Optimized wave functions for quantum Monte Carlo studies of atoms and solids.

Wavefunctions for the homogeneous electron gas, a germanium pseudo-solid, and a germanium pseudo-atom are optimized using the method of variance minimization. New forms for the Jastrow factor which are convenient to optimize and may be evaluated rapidly are devised and tested and we stress the advantages of using expressions which are linear in the variable parameters. For each system studied we have performed variational and diiusion quantum Monte Carlo calculations to test the accuracy of the optimized wavefunctions. The results of our study are very promising for future applications of quantum Monte Carlo methods to real materials.