[DFTB-Plus-User] NPT Simulation and Cell volume

[Jeongmin Park]

Hi, everyone

I'm a new user of DFTB+ and I'm trying to test NPT molecular dynamics, but
I have some problems.

I thought that cell volume should be changed at each step. However, I could
not find any change in cell volume during the NPT simulation at all. I used
the Nose-Hoover chain thermostat and the Berendsen barostat to get an NPT
ensemble.
 Is there any problem in my input? Please let me know how to prepare input
for NPT simulation. Thank you for your answer in advance.


Here's the input and output details:

"Input file"
Geometry = GenFormat {
<<< "nvt2npt.gen"
}

Hamiltonian = xTB {
  Method = "GFN2-xTB"
  KPointsAndWeights = {
  0 0 0 1.0
  }
}

Driver = VelocityVerlet{
  TimeStep [fs] = 1.0
  Thermostat = NoseHoover {
    Temperature [Kelvin] = 300
    ChainLength = 10
    CouplingStrength [cm^-1] = 3200
    }
  Barostat = {
    Pressure [Pa] = 101325
    Timescale [fs] = 50
    isotropic = YES
    }
  OutputPrefix = "npt_test_v3"
  Steps = 50000
  MovedAtoms = 1:-1
  MDRestartFrequency = 10

}
  Options = {
  }


"Output  file"

MD step: 0
 Nose-Hoover chain variables
 x:
    0.1000000000E+01    0.1000000000E+01    0.1000000000E+01
    0.1000000000E+01    0.1000000000E+01    0.1000000000E+01
    0.1000000000E+01    0.1000000000E+01    0.1000000000E+01
    0.1000000000E+01
 v:
    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
    0.0000000000E+00
 g:
    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
Lattice vectors (A)
          0.60000000E+02          0.00000000E+00          0.00000000E+00
          0.00000000E+00          0.60000000E+02          0.00000000E+00
          0.00000000E+00          0.00000000E+00          0.60000000E+02
Volume:                              0.145764E+07 au^3   0.216000E+06 A^3
Pressure:                           -0.902137E-07 au    -0.265418E+07 Pa
Potential Energy:                 -253.7914693521 H        -6906.0173 eV
MD Kinetic Energy:                   0.3490128664 H            9.4971 eV
Total MD Energy:                  -253.4424564857 H        -6896.5201 eV
MD Temperature:                      0.0009654574 au         304.8670 K
Warning: dipole moment is not defined absolutely!
Dipole moment:    0.17001813   -0.07880215    0.00097343 au
Dipole moment:    0.43214303   -0.20029510    0.00247420 Debye

MD step: 10000
 Nose-Hoover chain variables
 x:
    0.1080299671E+01   -0.2531480956E+02    0.3269191133E+02
   -0.4337194511E+02    0.3460555390E+02   -0.2191798289E+02
   -0.3465035632E+01    0.3524528531E+02   -0.2742140163E+02
    0.1056820091E+02
 v:
    0.5541851351E-05   -0.1496933698E-02    0.5024657243E-02
   -0.2094428251E-03   -0.3357823332E-02    0.8370813824E-03
   -0.2100047798E-02   -0.4551172093E-02    0.1286492827E-02
   -0.9429137284E-04
 g:
   -0.4771799581E-07   -0.5362620540E-05   -0.3144014905E-05
    0.1986235501E-04   -0.5340959103E-05    0.5890152131E-05
   -0.4684120159E-05   -0.9746246446E-06    0.1532834202E-04
   -0.3729761606E-05
Lattice vectors (A)
          0.59999848E+02          0.00000000E+00          0.00000000E+00
          0.00000000E+00          0.59999848E+02          0.00000000E+00
          0.00000000E+00          0.00000000E+00          0.59999848E+02
Volume:                              0.145763E+07 au^3   0.215998E+06 A^3
Pressure:                            0.349400E-07 au     0.102797E+07 Pa
Potential Energy:                 -253.8147832101 H        -6906.6517 eV
MD Kinetic Energy:                   0.3313643796 H            9.0169 eV
Total MD Energy:                  -253.4834188305 H        -6897.6348 eV
MD Temperature:                      0.0009166373 au         289.4508 K

MD step: 50000
 Nose-Hoover chain variables
 x:
    0.1065641562E+01   -0.3452498179E+02   -0.3868779521E+02
    0.2642677411E+02   -0.5577080631E+02    0.1145023781E+03
   -0.1288319615E+03    0.1325583957E+03   -0.7062173700E+02
    0.3749539828E+02
 v:
    0.1358714936E-03    0.1188347289E-02    0.2045260490E-03
   -0.1094006423E-02   -0.2156818853E-03   -0.1317494278E-03
    0.3719208091E-02    0.1029405553E-02   -0.2103652994E-02
   -0.1084972397E-03
 g:
    0.1101985092E-06    0.7962522987E-05   -0.3972656120E-05
   -0.5342994496E-05   -0.4187975347E-05   -0.5338306725E-05
   -0.5367467489E-05    0.8447683423E-05   -0.4325149607E-05
   -0.9594694798E-06
Lattice vectors (A)
          0.59999223E+02          0.00000000E+00          0.00000000E+00
          0.00000000E+00          0.59999223E+02          0.00000000E+00
          0.00000000E+00          0.00000000E+00          0.59999223E+02
Volume:                              0.145758E+07 au^3   0.215992E+06 A^3
Pressure:                           -0.156743E-06 au    -0.461152E+07 Pa
Potential Energy:                 -253.7973847854 H        -6906.1782 eV
MD Kinetic Energy:                   0.3414788359 H            9.2921 eV
Total MD Energy:                  -253.4559059495 H        -6896.8861 eV
MD Temperature:                      0.0009446164 au         298.2859 K
Warning: dipole moment is not defined absolutely!
Dipole moment:    0.25094055   -0.00643634    0.01642249 au
Dipole moment:    0.63782730   -0.01635956    0.04174182 Debye

Best regards,

Park
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