(Received: August 15, 2003; Accepted for publication: October 10, 2003; Published on Web: December 17, 2003)
Integral transformation from basis functions to molecular orbitals is necessary in configuration-based correlation treatments of molecular orbital calculations. In particular, the processing of two-electron integrals having fourth power dependence of the number of basis functions can be costly, thus care should be taken to reduce the operation counts as far as possible. In this contribution, we report a development of integral transformation modules, based on Yamamoto-Nagashima's algorithm (J. Comp. Chem., 9, 627 (1988)) by which only non-zero integrals within threshold are efficiently processed. The BLAS routines, DAXPY and DDOT are used in the innermost part of the transformation step.
Keywords: Molecular orbital calculations, Electron correlation, Integral transformation, Configuration interaction
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