A SYSTEMATIC STUDY ON THE FIXED-NODE AND LOCALIZATION ERROR IN QUANTUM MONTE-CARLO CALCULATIONS WITH PSEUDOPOTENTIALS FOR GROUP-III ELEMENTS

Short-time fixed-node pure diffusion quantum Monte Carlo (PDMC) calcul ations with pseudopotentials for the group III elements B, Al, Ga and In have been carried out in order to study the capability of multirefe rence trial wavefunctions to reduce the fixed-node and localization er ror. For this purpose PDMC energies for the 2P and 4P states of the ne utral atoms and for the 1S state of the positive ions have been compar ed with the results of MRCI calculations. For these simple systems, we demonstrate the possibility of a systematic reduction of these errors by adding supplementary configurations to the trial wavefunction.