Type not found in force fields

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?



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.