and SS-CASPT2 calculations have been performed to incorporate dynamic correlation by using CASSCF wave functions as the reference. In SS-CASPT2, 15 occupied orbitals outside of the active space have been treated as closed space where as for MS-CASPT2, apart from the active space, all the orbitals were treated as core orbitals. To avoid the convergence problem in calculating the perturbative energy, a level shift of 0.35 a.u. is used. No IEPA shift is used in these calculations.