Chemistry at HARvard Macromolecular Mechanics (CHARMM) is a program for macromolecular simulations, including energy minimization, molecular dynamics and Monte Carlo simulations. The primary concern of CHARMM has been to create a research instrument for theoretical studies of the properties and biological function of molecules. Consequently, emphasis has been placed on the versatility of the program and it is being continually modified as work proceeds into new areas.