fix nvt/tspin command

fix npt/tspin command

fix nph/tspin command

Syntax

fix ID group-ID style_name keyword value ...

  • ID, group-ID are documented in fix command

  • style_name = nvt/tspin or npt/tspin or nph/tspin

  • these fixes accept the corresponding keywords of fix nvt, npt and nph

  • additional keyword = spinmass or lattice or spin

    spinmass value = ms
  ms = spin mass multiplier relative to atomic mass (adim)
lattice value = moving or frozen
  moving = integrate the atomic positions and velocities
  frozen = hold the atoms on a fixed lattice, spins only
spin value = moving or frozen
  moving = integrate the spins
  frozen = hold the spins fixed, lattice only

Examples

fix 1 all nvt/tspin temp 300.0 300.0 0.05 spinmass 0.0075
fix 1 all nvt/tspin temp 10.0 600.0 0.1 lattice frozen tchain 5 spinmass 0.0075
fix 1 all npt/tspin temp 300.0 300.0 0.1 iso 0.0 0.0 1.0 spinmass 0.0075
fix 1 all nph/tspin iso 0.0 0.0 1.0 spinmass 0.0075

Description

Added in version TBD.

These fixes extend fix nvt, npt and nph to inertial spin dynamics. As described for fix nve/tspin, the auxiliary spin dynamics are intended for equilibrium sampling and do not represent physical spin precession.

The nvt/tspin and npt/tspin styles use a separate Nose-Hoover chain to thermostat the auxiliary spin velocities. The spin and lattice chains share the target temperature, damping time, tchain, tloop, and drag settings. The nph/tspin style applies a barostat without thermostatting either the lattice or the spins.

The spin thermostat uses the kinetic temperature defined by compute temp/tspin. Spin masses can be assigned with spinmass or velocity/tspin.

The lattice frozen option allows spin-only sampling with nvt/tspin; it cannot be combined with a barostat. The longitudinal-potential and magnetic-force requirements described for fix nve/tspin also apply here.

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

These fixes write their thermostat and barostat states to binary restart files. The tchain value must remain unchanged when restarting.

These fixes compute a global scalar containing the thermostat and barostat energy contribution, including the spin thermostat chain. The scalar is “extensive”.

The auxiliary spin kinetic energy is not included in econserve. Add the energy from compute temp/tspin to monitor the extended conserved energy for constant temperature and pressure targets, zero drag, and no other energy exchange. All relevant potential-energy contributions must be included in pe.

Standard fix_modify options and other output conventions are described in fix nvt, npt and nph. These fixes are not invoked during energy minimization.

Restrictions

These fixes require atom_style spin and the SPIN package. Dynamic groups are not supported, and at least one of lattice and spin must be moving. A barostat cannot be used with lattice frozen.

With SPIN pair styles, these fixes cannot be combined with fix nve/spin, even on disjoint groups.

There is no KOKKOS version. Magnetic interactions must satisfy the full-force requirement described for fix nve/tspin.

Default

The keyword defaults are the same as for fix nvt, fix npt and fix nph, plus lattice = moving and spin = moving.