|dc.description.abstract||We examined three different algorithms used in diffusion Monte Carlo (DMC) to study
their precisions and accuracies in predicting properties of isolated atoms, which are H
atom ground state, Be atom ground state and H atom first excited state.
All three algorithms — basic DMC, minimal stochastic reconfiguration DMC, and
pure DMC, each with future-walking, are successfully impletmented in ground state
energy and simple moments calculations with satisfactory results. Pure diffusion Monte
Carlo with future-walking algorithm is proven to be the simplest approach with the
Polarizabilities for Be atom ground state and H atom first excited state are not satisfactorily
estimated in the infinitesimal differentiation approach. Likewise, an approach
using the finite field approximation with an unperturbed wavefunction for the latter
system also fails. However, accurate estimations for the a-polarizabilities are obtained
by using wavefunctions that come from the time-independent perturbation theory.
This suggests the flaw in our approach to polarizability estimation for these difficult
cases rests with our having assumed the trial function is unaffected by infinitesimal
perturbations in the Hamiltonian.||en_US