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The role of d functions in ab initio calculations. II. The deformation densities of SO 2 , NO 2 , and their ions
Author(s) -
Cruickshank D. W. J.,
Eisenstein M.
Publication year - 1987
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540080103
Subject(s) - hypervalent molecule , atomic orbital , valence (chemistry) , ion , ab initio , atomic physics , atom (system on chip) , valence electron , electron , chemistry , charge density , physics , crystallography , molecular physics , quantum mechanics , reagent , computer science , embedded system
Comparison of the optimized geometries and SCF energies for the series XO 2 + , XO 2 , XO 2 − , XO 2 − , with X = S,N shows that d (S) functions cause larger bond shortening and energy drop than d functions centered on first‐row atoms. This is further emphasized on comparing the separate effects of d (central atom) and d (O) functions for SO 2 and NO 2 − , which are similar only for the first‐row molecule. The d (S) functions are also essential for proper prediction of the OSO angles. The deformation densities calculated for each series and the corresponding X–O shared populations, change as expected on adding electrons first into σ* then into π* molecular orbitals. In the regions around nuclei the deformation densities express the behavior of the atomic s and p valence orbitals or of their product inside their radial nodes. Introduction of d functions causes substantial polarization effects. For X = N these are mostly local except in the bonding regions where d (N) and d (O) functions are somewhat interchangeable. However, d (S) functions induce also unique changes in the deformation density near O. They cause π and π′ charge migration from O to S and a σ flow in the opposite direction. These effects are largest for the hypervalent species. The unique populations of the d (S) functions are much larger than those of d (N) and d (O) functions. The contribution of d (S) functions to bonding is related to the larger amplitude at small radii of the atomic 3 d (S) orbital as compared with that of 3 d (N). The difference in amplitudes is related to penetration effects. Diffuse p functions affect geometries and SCF energies of doubly, but not singly negative ions. However, they mostly describe the diffuse nonbonding clouds and do not affect bonding patterns.