\(\renewcommand{\AA}{\text{Å}}\)

# pair_style momb command

## Syntax

    pair_style momb cutoff s6 d

- cutoff = global cutoff (distance units)

- s6 = global scaling factor of the exchange-correlation functional used (unitless)

- d = damping scaling factor of Grimme’s method (unitless)

## Examples

    pair_style momb 12.0 0.75 20.0
    pair_style hybrid/overlay eam/fs lj/charmm/coul/long 10.0 12.0 momb 12.0 0.75 20.0 morse 5.5

    pair_coeff 1 2 momb 0.0 1.0 1.0 10.2847 2.361

## Description

Style momb computes pairwise van der Waals (vdW) and short-range interactions using the Morse potential and (Grimme) method implemented in the Many-Body Metal-Organic (MOMB) force field described comprehensively in (Fichthorn) and (Zhou). Grimme’s method is widely used to correct for dispersion in density functional theory calculations.

\[\begin{split} E & = D_0 [\exp^{-2 \alpha (r-r_0)} - 2\exp^{-\alpha (r-r_0)}] - s_6 \frac{C_6}{r^6} f_{damp}(r,R_r) \\ f_{damp}(r,R_r) & = \frac{1}{1 + \exp^{-d(r/R_r - 1)}}\end{split}\]

For the momb pair style, the following coefficients must be defined for each pair of atoms types via the pair_coeff command as in the examples above, or in the data file or restart files read by the read_data as described below:

- \(D_0\) (energy units)

- \(\alpha\) (1/distance units)

- \(r_0\) (distance units)

- \(C_6\) (energy*distance^6 units)

- \(R_r\) (distance units, typically sum of atomic vdW radii)

## Restrictions

This style is part of the EXTRA-PAIR package. It is only enabled if LAMMPS is built with that package. See the Build package page on for more info.

## Related commands

pair_coeff, pair_style morse

## Default

none

(Grimme) Grimme, J Comput Chem, 27(15), 1787-1799 (2006).

(Fichthorn) Fichthorn, Balankura, Qi, CrystEngComm, 18(29), 5410-5417 (2016).

(Zhou) Zhou, Saidi, Fichthorn, J Phys Chem C, 118(6), 3366-3374 (2014).