[DFTB-Plus-User] What causes convergence errors for excited state MD?

[Sarah Allec]

 Hello,

I am trying to run an MD simulation on the first excited state of
azobenzene. My approach is to sample various initial conditions
(coordinates and velocities) from a long (ground state) NVE simulation also
ran with DFTB+. However, at some point, each of these trajectories exhibits
SCC convergence errrors (or fractional fillings, which I know cannot be
treated with linear response in DFTB+ yet). What usually causes such SCC
errors when using the Casida block? Is there anything else I can do to
alleviate this problem?

Here is my input:

Geometry = GenFormat {
  <<< "coords.gen"
}

Driver = VelocityVerlet {
  MovedAtoms = 1:-1
  Steps = 1000000
  TimeStep [fs] = 0.2
  #TimeStep = 0.005
  #KeepStationary
  Thermostat = None{}
  OutputPrefix = "w1h_md_coords"
  MDRestartFrequency = 10
  Velocities [AA/ps] = {
   0.64481099      7.57423330      1.70718305
  -3.26628666     -2.20916913     -5.78763950
   5.40722402     -6.75314792      5.30978241
   5.30778618     -2.91911958      1.76799630
  -4.60343472     10.69041803     -1.35819145
   3.21118507     -3.17116410     -6.11374944
   5.17669335      1.08259474      2.85240779
   0.34820665      5.39521427      6.72207259
  -0.48756735      3.81039092     -3.54931726
  -5.39068025     -1.33915960     -4.23751820
  -0.18488624      2.06218228      9.34707866
  -3.61130283    -10.55745242     -2.97583485
  -2.00052315     -0.40626965     -6.55559752
  -3.33918373     -2.81142794     -2.26809748
  18.73727433      0.40692371     22.46695049
   2.01021748     21.18631899     41.45998743
 -23.33885620    -12.95186387      6.03628030
  -5.75826148      6.49553187     20.40770018
  -2.89001783     -6.55138378    -24.45858968
  25.47496930      9.98015540      1.36140634
  -7.18414811     -9.29242585     -1.58564830
  18.33698100      0.92487779     16.46682718
  14.19943876     -1.17927735    -18.07153124
  -1.17641620    -24.98710393      5.23523296
  }
  ConvergentForcesOnly = Yes
  KeepStationary = Yes
  #Xlbomd
  #XlbomdFast
  #Masses
}

Hamiltonian = DFTB {

SCC = Yes
SCCTolerance = 1.0e-5
MaxSCCIterations = 5000
SlaterKosterFiles = Type2FileNames {    # File names from two atom type
names
  Prefix =
"/rhome/salle008/bigdata/azobenzene_last_try/trans/W1H/3ob-3-1/"  # Path as
prefix
  Separator = "-"                  # Dash between type names
  Suffix = ".skf"                  # Suffix after second type name
}

MaxAngularMomentum {
C = "p"
H = "s"
N ="p"
H1 = "s"
}
Filling = Fermi {
     Temperature [Kelvin] = 0
}
  Mixer = Broyden {
    MixingParameter = 0.20000000000000001
}
   ReadInitialCharges =  No
   ForceEvaluation = "dynamics"
   DampXH = Yes
   DampXHExponent = 4.00
   ThirdOrderFull = Yes
   HubbardDerivs {
   N = -0.1535
   C = -0.1492
   H = -0.1857
   H1 = -0.1857
    }
  Dispersion = DftD3 {}
}
ExcitedState = Casida {
  NrOfExcitations=10
  StateOfInterest=1
  Symmetry=singlet
  WriteTransitions=yes
  WriteSPTransitions=yes
  WriteMulliken=yes
  WriteCoefficients=yes
  WriteEigenvectors=yes
  WriteTransitionDipole=yes
}
 Options = {
   WriteAutotestTag = Yes
   WriteDetailedXML = Yes
   WriteResultsTag = Yes
   WriteDetailedOut = Yes
   RandomSeed = 0
 }

ParserOptions {
ParserVersion = 4
}

Any help is appreciated!

Best,
*Sarah Allec*
Graduate Student
Nanoscale & Mesoscale Energy Materials Group
Department of Materials Science & Engineering
University of California Riverside
Email: sarah.allec at email.ucr.edu
Website: *www.bmwong-group.com <http://www.bmwong-group.com>*
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