Three-body interactions in the condensed phases of helium atom systems

In this work we investigate how the description of several properties of helium atoms in the condensed phases are affected by the three- body terms of a very accurate inter- atomic potential. We introduce two phenomenological parameters in the three- body part of the inter- atomic potential in order to describe properly the equations of state of the solid and liquid phases. The calculations were performed using the multi- weight extension to the diffusion Monte Carlo method which allows accurate calculations of small energy differences in a significant way. The results show how the equations of state for both the liquid and solid phases and properties like the isothermal compressibility, the equilibrium, melting and freezing densities are affected by three- body interactions.