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Study on Raffenetti's P File Format in Conventional *Ab Initio* Self-Consistent-Field Molecular Orbital Calculations in Parallel Computational Environment

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Hiroyuki TERAMAE^{a}* and Kazushige OHTAWARA^{b,c}

^{a}Department of Chemistry, Faculty of Science, Josai University

1-1 Keyakidai, Sakado, Saitama 350-0295, Japan

^{b}ATR Adaptive Communication Research Laboratories

2-2-2 Hikaridai, Seika-cho, Soraku-gun, Kyoto 619-0288, Japan

^{c} Present address: Technology Development Division, Victor Company of Japan, Ltd.

58-7 Shinmei-cho, Yokosuka, Kanagawa 239-8550, Japan

(Received: August 7, 2008; Accepted for publication: October 17, 2008; Advance publication: November 22, 2008)

We compare the CPU time and the wall clock time of the Raffenetti's P file algorithm with the usual algorithm on the two electron integrals storing with four suffixes of the *ab initio* Hartree-Fock calculations. The calculations are performed with the flutoprazepam, triazolam, clotiazepam, etizolam, and flutazolam molecules. These molecules are all minor-tranquilizers with the benzodiazepine or thienodiazepine backbone. The 3-21G basis sets are employed. Almost in all cases, P file algorithm gave slower speed than the usual algorithm. The number of two electron integrals increases almost two times larger than the usual algorithms. In a large molecule, the matrix of the two electron integrals becomes very sparse and the recombination of the integrals just increases the total number of the integrals. It is concluded that the P method sometimes calculates faster but sometimes does not. In a large scale calculation, it should be suggested to perform a test calculation to confirm which method is faster prior to the real calculations.

**キーワード:** Raffenetti's PK file, Parallel computation, Molecular orbital

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