P Wilson

Structural and magnetic phase transitions in simple oxides using hybrid functionals

We present the structural as well as elastic properties of the alkaline earth oxides and FeO, calculated using hybrid exchange functionals within DFT. We show that by empirically fitting the amount of Fock-exchange in the hybrid functionals, we can accurately reproduce the pressure-induced phase transitions for MgO, CaO, SrO and BaO. For FeO the hybrid functionals predict an insulator↔metal transition at ca. 150 GPa, associated with an i-B8↔B8 structural phase transition. The structural phase transition is accompanied by a spin transition from a high- to low-spin electron configuration on the Fe2+ ions. Hence, FeO undergoes a magnetic phase transition from an anti-ferromagnetic to non-magnetic structure. We also find that as the ionicity of the polymorphs increases a higher fraction of Fock-exchange is required to reproduce the structural volumes reported from experiments.

Collaborative grid infrastructure for molecular simulations: The eMinerals minigrid as a prototype integrated compute and data grid

This paper describes a prototype grid infrastructure, called the “eMinerals minigrid”, for molecular simulation scientists. which is based on an integration of shared compute and data resources. We describe the key components, namely the use of Condor pools, Linux/Unix clusters with PBS and IBMs LoadLeveller job handling tools, the use of Globus for security handling, the use of Condor-G tools for wrapping globus job submit commands, Condors DAGman tool for handling workflow, the Storage Resource Broker for handling data, and the CCLRC dataportal and associated tools for both archiving data with metadata and making data available to other workers.

Self diffusion of argon in flexible, single wall, carbon nanotubes

The high-throughput Condor environment now allows many simulations to be performed on related systems, whether the focus is on improving the statistics or on broadening the range of conditions under which these simulations run. We illustrate the scope of the approach by using equilibrium molecular dynamics (EMD) to calculate self-diffusivities of argon atoms diffusing through single wall carbon nanotubes (SWNT). The diameters of the tubes and their helicities were varied and different argon loadings were studied. We also considered the effect of the rigidity/flexibility of the tube on the diffusivity. We found that the helicity and flexibility of the tubes have almost no noticeable influences. The size of the pore had a small effect, but the diffusivity depended essentially on the fluid loading.

The eMinerals collaboratory: tools and experience

Collaboratories provide an environment where researchers at distant locations work together at tackling important scientific and industrial problems. In this paper we outline the tools and principles used to form the eMinerals collaboratory, and discuss the experience, from within, of working towards establishing the eMinerals project team as a functioning virtual organisation. Much of the emphasis of this paper is on experience with the IT tools. We introduce a new application sharing tool.

A computational study of the effect of Li-K solid solutions on the structures and stabilities of layered silicate materials—an application of the use of Condor pools in molecular simulation

Computer modelling techniques were used to investigate the structures and stabilities of Li–K solid solutions of three different disilicate structures, employing a newly developed program based on symmetry arguments to identify identical configurations and hence eliminate unnecessary duplication of calculations. Even so, the large number of calculations needed to sample the complete set of configurations of a wide range of solid solutions necessitated the use of an extensive Condor pool of PC clusters, which afforded the necessary computing resources for this study. The results of our calculations show that in the wide range of Li–K solid solutions investigated, the mixed-cationic KLiSi2O5 material retains its original structure when the composition was varied, where six-membered rings of silica tetrahedra are linked to form continuous channels throughout the structure. The channel positions are found to be preferentially occupied by the potassium ions rather than by the smaller lithium ions. The original framework of the experimental K2Si2O5 structure, containing 14-membered rings of silica tetrahedra, similarly remains intact with the introduction of smaller lithium atoms into the bigger potassium lattice sites. However, the replacement of potassium ions for lithium ions in the Li2Si2O5 material causes significant distortions of the original structure, which loses its symmetry, although the ring structure remains.

Erratum: The eMinerals collaboratory: tools and experience

M.T. DOVE†, M. CALLEJA, R. BRUIN, J. WAKELIN, M.G. TUCKER, G.J. LEWIS, S. MEHMOOD HASAN, V.N. ALEXANDROV, M. KEEGAN, S. BALLARD, R.P. TYER, I. TODOROV, P.B. WILSON, M. ALFREDSSON, G.D. PRICE, C. CHAPMAN, W. EMMERICH, S.A. WELLS, A. MARMIER, S.C. PARKER and Z. DU Several of the figures in this paper did not reproduce correctly. For higher quality figures, please see the online version of this paper at http://www.tandf.co.uk/journals/ titles/08927022.asp