# pair_style edip command

Accelerator Variants: *edip/omp*

# pair_style edip/multi command

## Syntax

``` LAMMPS
pair_style style
```

-   style = *edip* or *edip/multi*

## Examples

``` LAMMPS
pair_style edip
pair_coeff * * Si.edip Si
```

## Description

The *edip* and *edip/multi* styles compute a 3-body [EDIP](EDIP)
potential which is popular for modeling silicon materials where it can
have advantages over other models such as the
[Stillinger-Weber](pair_sw) or [Tersoff](pair_tersoff) potentials. The
*edip* style has been programmed for single element potentials, while
*edip/multi* supports multi-element EDIP runs.

In EDIP, the energy E of a system of atoms is

$$\begin{aligned}
E  = & \sum_{j \ne i} \phi_{2}(R_{ij}, Z_{i}) + \sum_{j \ne i} \sum_{k \ne i,k > j} \phi_{3}(R_{ij}, R_{ik}, Z_{i}) \\
\phi_{2}(r, Z)  = & A\left[\left(\frac{B}{r}\right)^{\rho} - e^{-\beta Z^2}\right]exp{\left(\frac{\sigma}{r-a}\right)} \\
\phi_{3}(R_{ij}, R_{ik}, Z_i)  = & exp{\left(\frac{\gamma}{R_{ij}-a}\right)}exp{\left(\frac{\gamma}{R_{ik}-a}\right)}h(cos\theta_{ijk},Z_i) \\
Z_i  = & \sum_{m \ne i} f(R_{im}) \qquad
f(r) = \begin{cases}
       1 & \quad r<c \\
       \exp\left(\frac{\alpha}{1-x^{-3}}\right) & \quad c<r<a \\
       0 & \quad r>a
       \end{cases} \\
h(l,Z)  = & \lambda [(1-e^{-Q(Z)(l+\tau(Z))^2}) + \eta Q(Z)(l+\tau(Z))^2 ] \\
Q(Z)  = & Q_0 e^{-\mu Z} \qquad \tau(Z) = u_1 + u_2 (u_3 e^{-u_4 Z} - e^{-2u_4 Z})
\end{aligned}$$

where $\phi_2$ is a two-body term and $\phi_3$ is a three-body term. The
summations in the formula are over all neighbors J and K of atom I
within a cutoff distance = a. Both terms depend on the local environment
of atom I through its effective coordination number defined by Z, which
is unity for a cutoff distance \< c and gently goes to 0 at distance =
a.

Only a single pair_coeff command is used with the *edip* style which
specifies a EDIP 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 EDIP 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 a file Si.edip has EDIP values for Si.

EDIP files in the *potentials* directory of the LAMMPS distribution have
a \".edip\" suffix. Lines that are not blank or comments (starting with
#) define parameters for a triplet of elements. The parameters in a
single entry correspond to the two-body and three-body coefficients in
the formula above:

-   element 1 (the center atom in a 3-body interaction)
-   element 2
-   element 3
-   A (energy units)
-   B (distance units)
-   cutoffA (distance units)
-   cutoffC (distance units)
-   $\alpha$
-   $\beta$
-   $\eta$
-   $\gamma$ (distance units)
-   $lambda$ (energy units)
-   $\mu$
-   $\tau$
-   $\sigma$ (distance units)
-   Q0
-   u1
-   u2
-   u3
-   u4

The A, B, beta, sigma parameters are used only for two-body
interactions. The eta, gamma, lambda, mu, Q0 and all u1 to u4 parameters
are used only for three-body interactions. The alpha and cutoffC
parameters are used for the coordination environment function only.

The EDIP potential file must contain entries for all the elements listed
in the pair_coeff command. It can also contain entries for additional
elements not being used in a particular simulation; LAMMPS ignores those
entries.

For a single-element simulation, only a single entry is required (e.g.
SiSiSi). For a two-element simulation, the file must contain 8 entries
(for SiSiSi, SiSiC, SiCSi, SiCC, CSiSi, CSiC, CCSi, CCC), that specify
EDIP parameters for all permutations of the two elements interacting in
three-body configurations. Thus for 3 elements, 27 entries would be
required, etc.

At the moment, only a single element parameterization is implemented.
However, the author is not aware of other multi-element EDIP
parameterization. If you know any and you are interest in that, please
contact the author of the EDIP package.

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

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.

This pair style does not write its information to [binary restart
files](restart), since it is stored in potential files. Thus, you need
to re-specify the pair_style and pair_coeff commands 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 can only be used if LAMMPS was built with the MANYBODY
package. See the [Build package](Build_package) doc page for more info.

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

The EDIP potential files provided with LAMMPS (see the potentials
directory) are parameterized for metal [units](units). You can use the
EDIP potential with any LAMMPS units, but you would need to create your
own EDIP potential file with coefficients listed in the appropriate
units if your simulation does not use \"metal\" units.

## Related commands

[pair_coeff](pair_coeff)

## Default

none

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

::: {#EDIP}
**(EDIP)** J F Justo et al, Phys Rev B 58, 2539 (1998).
:::