[DFTB-Plus-User] Extremely slow MD

[Abdullah Bin Faheem]

Dear DFTB+ users,

I am using DFTB+ 19.1 to run MD of a box of water molecules, with graphene and CaF2 layers (882 atoms) and using the 3ob parameters for DFTB3. However, it takes a very long time to finish even one MD step. I have tried to use different Solvers (ELPA, NTPoly, OMM), but it does not make a difference. I am using the MPI version of DFTB+ and have tried out using 6, 12, 15, and 30 mpi processes, but it does not improve the results. Changing the Mixer from Broyden to Anderson gives the same time results.

The input file is as follows:

Geometry = GenFormat {
882 S
 Ca F C O H
    1 1    0.7202443272E-01    0.7032980539E+01    0.4107560989E+01
    2 1    0.4004118083E+01    0.6999144781E+01    0.4161273297E+01
    3 1    0.7890550957E+01    0.7070604493E+01    0.4106813778E+01
    4 1    0.1168937823E+02    0.7005426600E+01    0.4039285473E+01
    5 1    0.9944288762E-01    0.2736434439E-01    0.4168457924E+01
.
.
.
  877 4    0.1421618759E+02    0.6309258063E+01    0.3225699778E+02
  878 5    0.1353106869E+02    0.6940379596E+01    0.3241309410E+02
  879 5    0.1509388546E+02    0.6646394136E+01    0.3226620183E+02
  880 4    0.7717108287E+00    0.7430108512E+01    0.4311866219E+02
  881 5    0.1500101168E+01    0.6928998668E+01    0.4275502506E+02
  882 5    0.4968721117E+00    0.7268172745E+01    0.4401107775E+02
0.0000 0.0000 0.0000
16.500 0.0000 0.0000
0.0000 14.900 0.0000
0.0000 0.0000 69.000
}
Driver = VelocityVerlet {
  MovedAtoms = 1:-1
  Steps = 1
  TimeStep [Femtosecond] = 0.5
  MDRestartFrequency = 1
  Thermostat = NoseHoover {
    Temperature [Kelvin] = 298.00
CouplingStrength [cm^-1] = 3200
  }
  OutputPrefix = "geo_end"
}

Hamiltonian = DFTB {
  Solver = ELPA {
  Mode = 2
  }
  Mixer = Anderson {
  MixingParameter = 0.2
  }
  SCCTolerance = 1.000E-004
  ForceEvaluation = Dynamics
  SCC = Yes
  SlaterKosterFiles = Type2FileNames {
  Separator = "-"
  Suffix = ".skf"
  }
  Filling = Fermi {
  Temperature [Kelvin] = 298
  }
  MaxSCCIterations = 300
  ReadInitialCharges = No
  MaxAngularMomentum {
    O = "p"
    H = "s"
    C = "p"
    F = "p"
   Ca = "p"
  }
  ThirdOrder = Yes
  HubbardDerivs {
   O = -0.1575
   H = -0.1857
   C = -0.1492
   F = -0.1623
   Ca = -0.0340
  }
  Dispersion = DftD3 {
   Damping = BeckeJohnson {
    a1 = 0.746
    a2 = 4.191
  }
    s6 = 1.0
    s8 = 3.209
 }
  HCorrection = Damping {
  Exponent = 4.00
 }
KPointsAndWeights = {
    1 0 0
    0 1 0
    0 0 1
 0.5 0.5 0.5
  }
}
Options {
  WriteAutotestTag = Yes
  WriteChargesAsText = Yes
}
Parallel {
  UseOmpThreads = no
  Groups = 3
 }

Is there perhaps something wrong with my approach? Any suggestions would be greatly appreciated. Thank you for your time.

Regards,
Abdullah
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