\(\renewcommand{\AA}{\text{Å}}\)

# pair_style eam/apip command

Constant precision variant: eam

# pair_style eam/fs/apip command

Constant precision variant: eam/fs

## Syntax

    pair_style eam/apip
    pair_style eam/fs/apip

## Examples

    pair_style hybrid/overlay eam/fs/apip pace/precise/apip lambda/input/csp/apip fcc cutoff 5.0 lambda/zone/apip 12.0
    pair_coeff * * eam/fs/apip Cu.eam.fs Cu
    pair_coeff * * pace/precise/apip Cu_precise.yace Cu
    pair_coeff * * lambda/input/csp/apip
    pair_coeff * * lambda/zone/apip

## Description

Style eam computes pairwise interactions for metals and metal alloys using embedded-atom method (EAM) potentials (Daw). The total energy \(E_i\) of an atom \(i\) is given by

\[E_i^\text{EAM} = F_\alpha \left(\sum_{j \neq i}\ \rho_\beta (r_{ij})\right) + \frac{1}{2} \sum_{j \neq i} \phi_{\alpha\beta} (r_{ij})\]

where \(F\) is the embedding energy which is a function of the atomic electron density \(\rho\), \(\phi\) is a pair potential interaction, and \(\alpha\) and \(\beta\) are the element types of atoms \(i\) and \(j\). The multi-body nature of the EAM potential is a result of the embedding energy term. Both summations in the formula are over all neighbors \(j\) of atom \(i\) within the cutoff distance. EAM is documented in detail in pair_style eam.

The potential energy \(E_i\) of an atom \(i\) of an adaptive-precision interatomic potential (APIP) according to (Immel) is given by

\[E_i^\text{APIP} = \lambda_i E_i^\text{(fast)} + (1-\lambda_i) E_i^\text{(precise)}\,,\]

whereas the switching parameter \(\lambda_i\) is computed dynamically during a simulation by fix lambda/apip or set prior to a simulation via set.

The pair style eam/fs/apip computes the potential energy \(\lambda_i E_i^\text{EAM}\) and the corresponding force and should be combined with a precise potential like pair_style pace/precise/apip that computes the potential energy \((1-\lambda_i) E_i^\text{(precise)}\) and the corresponding force via pair_style hybrid/overlay.

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

For atom type pairs I,J and I != J, where types I and J correspond to two different element types, mixing is performed by LAMMPS as described above with the individual styles. You never need to specify a pair_coeff command with I != J arguments for the eam/apip styles.

This pair style does not support the pair_modify shift, table, and tail options.

The eam/apip pair styles do not write their information to binary restart files, since it is stored in tabulated potential files. Thus, you need to re-specify the pair_style and pair_coeff commands in an input script that reads a restart file.

The eam/apip pair styles can only be used via the pair keyword of the run_style respa command. They do not support the inner, middle, outer keywords.

## Restrictions

This pair styles are part of the APIP package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.

## Related commands

pair_style eam, pair_style hybrid/overlay, fix lambda/apip, fix lambda_thermostat/apip, pair_style lambda/zone/apip, pair_style lambda/input/apip, pair_style pace/apip, fix atom_weight/apip

## Default

none

(Immel) Immel, Drautz and Sutmann, J Chem Phys, 162, 114119 (2025)

(Daw) Daw, Baskes, Phys Rev Lett, 50, 1285 (1983). Daw, Baskes, Phys Rev B, 29, 6443 (1984).