ELECTRONIC STATES OF AL AND AL-2 USING QUANTUM MONTE-CARLO WITH AN EFFECTIVE CORE POTENTIAL

The diffusion Monte Carlo method is applied in conjunction with an ab initio effective core potential to compute energies of some neutral an d charged states of Al and Al-2. The computed ionization potentials, e lectron affinities and dissociation energies differ from measured valu es by at most a few hundredths of eV. The computed dissociation energy of Al-2 agrees with the most extensive CI calculations. It appears th at our dissociation energy for Al-2(-) is the most accurate to date. T he quality of the results indicates that the use of the pseudopotentia l is not an important limitation on the accuracy of these calculations . Variational wavefunctions with Boys-Handy correlation functions are found to give more than 70% of the correlation energy with 8 optimized parameters. These optimized trial functions are used together with nu merical integration to localize the pseudopotential. (C) 1996 American Institute of Physics.