# Crystalline silicon
# Calculation of the GW correction to the direct band gap in Gamma
# Dataset 1: ground state calculation 
# Dataset 2: calculation of the kss file 
# Dataset 3: calculation of the screening (epsilon^-1 matrix for W)
# Dataset 4: calculation of the Self-Energy matrix elements (GW corrections)

ndtset      4

kptopt   1            # Option for the automatic generation of k points
ngkpt    4 4 4        # Density of k points

# Dataset1: usual self-consistent ground-state calculation
# Definition of the k-point grid
 nkpt1    12
 nshiftk1  1
#shiftk1               # This grid is the most economical
#         0.5 0.0 0.0
#         0.0 0.5 0.0
#         0.0 0.0 0.5
prtden1  1         # Print out density


# Dataset2: calculation of kss file
# Definition of k-points
nkpt2    21             # A set of 19 k-points containing Gamma
nshiftk2  1
shiftk2  0.0 0.0  .0  # This grid contains the Gamma point

istwfk2  21*1                    # Option needed for Gamma
iscf2    -2             # Non self-consistent calculation
getden2  -1             # Read previous density file
nband2   16
nbandkss2 100        # Number of bands to store in KSS file

# Dataset3: Calculation of the screening (epsilon^-1 matrix)
optdriver3  3        # Screening calculation
getkss3     -1       # Obtain KSS file from previous dataset
nband3      25       # Bands to be used in the screening calculation
ecutwfn3    3.6      # Planewaves to be used to represent the wavefunctions
ecuteps3    6.0      # Dimension of the screening matrix
ppmfrq3    16.7 eV  # Imaginary frequency where to calculate the screening

# Dataset4: Calculation of the Self-Energy matrix elements (GW corrections)
optdriver4  4        # Self-Energy calculation
getkss4     -2       # Obtain KSS file from dataset 1
getscr4     -1       # Obtain SCR file from previous dataset
nband4      100      # Bands to be used in the Self-Energy calculation
ecutwfn4    5.0      # Planewaves to be used to represent the wavefunctions
ecutsigx4    6.0      # Dimension of the G sum in Sigma_x
                     # (the dimension in Sigma_c is controlled by npweps)
nkptgw4      1                # number of k-point where to calculate the GW correction
kptgw4                       # k-points
  0.000    0.000    0.000    # (Gamma)
bdgw4       8  9             # calculate GW corrections for bands from 4 to 5


# Definition of the unit cell: fcc
acell  3*7.90          # This is equivalent to   10.217 10.217 10.217
rprim  0.5  -0.866  0.0 #FCC primitive vectors (to be scaled by acell)
       0.5  0.866   0.0
       0.0  0.0  1.62

# Definition of the atom types
ntypat  2         # There is only one type of atom
znucl 12  34      # The keyword "znucl" refers to the atomic number of the 
                  # possible type(s) of atom. The pseudopotential(s) 
                  # mentioned in the "files" file must correspond
                  # to the type(s) of atom. Here, the only type is Silicon.
                         
# Definition of the atoms
natom 2           # There are two atoms
typat  1 1  2  2  # They both are of type 1, that is, Silicon.
xred              # Reduced coordinate of atoms
      0.3333   0.6666   0.0                                          
      0.6666   0.3333   0.5
      0.3333   0.6666   0.378
      0.6666   0.3333   0.878

# Definition of the planewave basis set (at convergence 16 Rydberg 8 Hartree)
ecut 8.0          # Maximal kinetic energy cut-off, in Hartree

# Definition of the SCF procedure
nstep   90        # Maximal number of SCF cycles
diemac  12.0      # Although this is not mandatory, it is worth to
                  # precondition the SCF cycle. The model dielectric
                  # function used as the standard preconditioner
                  # is described in the "dielng" input variable section.
                  # Here, we follow the prescription for bulk silicon.
tolwfr  1.0d-10