Are there exisiting doxorubicin topology in charmm, I have the Gromacs one, are there any top and param converting tool for CHARMM from GROMACS.
Have you tried obtaining parameters from CGenFF/Paramchem? Doxorubicin contains a sugar so you may want to obtain the parameters for the sugar moiety from the C36 carbohydrate FF and the remainder from CGenFF.
Note that one should not mix parameters from different force fields. Thus, it is not recommneded to use Gromacs parameters with the CHARMM biological force field.