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} [1 - 2.55 (r - r_{0}) + \frac{7}{12} {2.55}^{2} (r - r_{0})^{2}]

where $r_{0}$ is the equilibrium value of the bond, and $K$ is a prefactor. The anharmonic prefactors have units $Å^{- n}$ : $- 2.55 Å^{- 1}$ and $\frac{7}{12} {2.55}^{2} Å^{- 2}$ . 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),