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Kinetic and potential energies of systems of 4He atoms in the solid phase are computed at T = 0. Results at two densities of the liquid phase are presented as well. Calculations are performed by the multiweight extension to the diffusion Monte Carlo method that allows the application of the Hellmann-Feynman theorem in a robust and efficient way. This is a general method that can be applied in other situations of interest as well. [ABSTRACT FROM AUTHOR]

The effect of three-body interatomic contributions in the equation of state of [sup 4]He are investigated. A recent two-body potential together with the Cohen and Murrell [Chem. Phys. Lett. 260, 371 (1996)] three-body potential are applied to describe bulk helium. The triple-dipole dispersion and exchange energies are evaluated subjected only to statistical uncertainties. An extension of the diffusion Monte Carlo method is applied in order to compute very small energies differences. The results show how the three-body contributions affect the ground-state energy, the equilibrium, melting and freezing densities. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Effects on the elastic constants of a system formed from He atoms with a He impurity concentration of 0.14 % are investigated in a range of densities varying from 0.029 to 0.035 Å. A model wave function of the shadow class is used to compute elastic constants and quantities defined through relations satisfied by them. The linear compressibility assumes the isotropic character expected for an hcp crystal with a constant value of the structure axis ratio c/ a. This is in contrast with bulk He where an anisotropic behavior is observed. [ABSTRACT FROM AUTHOR]

Kinetic energies for systems formed from He atoms at T=0 in the solid and liquid phases are reported. The 'exact' results are obtained by an extension of the diffusion Monte Carlo method. The overall agreement of the results with experimental values and calculations at finite temperatures is very good. [ABSTRACT FROM AUTHOR]

The effects of interatomic potentials in the equation of state of 4He and other properties of the system are investigated. A multi-weight diffusion Monte Carlo method is applied in order to compute very small energies differences with great accuracy. From our analysis we identify the best current description for the helium systems. [ABSTRACT FROM AUTHOR]