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Non-empirical Force-Field Development for Weakly-Bound Organic Molecules

Aina, Alexander; (2020) Non-empirical Force-Field Development for Weakly-Bound Organic Molecules. Doctoral thesis (Eng.D), UCL (University College London). Green open access

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Abstract

This thesis pioneers the development of non-empirical anisotropic atom-atom force-fields for organic molecules, and their use as state-of-the-art intermolecular potentials for modelling the solid-state. The long-range electrostatic, polarization and dispersion terms have been derived directly from the molecular charge density, while the short-range terms are obtained through fitting to the symmetry-adapted perturbation theory (SAPT(DFT)) intermolecular interaction energies of a large number of different dimer configurations. This study aims to establish how far this approach, previously used for small molecules, could be applied to specialty molecules, and whether these potentials improve on the current empirical force-fields FIT and WILLIAMS01. The scaling of the underlying electronic structure calculations with system size means many adaptions have been made. This project aims to generate force-fields suitable for use in Crystal Structure Prediction (CSP) and for modelling possible polymorphs, particularly high-pressure polymorphs. By accurately modelling the repulsive wall of the potential energy surface, the high pressure/temperature conditions typically sampled by explosive materials could be studied reliably, as shown in a CSP study of pyridine using a non-empirical potential. This thesis also investigates the transferability of these potentials from the gas to condensed-phase, as well as the transferability and importance of the intermolecular interactions of flexible functional groups, in particular NO2 groups. The charge distribution was found to be strongly influenced by variations in the observed NO2 torsion angle and the conformation of the rest of the molecule. This conformation dependence coupled with the novelty of the methods and size of the molecules has made developing non-empirical models for flexible nitro-energetic materials very challenging. The thesis culminates in the development of a bespoke non-empirical force-field for rigid trinitrobenzene and its use in a CSP study.

Type: Thesis (Doctoral)
Qualification: Eng.D
Title: Non-empirical Force-Field Development for Weakly-Bound Organic Molecules
Event: UCL
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © UK Ministry of Defence © Crown Owned Copyright 2020/AWE. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10112993
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