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RESEARCH PRODUCT

Quantum Thermodynamic Perturbation Theory for Fermions

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The quantum version of classical thermodynamic perturbation theory is applied to the ground state of a fluid of spin-1/2 fermions interacting via the Aziz interatomic potential, as a model for liquid 3He. Results from the rapidly-convergent sixth-order calculation about the unperturbed hard-sphere fluid for energy, density and sound velocity at the zero-pressure liquid equilibrium point, lie within a few percent of computer-simulation values and appreciably closer than the most elaborate recent variational calculation. The procedure explicitly avoids crossing phase boundaries and is relatively insensitive to varying the close-packing density up to a value somewhat below the maximum possible (primitive hexagonal packing) value. With the aid of a rigorous energy bound principle, and as also occurs with extrapolations of low-density computer-simulation energies, this suggests the existence of a more stable high density phase (presumably crystalline), barring a breakdown at very high densities of Pade-like extrapolants based on only four series coefficients or on only four computer-simulation datapoints.