Implementing pair specific parameters in Buckingham Potential

[Robin Singh]

Hello Peter,

I want to use below mentioned Buckingham potential for my system (salt in water)

A*exp(-Br) - C/r^6

I want to use this form in <CustomNonBondedForce> tag and want to implement pair specific parameters for A, B and C for different non-bonding interaction pairs in my system that can overwrite parameters generated from combination rules (if any).

Can you kindly let me know what is the way to do this for the above mentioned functional form in OpenMM?

Regards,
Robin

[Peter Eastman]

You can do this by using tabulated functions for the parameters. Use the energy expression "A(type1, type2)*exp(-B(type1, type2)*r) - C(type1, type2)/r^6", where "type" is an integer valued per-particle parameter giving the type of each particle, and A, B, and C are Discrete2D functions.