# pair_style mesocnt command

## Syntax

pair_style mesocnt


## Examples

pair_style mesocnt
pair_coeff * * 10_10.cnt

## Description

Style mesocnt implements a mesoscopic potential for the interaction of carbon nanotubes (CNTs). In this potential, CNTs are modelled as chains of cylindrical segments in which each infinitesimal surface element interacts with all other CNT surface elements with the Lennard-Jones (LJ) term adopted from the airebo style. The interaction energy is then computed by integrating over the surfaces of all interacting CNTs.

The potential is based on interactions between one cylindrical segment and infinitely or semi-infinitely long CNTs as described in (Volkov1). Chains of segments are converted to these (semi-)infinite CNTs bases on an approximate chain approach outlined in (Volkov2). This allows to simplify the computation of the interactions significantly and reduces the computational times to the same order of magnitude as for regular bead spring models where beads interact with the standard pair_lj/cut potential.

In LAMMPS, cylindrical segments are represented by bonds. Each segment is defined by its two end points (“nodes”) which correspond to atoms in LAMMPS. For the exact functional form of the potential and implementation details, the reader is referred to the original papers (Volkov1) and (Volkov2).

The potential requires tabulated data provided in a single ASCII text file specified in the pair_coeff command. The first line of the file provides a time stamp and general information. The second line lists four integers giving the number of data points provided in the subsequent four data tables. The third line lists four floating point numbers: the CNT radius R, the LJ parameter sigma and two numerical parameters delta1 and delta2. These four parameters are given in Angstroms. This is followed by four data tables each separated by a single empty line. The first two tables have two columns and list the parameters uInfParallel and Gamma respectively. The last two tables have three columns giving data on a quadratic array and list the parameters Phi and uSemiParallel respectively. uInfParallel and uSemiParallel are given in eV/Angstrom, Phi is given in eV and Gamma is unitless.

Potential files for CNTs can be readily generated using the freely available code provided on

https://github.com/phankl/cntpot


Using the same approach, it should also be possible to generate potential files for other 1D systems such as boron nitride nanotubes.

Note

LAMMPS comes with one mesocnt style potential file where the default number of data points per table is 1001. This is sufficient for NVT simulations. For proper energy conservation, we recommend using a potential file where the resolution for Phi is at least 2001 data points.

Note

The mesocnt style requires CNTs to be represented as a chain of atoms connected by bonds. Atoms need to be numbered consecutively within one chain. Atoms belonging to different CNTs need to be assigned different molecule IDs.

A full summary of the method and LAMMPS implementation details is expected to soon become available in Computer Physics Communications.

Mixing, shift, table, tail correction, restart, rRESPA info:

This pair style does not support mixing.

This pair style does not support the pair_modify shift, table, and tail options.

The mesocnt pair style do not write their information to binary restart files, since it is stored in tabulated potential files. Thus, you need to re-specify the pair_style and pair_coeff commands in an input script that reads a restart file.

This pair style can only be used via the pair keyword of the run_style respa command. They do not support the inner, middle, outer keywords.

## Restrictions

This style is part of the USER-MISC package. It is only enabled if LAMMPS was built with that package. See the Build package doc page for more info.

This pair potential requires the newton setting to be “on” for pair interactions.