Simulating a metallo-protein Apo form

[saraujo2023]

Hi,
How do I prepare a metalloprotein system in Apo form?
It is a system with two proteins, and zinc coordinates the site. I need to learn how to fix this error in the preparation.

=======================Building models==========================*

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***Creating the small model...
It contains the residue 4-THR as keeping sidechain and CO group.
Creating the residue 5-VAL into NME...
Totally there are 19 atoms in the small model.
Totally there are 64 electrons in the small model.
***Creating the standard model...
It contains the residue 4-THR as normal.
It contains the residue 5-VAL as normal.
Totally there are 30 atoms in the standard model.
***Creating the large model...
Creating the residue 3-ARG into ACE...
It contains the residue 4-THR as normal.
It contains the residue 5-VAL as normal.
Creating the residue 6-ARG into NME...
Totally there are 42 atoms in the large model.
Totally there are 148 electrons in the large model.
Traceback (most recent call last):
File "/opt/amber/amber22/bin/MCPB.py", line 651, in
gene_model_files(orpdbf, ionids, addres, addbpairs, gname, ff_choice,
File "/opt/amber/amber22/lib/python3.12/site-packages/pymsmt/mcpb/gene_model_files.py", line 1909, in gene_model_files
build_large_model(mol, reslist, lmsresids, lmsresace, lmsresnme, lmsresgly,
File "/opt/amber/amber22/lib/python3.12/site-packages/pymsmt/mcpb/gene_model_files.py", line 1603, in build_large_model
write_gau_mkf(outf, gmkf, lgchg, SpinNum, gatms, ionnames,
File "/opt/amber/amber22/lib/python3.12/site-packages/pymsmt/mol/gauio.py", line 286, in write_gau_mkf
chg = int(round(chargedict[ionname], 0))
~~~~~~~~~~^^^^^^^^^
KeyError: 'C'

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Can I accomplish this using Colab?
Also, is it essential to create this small system for the Apo form?

I want to express my sincere gratitude in advance for any guidance.