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Uncertainty quantification for classical effective potentials
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Longbottom, Sarah (2019) Uncertainty quantification for classical effective potentials. PhD thesis, University of Warwick.
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WRAP_Theses_Longbottom_2019.pdf - Submitted Version - Requires a PDF viewer. Download (11Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b3466773~S15
Abstract
Effective potentials are an essential ingredient of classical molecular dynamics simulations. Little is understood of the errors incurred in representing the complex energy landscape of an atomic configuration by an effective potential containing considerably fewer parameters. This thesis details the introduction of an uncertainty quantification framework into the potential fitting process within the potfit force matching code. The probabilistic sloppy model method has been implemented within potfit as a means to quantify the uncertainties in analytic potential parameters, and in subsequent quantities measured using the fitted potential. Uncertainties in the effective potential are propagated through molecular dynamics simulations to obtain uncertainties in quantities of interest, which are a measure of the confidence in the model predictions.
The implementation has been designed to fit flexibly within the existing potfit workflow, and is generalised to work with any potential model or material. The uncertainty quantification software contains a variety of controllable parameters, which provide the user with diagnostic capabilities to understand the nature of the fitting landscape defined by their potential model and reference data. The implementation is available for use by the materials modelling community as part of the open source potfit software.
The uncertainty quantification technique is demonstrated using three potentials for nickel: two simple pair potentials, Lennard-Jones and Morse, and a local density dependent EAM potential. A sloppy model fit to ab initio reference data is constructed for each potential to calculate the uncertainties in lattice constants, elastic constants and thermal expansion. These can be used to show the unsuitability of pair potentials for nickel. In contrast, with EAM we observe a decreased uncertainty in the model predictions. This shows that our method can capture the effects of the error incurred in the potential generation process without resorting to comparison with experiment or ab inito calculations, which is an essential part to assess the predictive power of molecular dynamics simulations.
| Item Type: | Thesis (PhD) | ||||
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| Subjects: | Q Science > QC Physics Q Science > QD Chemistry |
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| Library of Congress Subject Headings (LCSH): | Uncertainty, Nuclear forces (Physics), Molecular dynamics, Density functionals, Nickel | ||||
| Official Date: | November 2019 | ||||
| Dates: |
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| Institution: | University of Warwick | ||||
| Theses Department: | School of Engineering | ||||
| Thesis Type: | PhD | ||||
| Publication Status: | Unpublished | ||||
| Supervisor(s)/Advisor: | Brommer, Peter | ||||
| Sponsors: | Engineering and Physical Sciences Research Council | ||||
| Format of File: | |||||
| Extent: | xii, 126 leaves : illustrations | ||||
| Language: | eng |
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