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### pair_style soft command

Syntax:

    pair_style soft cutoff

- cutoff = global cutoff for soft interactions (distance units)

Examples:

    pair_style soft 2.5
    pair_coeff * * 0.0 60.0
    pair_coeff 1 1 0.0 60.0 3.0

Description:

Style soft computes pairwise interactions with the formula

It is useful for pushing apart overlapping atoms, since it does not blow up as r goes to 0. A is a pre-factor that varies in time from the start to the end of the run. The run command documents how to make the ramping take place across multiple runs. Rc is the cutoff. See the fix nve/limit command for another way to push apart overlapping atoms.

The following coefficients must be defined for each pair of atom types via the pair_coeff command as in the examples above, or in the data file or restart files read by the read_data or read_restart commands, or by mixing as described below:

- Astart (energy units)
- Astop (energy units)
- cutoff (distance units)

Astart and Astop are the values of the prefactor at the start and end of the next run. At intermediate times the value of A will be ramped between these 2 values. Note that before performing a 2nd run, you will want to adjust the values of Astart and Astop for all type pairs, or switch to a new pair style.

The last coefficient is optional. If not specified, the global soft cutoff is used.

Mixing, shift, table, tail correction, restart, rRESPA info:

For atom type pairs I,J and I != J, the Astart, Astop coefficients and cutoff distance for this pair style can be mixed. Astart and Atop are always mixed via a geometric rule. The cutoff is mixed according to the pair_modify mix value. The default mix value is geometric. See the "pair_modify" command for details.

This pair style does not support the pair_modify shift option, since the pair interaction goes to 0.0 at the cutoff.

The pair_modify table and tail options are not relevant for this pair style.

This pair style writes its information to binary restart files, so pair_style and pair_coeff commands do not need to be specified in an input script that reads a restart file.

This pair style can only be used via the pair keyword of the run_style respa command. It does not support the inner, middle, outer keywords.

Restrictions: none

Related commands:

pair_coeff, fix nve/limit

Default: none