The properties of hexagonal close packed (hcp) solid 4He are dominated by large atomic zero point motions, which make the primary contribution to the solid’s low-temperature Debye-Waller (DW) factor. It is proposed that an accurate understanding of these zero point motions requires consideration of three-body interactions, which can significantly increase computational cost. We utilize quantum Monte Carlo (QMC) methods and either a 2-body or a 2+3-body potential energy function to calculate the ground state energy and DW factors for hcp 4He at T = 0 K in crystals with molar volumes ranging from 2.5 cm3 to 21.3 cm3. We perform two sets of QMC simulations. One set of simulations incorporates the three-body interactions into the solid’s potential energy function for the entire simulation; the other set of simulations treats the three-body interactions as a small perturbation, or correction, to the two-body potential energy function. Theoretical equations of state for each set of simulations are reported and compared to experimental data, and we observe that simulations accounting for three-body interactions show improved agreement with experiment over two-body calculations. At this stage, only a negligible difference is observed between the two treatments of the three-body interactions, indicating that the more computationally efficient perturbative approach may be sufficient for an accurate description of the system. None of our simulations reveal significant anisotropy in the DW factors for atomic motion parallel or perpendicular to the crystal’s basal plane; this is in contrast to recent experimental findings of Blackburn et al. [Blackburn et al., Phys. Rev. B 76, 024523 (2007)] where substantial anisotropy of this type was observed at temperatures near T = 0 K. Elastic constants are also extracted from simulation results in order to further assess the importance of three-body interactions in the system.

Evaluation of a perturbative treatment of three-body interactions in HCP 4He

251st National Meeting (2016)

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