Hi all.
I had a question about the difference between several potential implementations in LAMMPS. Many potentials come with the coulomb interaction included for example: buck/coul/long, born/coul/long, lj/cut/coul/long. What is the difference between that and just using a 'hybrid/overlayto include the coulomb interactioncoul/long`?
I have done a simple test with the buckingham potential and found the energy and an pressure to be identical. I did some benchmarks with 1000 atoms on how long the run 0 command takes for each buck/coul/long 46ms±1ms vs. buck + coul/long 54ms±1ms. So it looks like the only difference is performance? Obviously 1000 atoms does not highlight the performance difference but it does show it.
The benchmarks were done with a fairly mature python lammps wrapper I have written lammps-cython.
buck/coul/long
kspace_style pppm 1e-6
set atom 1 charge 1.400000
set atom 2 charge -1.400000
pair_style buck/coul/long 10.0 10.0
pair_coeff 1 1 1309362.276647 0.104000 0.00000
pair_coeff 1 2 9892.357000 0.201990 0.000000
pair_coeff 2 2 2145.734500 0.300000 30.222200
buck + coul/long
kspace_style pppm 1e-6
set atom 1 charge 1.400000
set atom 2 charge -1.400000
pair_style hybrid/overlay coul/long 10.0 buck 10.0
pair_coeff * * coul/long
pair_coeff 1 1 buck 1309362.276647 0.104000 0.000000
pair_coeff 1 2 buck 9892.357000 0.201990 0.000000
pair_coeff 2 2 buck 2145.734500 0.300000 30.222200