There is more than one version of CASTEP available on elvis. You need to load the appropriate one and all its supporting modules, and call it with the right launcher to start the MPI processes. You would normally put the 'module add' commands into your .bash_profile file and then call the launcher inside a qsub script.
These were built from source with the modules
This was a precompiled version which has to be used with OpenMPI 1.4.2 compiled with Intel compilers.
module add openmpi/intel11 # make mpi library available, includes a launcher module add castep/5.5.1 # load castep mpirun castep
This was built locally with PGI compilers and needs MVAPICH2.
module add pgi/64/10.0 # make appropriate compiler libs available module add mvapich2/pgi # make MPI library avialable module add mpiexec # make launcher available module add castep/4.4 # load castep mpiexec castep