charmm is available to individuals for nonprofit use free of charge. For-profit companies should contact BIOVIA, which distributes the commercial version, called CHARMm. charmm has all of the features of CHARMM except for high-performance MD functionality (e.g. GPU acceleration or domain decomposition modules are not included in charmm). To obtain charmm, please register here. You will be asked to review an on-line license agreement. Upon acceptance, a download link and password will be sent to the email address provided. If the download password is lost or misplaced, you may simply re-register. If you have previously obtained charmm and would like to upgrade to CHARMM, you may update your request.