Hi Weihao,
Which version of MCPB.py did you use?
Best,
Pengfei
> On May 19, 2026, at 2:35 AM, 张玮豪 via AMBER <amber.ambermd.org> wrote:
>
> Dear Amber Developersand Users,
>
> I want to use MCPB.py to construct a nonbonded model (12-6 LJ Nonbonded Model) for a ligand-bound metalloprotein. Following the workflow described in the Amber 24 manual: “For the modeling of a non-bonded model with a refitted charge, users can follow the workflow (3 steps): 1m → 3b → 4n1.”
>
>
>
> ”””
>
> MCPB input file (mcpb.in) is as follows:
>
> original_pdb 6wfj_H.pdb
>
> group_name 6wfj
>
> ion_ids 12980 12981
>
> ion_mol2files ZN1.mol2 ZN2.mol2
>
> force_field ff14SB
>
> water_model SPCE
>
> gaff 1
>
> large_opt 1
>
> cut_off 2.8
>
> lgmodel_chg 0
>
> lgmodel_spin 1
>
> ”””
>
>
>
> Step 1 (MCPB.py -i mcpb.in -s 1m) and Step 2 (MCPB.py -i mcpb.in -s 3b) successfully ran. However, when doing Step3 (MCPB.py -i mcpb.in -s4n1), the following error was encountered:
>
>
>
> Traceback (most recent call last):
>
> File "/share/apps/amber/cpu/21/bin/MCPB.py", line 712, in <module>
>
> gene_leaprc(gname, orpdbf, fipdbf, stpdbf, stfpf, ionids, ionmol2fs,
>
> File"/share/apps/amber/cpu/21/lib/python3.8/site-packages/pymsmt/mcpb/amber_modeling.py", line 201, in gene_leaprc
>
> frcmodf = get_frcmod_fname(element, chg, watermodel, paraset)
>
> File "/share/apps/amber/cpu/21/lib/python3.8/site-packages/pymsmt/mcpb/amber_modeling.py", line 108, in get_frcmod_fname
>
> return frcmodf
>
> UnboundLocalError: local variable 'frcmodf' referenced before assignment
>
>
>
> I tried to change the water_model as TIP3P, but the error is already existed.Could anyone tell me why this error occurs?
>
> Thank you very much for your time and assistance.
>
>
>
> Best regards,
> Weihao Zhang
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Received on Tue May 19 2026 - 19:00:02 PDT
