Added DFTB+ input example

example/diamond-dftb/README

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+This is an example of the use of the DFTB+ interface. An input is
+given in the dftb_in.hsd file along with the conventional unit cell in
+geo.gen. This example also requires the pbc-0-3 Slater-Koster
+parameteters for carbon
+(https://www.dftb.org/parameters/download/pbc/pbc-0-3-cc/).
+
+1) Create the (one) displaced supercell(s):
+   phonopy -d --dim="2 2 2" --dftb+ 
+
+2) Run the supercell input with dftb+. This has been pre-calculated
+   with DFTB+ version 18.2, with the required data stored in
+   detailed.out.
+
+3) Collect the forces:
+   phonopy -f detailed.out --dftb+  ...
+
+4) Calculate phonon dispersion data into band.yaml and save band.pdf:
+   phonopy --dftb+ --dim="2 2 2" -p -s band.conf

example/diamond-dftb/band.conf

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+BAND = 0 0 0    1/2 0 1/2    1/2 1/4 3/4    3/8 3/8 3/4    0 0 0    1/2 1/2 1/2    5/8 1/4 5/8    1/2 1/4 3/4    1/2 1/2 1/2    3/8 3/8 3/4,    5/8 1/4 5/8    1/2 0 1/2
+BAND_LABELS = $\Gamma$ X W K $\Gamma$ L U W L K:U X
+BAND_POINTS = 101

example/diamond-dftb/dftb_in.hsd

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+Geometry = GenFormat {
+<<< geo.genS-001
+}
+
+Hamiltonian = DFTB {
+  SCC = No
+  MaxAngularMomentum = {
+    C = "p"
+  }
+  SlaterKosterFiles = Type2FileNames {
+    Separator = "-"
+    Suffix = ".skf"
+  }
+  KPointsAndWeights = SupercellFolding {
+   6 0 0
+   0 6 0
+   0 0 6
+   0.5 0.5 0.5
+  }
+}
+
+Options = {
+  WriteAutotestTag = Yes
+}
+
+ParserOptions = {
+  ParserVersion = 6
+}
+
+Analysis = {
+  CalculateForces = Yes
+}
+
+Parallel {
+  # Allow OMP threads explicitely to test for hybrid parallelisation with
+  # MPI-binary. (Check the manual before using this in production runs!)
+  UseOmpThreads = Yes
+}

example/diamond-dftb/geo.gen

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+    8  F
+  C
+    1 1    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
+    2 1    0.2500000000E+00    0.2500000000E+00    0.2500000000E+00
+    3 1    0.5000000000E+00    0.5000000000E+00    0.0000000000E+00
+    4 1    0.7500000000E+00    0.7500000000E+00    0.2500000000E+00
+    5 1    0.5000000000E+00    0.0000000000E+00    0.5000000000E+00
+    6 1    0.7500000000E+00    0.2500000000E+00    0.7500000000E+00
+    7 1    0.0000000000E+00    0.5000000000E+00    0.5000000000E+00
+    8 1    0.2500000000E+00    0.7500000000E+00    0.7500000000E+00
+    0.0000000000E+00    0.0000000000E+00    0.0000000000E+00
+    0.3561772125E+01    0.0000000000E+00    0.0000000000E+00
+    0.0000000000E+00    0.3561772125E+01    0.0000000000E+00
+    0.0000000000E+00    0.0000000000E+00    0.3561772125E+01