Constrained variation in Jastrow method at high density

A method is derived for constraining the correlation function in a Jastrow variational calculation which permits the truncation of the cluster expansion after two-body terms, and which permits exact minimization of the two-body cluster by functional variation. This method is compared with one previously proposed by Pandharipande and is found to be superior both theoretically and practically. The method is tested both on liquid ³He using the Lennard-Jones potential and on the model system of neutrons treated as Boltzmann particles ("homework" problem). Good agreement is found both with experiment and with other calculations involving the explicit evaluation of higher-order terms in the cluster expansion. The method is then applied to a more realistic model of a neutron gas up to a density of 4 neutrons per F³, and is found to give ground-state energies considerably lower than those of Pandharipande.