Benchmark full configuration-interaction calculations on HF and NH2

Abstract

Full configuration-interaction (FCI) calculations are performed at selected geometries for the 1∑+ state of HF and the 2B1 and 2A1 states of NH2 using both DZ and DZP Gaussian basis sets. Higher excitations become more important when the bonds are stretched and the SCF reference becomes a poorer zeroth-order description of the wave function. The CASSCF-MRCI procedure gives excellent agreement with the FCI potentials, especially when corrected with a multireference analog of the Davidson correction.