A SOFT HARTREE-FOCK PSEUDOPOTENTIAL FOR CARBON WITH APPLICATION TO QUANTUM MONTE-CARLO

We describe the development of an ab initio Hartree-Fock (HF) pseudopo tential for C that has neither repulsive r(-2) nor attractive Coulomb singularities at the nucleus. This potential is tested: in HF calculat ions on small hydrocarbons and shown to give good accuracy in comparis on to all-electron calculations. The new pseudopotential is demonstrat ed to give superior basis;set convergence in HF calculations compared to standard ones with r(-2) singularities. Diffusion Monte Carlo (DMC) calculations on C and CH with the new potential show substantial impr ovements in stability at larger time steps compared with conventional pseudopotentials, with negligible time Step dependence of the total en ergy. The resultant CH bond energy, D-e = 83.3(4) kcal/mol, is in good agreement with experiment and with a similar all-electron DMC calcula tion. (C) 1998 American Institute of Physics.