DIAGONALIZATION-FREE SCF

The diagonalization in a standard self-consistent field (SCF) procedure is replaced by a Newton-Raphson or augmented Hessian relaxation step, using a one-electron representation of the Hessian. The direct inversion of the iterative subspace (DIIS) method is used to extrapolate between iterations. The convergence properties and number of Fock builds required is found to be roughly equivalent to a DIIS/diagonalization based SCF procedure. The new algorithm should be better suited to parallelization, but may also be faster on sequential machines.