Molecular dynamics study of cristobalite silica using a charge transfer three-body potential: Phase transformation and structural disorder

Abstract

Structural and dynamic properties of cristobalite silica have been studied using molecular dynamics simulations based on a charge transfer three-body potential model. In this potential model, the directional covalent bonding of SiO 2 is characterized by a charge transfer function of the interatomic distance between Si and O atoms, and in the form of Si-O-Si and O-Si-O three-body interactions. The dynamic properties such as infrared spectra and density of states at room and elevated temperatures are in excellent agreement with experiments, and are also consistent with the recently proposed rigid unit modes model. The ␣and ␤-cristobalite crystallographic structures are well reproduced in this model, and the transition between these modifications occurs reversibly and reproducibly in simulations, both as a result of changes in pressure and temperature. The thermally induced transition results in a significantly more disordered ␤-cristobalite than the pressure-induced ␤-cristobalite at room temperature. While simulated ␣-cristobalite exhibits a positive thermal expansion coefficient, it is almost zero for ␤-cristobalite up to 2000 K and slightly negative at higher temperatures, confirming results from recent x-ray diffraction experiments and other simulations with potential models based on ab initio calculations.

Diffusional anomaly and network dynamics in liquid silica

“…Based on the similarity in power spectral behaviour of SPC/E and TIP5P-E models for water 19 , we would expect different effective pair potentials for silica to have very similar qualitative behaviour. It is possible, however, that three-body potentials for silica will show more significant deviations, such as a reversal in the relative order of the two types of anomalies 35 .…”

“…The sampling interval of 10 fs corresponds to a Nyquist frequency of 1666 cm The S Si (f ) spectrum shows a sharp peak at 1100 cm −1 corresponding to the to the Si-O-Si asymmetric stretch vibration seen in both the experimental as well as simulated IR spectrum 35,36 . The power spectrum also shows a secondary, less intense peak at 800 cm…”

α–βtransformation and disorder inβ-cristobalite silica

“…For our MD simulations, we used a charge transfer three-body potential 17 that can describe very well both crystalline and amorphous silica (α-and β-cristobalite, α-and β-quartz, high pressure X-I phase, stishovite, phase transformations between α-and β-cristobalite, α-and β-quartz, negative thermal expansion in β-cristobalite and β-quartz, as well as thermomechanical anomalies in silica glass) [17][18][19][20][21] . Essentials for the success of such a potential are that it realistically accounts for the charge redistribution associated with changes in bonding structure and the directional character of the covalent bonding is modeled by angular constraints in terms of threebody interactions.…”

Response to Extreme Temperatures of Mesoporous Silica MCM-41: Porous Structure Transformation Simulation and Modification of Gas Adsorption Properties

“…This can lead to simulations producing unrealistic melting points and other phase transition temperatures. 12 The capture of different gases by MCM-41 has been widely studied in both experimental and simulation studies, including N 2 , 13 noble gases, 9,10 CO 2 , 8,11 and alkanes. 8 The application to adsorption and storage of noble gases is very important during nuclear power operations and waste treatment.…”