# pair_style lebedeva/z command¶

## Syntax¶

pair_style [hybrid/overlay ...] lebedeva/z cutoff


## Examples¶

pair_style hybrid/overlay lebedeva/z 20.0
pair_coeff * * none
pair_coeff 1 2 lebedeva/z  CC.Lebedeva   C C

pair_style hybrid/overlay rebo lebedeva/z 14.0
pair_coeff * * rebo        CH.rebo       C C
pair_coeff 1 2 lebedeva/z  CC.Lebedeva   C C


## Description¶

The lebedeva/z style computes the Lebedeva interaction potential as described in (Lebedeva et al.). An important simplification is made, which is to take all normals along the z-axis.

$\begin{split}E = & \frac{1}{2} \sum_i \sum_{i \neq j} V_{ij}\\ V_{ij} = & B e^{-\alpha(r_{ij} - z_0)} \\ & + C(1 + D_1\rho^2_{ij} + D_2\rho^4_{ij} e^{-\lambda_1\rho^2_{ij}} e^{-\lambda_2 (z^2_{ij} - z^2_0)} \\ & - A \left(\frac{z_0}{r_ij}\right)^6 + A \left( \frac{z_0}{r_c} \right)^6 \\ \rho^2_{ij} = & x^2_{ij} + y^2_{ij} \qquad (\mathbf{n_i} \equiv \mathbf{\hat{z}})\end{split}$

It is important to have a sufficiently large cutoff to ensure smooth forces. Energies are shifted so that they go continuously to zero at the cutoff assuming that the exponential part of $$V_{ij}$$ (first term) decays sufficiently fast. This shift is achieved by the last term in the equation for $$V_{ij}$$ above.

The parameter file (e.g. CC.Lebedeva), is intended for use with metal units, with energies in meV. An additional parameter, S, is available to facilitate scaling of energies.

This potential must be used in combination with hybrid/overlay. Other interactions can be set to zero using pair_style none.

## Restrictions¶

This fix is part of the USER-MISC package. It is only enabled if LAMMPS was built with that package. See the Build package doc page for more info.

## Default¶

none

(Lebedeva et al.) I. V. Lebedeva, A. A. Knizhnik, A. M. Popov, Y. E. Lozovik, B. V. Potapkin, Phys. Rev. B, 84, 245437 (2011)