Many-Body Contributions to Cohesive Energy of Highly Compressed Solid ⁴He

A many-body expansion of cohesive energy of solid ⁴He is made up to five-body term, and short-range two-, three-, four- and five-body contributions have been computed by using the Hartree-Fock self-consistent-field technique and the same atomic basis set (6311G). At high densities the Hartree-Fock part of two- and four-body contributions are repulsive, whereas the three- and five-body ones are attractive. The four-body term increases as much as 15% repulsion of two-body term, and at the same time the five-body term reduces 4% of two-body repulsion at 2.5cm³/mol. The four- and five-body terms are found to be important to describe short-range inter-atomic interaction correctly and to compute the cohesive energy accurately in a wide compression range from 2.5 to 7.5cm³/mol.