\(\renewcommand{\AA}{\text{Å}}\)

angle_style mwlc command

Accelerator Variant: mwlc/omp

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)

Styles with a gpu, intel, kk, omp, or opt suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed on the Accelerator packages page. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues.

These accelerated styles are part of the GPU, INTEL, KOKKOS, OPENMP, and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package page for more info.

You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the -suffix command-line switch when you invoke LAMMPS, or you can use the suffix command in your input script.

See the Accelerator packages page for more instructions on how to use the accelerated styles effectively.

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).