# pair_style meam/spline command

Accelerator Variants: *meam/spline/omp*

## Syntax

``` LAMMPS
pair_style meam/spline
```

## Examples

``` LAMMPS
pair_style meam/spline
pair_coeff * * Ti.meam.spline Ti
pair_coeff * * Ti.meam.spline Ti O
```

## Description

The *meam/spline* style computes pairwise interactions for metals using
a variant of modified embedded-atom method (MEAM) potentials
[(Lenosky)](Lenosky1). For a single species (\"old-style\") MEAM, the
total energy E is given by

$$\begin{aligned}
E & =\sum_{i<j}\phi(r_{ij})+\sum_{i}U(n_{i}) \\
n_{i} & =\sum_{j}\rho(r_{ij})+\sum_{\substack{j<k,\\j,k\neq i}}f(r_{ij})f(r_{ik})g[\cos(\theta_{jik})]
\end{aligned}$$

where $\rho_i$ is the density at atom I, $\theta_{jik}$ is the angle
between atoms J, I, and K centered on atom I. The five functions
$\phi, U, \rho, f,$ and *g* are represented by cubic splines.

The *meam/spline* style also supports a new style multicomponent
modified embedded-atom method (MEAM) potential [(Zhang)](Zhang4), where
the total energy E is given by

$$\begin{aligned}
E &= \sum_{i<j}\phi_{ij}(r_{ij})+\sum_{i}U_i(n_{i}) \\
n_{i} & = \sum_{j\ne i}\rho_j(r_{ij})+\sum_{\substack{j<k,\\j,k\neq i}}f_{j}(r_{ij})f_{k}(r_{ik})g_{jk}[\cos(\theta_{jik})]
\end{aligned}$$

where the five functions $\phi, U, \rho, f,$ and *g* depend on the
chemistry of the atoms in the interaction. In particular, if there are N
different chemistries, there are N different *U*, $\rho$, and *f*
functions, while there are N(N+1)/2 different $\phi$ and *g* functions.
The new style multicomponent MEAM potential files are indicated by the
second line in the file starts with \"meam/spline\" followed by the
number of elements and the name of each element.

The cutoffs and the coefficients for these spline functions are listed
in a parameter file which is specified by the [pair_coeff](pair_coeff)
command. Parameter files for different elements are included in the
\"potentials\" directory of the LAMMPS distribution and have a
\".meam.spline\" file suffix. All of these files are parameterized in
terms of LAMMPS [metal units](units).

Note that unlike for other potentials, cutoffs for spline-based MEAM
potentials are not set in the pair_style or pair_coeff command; they are
specified in the potential files themselves.

Unlike the EAM pair style, which retrieves the atomic mass from the
potential file, the spline-based MEAM potentials do not include mass
information; thus you need to use the [mass](mass) command to specify
it.

Only a single pair_coeff command is used with the *meam/spline* style
which specifies a potential file with parameters for all needed
elements. These are mapped to LAMMPS atom types by specifying N
additional arguments after the filename in the pair_coeff command, where
N is the number of LAMMPS atom types:

-   filename
-   N element names = mapping of spline-based MEAM elements to atom
    types

See the [pair_coeff](pair_coeff) page for alternate ways to specify the
path for the potential file.

As an example, imagine the Ti.meam.spline file has values for Ti (old
style). In that case your LAMMPS simulation may only have one atom type
which has to be mapped to the Ti element as follows:

``` LAMMPS
pair_coeff * * Ti.meam.spline Ti
```

The first 2 arguments must be \* \* and there may be only one element
following or NULL. Systems where there would be multiple atom types
assigned to the same element are **not** supported by this pair style
due to limitations in its implementation. If a mapping value is
specified as NULL, the mapping is not performed. This can be used when a
*meam/spline* potential is used as part of the *hybrid* pair style. The
NULL values are placeholders for atom types that will be used with other
potentials.

An example with a two component spline (new style) is TiO.meam.spline,
where the command

``` LAMMPS
pair_coeff * * TiO.meam.spline Ti O
```

will map the first atom type to Ti and the second atom type to O. Note
in this case that the species names need to match exactly with the names
of the elements in the TiO.meam.spline file; otherwise an error will be
raised. This behavior is different than the old style MEAM files.

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

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

This pair style does not support the [pair_modify](pair_modify) shift,
table, and tail options.

The *meam/spline* pair style does not write its information to [binary
restart files](restart), since it is stored in an external potential
parameter file. Thus, you need to re-specify the pair_style and
pair_coeff commands in an input script that reads a restart file.

The *meam/spline* pair style can only be used via the *pair* keyword of
the [run_style respa](run_style) command. They do not support the
*inner*, *middle*, *outer* keywords.

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

## Restrictions

This pair style requires the [newton](newton) setting to be \"on\" for
pair interactions.

This pair style does not support mapping multiple atom types to the same
element.

This pair style is only enabled if LAMMPS was built with the MANYBODY
package. See the [Build package](Build_package) page for more info.

## Related commands

[pair_coeff](pair_coeff), [pair_style meam](pair_meam)

## Default

none

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

::: {#Lenosky1}
**(Lenosky)** Lenosky, Sadigh, Alonso, Bulatov, de la Rubia, Kim, Voter,
Kress, Modelling Simulation Materials Science Engineering, 8, 825
(2000).
:::

::: {#Zhang4}
**(Zhang)** Zhang and Trinkle, Computational Materials Science, 124,
204-210 (2016).
:::