Calculation of the hyperfine constants of Vk center in CaF2, SrF2 and BaF2

The magnetic hyperfine constants of the V sub(K) center in CaF2, SrF2 and BaF2 have been calculated, assuming a phenomenological model, based on the F2 central molecule, to describe the wave function of the defect. The introduction of covalence, with the ions neighboring the central molecule, have shown that this is a better description for the defect than a simple central molecule model. It was also shown that the results for the hyperfine constants are strongly dependent on the relaxations of these neighboring ions, which have been determined by fitting the experimental data. The present results are compared with other previous calculations where similar and different methods have been used. A better description for the wave function of the defect is suggested