General Utility Lattice Program

The General Utility Lattice Program, or GULP to its friends, is designed to perform a variety of tasks relating to three dimensional solids. Although it started life as an attempt to produce an input file driven program for interatomic potential fitting, it has now expanded to encompass energy minimisation, phonon calculations and other hopefully useful facilities. More utilities are constantly being added, often at the request of end users. So if your favourite solid state property isn't currently available then speak up! In many respects GULP parallels the suite of codes THBREL (METAPOCS), THBFIT, THBPHON, CASCADE and to some extent PARAPOCS. One major difference is that GULP tries to use the crystal symmetry both to make it easier to generate structures and where possible to speed up the calculations by only considering the asymmetric unit. GULP will now also perform calculations on non-periodic systems subsuming what was once a separate program called CLUSTER. This facility is useful when calculating defect energies for molecular defects. It also allows the combined fitting of potentials to bulk and cluster information. As with any large computer program (and GULP currently runs to about 160,000 lines) there is always the possibility of bugs. While every attempt is made to ensure that there aren't any and to trap incorrect input there can be no guarantee that a user won't find some way of breaking the program. So it is important to be vigilant and to think about your answers-remember GIGO! Immature optimising compilers can also be a common source of grief. As with most programs, the author accepts no liability for any errors but will attempt to correct any that are reported.