pair_modify shift yes

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1

All

I wanted to use F3C water potential in my MD simulations, which uses typical form for truncation shift function. I wanted to check if lammps uses the same (for its pair_modify shift yes function), or i need to modify it. I tried looking for .cpp file which does this, but could not find it. Could anyone tell me in which file this calculation is hidden?

Thanks a lot!
Chetan

2

The shifting is done in the pair*.cpp file for each pair style that
supports it. E.g. pair_lj_cut.cpp. Look for code using "offset"
which is the amount of the applied shift for each atom type pair.

Steve

3

Thanks, Steve. Offset seems to be referring to shift for LJ potential. While that helps, I also want to define truncation shift for Coulombic interactions. I could not find corresponding offset in pair_lj_cut_coul_long.cpp?

Also what is the default value of constant C (for Coulombic interactions) that lammps takes ?

Thanks
Chetan

4

For any coul/long potential there is no shift, as it is not
truncated.

The C is simply the conversion factor from qq/r to the native
units system like Kcal/mole. You don't have to worry
about it - LAMMPS handles it for you.

Steve