A molecular dynamics study of ambient and high pressure phases of silica: Structure and enthalpy variation with molar volume

Rajappa, Chitra and Sringeri, Bhuvaneshwari S and Subramanian, Yashonath and Gopalakrishnan, J (2014) A molecular dynamics study of ambient and high pressure phases of silica: Structure and enthalpy variation with molar volume. In: JOURNAL OF CHEMICAL PHYSICS, 140 (24).

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Abstract

Extensive molecular dynamics studies of 13 different silica polymorphs are reported in the isothermal-isobaric ensemble with the Parrinello-Rahman variable shape simulation cell. The van Beest-Kramer-van Santen (BKS) potential is shown to predict lattice parameters for most phases within 2%-3% accuracy, as well as the relative stabilities of different polymorphs in agreement with experiment. Enthalpies of high-density polymorphs - CaCl2-type, alpha-PbO2-type, and pyrite-type for which no experimental data are available as yet, are predicted here. Further, the calculated enthalpies exhibit two distinct regimes as a function of molar volume-for low and medium-density polymorphs, it is almost independent of volume, while for high-pressure phases a steep dependence is seen. A detailed analysis indicates that the increased short-range contributions to enthalpy in the high-density phases arise not only from an increased coordination number of silicon but also shorter Si-O bond lengths. Our results indicate that amorphous phases of silica exhibit better optimization of short-range interactions than crystalline phases at the same density while the magnitude of Coulombic contributions is lower in the amorphous phase. (C) 2014 AIP Publishing LLC.

Item Type:	Journal Article
Publication:	JOURNAL OF CHEMICAL PHYSICS
Additional Information:	Copyright for this article belongs to the AMER INST PHYSICS, CIRCULATION & FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	26 Aug 2014 06:41
Last Modified:	26 Aug 2014 06:41
URI:	http://eprints.iisc.ac.in/id/eprint/49675

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