The CASTEP code originated in the University of Cambridge and was widely used in the UK condensed matter theory community before becoming commercially available from Molecular Simulations. Both academic and commercial versions are currently in use although most new developments are collected and incorporated into the commercial version. CASTEP is a total-energy code employing density-functional theory (DFT) (1; 2; 3), pseudopotentials and either the local density approximation (LDA) (4) or generalised gradient approximation (GGA) (5; 6) for electronic exchange and correlation, and plane-waves as a basis set. The method is well described elsewhere (7), and is outlined by Victor Milman in this volume.
A parallel implementation of the total-energy pseudopotential method, CETEP (8), is also widely used within the UK Car-Parrinello (UKCP) consortium. UKCP encompasses groups at Bath, Belfast, Cambridge, Daresbury Laboratory, Edinburgh, Keele and Oxford, using the Cray T3E at Edinburgh and Hitachi SR2201 in Cambridge. The computational resources available from the use of parallel machines is essential for the more complex applications: supercells of perhaps fifty atoms may be treated with modern workstations but larger simulations become unwieldy and memory-intensive.