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

[范芫钟]

Dear Ben Hourahine,
     Thank you, I've checked the two words and can sure the Barostat is working as you said. 
 
------------------ Original ------------------
From:  "Ben Hourahine"<benjamin.hourahine at strath.ac.uk>;
Date:  Thu, May 7, 2015 01:29 AM
To:  "dftb-plus-user"<dftb-plus-user at mailman.zfn.uni-bremen.de>; 

Subject:  Re: [DFTB-Plus-User] Does Barostat really work?

 
                   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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