Short range electronic distortion and the density dependent dielectric function of simple gases

• Published in: Chemical physics letters 1974-08, Vol.27 (3), p.359-364
• Main Authors: Heller, Donald F., Gelbart, William M.
• Format: Article
• Language: English
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/0009-2614(74)90241-3

The coefficient defining the density expansion of the dielectric function of a simple gas are expressed as thermal averages of products of two-body adiabatic polarizabilities. To allow this description a superposition form has been introduced for the three-body polarizability: this approximation leads to results which reduce to the well-known Kirkwood, dipole-induced-dipole (DID) theory only when the pair polarizabilities are replaced by their long range (dispersional) form. When non-DID effects are retained, i.e., when ab initio (e.g., Hartree-Fock) pair polarizabilities are used, significant corrections are found, but the triplet contributions are still small except at very high densities and pressures. In particular, we evaluate the second and third dielectric virial coefficients for room temperature helium, and compare our calculated values with those obtained in recent DID treatments. The marked differences found in the resulting density dependence of the Clausius-Mossotti function, and the relative insensitivity to the choice of interaction potential, are discussed in terms of short range electronic distortion.