiempirical valence bond potential energy surfaces (an early example of specific reaction parameters), by multiconfiguration molecular mechanics, by the combined valence bond-molecular mechanics method, and by the use of valence bond states as coupled diabatic states for describing electronically nonadiabatic processes (photochemistry). The essay includes both ab initio and semiempirical approaches.

Implementation of Umbrella Integration within the Framework of the Empirical Valence Bond Approach

“…The Gram-Charlier expansion is of the form 24 (13) where are Chebyshev-Hermite polynomials, σ i b is the variance, and κ n are the cumulants of the distribution P i b (ξ). The asymptotic Edgeworth expansion can be presented in the following compact form 25 (14) where , {k m } are the solutions of the Diophantine eqution k 1 + 2k 2 +…+sk s = s, and r = k 1 + k 2 +…+k s . These asymptotic expansions are useful when the biased distributions for some windows differ from the normal distributions.…”

The Diabatic Picture of Electron Transfer, Reaction Barriers, and Molecular Dynamics

“…• Valence Bond Theory Although not widely publicized, Pauling's idea of resonance structures within valence bond (VB) theory [44] provides a natural definition of diabatic states [45,46]. For example, bonding in NaCl involves two resonance structures -|Na + Cl − and |Na : Cl -which clearly have diabatic character from an electron transfer perspective.…”

Empirical Valence Bond Theory Studies of the CH4 + Cl → CH3 + HCl Reaction

“…A popular approach is to fit the ab initio energies with a suitably chosen set of analytical functions. [6][7] This method works best if only a few atoms are included in the system.…”