Type not found in force fields

EMC
1

Hi everyone,

I just started to use EMC and I want to build a PEI polymeric chain. I need for plenty of the monomers to be protonated, so in the .esh file I defined three different groups:
PEI * CNC * ,1,PEP:2,1,PEI:2
PEP * C[NH2+]C * ,1,PEI:2,1,PEP:2
PEC * C,1,PEI:1,1,PEI:2,1,PEP:1,1,PEP:2

I wanted to use OPLS-AA force field, but when I run the build.emc file this error pops up:
Error: core/chemistry/entry.c:419 ChemistryEntry:
Type ‘Nh2’ not found (field not set?).

I’ve been looking around at the OPLS files and it seems this type is not defined, so I should add it. Is there any better approach to this problem? In case there is not, could anyone refer me to any documentation on adding types to OPLS?

Thanks,

Roger

2

Hi Roger,

Try leaving out H2 in [NH2+], i.e. [N+]. Everything between square brackets is seen as a type or possible element by EMC, hence the report for the missing type Nh2. EMC will perform hydrogen completion.

Pieter