Quantum Monte Carlo study of the ground state and low-lying excited states of the scandium dimer

Abstract

A large set of electronic states of scandium dimer has been calculated using high-level theoretical methods such as quantum diffusion Monte Carlo (DMC), complete active space perturbation theory as implemented in GAMESS-US, coupled-cluster singles, doubles, and triples, and density functional theory (DFT). The u3 and u5 states are calculated to be close in energy in all cases, but whereas DFT predicts the u5 state to be the ground state by 0.08 eV, DMC and CASPT2 calculations predict the u3 to be more stable by 0.17 and 0.16 eV, respectively. The experimental data available are in agreement with the calculated frequencies and dissociation energies of both states, and therefore we conclude that the correct ground state of scandium dimer is the u3 state, which breaks with the assumption of a u5 ground state for scandium dimer, believed throughout the past decades. © 2008 American Institute of Physics.