# H2 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.
#



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

#First dataset : find the optimal bond length of H2, and associated total energy
   natom 10             # There are two atoms

typat 4*1 6*2           # They both are of type 1, that is, Aluminum.
xcart              # This keyword indicate that the location of the atoms
                  # will follow, one triplet of number for each atom
          4.992698581      4.992698581      4.992698581
      -4.992698581     -4.992698581     -4.992698581
       2.093566007      2.093566007      2.093566007
      -2.093566007     -2.093566007     -2.093566007
        5.491168518      1.595096070      3.543132294
       -5.491168518     -1.595096070     -3.543132294
        1.595096070      3.543132294      5.491168518
       -1.595096070     -3.543132294     -5.491168518
        3.543132294      5.491168518      1.595096070
       -3.543132294     -5.491168518     -1.595096070   # Triplet giving the REDUCED coordinate of atom 1.
  ionmov 3             # Use the modified Broyden algorithm
  ntime 50            # Maximum number of Broyden "timesteps"
  tolmxf 5.0d-4        # Stopping criterion for the geometry optimization : when 
                         # the residual forces are less than tolmxf, the Broyden 
                         # algorithm can stop

  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)
   nband  35            # Just one band



#Definition of the atom types
ntypat 2          # There is only one type of atom
znucl 26 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.
nsym 0

#Definition of the atom types

                         


#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 500          # 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