Arrangement of bases and quantitative results

A goal of this chapter is to show, for the diatomic molecules under discussion, both the capability of the VB method in providing quantitative estimates of molecular properties and its capability of giving qualitative pictures of the bonding. The quantitative results are illustrated in Table 11.1, where we give values for Rg, the equilibrium bond distance, and determined theoretically with ST03G, 6-3IG, 

In Chapter 9 we gave a somewhat generic description of the way we arrange basis sets. More details are given here. 

ST03G Each of the treatments may be described as a full valence calculation. The details of numbers of VB stmctures is given below in Table 11.4. 

6-31G The VB stmcture basis is a full valance set augmented by stractmes involving a single excitation from one valence orbital to one virtual orbital, using all possible combinations of the excitation (outside the s shells). Table 11.2 shows the number of symmetry functions (the dimension of the H and S matrices) for each case. 

6-31G The AO basis in this case is the same as that for the 6-31G set with a set of d orbitals added. In these calculations the d and the d oibitals are included in the virtual orbital set in which single excitations are included in generating stmctmes. The ds orbitals were not used. The inclusion of these d orbitals provides polarization when the molecule is formed. 

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