Valence bond study on excited states of molecules

Based on the correspondence of the molecular orbital theory and valence bond theory to the description of chemical bonds, theab initio valence bond (VB) calculations of the low-lying states of diatomic molecules are realized. The calculation results for the low-lying states of B2 show that the VB calculation has clear-cut physical significance, and its simulation of the behavior of the potential energy surface about the equilibrium position is superior to that of the molecular orbital theory. The valence bond calculation involving only a few bonded tableaus can correctly reflect the effect of electronic correlation.