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Molecular orbital calculations of valency within the framework of a general non-singular transformation of the atomic orbital basis sets

1990; Elsevier BV; Volume: 209; Issue: 1-2 Linguagem: Inglês

10.1016/0166-1280(90)85044-n

1872-7999

Tapas Kar, Lingaraj Behera, A.B. Sannigrahi,

Advanced Chemical Physics Studies

Atomic charges, valencies and molecular orbital (MO) valencies of a number of simple molecules containing first- and second-row atoms were calculated within the framework of the general non-singular transformation. Φ = χ S−, where {χa} is a non-orthogonal atomic orbital (AO) basis set with the overlap matrix S, and n can take any finite value. The parameter n was varied within the range −0.50 ⩽ = n ⩽ = 0.50, and basis sets ranging from 4-31G to 6-31G∗∗ were used. Apart from a few molecules with a second-row atom and basis sets like 6-31G∗, 6-31G∗∗, etc., the lowest values of atomic charges are obtained for n = 0.50. This value of n predicts maximum valencies in all cases. With the exception of highly ionic molecules, quite absurd values of atomic charges and valencies were obtained for n < 0.0. The plots of molecular valency (VM) vs. θ in linear molecules show maxima at θ = 180° for positive values of n and all basis sets. However, in the case of non-linear molecules the θ values corresponding to maximum VM deviate considerably from those obtained by minimising energy. Mulliken-Walsh type correlation diagrams were plotted for a few molecules using MO valencies as the ordinate. For n < 0.0, these plots generally show erratic behaviour. Finally the localised MO (LMO) valencies of a number of molecules were calculated for n = 1 and their possible usefulness is discussed.