# bond_style mm3 command

## Syntax

bond_style mm3


## Examples

bond_style mm3
bond_coeff 1 100.0 107.0


## Description

The mm3 bond style uses the potential that is anharmonic in the bond as defined in (Allinger)

$E = K (r - r_0)^2 \left[ 1 - 2.55(r-r_0) + (7/12) 2.55^2(r-r_0)^2 \right]$

where $$r_0$$ is the equilibrium value of the bond, and $$K$$ is a prefactor. The anharmonic prefactors have units angstrom^(-n): -2.55 angstrom^(-1) and (7/12)2.55^2 angstrom^(-2). The code takes care of the necessary unit conversion for these factors internally. Note that the MM3 papers contains an error in Eq (1): (7/12)2.55 should be replaced with (7/12)2.55^2

The following coefficients must be defined for each bond type via the bond_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands:

• $$K$$ (energy/distance^2)

• $$r_0$$ (distance)

## Restrictions

This bond style can only be used if LAMMPS was built with the USER_YAFF package. See the Build package doc page for more info.

## Default

none

(Allinger) Allinger, Yuh, Lii, JACS, 111(23), 8551-8566 (1989),