# pair_style lj/smooth/linear command

Accelerator Variants: *lj/smooth/linear/omp*

## Syntax

``` LAMMPS
pair_style lj/smooth/linear cutoff
```

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

## Examples

``` LAMMPS
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 Rc [(Toxvaerd)](Toxvaerd):

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

The following coefficients must be defined for each pair of atoms types
via the [pair_coeff](pair_coeff) command as in the examples above, or in
the data file or restart files read by the [read_data](read_data) or
[read_restart](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](Speed_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](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](Run_options) when you invoke LAMMPS, or you can use the
[suffix](suffix) command in your input script.

See the [Accelerator packages](Speed_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](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](pair_modify) table option is not relevant for this
pair style.

This pair style does not support the [pair_modify](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](restart), 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](run_style) 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](Build_package) page for more info.

## Related commands

[pair_coeff](pair_coeff), [pair lj/smooth](pair_lj_smooth)

## Default

none

------------------------------------------------------------------------

::: {#Toxvaerd}
**(Toxvaerd)** Toxvaerd, Dyre, J Chem Phys, 134, 081102 (2011).
:::