Biomedical subjects

M I J Probert

Publications and source records attributed to M I J Probert.

3 recordsLinked to original sources

PubMed2005

Progression of phase behavior for a sequence of model core-softened potentials.

A series of phase diagrams is obtained in three dimensions for a smooth pair potential with an outer well and a repulsive inner shoulder. Condensed phase boundaries are located using free energy calculations. Liquid-vapor equilibria are obtained with multicanonical methods. As the depth of the outer well is increased, a simple-hexagonal to close-packed transition appears in the solid, leading to a discontinuity in the slope of the melting curve. For deeper wells the simple hexagonal melting temperature exhibits a maximum with respect to pressure. The onset of the predicted metastable isostructural transition is also studied.

Journal Article↗

PubMed2005

Phase behavior of a three-dimensional core-softened model system.

The phase behavior of a three-dimensional model substance interacting via a continuous core-softened pair potential is studied. A combination of thermodynamic integration and free-energy augmented metadynamics is employed to identify the ground state structure as simple hexagonal. A transition to close packing is predicted at high pressure. The melting line is traced, which when combined with the liquid-vapor line, allows the liquid to be studied over its entire thermodynamically stable range. We find no liquid anomalies in the range of pressures for which the vaporization transition exists. Our results therefore support suggestions that the anomalous behavior of such fluids is unique to the two-dimensional case.

Journal Article↗

PubMed2004

Langevin dynamics in constant pressure extended systems.

The advantages of performing Langevin dynamics in extended systems are discussed. A simple Langevin dynamics scheme for producing the canonical ensemble is reviewed, and is then extended to the Hoover ensemble. We show that the resulting equations of motion generate the isobaric-isothermal ensemble. The Parrinello-Rahman ensemble is then discussed and we show that despite the presence of intrinsic probability gradients in this system, a Langevin dynamics approach samples the extended phase space in the correct fashion. The implementation of these methods in the ab initio plane wave density functional theory code CASTEP [M. D. Segall, P. L. D. Lindan, M. J. Probert, C. J. Pickard, P. J. Hasnip, S. J. Clarke, and M. C. Payne, J. Phys.: Condens. Matter 14, 2717 (2003)] is demonstrated.

Journal Article↗