Missing rules for field '~/Desktop/v9.4.4/field/opls/2012/opls-aa.prm'

Hi everyone, I wanted to create a polymerized ionic liquids system with the monomer as follows:
CCCC[N+]1=CN(C=C1)*CC *
I am able to run the esh file to create a build.emc file for it; however, when I tried to run the build.emc file using build.emc 2>&1 | tee build.out command, errors occurred like this:

Info: applying ‘~/Desktop/v9.4.4/field/opls/2012/opls-aa.prm’
Warning: missing rules for field ‘~/Desktop/v9.4.4/field/opls/2012/opls-aa.prm’.
Warning: missing rule for {group, site} = {monomer, 16}.
Warning: missing rule for {group, site} = {monomer, 21}.
Error: core/fields.c:432 FieldsApply:
Missing rules.
Program aborted.

I specified opls-aa ff as the force field in the esh file. What should I do to solve these errors? Should I modify the opls-aa prm file or what? Thank you all. Really appreciate it!

note: I followed the previous post and found my site 16 and site 21 are two atoms: N in an imidazole ring and C that is bonded to it.

I checked the opls-aa.define file and found there is some kind of definition of imidazole:

But this piece of information is missing in opls-aa.prm file, so the errors occurred.
I followed the other post, used the emc_opls.pl file to execute the convert.sh file in the same directory, and then ran build.emc again, the errors still occurred. What should be done next? Thank you all.

Using field_debug reduced in the esh file, you can check the missing rule. In your case, one of the missing rule is

You can add the missing rule in the opls-aa.top file. You have to check the exact atom type, reference number and charge in the oplaa.par file.

Hi there, thank you very much for commenting on this. I can now find the missing rules for the atoms in the build.out file. for example, I have a site 10 whose rule is missing, I can locate site = 10 in the build.out file and to see which rule should be satisfied, just like this:

Then I should check relevant literature and then add this rule in the opls-aa.top file, so do other missing rules. Thank you for your explanation! I’ll try that asap.