From version 2 onwards GMIN was recoded in fortran90. Dynamic memory allocation is now used, so there are no hard limits on parameters such as the number of atoms. A number of new keywords have also been added since the first version of the code, as well as numerous potentials. The most important are probably SYMMETRY, AVOID, and COOPMOVE, which are directly used in global optimisation, and HISTOGRAM, which specifies a `basin-sampling' calculation of the energy density of states. A new algorithm (bipartite matching) has also been introduced for use with PERMDIST and AVOID to deal with permutational isomers. The implementation of PERMDIST is now the same as in OPTIM and PATHSAMPLE, with a perm.allow file to specify groups of permutable atoms and secondary sets that can only permute together. Finally, GMIN has been interfaced with CHARMM in much the same way as OPTIM, and there are new keywords to specify how the current geometry should be perturbed in the step-taking process. Keyword CHARMMTYPE specifies the type of CHARMM potential, while CHPMAX, CHPMIN, CHNMAX, CHNMIN, NOPHIPSI, and TOMEGA govern the step-taking procedure in charmmgmin.src. Keyword INTMIN specifies that minimisation should be performed in internal coordinates, but this seems to be slower than Cartesian coordinates in general.

Also new from version 2.3, the global minimisation basin-hopping algorithm has been enhanced with a parallel tempering option, which is implemented using MPI. Please see the notes in the Makefile when loading compilers and MPI libraries. (Note that the LAM MPI 32-bit library is currently broken! MPICH has not been tested yet.) The keyword MPI specifies the number of processors for the parallel job and BHPT allows the user to specify the temperature range over which the replicas are exponentially distributed and the probability of attempting an exchange.

Currently under development is a new implementation of basin-sampling where the quench probability for local minima is obtained using parallel-tempering rather than a flat-histogram Wang-Landau method. This approach also employs MPI and can be invoked with the keyword BSPT.

David Wales 2018-06-21