details about vdw interactions

[Daniel Konstantinovsky]

Hi OpenMM,

I am building an MD engine for a specific project that is difficult to do with standard MD software. I was wondering two things:

1. in the xml files of OpenMM force fields, what are the units of epsilon and sigma in the vdw sections?
2. for vdw interactions, how do you combine the sigmas and epsilons of two interacting atoms to create the VDW potential between them? I know there is a standard way to do this but I want to know the exact OpenMM way so I will use the sigma and epsilon parameters correctly.

Thank you!

[Peter Eastman]

See the documentation at http://docs.openmm.org/latest/userguide ... html#units and http://docs.openmm.org/latest/userguide ... ondedforce. Sigma is in nm and epsilon is in kJ/mol. It uses Lorentz-Berthelot combining rules.

[Daniel Konstantinovsky]

thanks!