THE MULTICONFIGURATIONAL SPIN TENSOR ELECTRON PROPAGATOR METHOD (MCSTEP) - COMPARISON WITH EXTENDED KOOPMANS THEOREM RESULTS

We applied the multiconfigurational spin tenser electron propagator me thod (MCSTEP) for determining the lowest few (in energy) vertical ioni zation potentials (IPs) of HF, H2O, NH3, CH4, N-2, CO, HNC, HCN, C2H2, H2CO, and B2H6. We chose these molecules so that we could compare MCS TEP IPs with recently reported extended Koopmans' theorem (EKT) IPs on the same molecules. Using standard Dunning core-valence basis sets wi th relatively small complete active spaces, MCSTEP results are in very good to excellent agreement with experiment. These MCSTEP IPs are obt ained using matrices no larger than 400 x 400. EKT matrices are even s maller; however, to obtain similar but generally slightly worse agreem ent with experiment, fairly large active spaces are required with EKT.