Novel orthogonalization and biorthogonalization algorithms
Orthogonalization with the prerequisite of keeping several vectors fixed is examined. Explicit formulae are derived both for orthogonal and biorthogonal vector sets. Calculation of the inverse or square root of the entire overlap matrix is eliminated, allowing computational time reduction. In this special situation, it is found sufficient to evaluate the functions of matrices of the dimension matching the number of fixed vectors. The (bi)orthogonal sets find direct application in extending multiconfigurational perturbation theory to deal with multiple reference vectors.
KeywordsOverlap Orthogonalization Biorthogonal sets Multiconfiguration perturbation theory Multistate theory
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