科研之友
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摘要
To investigate the significance of various many-body effects on the equation of state (EOS) of solid helium, the interaction energy of hep crystal structure is expanded as a sum of two- to five-body potentials in the present work. Each short-range many-body term between helium atom clusters is computed by means of Hartrec-Fock (HF) self-consistent-field (SCF) method. It is indicated that. at high densities the many-body expansion formula is an alternative series, in which two-, and four-body terms are positive, whereas three- and five-body terms are negative. According to such an expansion of crystal interaction energy, the equation of state of solid helium at 0 K is obtained. The specific characteristics of each of the tip to five-body contributions in highly compressed helium are discussed. Between 0.26 to 0.23nm, the interaction energy may be well described by two- and three-body interactions. Over a distance range 0.23-0.20nm, truncated many-body expansion after the four-body term recovers the main part of atomic potential energy. Below 0.20nm the five-body contributions have to be iucluded. The sum of two- to five-body term accurately reproduces the atomic potential energy from 0.20 to 0.175nm. The inclusion up to five-body potential satisfactorily describes the available experimental data from 7.5 to 2.5 cm(3)/Mol, corresponding to 1-60 GPa.
