Upon introduction of correlation, the one-particle density relaxes both electrons and holes within their respective spaces, as well as moves electrons from the occupied space to the virtual space. Each of the four parameters corresponds to the effect of each of these processes on the two-electron interaction. A 13 and B x rearrange electron and hole density within their respective spaces, A 9 removes electrons from the occupied space and B 9 adds electrons to the virtual space. We can therefore speculate that their value is also significant and that A 9 = -B 9 to conserve the electron number.