ensemble (NPHug)

This keyword sets up a Hugoniot thermostat integrator.

This integrator lets you specify a target stress, and adjust temperature to make the system converge to Hugoniot.

In this implementation, we use the barostat and thermostat of MTTK integrator, so it is very similiar to mttk ensemble.

Please check [Ravelo2004] for more details.


The parameters can be specified as follows:

ensemble nphug <direction> <p_1> <p_2> tperiod <tau_temp> pperiod <tau_press>

The <direction> parameter can assume one or more of the following values: iso, aniso, tri, x, y, z. Here, iso, aniso, and tri use hydrostatic pressure as the target pressure. iso updates the simulation cell isotropically. aniso updates the dimensions of the simulation cell along \(x\), \(y\), and \(z\) independently. tri updatess all six degrees of freedom of the simulation cell. Using x, y, z allows one to specify each stress component independently.

The parameters <p_1> and <p_2> specify the target pressure, and they should be equal. Finally, the optional parameter <tau_press>, which defaults to 1000, determines the period of the barostat in units of the timestep. It determines how strongly the system is coupled to the barostat.


ensemble nphug x 300 300

This command performs a simulation using a Hugoniot thermostat with a 300 GPa Hugoniot pressure in the \(x\) direction.