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Substituent effects in second‐row molecules: Basis set performance in calculations of normal valency phosphorus and sulfur compounds
Author(s) -
Magnusson Eric
Publication year - 1984
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.540050616
Subject(s) - basis set , chemistry , valence (chemistry) , substituent , isodesmic reaction , computational chemistry , valence electron , molecule , valency , density functional theory , molecular orbital , crystallography , atomic physics , molecular physics , electron , stereochemistry , physics , quantum mechanics , organic chemistry , linguistics , philosophy
Abstract Ab inito molecular orbital calculations of the phosphorus‐ and sulfur‐containing series PH 2 X , PH 3 X + , SH X , and SH 2 X + ( X = H, CH 3 , NH 2 , OH, F) have been carried out over a range of Gaussian basis sets and the results (optimized geometrical structures, relative energies, and electron distributions) critically compared. As in first‐row molecules there are large discrepancies between substituent interaction energies at different basis set levels, particularly in electron‐rich molecules; use of basis sets lower than the supplemented 6‐31G basis incurs the risk of obtaining substituent stabilizations with large errors, including the wrong sign. Only a small part of the discrepancies is accounted for by structural differences between the optimized geometries. Supplementation of low level basis sets by d functions frequently leads to exaggerated stabilization energies for π‐donor substituents. Poor performance also results from the use of split valence basis sets in which the valence shell electron density is too heavily concentrated in diffuse component of the valence shell functions, again likely to occur in electron‐rich molecules. Isodesmic reaction energies are much less sensitive to basis set variation, but d function supplementation is necessary to achieve reliable results, suggesting a marginal valence role for d functions, not merely polarization of the bonding density. Optimized molecular geometries are relatively insensitive to basis set and electron population analysis data, for better‐than‐minimal bases, are uniform to an unexpected degree.