Dear Sir/Mam I used antechamber in chimera to add charges to ligand "FAD" using am-bcc, amber ffo3r.1 and +5 charge (as depicted by chimera). The procedure was Tools > structure editing > add H and then add charge. The error shown is : Charge model: AMBER ff03.r1 Assigning partial charges to residue FAD (net charge +1) with am1-bcc method Running ANTECHAMBER command: C:/Program Files/Chimera 1.8.1/bin/amber12/binantechamber -ek qm_theory='AM1', -i c:usersamehtaappdatalocaltemptmpjjpoaqante.in.mol2 -fi mol2 -o c:usersamehtaappdatalocaltemptmpjjpoaqante.out.mol2 -fo mol2 -c bcc -nc 1 -j 5 -s 2 (FAD) (FAD) Running: "C:/Program Files/Chimera 1.8.1/bin/amber12/bin/bondtype" -j part -i ANTECHAMBER_BOND_TYPE.AC0 -o ANTECHAMBER_BOND_TYPE.AC -f ac (FAD) (FAD) Running: "C:/Program Files/Chimera 1.8.1/bin/amber12/bin/atomtype" -i ANTECHAMBER_AC.AC0 -o ANTECHAMBER_AC.AC -p gaff (FAD) Total number of electrons: 412; net charge: 1 (FAD) (FAD) Running: "C:/Program Files/Chimera 1.8.1/bin/amber12/bin/sqm" -O -i sqm.in -o sqm.out (FAD) Error: cannot run ""C:/Program Files/Chimera 1.8.1/bin/amber12/bin/sqm" -O -i sqm.in -o sqm.out" of bcc() in charge.c properly, exit Failure running ANTECHAMBER for residue FAD Please help as it is very urgent. Hope for your reply. I have also attached the ligand. Please find the attachment. With Regards, Isha C/O Dr. Raman Parkesh Protein Science & Engg. Institute of Microbial Technology Sector 39A, Chandigarh 160036 Ext: 0172-6665489