IONIZATION-POTENTIALS OF CH2 - A COMPARISON OF THE MULTICONFIGURATIONAL SPIN TENSOR ELECTRON PROPAGATOR METHOD WITH BENCHMARK FULL CONFIGURATION-INTERACTION AND LARGE-SCALE MULTIREFERENCE CONFIGURATION-INTERACTION CALCULATIONS

Using the same basis sets and geometries as were previously used in '' benchmark'' full configuration interaction (FCI) calculations we compa re the multiconfigurational spin tensor electron propagator method (MC STEP) with FCI for the vertical ionization potentials (IPs) in CH2 bel ow 19.0 eV. Our results show that MCSTEP using a full valence complete active space MCSCF initial state accurately obtains the lowest severa l principal vertical ionization potentials. We also determine vertical and adiabatic IPs in CH2 with MCSTEP using larger bases and compare t o accurate large scale multireference singles and doubles CI with quad rupole excitations estimated via a Davidson correction.