4.1 Temperature and pressure

Several quantities in thermo_pw can be calculated as a function of temperature. Moreover the equilibrium geometry can be searched at fixed pressure minimizing the enthalpy instead of the energy. For the options where these features are active, the values of temperature and pressure are controlled by the following variables:

tmin       : minimum temperature.
             Default: real 1 K
tmax       : maximum temperature.
             Default: real 800 K
deltat     : interval between two temperatures. Be careful with this value
             because it is used also to compute temperature derivatives
             numerically. Too small or too large values could give
             inaccurate anharmonic properties.
             Default: real 3 K
ntemp      : number of temperatures
             Default: integer determined from previous data
pressure   : The external pressure. The crystal parameters are
             calculated minimizing the enthalpy at this pressure. 
             Given in kbar units. 
             Default: real 0.0 kbar

Note that when you fix the external pressure, the geometries chosen to fit the enthalpy must be about the minimum geometry at that pressure.