Beyond Classical Molecular Dynamics: Developing DL_POLY

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DL_POLY is a CCP5 flagship UK code, one of a handful of international codes to carry out classical molecular dynamics simulations. These are a powerful form of computational microscope, a real Laplace's demon, in which, given a specified set of forces between atoms, one follows their changing positions and velocities by Newtonian mechanics. One can thus analyse and understand the behaviour of condensed matter at the atomic level. However, classical molecular dynamics has two major limitations which dominate the majority of community requests for new functionality. First, the use of classical force fields limits the accuracy of the model and restricts its applicability -- quantum effects, bond breaking and making and charge transfer are, for example, not included. Secondly, the timescales (the time over which the system can be followed) accessible via molecular dynamics are too short to study properly many phenomena and processes in chemistry, physics, materials science and biology where events occur only rarely. We aim to address both these methodological limitations. We shall implement in DL_POLY: (a) density functional tight binding (DFTB) to address the accuracy and quantum effects problem and (b) forward flux sampling (FFS) to enable simulations of rare events and thus address long timescale phenomena.We shall involve members of the community both as advisers and early users right from the start of the project. A number of test applications are planned to demonstrate the power of the new software: i) examination of the effects of nanostructuring on the electronic structure of potential thermoelectrics and the link between local structure and conductivity in highly disordered bismuth oxides which are among the very best superionic conductors (DFTB) ii) heterogeneous nucleations, such as those promoted by nanoparticles and exploited in enhanced drug delivery by nanobubbles in cancer treatment (FFS). The new functionality will open up a myriad of new applications in areas such as functional materials (an EPSRC priority) -- e.g., energy materials, battery materials, nanomaterials, ferroelectrics, superconductors, thermoelectrics for use in information and communications technology, energy generation storage, transport, healthcare, defence and consumer goods. FFS implementation will enable users to tackle problems as diverse as crystal nucleation, protein folding, pore formation, protein translocation through pores, rare switching in magnetic nanostructures, isomerization, wetting of rough surfaces, droplet coalescence and flipping of genetic switches. The new software produced will be freely available to academics worldwide. The new features will assure that DL_POLY remains internationally competitive. Comprehensive manuals, documentation and training will be made available to both academia and industry.