[DFTB-Plus-User] NPT simulation

[Puja Goyal]

Hi all,

Has anyone tried doing an NPT simulation with DFTB+? I am doing an NPT simulation on a water box and am unable to figure out why the pressure printed in the md.out file and in the output are different for a given step? I am using the Andersen thermostat with the Berendsen barostat to get an NPT ensemble. The 'driver' section of my input file is as follows:

Driver = VelocityVerlet {
  Steps = 50000
  TimeStep [Femtosecond] = 1.0
  Thermostat = Andersen {
    Temperature [Kelvin] = 300.0
    ReselectProbability = 0.200000000000000
    ReselectIndividually = No
    AdaptFillingTemp = Yes
  }
  Barostat = {
    Pressure [Pa] = 101325.0
    Timescale [ps] = 0.1
  }
}

At step 0, the output is:

 Pressure:                           0.997522E-04 au     0.293481E+10 Pa

On the other hand, in the md.out file, I have the following for step 0:

Pressure:                           0.854304E-04 au     0.251345E+10 Pa

Could anybody please tell me if my input is OK? Is the timescale value I am using OK (although I am confused by the manual which says the timescale is beta/tau which means that if we neglect the unit of beta, the unit should be time^(-1) )?

I would really appreciate any help.

Puja.