RELATION BETWEEN THE SUPER-TRANSITION-ARRAY METHOD IN OPACITY CALCULATIONS AND THE HARTREE-FOCK APPROXIMATION AT NONZERO TEMPERATURE

We consider the photoabsorption cross section of dense plasmas in thermodynamic equilibrium. We transform the exact expression of this cross section into a form suitable for the calculation of moments with respect to frequency. We show that the super-transition-array (STA) method, which is successfully applied in opacity calculations, is consistent with the thermal Hartree-Fock approximation. The Hartree-Fock theory justifies the use of the noninteracting partition function inside each superconfiguration, which is an important approximation in the STA method. © 1995 The American Physical Society.