\(\renewcommand{\AA}{\text{Å}}\)

# pair_style lj/smooth/linear command

Accelerator Variants: lj/smooth/linear/omp

## Syntax

    pair_style lj/smooth/linear cutoff

- cutoff = global cutoff for Lennard-Jones interactions (distance units)

## Examples

    pair_style lj/smooth/linear 2.5
    pair_coeff * * 1.0 1.0
    pair_coeff 1 1 0.3 3.0 9.0

## Description

Style lj/smooth/linear computes a truncated and force-shifted LJ interaction (aka Shifted Force Lennard-Jones) that combines the standard 12/6 Lennard-Jones function and subtracts a linear term based on the cutoff distance, so that both, the potential and the force, go continuously to zero at the cutoff \(r_c\) (Toxvaerd):

\[\begin{split}\phi\left(r\right) & = 4 \epsilon \left[ \left(\frac{\sigma}{r}\right)^{12} - \left(\frac{\sigma}{r}\right)^6 \right] \\ E\left(r\right) & = \phi\left(r\right) - \phi\left(r_c\right) - \left(r - r_c\right) \left.\frac{d\phi}{d r} \right|_{r=r_c} \qquad r < r_c\end{split}\]

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, or by mixing as described below:

- \(\epsilon\) (energy units)

- \(\sigma\) (distance units)

- cutoff (distance units)

The last coefficient is optional. If not specified, the global LJ cutoff specified in the pair_style command is used.

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 epsilon and sigma coefficients and cutoff distance can be mixed. The default mix value is geometric. See the “pair_modify” command for details.

This pair style does not support the pair_modify shift option for the energy of the pair interaction, since it goes to 0.0 at the cutoff by construction.

The pair_modify table option is not relevant for this pair style.

This pair style does not support the pair_modify tail option for adding long-range tail corrections to energy and pressure, since the energy of the pair interaction is smoothed to 0.0 at the cutoff.

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

This pair style is part of the EXTRA-PAIR package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.

## Related commands

pair_coeff, pair lj/smooth

## Default

none

(Toxvaerd) Toxvaerd, Dyre, J Chem Phys, 134, 081102 (2011).