# This is a pretty minimal pw.x input file that makes extensive use of the
 # values in the three sections 'control', 'system' and 'electrons'. Typically
 # you'll want to specify many more things than we have here.

 # The help file with details of all the parameters and their values is at
 # /opt/share/quantum-espresso/doc-6.1/INPUT_PW.txt

 # While we accept all defaults in the CONTROL and ELECTRONS sections, all
 # the sections used here must always be present (there are a number of
 # additional sections which may also be needed depending on the values used
 # the CONTROL and SYSTEM sections.

 &CONTROL
    ! This section is used to control the calculation we want to do, such as
    ! change the calculation type, the level of output, the directory where
    ! output is stored, etc.
    !
    ! We can accept most defaults to start with.
    !
    ! For example the default type of calculation is 'scf' which is what we
    ! want.
    ! The only thing we'll set is the parameter that says it should look in
    ! the same directory where you run the code for the pseudopotential file.
    pseudo_dir = '.'
 /

 &SYSTEM
    ! There are a number of required input variables in the "system" section.

    ! This is the index of the type of Bravais-lattice we have. 2 is for fcc.
    ! This tells the code what parameters need to be specified for the
    ! lattice.
    ibrav = 2

    ! This is the lattice length, which is the only free parameter for fcc.
    ! A is in Angstrom. We've taken the experimental value here.
    A = 3.567

    ! This is the number of atoms in the cell. For the fcc cell there are 2.
    nat = 2

    ! This is the number of types of atoms. We only have carbon so this is 1.
    ntyp = 1

    ! This is the planewave energy cutoff in Rydberg
    ecutwfc = 18.0
 /

 &ELECTRONS
    ! This section is used to set how the electronic calculations converge for
    ! self-consistent calculations.
    !
    ! Again we can accept all defaults.
    !
    ! Here we could, for example, set a lower convergence threshold for when
    ! the code decides the self-consistent calculation is converged. Or
    ! increase the maximum number of iterations.
 /

# In this section we list all the atomic species, so we need to have as many
# entries as 'ntyp' above. These should be entered one per line, with the
# atomic symbol, followed by the mass (only used for certain types of
# calculations), followed by the name of the pseudopotential. In the same
# directory as the input file we have a symbolic link to the pseudotential
# file we need. This saves us from making multiple copies of the same file
# for different calculations.
ATOMIC_SPECIES
 C  12.011  C.pz-vbc.UPF

# Now we list the postitions of all the atoms. There are several possible ways
# to do this. Here we use the 'crystal' option, which specifies that they are
# given in fractional coordinates along each of the crystal axes. There should
# be one line for each atom in the cell - so 'nat' lines in total.
ATOMIC_POSITIONS crystal
 C 0.00 0.00 0.00
 C 0.25 0.25 0.25

# Finally we specify the k-point sampling to use. Again there are several
# options. Here we use automatic, which allows use to easily specify a regular
# 4x4x4 grid of points along the crystal axes. The next three numbers specify
# whether to offset the grid by half a lattice spacing our not. Often
# convergence is a little better if you do this, but it varies.
K_POINTS automatic
  4 4 4 1 1 1