Designing algorithms for improving quantum chemical calculations

El Sherbiny, Aisha (2008) Designing algorithms for improving quantum chemical calculations. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This work involves studying and developing new algorithms for molecular numerical integration used for density functional theory and new algorithms for Hartree-Fock method. -- New insight about molecular numerical integration is presented through a detailed study of the performance of some of the well known grids in addition to our implementation of the most recently developed MultiExp grid. A comprehensive study of numerical integration was conducted by evaluating several molecular properties: number of electrons, dipole moment, potential energy, and Coulomb repulsion energy using fifteen grids including a large benchmark grid. The standard grid (SG-1) and a slightly modified version of the Treutler and Alhrichs (TA) grid performed reasonably well. The MultiExp grid, which is more efficient, was studied as well and found to be less accurate. -- Studying large molecules using Hartree-Fock method is a challenge both in terms of CPU time and memory requirements. However, there is a high demand to perform quantum chemical calculations for large molecules. Projection from a smaller basis set to a larger basis set was studied in detail. It was found that projection from the STO-3G basis set to the 6-31G basis set performed well. Projection was used to develop a new version of a divide and conquer algorithm. Our divide and conquer algorithm was used to calculate the protonation energy for a series of peptides. Algorithms to skip calculating two-electron integrals of zero or negligible values are presented in addition to an algorithm to generate a better initial guess.

Item Type: Thesis (Doctoral (PhD))
URI: http://research.library.mun.ca/id/eprint/10463
Item ID: 10463
Additional Information: Includes bibliographical references (leaves 276-279).
Department(s): Science, Faculty of > Chemistry
Date: 2008
Date Type: Submission
Library of Congress Subject Heading: Hartree-Fock approximation; Quantum chemistry--Mathematical models.

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