\(\renewcommand{\AA}{\text{Å}}\)

angle_style mwlc command

Syntax

angle_style mwlc

Examples

angle_style mwlc
angle_coeff * 25 1 10 1

Description

Added in version 4Feb2025.

The mwlc angle style models a meltable wormlike chain and can be used to model non-linear bending elasticity of polymers, e.g. DNA. mwlc uses a potential that is a canonical-ensemble superposition of a non-melted and a melted state (Farrell). The potential is

\[E = -k_{B}T\,\log [q + q^{m}] + E_{0},\]

where the non-melted and melted partition functions are

\[\begin{split}q = \exp [-k_{1}(1+\cos{\theta})/k_{B}T]; \\ q^{m} = \exp [-(\mu+k_{2}(1+\cos{\theta}))/k_{B}T].\end{split}\]

\(k_1\) is the bending elastic constant of the non-melted state, \(k_2\) is the bending elastic constant of the melted state, \(\mu\) is the melting energy, and \(T\) is the reference temperature. The reference energy,

\[E_{0} = -k_{B}T\,\log [1 + \exp[-\mu/k_{B}T]],\]

ensures that E is zero for a fully extended chain.

This potential is a continuous version of the two-state potential introduced by (Yan).

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

  • \(k_1\) (energy)

  • \(k_2\) (energy)

  • \(\mu\) (energy)

  • \(T\) (temperature)


Restrictions

This angle style can only be used if LAMMPS was built with the EXTRA-MOLECULE package. See the Build package doc page for more info.

Default

none


(Farrell) Farrell, Dobnikar, Podgornik, Curk, Phys Rev Lett, 133, 148101 (2024).

(Yan) Yan, Marko, Phys Rev Lett, 93, 108108 (2004).