Seminar 25th May 2010 3:30 p.m. 53/4025
Crystal structures from nothing - dense matter from random numbers
Professor Chris Pickard
Department of Physics, University College London
- Categories
- Biomolecular Organisation, Biomolecular simulations, CASTEP, Complex Systems, Density functional Theory, Evolutionary Algorithms, Fortran, HECToR, Materials, Molecular Dynamics, Multi-physics, Multi-scale, Structural biology, Structural dynamics
- Submitter
- Chris-Kriton Skylaris
Left: Ammonia is amonium amide at high pressure [3]. Right: Lithium is an “elemental electride” [4]
15:30 Coffee, tea and biscuits
16:00 Start of seminar
Abstract
It is an obvious goal for a full theory of the solid state to enable the prediction of the structures adopted by large collections of atoms under a variety of conditions, including high pressure. But until relatively recently it is one that has been largely avoided.
I will present a strikingly simple and effective approach to the unbiased prediction of crystal structures. It is based on an initial uniform random sampling of the space of possible structures, followed by robust structural optimisation to the local enthalpy minimum of each initial structure under quantum mechanical (density functional theory) forces and stresses [1]. More complex structures can be discovered by a judicious application of constraints to the search space.
I will illustrate the use of this technique with applications to situations which present considerable experimental challenges. This will include hydrogen [2], ammonia [3] and lithium [4] at high pressures. I will discuss recent progress in the study of extremely dense matter, including iron, silicon and oxygen.
References
[1] High pressure phases of silane, C.J. Pickard and R.J. Needs, Physical Review Letters, 2006, 97, 45504
[2] Structure of phase III of solid hydrogen, C.J. Pickard and R.J. Needs, Nature Physics, 2007, 3, 473-476
[3] Highly compressed ammonia forms an ionic crystal, C.J. Pickard and R.J. Needs, Nature Materials, 2008, 7, 775-779
[4] Dense low-coordination phases of lithium, C.J. Pickard and R.J. Needs, Physical Review Letters, 2009, 102, 146401