MOLCAS manual: 4.2 MOLCAS Environment Setup The environment variable (MOLCAS) and MOLCAS driver (molcas) must be defined in order to run MOLCAS. The MOLCAS environment variable points to the root directory of the MOLCAS installation and can be defined by the bash shell command export MOLCAS=/home/molcas/molcas.version The location of the MOLCAS driver is defined at installation time and is typically located in /usr/local/bin or $HOME/bin. Check to ensure that this directory is included in your path. Otherwise, the path can be extended by the following command: export PATH=$PATH:$HOME/bin In addition, the variable MOLCAS_NPROCS is needed to run MOLCAS in parallel. This specifies the number of MPI processes that will be used. It may be also convenient to define environment variables such as WorkDir which points to a directory for intermediate files and Project to define the name of a project: export Project=MyMolecule MOLCAS will provide default values if they are not explicitly defined. For a discussion of other MOLCAS environment variables, please see the section on Environment and EMIL Command . All environment variables can either be defined explicitly or entered in a shell script which can be subsequently executed.