GENERALIZED VALENCE-BOND MOLECULAR EQUILIBRIUM GEOMETRIES

Equilibrium geometries have been obtained at the generalized valence bond (GVB) level for one- and two-heavy-atom molecules and radicals (AH(n) and AH(m)BH(n)) containing first- or second-row elements. The results are compared with the available experimental and theoretical (HF, MP2 and CID) values. The effect of basis set on the GVB equilibrium geometries is also discussed. The results indicate that the addition of d-polarization or diffuse functions to the split valence basis set is necessary to obtain reasonable GVB geometries. In general, geometrical parameters from the GVB/6-31G* calculations, which treat electron correlation by using the coupling of GVB perfect-pairing orbitals, are in better agreement with the experimental data than those obtained from the corresponding HF wavefunction. The GVB/6-31G* geometries are close to the corresponding MP2 or CID geometries. GVB calculations are especially useful for the proper description of multiple bonds.