α dependence of transition frequencies for ions SiII, CrII, FeII, NiII, and ZnII -: art. no. 022501

We perform an improved calculation of the alpha dependence (alpha=e(2)/hc) of the transition frequencies for ions, which are used in a search for the variation of the fine-structure constant alpha in space-time. We use the Dirac-Hartree-Fock method as a zero approximation and then the many-body perturbation theory and configuration-interaction methods to improve the results. The important problem of level pseudocrossing (as a function of alpha) is considered. Near the crossing point the derivative of the frequency over alpha varies strongly (including a change of sign). This makes it very sensitive to the position of the crossing point. We propose a semiempirical solution of the problem, which allows us to obtain accurate results.