A generalized direct inversion in the iterative subspace approach for generalized valence bond wave functions

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Abstract
We present a greatly improved method for converging generalized valence bond (GVB) self-consistent wave functions. This method starts with the direct inversion in the interative subspace (DIIS) ideas of Pulay. Previously implemented DIIS methods were limited to special cases: closed-shell Hartree–Fock (HF), restricted open-shell HF, or a single pair GVB wave function. Here we extend this method to general wave functions including arbitrary numbers of closed-shell, restricted open-shell, and GVB orbitals (including second-order orbital mixing terms). The efficacy of GVB-DIIS is illustrated by applying it to several cases (including GVB wave functions with up to ten pairs) and comparing with other standard methods.