Convergence and efficiency of the valence bond self-consistent field method

Abstract

A previously described method to optimize the non-orthogonal orbitals in a general valence bond wavefunction using the generalized Brillouin theorem is explored. The valence bond self consistent field (VBSCF) method has gained in efficiency by introducing the Direct Inversion in the Iterative Subspace (DIIS) method to cut the number of iterations and by reducing the number of matrix-elements calculated to minimize the time spent per iteration. Calculations on OH, Cr2 and F2 show considerable improvement in efficiency and illustrate the size and complexity of wavefunction that the method can handle.