Molecular orbital calculation using spectral representation technique

The spectral representation technique as a tool for molecular orbital calculation is introduced. The procedure for getting a potential in spectral representation is simple and straightforward. The technique is also shown to be versatile to apply to the so-called effective core-potential case, to the relativistic case, to the non-spherical frozen-area case, to the case of approximate estimation of the electronic structures of molecules without the self-consistent-field process, and to the case of incorporating external effect into the cluster by environment potential. Keywords: spectral representation, molecular orbital calculation, electronic structure, relativistic potential, environment potential.