Other| February 01, 1998 Simulation of the structure and stability of sphalerite (ZnS) surfaces K. Wright; K. Wright University of Manchester, Department of Earth Sciences, Manchester, United Kingdom Search for other works by this author on: GSW Google Scholar G. W. Watson; G. W. Watson Search for other works by this author on: GSW Google Scholar S. C. Parker; S. C. Parker Search for other works by this author on: GSW Google Scholar D. J. Vaughan D. J. Vaughan Search for other works by this author on: GSW Google Scholar American Mineralogist (1998) 83 (1-2): 141–146. https://doi.org/10.2138/am-1998-1-214 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation K. Wright, G. W. Watson, S. C. Parker, D. J. Vaughan; Simulation of the structure and stability of sphalerite (ZnS) surfaces. American Mineralogist 1998;; 83 (1-2): 141–146. doi: https://doi.org/10.2138/am-1998-1-214 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Atomistic simulation techniques were used to investigate the surface energies and stabilities of the sphalerite form of ZnS. The results show that for pure ZnS the lowest energy surfaces are type I and all of the form {110} with a calculated surface energy of 0.65 J/m 2 . In addition, we illustrate how type III surfaces, such as {111}. can be stabilized with respect to {110} by the introduction of point defects to the surface layer. Such defects lead to changes in stoichiometry and to the valence state of surface species. In general, the results suggest that for Zn-poor surface stoichiometries, the (111) surface becomes the most stable, whereas for Zn-rich compositions the (111) is stabilized to the greatest extent. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.
In this paper we outline an approach for calculating the vibrational thermodynamic properties of an inorganic solid from a molecular dynamics simulation and then compare them with those evaluated, using the more established lattice dynamics approach. Our motivations are twofold. First, lattice dynamics is impractical for simulations of more than a few hundred atoms, whereas molecular dynamics can readily be applied to systems of several thousand atoms. Second, lattice dynamics incorporates a quasiharmonic approximation and is therefore unreliable when anharmonic effects dominate. The vibrational properties of three oxides, MgO, ${\mathrm{TiO}}_{2},$ and ${\mathrm{Fe}}_{2}{\mathrm{O}}_{3},$ were calculated over a range of temperatures between 300 K and 1500 K. The results show good agreement in their predicted phonon density of states and in the calculated vibrational contribution to the free energy over the entire temperature range considered.
Energy minimization techniques in conjunction with ionic model potentials can now be used to predict the crystal structures of many classes of inorganic solids; the present communication, which is concerned with their application to mineral systems, in particular forsterite and beryl, demonstrates their viability as a technique in structural mineralogy.
The structures and energies of a series of tilt grain boundaries and corresponding surfaces were calculated to obtain a general relationship between the grain boundary energy and the tilt angle for NiO and MgO. We show that the simple elastic expressions for the grain boundary energy give reasonable results for low-angle grain boundaries. We investigate the assumptions that lie behind thermal grooving experiments and show that the torque terms should be large, even when far from a major pole [the (100), (110), or (111) directions]. However, the measured angles agree better with the calculations when torque terms are ignored. We discuss this effect in terms of faceting and oxidation of the surface.
Abstract We use an approach based upon the atomistic or Born model of solids, in which potential functions represent the interactions between atoms in a structure, to calculate the infrared and Raman vibrational frequencies of forsterite. We investigate a variety of interatomic potentials, and find that although all the potentials used reproduce the structural and elastic behaviour of forsterite, only one potential (THB1) accurately predicts its lattice dynamics. This potential includes ‘bond-bending’ terms, that model the directionality of the Si-O bond, which we suggest plays a major role in determining the structural and physical properties of silicates. The potential was derived empirically from the structural and physical data of simple oxides, and its ability to model the lattice dynamics of forsterite is a significant advance over previous, force-constant models, which have been simply derived by fitting to the spectroscopic data that they aim to model. The success that we have had in predicting the lattice dynamics of forsterite indicates that the potential provides the previously elusive yet fundamental, quantitative link between the microscopic or atomistic behaviour of a mineral and its macroscopic or bulk thermodynamic properties.
Abstract The structure and elastic properties of MgSiO 3 , a major mantle-forming phase, have been simulated using computer models which predict the minimum energy structure by using interatomic pair potentials to describe the net forces acting between the atoms. Four such interatomic potentials were developed in this study, and are compared with potential N1 of Miyamoto and Takeda (1984). The most successful potential (W3) was derived by fitting the short range potential parameters to both the experimentally obtained structural and elastic properties of MgSiO 3 perovskite. The relative stabilities of some of the possible perovskite polymorphs, the orthorhombic, cubic, and tetragonal phases and hexagonal polytypes, were evaluated at 0 K and between 1 bar and 2 Mbar. The orthorhombic phase is found to be stable at all but the highest pressures, where the cubic phase may be stable. The temperature of the ortho-rhombic to cubic transition may decrease with increasing pressure. The energy of a stacking fault on (110) in the cubic phase was estimated using the ANNNI model and found to be about 1.95 J m −2 using potential W3. The distance of separation of partial dislocations of this type is predicted to increase with increasing pressure from 8.4 Å at 1 bar to 9.2 Å at 1 Mbar.
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