Perturbation corrections to the variational ground-state energy of liquidHe4

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Abstract
The ground state of liquid He4 is studied by means of a variation-perturbation procedure based on the method of correlated basis functions. The main purpose of the study is to evaluate leading corrections to the variational ground-state energy optimized in the Bijl-Dingle-Jastrow (BDJ) type of trial-wave-function space. The total energy correction consists of: (i) a two-ring type of second-order perturbation energy calculated by including the leading correction to the convolution approximation for the three-particle distribution function, (ii) eight three-ring types of third- and fourth-order perturbation energies computed with the use of convolution approximations for the three- and four-particle distribution functions, and (iii) contribution from the triple-dipole three-body interaction evaluated with the use of the Kirkwood superposition approximation. The formulation for the perturbation energies is given in terms of the liquid-structure function generated by the optimum BDJ-type wave function. The numerical values of the energy corrections are obtained by using the liquid-structure function determined by Pokrant. The resulting ground-state energy per particle is -7.16°K in close agreement with experimental value -7.20°K.