# pair_style coul/shield command

## Syntax

``` LAMMPS
pair_style coul/shield cutoff tap_flag
```

-   cutoff = global cutoff (distance units)
-   tap_flag = 0/1 to turn off/on the taper function

## Examples

``` LAMMPS
pair_style coul/shield 16.0 1
pair_coeff 1 2 0.70
```

## Description

Style *coul/shield* computes a Coulomb interaction for boron and
nitrogen atoms located in different layers of hexagonal boron nitride.
This potential is designed be used in combination with the pair style
[ilp/graphene/hbn](pair_ilp_graphene_hbn)

:::: note
::: title
Note
:::

This potential is intended for electrostatic interactions between two
different layers of hexagonal boron nitride. Therefore, to avoid
interaction within the same layers, each layer should have a separate
molecule id and is recommended to use the \"full\" atom style, so that
charge and molecule ID information is included.
::::

$$\begin{aligned}
E      = & \frac{1}{2} \sum_i \sum_{j \neq i} V_{ij} \\
V_{ij} = & {\rm Tap}(r_{ij})\frac{\kappa q_i q_j}{\sqrt[3]{r_{ij}^3+(1/\lambda_{ij})^3}}\\
{\rm Tap}(r_{ij}) = & 20\left ( \frac{r_{ij}}{R_{cut}} \right )^7 -
                       70\left ( \frac{r_{ij}}{R_{cut}} \right )^6 +
                       84\left ( \frac{r_{ij}}{R_{cut}} \right )^5 -
                       35\left ( \frac{r_{ij}}{R_{cut}} \right )^4 + 1
\end{aligned}$$

Where Tap($r_{ij}$) is the taper function which provides a continuous
cutoff (up to third derivative) for inter-atomic separations larger than
$r_c$ [(Leven1)](Leven3), [(Leven2)](Leven4) and [(Maaravi)](Maaravi1).
Here $\lambda$ is the shielding parameter that eliminates the
short-range singularity of the classical mono-polar electrostatic
interaction expression [(Maaravi)](Maaravi1).

The shielding parameter $\lambda$ (1/distance units) must be defined for
each pair of atom types via the [pair_coeff](pair_coeff) command as in
the example above, or in the data file or restart files read by the
[read_data](read_data) or [read_restart](read_restart) commands:

The global cutoff ($r_c$) specified in the pair_style command is used.

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

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

This pair style does not support parameter mixing. Coefficients must be
given explicitly for each type of particle pairs.

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.

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 INTERLAYER 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_style
ilp/graphene/hbn](pair_ilp_graphene_hbn)

## Default

tap_flag = 1

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

::: {#Leven3}
**(Leven1)** I. Leven, I. Azuri, L. Kronik and O. Hod, J. Chem. Phys.
140, 104106 (2014).
:::

::: {#Leven4}
**(Leven2)** I. Leven et al, J. Chem.Theory Comput. 12, 2896-905 (2016).
:::

::: {#Maaravi1}
**(Maaravi)** T. Maaravi et al, J. Phys. Chem. C 121, 22826-22835
(2017).
:::