Download the package simmolvmd and unpack it. It contains a directory called "simmol". Follow the platform-specific information below.
Copy "simmol" to
C:\Program Files (x86)\University of Illinois\VMD\plugins\noarch\tcl
Copy "simmol" to /usr/local/lib/vmd/plugins/noarch/tcl
Make sure everybody can read the directory. Eventually fix by the command
> chmod -R ugo+rX /usr/local/lib/vmd/plugins/noarch/tcl/simmol
Copy "simmol" to /Applications/VMD 1.9.1.app/Contents/vmd/plugins/noarch/tcl
To check that your installation has been completed, launch VMD, open Extensions>Tk Console and type "package require simmol". Should not complain but print out the simmol library version.