A study of the energy hypersurface of silicon dioxide (Doctoral thesis)

Φαλαγκάρα, Όλγα

We have developed a Consistent Force Field for silica that does not include explicit terms for the long range interactions, which disproportionately burden the cost of a molecular dynamics simulation, and provides a satisfactory description of the structure and properties of silica. We have analyzed the energy hypersurface of silica using a series of ab initio (always italics for "ab initio") methods that i) do not include electron correlation and ii) include it either through an appropriate density functional or through a perturbative corrective correction (with full or frozen core orbitals). As for bonded interactions, we examined i) the effect of the selected ab initio method, ii) the effect of the basis set size and the addition of diffuse functions, and iii) the effect of the selected structure's size on the energy hypersurface. As for non-bonded interactions, we have examined the effect of the Basis Set Superposition error, ii) the effect of the basis set size and the addition of diffuse functions, and iii) the effect of r∞, ε0 and r0 within the energy curves. We have developed the necessary methodology to spread from the energy hypersurface to an analytical expression for the potential energy, both for bonded and for non-bonded interactions. The force field was then validated both internally and externally. During the validation procedure, we have made all necessary modifications to the parameter values and its terms to properly reproduce both ab initio (equilibrium structures, energycurves) and experimental (crystalline structures, densities, thermodynamics quantities, etc.) data, and we have examined the effect of those modifications on the calculated density and radial distribution function for the α-quartz. The resulting force field contains bonded terms for bond stretch and angle bend and does not contain dihedral or improper angle terms. Non-bonded interactions are included through a simple Lennard-Jones potential function. This force field is capable to reproduce, to a sufficient extent, the i) crystalline structure, ii) density, iii) radial distribution function and basic thermodynamic quantities for α-quartz, indicating its capability to respond fast and efficiently. In the future, we plan to replace the Lennard-Jones potential with a more appropriate non-bonded interaction (Buckingham orMorse) and to further improve its transferability in the β-quartz structure by introducing a coupling term, so as to adequately describe the properties of β- quartz as well as the transition α -> β quartz.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
Subject classification: Πυρίτιο
Μοριακή δυναμική
Keywords: Διοξείδιο του πυριτίου,Δυναμικό αλληλεπίδρασης,Μοριακή δυναμική,Silica,Force field,Force field development,Molecular dynamics,Α-quartz
URI: http://olympias.lib.uoi.gr/jspui/handle/123456789/28174
Appears in Collections:Διδακτορικές Διατριβές

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