Options tab

The Options tab allows you to specify parameters which control the details of the dynamics algorithm.

Thermostat: Specify the thermostat to be used for NVT or NPT dynamics. Available options are:

Langevin
Nose
NHL

This option in enabled only if the NVT or NPT ensemble is selected on the Dynamics tab. The Nosé-Hoover-Langevin (NHL) thermostat is only available for the NVT ensemble.

Barostat: Specify the barostat to be used for NPH or NPT dynamics. Available options are:

Andersen - scales the cell uniformly
Parrinello - allows variation in the cell shape

This option in enabled only if the NPT or NPH ensemble is selected on the Dynamics tab.

Langevin constant: Specify the damping time of temperature fluctuations during Langevin NVT dynamics. This time should normally be larger than the time scale of any motions of interest.

Nose Q ratio: Specify a scaling factor for the fictitious mass Q of the Nosé thermostat for Nosé or Nosé-Hoover-Langevin NVT dynamics. A larger Q ratio implies increased damping of temperature fluctuations.

Cell time constant: Specify the characteristic cell time, which is used to estimate the mass associated with the barostat. A larger value implies increased damping of pressure fluctuations.

Wavefunction extrapolation scheme: Specify the method to be used for wavefunction extrapolation between molecular dynamics steps. This selection is not available when Use Extended Lagrangian (XL-BOMD) is selected.

None - no extrapolation is performed.
1st VV - 1st order extrapolation with variable coefficients.
2nd VV - 2nd order extrapolation with variable coefficients.
2/1 VV - Alternate 2nd and 1st order extrapolation with variable coefficients.
1st CC - 1st order extrapolation with constant coefficients.
2nd CC - 2nd order extrapolation with constant coefficients.
2/1 CC - Alternate 2nd and 1st order extrapolation with constant coefficients.

Use eXtended Lagrangian (XL-BOMD): When checked, indicates that the extended Lagrangian molecular dynamics (Steneteg 2010, Niklasson 2011) is used instead of the wavefunction extrapolation schemes. The extended Lagrangian formulation allows significantly higher time step values to be used, while conserving the constant of motion. This option is available only for fixed-cell (NVE and NVT) ensembles. Default = checked.

Fix center of mass: When checked, indicates that the center of mass will be fixed during the dynamics simulation. Default = unchecked.

Access methods

Menu	Modules \| CASTEP \| Calculation \| Setup \| More... \| Options
Toolbar	\| Calculation \| Setup \| More... \| Options

Options tab

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