Langevin Piston Integrator (NPT)

Tinker9

There are two implementations of the Langevin Piston integrator in Tinker9.

Implementation 1

This implementation is contributed from Wei Yang’s group at Florida State University. This is a leap-frog style single time-step isotropic integrator similar to the one in CHARMM. The keywords used to invoke this method are:

integrator lpiston
friction        20

or

thermostat lpiston
barostat   lpiston
friction        20

It was suggested to set the keyword FRICTION to 20 for this integrator.

Implementation 2

This implements the Langevin Piston integrator in two ways: a single time-step integrator similar to Velocity-Verlet and a multiple time-step integrator similar to RESPA. They can be employed by the following keywords, respectively. The thermostat method is built in the integrator, thus the thermostat keyword is ignored.

# Velocity-Verlet Style
barostat     langevin
integrator     verlet

# RESPA Style
barostat     langevin
integrator      respa

See also

  • New usage
    • BAROSTAT [LANGEVIN]

      Must be set to LANGEVIN.

    • FRICTION [real]

      Sets the value of the frictional coefficient in 1/ps for the Langevin dynamics of piston. The default is 20 in the absence of the keyword.

    • VOLUME-TRIAL [integer]

      This keyword is borrowed from the Monte Carlo barostat to set the number of molecular dynamics steps between two changes in the periodic box size. The default is 1 step in the absence of the keyword.

    • PRINTOUT [integer]

      Sets the number of MD steps between writes of the instantaneous pressure. The default value 0 will not print the instantaneous pressure. If the current MD step does not invoke the barostat, the instantaneous pressure will not be printed.

  • Relavent keywords
    • ANISO-PRESSURE

      Invokes anisotropic cell fluctuations.

    • SEMIISO-PRESSURE

      Invokes isotropic cell fluctuations in the xy-plane and independent fluctuation in the z-axis. This feature is in development, and this new keyword will be documented.

    • INTEGRATOR [VERLET / RESPA]

      Only VERLET and RESPA are valid values.

    • RESPA-INNER [real]

      The program listens to the RESPA-INNER keyword to set the length of inner time-step in femtosecond only if the RESPA version is used.

    • TAU-PRESSURE [real]

      Tinker9 does not change its default value.

    • TAU-TEMPERATURE [real]

      Tinker9 does not change its default value.

  • Ignored keywords
    • THERMOSTAT

      The integrator uses a built-in thermostat.

    • VOLUME-SCALE

      The integrator uses molecular scaling if holonomic constraints are used, or atomic scaling otherwise.

Nosé–Hoover Chain Integrator (NPT) Accelerating MD Simulation in Tinker9