DHARMA-WARDANA-PERROT THEORY AND THE QUANTAL HYPERNETTED-CHAIN EQUATION FOR STRONGLY COUPLED PLASMAS

The Dharma-wardana and Perrot (DP) theory for a dense plasma is rewritten in another equivalent form in order to clarify its structure and approximations involved in it in comparison with the exact expression of structure factors in terms of the direct correlation functions (DCF) for a plasma as an ion-electron mixture. Thus it is shown that the DP theory breaks down when it treats a dense plasma with large bound-electron contribution, that is, with a significant number of bound electrons, as an ion. Also, this situation is numerically examined by using liquid metallic lithium as a test case, to which the quantal hypernetted-chain (QHNC) formulation is successfully applied. The breakdown in the DP theory is attributed to neglect of the electron-ion correlation given by the non-Coulomb part of the electron-ion DCF, C(eI)NC(r), which is taken into account in the QHNC formulation. The non-Coulomb part C(eI)NC(r) plays an important role in the reduction of a bare-electron-ion interaction upsilon-eI(C)(r) to a weak pseudopotential, when a nucleus in a plasma begins to have core electrons forming an ion, since the DCF C(eI)(r) = -beta-upsilon-eI(C)(r) + C(eI)NC(r) becomes a "weak" nonlinear pseudopotential W(b)NL(r). Nevertheless, it turned out that one of the equations in the DP theory is useful to determine the nonlinear pseudopotential W(b)NL(r) with use of the step-function approximation for the radial distribution g(II)(r) between ions. Recently Perrot, Furutani, and Dharma-wardana [Phys. Rev. A 41, 1096 (1990)] tried to take account of the electron-ion correlation by using the QHNC approximation. However, it is shown that their improvement is not adequate to treat a plasma with core electrons in ions because of improper handling of the bound-electron density distribution in the definition of the electron-ion and electron-electron DCF's. From the comparison between the DP and QHNC approaches, a simplified method for treating a dense plasma is proposed to calculate a pseudopotential W(b)NL(r), an effective interionic potential, and the electron-ion radial distribution function g(eI)(r), in addition to g(II)(r), with the use of the jellium-vacancy model.