Abstract
Potential energy surfaces of H2, H2+ and H2- molecules calculated by MP2, B3LYP with 6-311G** basis set are compared with those calculated by Hartree-Fock (HF). H2+ has no exchange correlation, and no electron correlation. H2 has exchange correlation and electron correlation. H2- has larger exchange correlation and electron correlation than H2. In the case of H2, potential surfaces of HF and B3LYP are almost the same not only in the equilibrium region but also in the long inter-atomic distance region. However, the potential surfaces of H2+ and H2- generated by B3LYP are different from those of HFs, especially in the long inter-atomic distance region. The potential surfaces have maxima at about 3Å and are qualitatively wrong at long distances.Potential energy surfaces for H2 and H2- obtained by MP2 are qualitatively the same as HF.
