Calculation of the Ground States of H^- Ion and He Atom in Magnetic Field with a Modified Configuration Interaction Method

The modified configuration interaction method is extended to double electronic systems in magnetic fields. Eigen-values and binding energies of ground state of H^- ion and He atom in uniform magnetic fields are calculated. In a range running from low to intermediate magnetic fields, the best results with relative errors of 1.0 X10^-5 and 1.4x10^-6 for H^- and He, respectively, are obtained. The accuracy of our results are almost 2 orders of magnitude better than those obtained by the other methods.