Si_relax.in

 &control
    calculation = 'vc-relax'
    restart_mode='from_scratch',
    prefix='Si_relax',
    tstress = .true.
    tprnfor = .true.
    pseudo_dir = '/qe-6.3/pseudo',
    outdir='/qe-6.3/tempdir/'
 /
 &system
    ibrav=  2, celldm(1) =9.50, nat=  2, ntyp= 1,
    ecutwfc =40.0,
 /
 &electrons
    diagonalization='david'
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-8
/
&IONS
ion_dynamics = 'bfgs'
 
/
&CELL
cell_dynamics='bfgs'
cell_dofree='all'

/
ATOMIC_SPECIES
 Si  28.086  Si.pz-vbc.UPF
ATOMIC_POSITIONS
 Si 0.00 0.00 0.00
 Si 0.26 0.25 0.27
K_POINTS {automatic}
4 4 4   0 0 0