# O2 molecule in a big box
#
# This file to optimize the H2 bond length, compute the associated total
# energy, then to compute the total energy of the isolated H atom.
# Here, a double loop has been used.
#

 ndtset 1 udtset 1 1

#Definition of the unit cell and ecut, 
#for which one will have to make a convergence study
  acell:? 10 10 10 acell+? 5 5 5

#First dataset:
   natom 2             # There are two atoms
  ionmov 3             # Use the modified Broyden algorithm
   ntime 10            # Maximum number of Broyden "timesteps"
  nsppol 2             # Spin-polarized calculation
   nsym  1
   symrel 1 0 0 
          0 1 0 
          0 0 1
  occopt 2             # Allow occupation numbers to be set by hand
  nband 7 7         # Number of bands for spin up and spin down
     occ 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.0 0.0 # Occupation numbers for spin up state and spin down state1

  tolmxf 5.0d-4        # Stopping criterion for the geometry optimization : when 
                         # the residual forces are less than tolmxf, the Broyden 
                         # algorithm can stop
  xangst       -0.60000000    0.00000000    0.00000000 # The starting values of the
                0.60000000    0.00000000    0.00000000 

  toldff 5.0d-5        # Will stop the SCF cycle when, twice in a row, 
                       # the difference between two consecutive evaluations of
                       # forces differ by less than toldff (in Hartree/Bohr)

  pawecutdg 40

#Definition of the atom types
ntypat 1          # There are two types of atoms
znucl  8          # 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 Hydrogen.
                         

#Definition of the atoms
typat 1 1         # Oxygen is type 1

#Definition of the k-point grid
nkpt 1            # Only one k point is needed for isolated system,
                  # taken by default to be 0.0 0.0 0.0

#Definition of the SCF procedure
nstep 40          # Maximal number of SCF cycles
#toldfe is no more defined, as toldff is used above... 
diemac 2.0        # 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 prescriptions for molecules
                  # in a big box
ecut:? 20  ecut+? 5