[lammps-users] intermolecular interaction energy

Dear LAMMPS Users,

I want to compute the inter-molecular interaction energy during an NVT run of an ion-pair of an ionic liquid. The cation atom types
range from 1 to 10 and the anion atom types range >10. The script I am using as follows:

group cation type <=10
group anion type >10

compute 1 cation group/group anion molecule inter

This gives an ERROR: Illegal compute group/group command.

If the “molecule inter” keyword/value pair is omitted, the computation is working. However, for a bulk system, to compute intermolecular cation-cation or anion-anion interaction energy, this keyword/value pair should be there.

Please help me to debug this issue.



Penn State

please always report which version of LAMMPS you are using and what platform you are running on.

in this case it would be crucial information since the error message suggests that you are using an old version of LAMMPS (older than February 2017), which does not have the feature you want to use included.
please note that when looking at the LAMMPS documentation online, you will get the documentation of the latest patch release and given the speed at which changes are contributed to LAMMPS, there are always new features and additional or changed flags and settings versus older versions.

you will have to upgrade your LAMMPS version to get access to the feature you want to use.