Computational studies of silica

摘要: There are three areas of research in this thesis. The �first is concerned with the silica polymorph, tridymite, simulations carried out using computational methods: free energy minimisation, molecular dynamics and Density Functional Theory. A number of tridymite structures di�fferent atomic configurations have been found nature. explore various properties of these forms investigate whether it possible to distinguish between them computational techniques. It was that interatomic potential simulation technique used, rather than simulation temperature, were the main factors a�ffecting resulting structure. a possible explanations for result: techniques may not be sensitive enough to deal an landscape as at case tridymite. Another reason potentials have been parameterised which reconstructive transitions (where bonds broken formed) may not able displacive transitions only angles between atoms change) �final explanation is number known meta-stable and/or poorly characterised. For second area molecular using a rigid ion two body were carried out order investigate the melts glasses. different silica crystals melted see all similar or whether their can di�fferentiated according original crystal At sufficiently high temperatures starting structure did a�ffect melt. Several properties of glasses investigated: mean square displacement, autocorrelation functions, pair distribution extent to silicon oxygen move together, Arrhenius plots, coordination number, bond lengths angles. Investigations were also use shell model to simulate Various calculated it was agreement experiment accurate as when model. The third exploration amorphous silica elevated pressures range temperatures, using molecular potential. Calculations show that, low distortion tetrahedra is recovered upon decompression whereas experimental results �find complete recovery tetrahedra. little available experimental data on behaviour both high pressures temperatures. Calculations show temperatures all initial before compression are recovered.