Path integral Monte Carlo calculations of⁴He and⁶Li

We have performed Monte Carlo calculations to estimate the exact energies of model problems for⁴He and the L=0,1, and 2 states of⁶Li. Using a Feynman path-integral expression for the imaginary-time evolution operator, we recast the ground state energy as a sum over histories, which are then sampled stochastically. Use of a trial wave function dramatically improves the efficiency of the Monte Carlo method. For a state-independent Malfliet-Tjon potential, together with the Coulomb interaction, we find a ground state energy of -28.00+0.20 MeV for⁴He, and a degeneracy of the L=0,1, and 2 states in⁶Li at about -59.65+-0.50 MeV. Density distributions for these nuclei are also calculated.