Hi everyone,

I’m simulating a lennard jones solid solution and attempting free energy calculations over a range of compositions.

according to the documentation of pair_modify tail corrections are available only for liquids, so the only option is supposed to be truncation and shift. The question is: does the pair_modify shift command add to the energy and pressure computation both the correction to compensate for the shift or only the former?

Is there any option in the second case to compute the long range contribution to the potential energy and pressure or I’m supposed to explicitly add it in postprocessing?

best,

Mattia

Free energy of what?

That is not what it says. It says that it assumes a liquid and a g(r) that is unity beyond the cutoff, otherwise the result will not be correct.

That is not correct, either.

With `pair_modify shift`

you have a potential function that is essentially unchanged, only the absolute value of the potential *energy* is shifted, so that the potential energy is zero at the cutoff distance. With such a partially defined potential function, there are no contributions to the pressure from atoms outside the cutoff.

No.

How would you compute it?

If you want proper treatment of the long-range contributions of the r**6 term of the LJ potential, you need to use an lj/long pair style in combination with ewald/disp or pppm/disp.