A slater parameter optimization method applied to the computation of collision strengths for Fe XIII

Abstract Details of a new computational method for calculating collision strengths are presented through an application to Fe XIII. The method, which enables the computation of collision strengths for complex ions, is adapted from long-established optimization techniques previously used for the calculation of atomic energy levels and oscillator strengths. The procedure involves the adjustment of Slater parameters and average energies of configurations so that they result in improved energy levels and eigenvectors. These improved values can then provide a basis for collision strength calculations in ions where ab initio computations break down or result in unnecessarily large errors. The present application is implemented through modifications of the DISTORTED WAVE collision code and SUPERSTRUCTURE atomic-structure code interfaced via a transformation code JAJOM, which also processes their output; these atomic codes were written at University College London. It should be feasible to make similar adaptions to other collision codes. The Cowan suite of atomic-structure codes generated the optimized parameters. Fe XIII collision strengths are tabulated for 3 s 2 3 p 2 -3 s 3 p 3 and 3 s 2 3 p 2 -3 s 2 3 p 3 d transitions. Six configurations, 3 s 2 3 p 2 , 3 p 4 , 3 s 3 p 3 , 3 s 2 3 p 3 d , 3 s 3 p 3 d 2 , and 3 p 3 3 d , were included in these computations.