! E13: Born-Oppenheimer MD on the bulk FeO(+U) cell, the starting point for
! sampling ML training data. Every step converges an SCF and moves the ions
! on the resulting forces.
! dt is in Rydberg atomic units: 20.0 a.u. = 0.968 fs

&CONTROL
  calculation = 'md'
  prefix      = 'feo_md'
  outdir      = './tmp/'
  pseudo_dir  = './pseudo/'
  nstep       = 2000         ! 2000 steps x 0.968 fs ~ 1.9 ps
  dt          = 20.0         ! TIME STEP IN RYDBERG A.U., not femtoseconds
  tprnfor     = .true.       ! forces on every step: that is the training data
  tstress     = .false.      ! Hubbard stress dies with stres_hub under nosym+U (measured on QE 7.5);
                             ! if you need stress, recompute it on extracted frames with scf runs
  disk_io     = 'none'       ! do not write wavefunctions every step: I/O kills MD
/
&SYSTEM
  ibrav       = 0
  celldm(1)   = 8.18         ! bohr (= 4.33 Angstrom)
  nat         = 4
  ntyp        = 3
  ecutwfc     = 70
  ecutrho     = 700
  occupations = 'smearing'
  smearing    = 'mv'
  degauss     = 0.01
  nspin       = 2
  starting_magnetization(1) =  0.6
  starting_magnetization(2) = -0.6
  starting_magnetization(3) =  0.0
  nosym       = .true.       ! mandatory for MD: thermal motion breaks the initial
                             ! symmetry in step 1 (checkallsym error without this)
/
&ELECTRONS
  conv_thr    = 1.0d-6       ! BOMD-level threshold; nosym+U struggles below this (measured)
  mixing_beta = 0.2
  mixing_mode = 'local-TF'
  electron_maxstep = 300
  mixing_fixed_ns  = 30      ! freeze the DFT+U ns matrix for the first 30 iterations:
                             ! without symmetry the degenerate t2g orbitals rotate freely
                             ! and the SCF stalls otherwise (measured)
/
&IONS
  ion_dynamics    = 'verlet' ! velocity-Verlet integrator
  ion_temperature = 'svr'    ! stochastic velocity rescaling thermostat (canonical sampling)
  tempw           = 300.0    ! target temperature in K
  nraise          = 100      ! thermostat coupling period, in steps (~0.1 ps here)
/

ATOMIC_SPECIES
  Fe1  55.845  Fe.pbe-spn-kjpaw_psl.1.0.0.UPF
  Fe2  55.845  Fe.pbe-spn-kjpaw_psl.1.0.0.UPF
  O    15.999  O.pbe-n-kjpaw_psl.1.0.0.UPF

CELL_PARAMETERS (alat)
  0.5  0.5  1.0
  0.5  1.0  0.5
  1.0  0.5  0.5

ATOMIC_POSITIONS (crystal)
  Fe1  0.00  0.00  0.00
  Fe2  0.50  0.50  0.50
  O    0.25  0.25  0.25
  O    0.75  0.75  0.75

! MD needs less k-resolution than a static DOS; with nosym this 4^3 grid
! is not symmetry-reduced, which is part of the per-step cost
K_POINTS (automatic)
  4 4 4  0 0 0

! keep U identical across every frame of a training set
HUBBARD (ortho-atomic)
U Fe1-3d 4.6
U Fe2-3d 4.6