LAMMPS WWW Site - LAMMPS Documentation - LAMMPS Commands

### pair_style line/lj command

### pair_style line/lj/omp command

Syntax:

    pair_style line/lj cutoff

cutoff = global cutoff for interactions (distance units)

Examples:

    pair_style line/lj 3.0
    pair_coeff * * 1.0 1.0
    pair_coeff 1 1 1.0 1.5 2.5

Description:

Style line/lj treats particles which are line segments as a set of small spherical particles that tile the line segment length as explained below. Interactions between two line segments, each with N1 and N2 spherical particles, are calculated as the pairwise sum of N1*N2 Lennard-Jones interactions. Interactions between a line segment with N spherical particles and a point particle are treated as the pairwise sum of N Lennard-Jones interactions. See the pair_style lj/cut doc page for the definition of Lennard-Jones interactions.

The cutoff distance for an interaction between 2 line segments, or between a line segment and a point particle, is calculated from the position of the line segment (its center), not between pairs of individual spheres comprising the line segment. Thus an interaction is either calculated in its entirety or not at all.

The set of non-overlapping spherical particles that represent a line segment, for purposes of this pair style, are generated in the following manner. Their size is a function of the line segment length and the specified sigma for that particle type. If a line segment has a length L and is of type I, then the number of spheres N that represent the segment is calculated as N = L/sigma_II, rounded up to an integer value. Thus if L is not evenly divisibly by sigam_II, N is incremented to include one extra sphere. In this case, the spheres must be slightly smaller than sigma_II so as not to overlap, so a new sigma-prime is chosen as the sphere diameter, such that L/N = sigma-prime. Thus the line segment interacts with other segments or point particles as a collection of N spheres of diameter sigma-prime, evenly spaced along the line segment, so as to exactly cover its length.

The LJ interaction between 2 spheres on different line segments of types I,J is computed with an arithmetic mixing of the sigma values of the 2 spheres and using the specified epsilon value for I,J atom types. Note that because the sigma values for line segment spheres is computed using only sigma_II values, specific to the line segment's type, this means that any specified sigma_IJ values (for I != J) are effectively ignored.

For style line/lj, the following coefficients must be defined for each pair of atoms types via the pair_coeff command as in the examples above, or in the data file or restart files read by the read_data or read_restart commands:

- epsilon (energy units)
- sigma (distance units)
- cutoff (distance units)

The last coefficient is optional. If not specified, the global cutoff is used.

Styles with a cuda, gpu, 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 in Section_accelerate of the manual. 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 USER-CUDA, GPU, USER-OMP and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Making LAMMPS section 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 Section_accelerate of the manual for more instructions on how to use the accelerated styles effectively.

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

For atom type pairs I,J and I != J, the epsilon and sigma coefficients and cutoff distance for all of this pair style can be mixed. The default mix value is geometric. See the "pair_modify" command for details.

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

This pair style does not write its information to binary restart files.

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

Restrictions:

This style is part of the ASPHERE package. It is only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.

Defining particles to be line segments so they participate in line/line or line/particle interactions requires the use the atom_style line command.

Related commands:

pair_coeff, pair_style tri/lj

Default: none