ligand is containing chlorine , I am facing problem in ligand.itp file (its showing that -

65 LPH 1 unk LP1 65 0.050 0.000 ;

66 LPH 1 unk LP2 66 0.050 0.000 ;) , I have used Charmm force field,

Also, getting error as,

ERROR 1 [file topol.top, line 77577]:

atom LP1 (Res unk-1) has mass 0 (state A) / 0 (state B). Please help me to solve my problem.

Thanks