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.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (5MB)

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.

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