Improved calculation for ion configuration distribution from the average-atom model

An improved binomial statistical formula to calculate ion configuration dis tribution from the average-atom model is presented, in which the interactio n between bound electrons is taken into account. The distribution of ion co nfiguration given by the conventional binomial formula without the interact ion is much wider than it should be. Improvement shows reproduction of the Boltzmann-Saha results in LTE and better agreement with the calculation of ion configuration model in non-LTE. (C) 1999 Elsevier Science Ltd. All righ ts reserved.