[DFTB-Plus-User] Does Barostat really work?

[Ben Hourahine]

Dear 范芫钟,

Looking at the code for the header printing, there is a bug as to
whether the code correctly announces that it is performing constant
volume or barostat MD or not. The internal code should be running a
Berendsen barostat though, even if the header is incorrect.

Can you check if

grep -A 3 ' Lattice vectors' md.out

shows any change at all between iterations? The variation in the lattice
vectors per md step will be small, but should be present (the time scale
for the barostat is 200 times longer than the MD step).

Similarly

grep Gibbs md.out

should show variations in the energy between MD steps even if you do not
use a thermostat (and would be absent if a barostat is not used). Note
that the 'Gibbs' free energy printed out here does not include the
kinetic energy, which is printed separately, so for an NPE ensemble the
sum of the two is the conserved quantity.

Regards

Ben


On 06/05/15 17:42, 范芫钟 wrote:
>
>
>     Dear Sirs,
>        I'm try to do some MD research of NPT ensemble, with the
> detailed information of Drive listed below. (DFTB+ Version 1.2)
>       Driver = {
>   VelocityVerlet = {
>   OutputPrefix = "XXX"
>   Steps = 100000
>   TimeStep[fs]= 0.5
>   KeepStationary = Yes
>   MDRestartFrequency = 10
>   Thermostat = Berendsen {
>   Temperature[K] = 298.15
>   CouplingStrength[ps] = 0.01
> }
>   Barostat = {
>   Pressure[Pa] = 101325.0
>   TimeScale[ps] = 0.1
> }
> }
> }
>
>        The system is periodic, with the LatticeVector is,
> 11.16658929  -4.884981308e-15  12.61723333
> -5.583294646  9.67055  12.61723333
> -5.583294646  -9.67055  12.61723333
>       However, the LatticeVector doesn't change in .gen, and the
> output in .dftb shows that the Mode is NVT.
> Mode:                        MD with scaling of velocities according
> to temperature
>                              (a.k.a. not NVT ensemble using Berendsen
> thermostating)
>      I know that if I employ Nose-Hoover, it'll be a standard NVT, but
> it should be NPT instead.
>     The similar output appears when I want to do the research of NPH,
> and it becomes NVE.
>     Therefore, I doubt that whether I have some mistakes in Drive or
> the /Barostat/ doesn't work at all?
>     I'm very grateful to receive any response from you!
>
>
>
>
>
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-- 
      Dr. B. Hourahine, SUPA, Department of Physics,
    University of Strathclyde, John Anderson Building,
            107 Rottenrow, Glasgow G4 0NG, UK.
    +44 141 548 2325, benjamin.hourahine at strath.ac.uk

2013/4 THE Awards Entrepreneurial University of the Year
      2012/13 THE Awards UK University of the Year

   The University of Strathclyde is a charitable body,
        registered in Scotland, number SC015263

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