[DFTB-Plus-User] The Raman calculation for a periodic structure

[Mohsen Modarresi]

Dear DFTB+ community,

I am using DFTB+ to calculate the Raman spectra of CNT with different
chiralities. After many trials, I realized that the DFTB+ predicts the
position of Raman peaks with acceptable accuracy (+7% in comparison
to experiments). But the relative intensities of the peak strongly depend
on the "KPointsAndWeights". For example, the relative intensities of peaks
are quite different for mesh 8 and 10 along the z-axis. I tried to increase
k-mesh and reach convergence but it is oscillating and does not converge to
a specific answer.

I also found out that the results are not good for "static=yes"
polarizability calculations. Is there any suggestion for determining the
"Frequencies"? Does "Frequencies" correspond to the frequency of
incident light in a typical Raman experiment?
Here is my input file,

    <<< "genSD.gen"
}
Driver = SecondDerivatives {Delta = 1.0000000000000000E-6}
Hamiltonian = DFTB {
    SCC = No
    MaxAngularMomentum = {
        C = "p"
    }
    Charge = 0.0
    Filling = Fermi {
        Temperature [Kelvin] = 300
    }
    SlaterKosterFiles = Type2FileNames {
Prefix = {/home/c12/Desktop/DFTB/CNT88/}
        Separator = "-"
        Suffix = ".skf"
    }

  KPointsAndWeights = SupercellFolding {
   1 0 0
   0 1 0
   0 0 8
   0.0 0.0 0.5
  }
 Solver = DivideAndConquer {}
}
Analysis = {
    Polarisability = {
        Static = No
        Frequencies [eV] = 6.792
     #  Frequencies [eV] = 1.96
    }
}
Options = {
    WriteAutotestTag = No
}
ParserOptions = {
    ParserVersion = 12
}
Parallel {
    # Allow OMP threads explicitely to test for hybrid parallelisation with
    # MPI-binary. (Check the manual before using this in production runs!)
    UseOmpThreads = Yes
}

Best regards,
Mohsen Modarresi



[image: C12] *Mohsen Modarresi*
Condensed Matter Scientist

www.c12qe.com
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