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The accurate modelling of atomistic processes requires the solution of the equations of quantum mechanics. However, for systems of many interacting particles, these equations are far too difficult to solve exactly, even using the most powerful supercomputers. Methods based on density-functional theory (DFT) employ well-controlled approximations which make the calculations tractable but without the need for a priori assumptions which would compromise the first-principles approach.
CASTEP, one of the earliest DFT codes, was originally developed in TCM. It has since been completely rewritten and is now maintained by a group associated with TCM. More recent research has focused on ONETEP, which is a modern linear-scaling DFT code, using localised orbitals to describe the single-particle density matrix and achieving computational effort that scales only linearly with system size. CASTEP and ONETEP are both freely available to all UK academics, and are also commercially available from Accelrys as part of the Materials Studio Package. Other research in the group focuses on developing new tools for use in combination with DFT, such as the calculation of NMR spectra and hybrid schemes coupling DFT and molecular mechanics.
As well as providing insight into complex processes occuring in technologically important materials and biological molecules, DFT calculations can also predict the properties of new or hypothetical systems. We are committed to pushing back the boundaries of applications, making use of large scale simulations enabled by supercomputing resources such as the Cambridge High Performance Computing Service and the UK National Supercomputing Service (HECToR). The TCM DFT Users and Developers Group meets fortnightly throughout the year.
Recent examples of our work include studies of low-speed fracture in silicon crystals (pictured right), defects and structural properties of carbon nanotubes and electronic properties of DNA (pictured below).