Here is the brief description I submitted: "PSI is a federal research institute in Switzerland. Charmm will be installed on the HPC cluster, upon request from structural biology groups."

Following accepting the license I got a download link by email.
Save the tarball as /opt/psi/var/distfiles/charmm-47.2.tar.gz (converting from c${V_MAJOR}b${V_MINOR}.tar.gz
Run ./build
Check the output directory for symlinks. These seem to come from post_install, but I don't have time to debug the script more so I'm going to just copy the directories manually.