[lammps-users] Improper parameter for COMPASS force field


     I am doing MD simulation of the pentacene molecule. I used the COMPASS parameter according to the description in the paper of Sun, J Phys Chem B 102, 7338-7364 (1998) . The problem is I can't get a flat pentacene molecule yet, so I want to add some improper coefficients into the data file. Does anybody know how I can get the values of the improper coefficients for pentacene in a COMPASS force field?