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VB2000 is an ab initio electronic structure package for performing modern Valence Bond (VB) calculations based on a highly efficient VB algorithm - the so called Algebrant Algorithm. It has also a general implementation of the Group Function (GF) Theory, in which a large molecule is described in terms of its constituent parts of physically identifiable "electron groups". It can be used as a stand-alone program, or as a plug-in module for GAMESS and Gaussian.