RELATIVISTIC EFFECTIVE POTENTIALS IN TRANSITION-METAL QUANTUM MONTE-CARLO SIMULATIONS

Relativistic effective potentials are used in fixed-node quantum Monte Carlo simulations, including branching, to compute the lowest Sc and Y atomic excitation energies. Using simple SCF trial wave functions multiplied by pair correlation functions we obtain values of 1.5(3) and 1.4(2) eV, respectively, for Sc and Y as compared to experimental values of 1.43 and 1.36 eV. The simulations included eleven electrons in the valence space and gave valence electron correlation energies of 13.7(3) and 14.4(2) eV, respectively, for the ground states of Sc and Y. The simulations exhibited none of the instabilities predicted by other workers in the field. There appears to be no barrier to the use of conventional relativistic effective potentials in fixed-node quantum Monte Carlo simulations.