Green's Function Monte Carlo Method for LiquidHe3

The Green's-function Monte Carlo method, which yields an exact ground-state solution to the Schrödinger equation for Bose systems, is applied to liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, a fermion system. With the use of a technique that projects out states of selected symmetry, strict upper bounds to the ground-state energy of many-fermion systems have been constructed. An upper bound has been found for liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ of - 2.20±0.05°K at the experimental equilibrium density. This energy is more than 1°K below Jastrow variational results and much nearer the experimental value of - 2.47±0.01°K.