Missing OPLS-AA parameters for furfural and acetonitrile

EMC
1

Hi all
I am attempting to build furfural and acetonitrile molecules using the OPLS-AA (2024) force field in EMC. However, I got these errors indicating missing rules for both molecules.

For furfural (c1cc(oc1)C=O), the following warnings and error are reported:

Warning: no rule found for {group, site} = {FF, 0}
Warning: no rule found for {group, site} = {FF, 2}
Warning: no rule found for {group, site} = {FF, 4}
Warning: no rule found for {group, site} = {FF, 6}
Warning: no rule found for {group, site} = {FF, 8}
Error: core/fields.c:433 FieldsApply: Missing rules. Program aborted.

For acetonitrile (SMILES: CC#N), I obtain the following error:

Warning: no rule found for {group, site} = {ACN, 4}.
Error: core/fields.c:433 FieldsApply: Missing rules. Program aborted.

I am a relatively new EMC user and am unsure how to properly define new force-field rules for these two molecules. However, the EMC itself on my PC is functioning correctly, as I can successfully generate DMSO (CS(=O)C), water molecules, and phenylene polymer chains using the same OPLS-AA force field. The issue appears to be specific to furfural and acetonitrile.

For reference, I have attached the relevant OPLS-AA field files and my .esh input file, excerpts of which are shown below.

#=======================================================
ITEM    OPTIONS
replace         true
field           opls-aa
number          true
field_charge    false
density         0.3
focus           true
build_dir       .
ITEM    END
#=======================================================

# Shorthands
ITEM        SHORTHAND
FF              c1cc(oc1)C=O,10
ACN             CC#N,20
SPCE:c=o        [O-0.8476]([H+0.4238])([H+0.4238]),3
ITEM        END
#=======================================================

I would appreciate any guidance on how to correctly define or extend the OPLS-AA rules to support furfural and acetonitrile in EMC.

opls-aa.define (101.5 KB)

opls-aa.top (16.7 KB)

opls-aa.prm (64.5 KB)

2

Dear user,

I included the extra terms needed for a family of furan and nitrile structures based on the available parameters as provided in the opls/2024/src directory. The resulting force field is based on the following define file

opls-aa.define (105.6 KB)

Check out the sections for furan and nitriles. Some missing angles and dihedrals were added based on existing parameters. The resulting force field is given by

opls-aa.prm (65.4 KB)
opls-aa.top (18.3 KB)

You can place these files in your $EMC_ROOT/field/opls/2024/ force field directory.

1 Like
3

Dear Veld,

Thank you very much for adding the furfural and acetonitrile structures. It was a wonderful Christmas gift.

Merry Christmas.

4

My pleasure. Happy simulating and a Merry Christmas!