fix nve/sphere command — LAMMPS documentation

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# fix nve/sphere command

Accelerator Variants: nve/sphere/omp, nve/sphere/kk

## Syntax

    fix ID group-ID nve/sphere

- ID, group-ID are documented in fix command

- nve/sphere = style name of this fix command

- zero or more keyword/value pairs may be appended

- keyword = update or disc

      update value = dipole or dipole/dlm
        dipole = update orientation of dipole moment during integration
        dipole/dlm = use DLM integrator to update dipole orientation
      disc value = none = treat particles as 2d discs, not spheres

## Examples

    fix 1 all nve/sphere
    fix 1 all nve/sphere update dipole
    fix 1 all nve/sphere disc
    fix 1 all nve/sphere update dipole/dlm

## Description

Perform constant NVE integration to update position, velocity, and angular velocity for finite-size spherical particles in the group each timestep. V is volume; E is energy. This creates a system trajectory consistent with the microcanonical ensemble.

This fix differs from the fix nve command, which assumes point particles and only updates their position and velocity.

If the update keyword is used with the dipole value, then the orientation of the dipole moment of each particle is also updated during the time integration. This option should be used for models where a dipole moment is assigned to finite-size particles, e.g. spheroids via use of the atom_style hybrid sphere dipole command.

The default dipole orientation integrator can be changed to the Dullweber-Leimkuhler-McLachlan integration scheme (Dullweber) when using update with the value dipole/dlm. This integrator is symplectic and time-reversible, giving better energy conservation and allows slightly longer timesteps at only a small additional computational cost.

If the disc keyword is used, then each particle is treated as a 2d disc (circle) instead of as a sphere. This is only possible for 2d simulations, as defined by the dimension keyword. The only difference between discs and spheres in this context is their moment of inertia, as used in the time integration.

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.

## Restart, fix_modify, output, run start/stop, minimize info

No information about this fix is written to binary restart files. None of the fix_modify options are relevant to this fix. No global or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during energy minimization.

## Restrictions

This fix requires that atoms store torque and angular velocity (omega) and a radius as defined by the atom_style sphere command. If the dipole keyword is used, then they must also store a dipole moment as defined by the atom_style dipole command.

All particles in the group must be finite-size spheres. They cannot be point particles.

Use of the disc keyword is only allowed for 2d simulations, as defined by the dimension keyword.

## Related commands

fix nve, fix nve/asphere

## Default

none

(Dullweber) Dullweber, Leimkuhler and McLachlan, J Chem Phys, 107, 5840 (1997).