Ab initio calculations of Coulomb U parameters for transition-metal impurities

We present ab initio calculations for the Coulomb U parameter of all transition-metal impurities in Rb. The U parameter increases in each row by filling up the d shell and decreases with increasing row number. In addition we find a strong configuration dependence, with the Hubbard U of 3d impurities being about 30% larger for the divalent configuration than for the monovalent one.