Unit Conversion Factor in Lammps

rqw1929 · August 28, 2024, 7:56am

Dear Lammps Users

I am trying to make user define potential by pair_style lepton command.

In doing that, I found that I have to set my own coulomb potential calculation.

The lammps document says the coulomb potential formula is

and C is the internal conversion factor.

I want to find the exact value of C when I use “units real”.

How can I find this in the lammps code?

Or do I have to do some math to find C corresponding with fundamental charge and kcal/mol unit

Currently I’m using Lammps 27Jun2024 Version

akohlmey · August 28, 2024, 11:11am

github.com

lammps/lammps/blob/6e791034f9ebe2eb0ea157d525d80e41df167639/src/update.cpp#L170


      
            dt = 0.005;
            neighbor->skin = 0.3;
          
          } else if (strcmp(style, "real") == 0) {
            force->boltz = 0.0019872067;
            force->hplanck = 95.306976368;
            force->mvv2e = 48.88821291 * 48.88821291;
            force->ftm2v = 1.0 / 48.88821291 / 48.88821291;
            force->mv2d = 1.0 / 0.602214129;
            force->nktv2p = 68568.415;
            force->qqr2e = 332.06371;    // see also force->qqr2d_lammps_real
            force->qe2f = 23.060549;
            force->vxmu2f = 1.4393264316e4;
            force->xxt2kmu = 0.1;
            force->e_mass = 1.0 / 1836.1527556560675;
            force->hhmrr2e = 0.0957018663603261;
            force->mvh2r = 1.5339009481951;
            force->angstrom = 1.0;
            force->femtosecond = 1.0;
            force->qelectron = 1.0;

rqw1929 · August 28, 2024, 11:40am

Really appreciate for your help professor.
force->qqr2e = 332.06371
I found this C matches with my conversion calculation!