[gmx-users] force fileds gromos and oplsaa

Justin Lemkul jalemkul at vt.edu
Thu Nov 16 14:31:28 CET 2017

On 11/16/17 8:28 AM, Faezeh Pousaneh wrote:
> Hi
> sorry for silly question, but I did not find my answer by searching.
> In gromos force fields, the file nonbonded.itp includes nonbonded
> parameters for two different atoms, e.g
> C O 1 2.300953E-03 2.222000E-06
> while I do not see oplsaa provides parameters for nonbonded interactions of
> different atoms, why?

The [nonbond_params] section specifies atom pairs for which normal 
combination rules do not apply, e.g. pair-specific Lennard-Jones 
parameters (CHARMM calls these NBFIX, for instance).

Some force fields use them, others don't (and calculate everything via 
combination rules). In the case of OPLS-AA, there are a huge number of 
atom types, more than any other force field (AFAIK), which is 
essentially doing the same thing - there are highly specific parameter 
optimizations for given interactions.



Justin A. Lemkul, Ph.D.
Assistant Professor
Virginia Tech Department of Biochemistry

303 Engel Hall
340 West Campus Dr.
Blacksburg, VA 24061

jalemkul at vt.edu | (540) 231-3129


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