General methods for geometry and wave function optimization

A combination of variable-metric second-order update schemes and the DIIS method for both geometry and Hartree-Fock wave function optimization is described. A recursive procedure for updating large Hessians is presented. The performances of geometry optimizations with respect to the choice of the coordinate system (symmetry-adapted, internal, and Cartesian coordinates), the initial nuclear Hessian, and the optimization procedure have been investigated by a series of benchmark molecules. Formulas for the generation of initial nuclear Hessians are given