[QE-users] Total Stress in Supercell

[Felipe Toledo Carrasco]

Dear Quantum Espresso community:
I optimized the cell vectors and atomic positions (vc-relax) of a
Perovskite, resulting in a total stress of -0.68 kbar.

However, when building the 3x3 Supercell of this oxide and performing
the "relax" calculation of this structure, I find a very high stress
of -13.34 kbar.  These calculations I used the functional PBE-D3.How
is it possible to reduce the Supercell Pressure to lower values?. Have
I used the correct calculation variables, that is, functional, k
points, ecutwfc, press_conv_thr or others?

Supercell Input information:

 &control
    calculation='relax',
    restart_mode='from_scratch',
    pseudo_dir = '.',
    outdir='./tmp'
    prefix='Superficie'
!   forc_conv_thr = 1d-2,
    nstep= 500
    tstress = .true.,
    tprnfor = .true.,
 /
 &system
    ibrav = 0,  nat= 117, ntyp= 3,
    ecutwfc = 50.0, ecutrho = 400.0
    vdw_corr = 'grimme-d3'
 /
 &electrons
    electron_maxstep= 500
    conv_thr = 1.0e-8
    mixing_beta = 0.7
 /
 &ions
  ion_dynamics = 'bfgs',
 /
! &CELL
!  cell_dynamics = 'bfgs',
!  press = 0.0,
!  press_conv_thr = 0.5,

 /
ATOMIC_SPECIES

 Sr 87.62 Sr.pbe-spn-rrkjus_psl.1.0.0.UPF
 Ti 47.87 Ti.pbe-spn-rrkjus_psl.1.0.0.UPF
 O 16.00 O.pbe-n-rrkjus_psl.1.0.0.UPF

CELL_PARAMETERS angstrom

.....

ATOMIC_POSITIONS angstrom

K_POINTS (gamma)

.....

Please, I will be grateful if you help me with this,
Regards,

-- 
Felipe Toledo Carrasco
PhD Student
Concepción - Chile
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