Higher-term contributions in the many-body calculation of the compressibility and thermodynamic properties of solid neon

Abstract

To investigate both compressibility and thermodynamic properties of solid face-centered cubic neon, the many-body potential energy, which is expanded as a sum of two- to five-body potentials, was calculated. The calculation used the ab initio Hartree–Fock self-consistent field method in combination with the many-body expansion method. The results indicate that the many-body expansion potential is an exchange convergent series, and the even many-body potential contributions to the cohesive energy are repulsive. The odd many-body potential contributions to the cohesive energy, on the other hand, are attractive. The absolute values of the many-body potential energy Un obey |Un| > |Un+1|. Both the many-body potential energy and the total potential energy tend to saturate with the increase in atomic numbers and neighboring shell numbers. When the atomic distance R exceeds 2.60 A, the interaction energy may be described by two-body interactions. For atomic distances between 1.80 and 2.60 A, a three-body contribution to the many-body expansion potential is required, while for distances between 1.60 and 1.80 A, four-body contributions need to be considered. The calculated isotherm is in good agreement with the obtained experimental results in the studied pressure range (0–237 GPa), which considers the four-body potential if the pressure reaches 240 GPa. Below 1.60 A, we have to consider the five-body potential to accurately match the experimental data (for the pressure up to 280 GPa). Overall, the inclusion of the high many-body interaction energy makes it possible to obtain the most accurate equation of the state for solid neon under ambient conditions and higher pressure.