Four-body Interaction and Equation of State for Solid Neon from Ab Initio Calculation

Using ab initio Hartree-Fock self-consistent field method combined with many-body expansion method, the investigation is based on the first-principles. We have considered two-, three- and four-body potential energies of face-centered cubic (fcc) solid neon of which the atomic distance ranges from 1.6 to 3.0 . By discussing the truncation and convergence of many-body potential of solid neon, we obtain the cohesive energy, the zero-point vibration energy and equation of state (EOS). The results show that, when the number of neighboring atoms increases, two-body, three-body, and four-body potential energy tend to a saturation value for a certain atomic distance ( ). The even many-body contributions to the cohesive energy, such as two-, four-body terms and so on, are positive, whereas the odd many-body contributions to the cohesive energy, such as three-, five-body terms and so on, are negative. The zero-point vibration energy of solid neon is only 6% of the total atomic interaction energy, but should not be neglected. Compared with the experimental data, the importance of the four-body interactions in compressed solid neon is emphasized. Only taking into account the two-body term, the pressure is overestimated, and our calculated results are in good agreement with the experimental values at the low-pressure regions (<15GPa). Adding three-body term up to 55GPa, considering the four-body term, it has a good consistency at the experimentally studied pressure range of 0~237GPa, and maybe helpful to accurately explain the phenomenon of the experiment above 237GPa when the higher many-body effects are considered.