An Implementation and Assessment of the Modern Antisymmetrized Product of Strongly Orthogonal Geminals Method for Open Shell and Closed Shell Systems

Abstract

Geminal based methods such as the antisymmetrized product of strongly orthogonal geminal (APSG) method have seen a resurgence of interest in recent years due to their ability to effectively capture static correlation. However, the test cases used for the APSG method have rarely been larger than diatomic or triatomic molecules, and the APSG method also neglects a large amount of dynamical correlation. This thesis employs the APSG method to perform a number of calculations on a series of diatoms, a reaction profile of benzene and an OH radical, and a C60 buckyball system, and attempts to correct the energies presented by the APSG method via the addition of density functional theory correlation factors. While both the corrected and uncorrected APSG energies were able to perform better than ROHF for the diatoms and the APSG method was able to describe the bonding of the large C60 molecule adequately, the method was found to have serious problems with large open-shell molecules, resulting in very poor quality energies in the reaction profile of benzene and an OH radical.

Date of Award	31 Dec 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Joseph J.W. Mcdouall (Supervisor) & Neil Burton (Supervisor)