$$\renewcommand{\AA}{\text{Å}}$$

# 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)

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

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

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 YAFF package. See the Build package doc page for more info.

## Default¶

none

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