! E06: variable-cell relaxation of silicon.
! Start from a deliberately wrong lattice constant and let BFGS find the
! PBE equilibrium. Afterwards, ALWAYS rerun scf on the final structure
! (Pulay stress: the plane-wave basis changed with the cell).

&CONTROL
  calculation   = 'vc-relax'
  prefix        = 'si_vc'
  outdir        = './tmp/'
  pseudo_dir    = './pseudo/'
  etot_conv_thr = 1.0d-5      ! stop when the energy change per ionic step is below this (Ry)
  forc_conv_thr = 1.0d-4      ! ... and every force component is below this (Ry/bohr)
  nstep         = 100         ! maximum number of ionic (BFGS) steps
  tprnfor       = .true.
  tstress       = .true.      ! vc-relax drives the stress to press_conv_thr
/
&SYSTEM
  ibrav       = 2
  celldm(1)   = 10.00         ! deliberately wrong starting value (compressed, ~+109 kbar)
  nat         = 2
  ntyp        = 1
  ecutwfc     = 40
  ecutrho     = 320
  occupations = 'fixed'
/
&ELECTRONS
  conv_thr    = 1.0d-10       ! tighter than usual: BFGS wanders on noisy forces/stress
/
&IONS
  ion_dynamics   = 'bfgs'     ! quasi-Newton optimizer for the atoms
/
&CELL
  cell_dynamics  = 'bfgs'     ! ... and for the cell
  press_conv_thr = 0.1        ! target |pressure| in kbar
  cell_dofree    = 'ibrav'    ! keep cubic symmetry: only the lattice constant may change
/

ATOMIC_SPECIES
  Si  28.0855  Si.pbe-n-kjpaw_psl.1.0.0.UPF

ATOMIC_POSITIONS (alat)
  Si  0.00  0.00  0.00
  Si  0.25  0.25  0.25

K_POINTS (automatic)
  8 8 8  0 0 0