Exciton states in solid rare gases

The problem of the exciton states in solid rare gases is studied within the framework of the integral-equation approach appropriate for intermediate-coupling interaction. The different contributions appearing in the integral equation are investigated and related to physical quantities by means of an analysis of their behavior in the two limiting situations in which the effective-mass approximation (EMA) or the atomic solution holds. An approximate solution is given for the intermediate case using the simplest trial wave functions having the correct behavior in both limits. Quantitative results, obtained by this simple approach, are remarkably more accurate than both the EMA and the atomic values.