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# pair_style harmonic/cut command

Accelerator Variants: harmonic/cut/omp

## Syntax

    pair_style style

- style = harmonic/cut

## Examples

    pair_style harmonic/cut
    pair_coeff * * 0.2 2.0
    pair_coeff 1 1 0.5 2.5

## Description

Added in version 17Feb2022.

Style harmonic/cut computes pairwise repulsive-only harmonic interactions with the formula

\[E = k (r_c - r)^2 \qquad r < r_c\]

where \(r_c\) is the cutoff. Note that the usual 1/2 factor is included in \(k\).

The following coefficients must be defined for each pair of atoms 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:

- \(k\) (energy/distance^2 units)

- \(r_c\) (distance units)

Styles with a gpu, intel, kk, omp, or opt suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed on the Accelerator packages page. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues.

These accelerated styles are part of the GPU, INTEL, KOKKOS, OPENMP, and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package page for more info.

You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the -suffix command-line switch when you invoke LAMMPS, or you can use the suffix command in your input script.

See the Accelerator packages page for more instructions on how to use the accelerated styles effectively.

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

For atom type pairs I,J and I != J, the \(k\) and \(r_c\) coefficients can be mixed. The default mix value is geometric. See the “pair_modify” command for details.

Since the potential is zero at and beyond the cutoff parameter by construction, there is no need to support the pair_modify shift or tail options for the energy and pressure of the pair interaction.

These pair styles write their 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.

These pair styles can only be used via the pair keyword of the run_style respa command. They do not support the inner, middle, outer keywords.

## Restrictions

The harmonic/cut pair style is only enabled if LAMMPS was built with the EXTRA-PAIR package. See the Build package page for more info.

## Related commands

pair_coeff

## Default

none