Electron-Following Mapping Transformations from the Electronegativity Equalization Principle

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 104; no. 23; pp. 5638 - 5646
• Main Authors: Nalewajski, Roman F, Sikora, Olga
• Format: Journal Article
• Language: English
• Published: American Chemical Society 15-06-2000
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp000372u

The so-called electron-following (EF) mapping relations for the closed molecular systems are derived within the charge sensitivity analysis (CSA) in atomic resolution, using the electronegativity equalization principle of Sanderson. They are tested on selected small molecules and model molecular adducts. For the fixed overall charge Q of a given molecular system, these relations determine the transformation T(Q → q) Q = (∂q/∂Q) Q of displacements ΔQ in the nuclear coordinates Q (perturbations) into the concomitant shifts (Δq) Q of atomic charges q (responses):  (Δq) Q = ΔQ T(Q → q) Q . The differential CSA EF “translators” T(Q → q) Q have been determined for diatomics (HX, X = F, Cl, Br), water, ethane, and model molecular complexes (HF- - -HF, H2O- - -HCl, ClH- - -NH3). The translator charge variation trends are then numerically validated by comparing them with the corresponding plots obtained from the equilibrium CSA charge distributions for several molecular geometries. The CSA EF charge variations are also compared with those resulting from the reference SCF MO [MNDO, ab initio] and Kohn−Sham calculations and several partitioning schemes of a molecular electron density into atomic charges. The charge variations accompanying bond stretches in HX are found to be strongly dependent on both the method and partitioning scheme applied.