Linear scaling Coulomb and SCF exchange/correlation algorithms are not the end of the story as the ${\cal{O}}({N^{3}})$ diagonalization step has been rate limiting in semi-empirical techniques and, been predicted to become rate limiting in ab initio approaches in the medium term.926 However, divide-and-conquer techniques1082, 1083, 1081, 564 and the recently developed quadratically convergent SCF algorithm701 show great promise for reducing this problem.