#author("2023-08-06T09:41:33+09:00","default:StatE","StatE")
* Oxygen molecule [#k112b541]
In this tutorial, how to perform calculation(s) of a molecule with the spin degree of freedom (or spin unrestricted calculation of a molecule) is discussed by taking an oxygen (O2) molecule as an example.

** Preliminary [#bc970db3]
In this tutorial, the O2 molecule is placed in a cubic box with the cell edges of 10 Angstroms.
The GBRV ultrasoft pseudopotential, kinetic energy cutoffs of 40 Ry and 320 Ry for the wave functions and augmentation charge, respectively, and the Gamma-point are used.

** SCF calculation [#b9138eba]
We start with an SCF calculation using the following input file
-o2_scf.in
 O2
 O2 molecule in a box
  &control
     calculation = 'scf'
     restart_mode = 'from_scratch'
     prefix = 'o2'
     pseudo_dir = '/home/ikutaro/QE/pseudo'
     outdir = './tmp/'
     verbosity = 'high'
  /
  &system
     ibrav = 1
     A = 10.d0
     nat = 2
     ntyp = 1
     nbnd = 12
     nosym = .true.
     nspin = 2
     tot_magnetization = 2.0
     starting_magnetization(1) = 0.5d0
     ecutwfc = 40.0
     ecutrho = 320.0
  /
  &electrons
     mixing_beta = 0.5
     conv_thr =  1.0d-10
  /
  &ions
  /
 ATOMIC_SPECIES
 O    15.9994   o_pbe_v1.2.uspp.F.UPF
 ATOMIC_POSITIONS (angstrom)
  O      0.000000000000      0.000000000000      0.000000000000
  O      0.000000000000      0.000000000000      1.200000000000
 K_POINTS (gamma)
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