OPTIMIZED SHADOW-WAVE FUNCTIONS FOR LIQUID AND SOLID HE-4

An efficient optimization scheme has been applied to shadow nave funct ions for tile ground state of liquid and solid He-4. Results improve o n previous variational energies in both phases. In the liquid, the gai n over a wave function with only pair and triplet correlations increas es with density, pointing to tile increasing importance of higher orde r correlations. Remarkably, the discrepancy with experimental data is nearly constant with density, yielding a very good equation of state. The estimate of the coexistence region is also satisfactory. Optimized shadow wave functions hold promise of an accurate variational descrip tion of inhomogeneous Helium systems.