[Pw_forum] Slab optimization with -24kbar stress!!!

David Foster davidfoster751 at yahoo.com
Thu Dec 4 19:26:16 CET 2014


Dear users
I have used 5.1.1 version to optimize conventional cell of CeO2 with 12 atoms.
I used PSLIBRARY to use USPP for Ce and O atoms. Here is my input for CeO2 conventional cell:
==================
&CONTROL
                       title = 'CeO2'
                 calculation = 'vc-relax'
                restart_mode = 'from_scratch'
                      outdir = './ceo2_vc_relax'
                  pseudo_dir = './'
                      prefix = 'ceo2'
                     disk_io = 'default'
                   verbosity = 'default'
                   etot_conv_thr=1.0D-9
                   forc_conv_thr=1.0D-4
                   nstep=1000
                  wf_collect=.true.
/
 &SYSTEM
                       ibrav = 0
                          nat = 12
                        ntyp = 2
                     ecutwfc = 173
                     ecutrho = 692
                       starting_magnetization(1)=0.5
                       starting_magnetization(3)=0.5
                      nspin=2
                      occupations='smearing'
                      degauss=0.001
                      smearing='mv'
                       nbnd=82
/
 &ELECTRONS
            electron_maxstep = 1000
                    conv_thr = 1.0D-10
                 mixing_mode = 'plain'
                 mixing_beta = 0.4
                 mixing_ndim = 8
             diagonalization = 'david'
/
 &IONS
            ion_dynamics = 'bfgs'
/
 &CELL
            cell_dynamics = 'bfgs'
/
ATOMIC_SPECIES
   O   15.9989995956   O.pbe-nl-rrkjus_psl.1.0.0.UPF
   Ce  140.1199951172  Ce.pbe-spdfn-rrkjus_psl.1.0.0.UPF

ATOMIC_POSITIONS crystal
  O   0.2500000000000000   0.2499999999999999   0.2499999999999999
  O   0.7500000000000000   0.7499999999999999   0.2499999999999999
  O   0.7500000000000000   0.2499999999999999   0.7499999999999999
  O   0.2500000000000000   0.7499999999999999   0.7499999999999999
  O   0.2500000000000000   0.2499999999999999   0.7499999999999999
  O   0.7500000000000000   0.7499999999999999   0.7499999999999999
  O   0.7500000000000000   0.2499999999999999   0.2499999999999999
  O   0.2500000000000000   0.7499999999999999   0.2499999999999999
 Ce   0.0000000000000000   0.0000000000000000   0.0000000000000000
 Ce   0.0000000000000000   0.4999999999999999   0.4999999999999999
 Ce   0.5000000000000000   0.0000000000000000   0.4999999999999999
 Ce   0.5000000000000000   0.4999999999999999   0.0000000000000000
K_POINTS automatic
3 3 3 0 0 0
CELL_PARAMETERS
   10.225308105044215     0.000000000000000     0.000000000000000
    0.000000000000000    10.225308105044215     0.000000000000000
    0.000000000000000     0.000000000000000    10.225308105044215
====================================================

Everything is OK for conventional cell vc-relax command (very low force and stress).
My problem is for slab optimization. I used following command to relax 2*2  110 surface slab with 6 layers and 4 bottom layers fixed.
You can see my input:

===================================================
&CONTROL
                       title = 'ceo2_110'
                 calculation = 'relax'
                restart_mode = 'from_scratch'
                      outdir = './ceo2_110'
                  pseudo_dir = './'
                      prefix = 'ceo2_110'
                     disk_io = 'default'
                   verbosity = 'default'
                      tstress = .true.
                     tprnfor = .true.
                  etot_conv_thr=1.0D-9
                   forc_conv_thr=1.0D-4
                   nstep=1000
                  wf_collect=.true.
 /
 &SYSTEM
                       ibrav = 0
                         nat = 72
                        ntyp = 2
                     ecutwfc = 173
                     ecutrho = 692
                       starting_magnetization(1)=0.5
                       starting_magnetization(3)=0.5
                      nspin=2
                      occupations='smearing'
                      degauss=0.001
                      smearing='mv'
                       nbnd=490
 /
 &ELECTRONS
            electron_maxstep = 1000
                    conv_thr = 1.0D-10
                 mixing_mode = 'plain'
                 mixing_beta = 0.4
                 mixing_ndim = 8
             diagonalization = 'david'
 /
&IONS
                ion_dynamics = 'bfgs'
 /


ATOMIC_SPECIES
    O   15.9989995956   O.pbe-nl-rrkjus_psl.1.0.0.UPF
   Ce  140.1199951172  Ce.pbe-spdfn-rrkjus_psl.1.0.0.UPF
ATOMIC_POSITIONS crystal
  O   0.1250000000000000  -0.0000000000000000   0.0000000000000003 0 0 0
  O   0.1250000000000000  -0.0000000000000000   0.1562436466930924 0 0 0
  O   0.1250000000000001   0.0000000000000001   0.3124872933861844
  O   0.3750000000000002   0.2499999999999999   0.2343654700396384 0 0 0
  O   0.3750000000000002   0.2499999999999999   0.0781218233465463 0 0 0
  O   0.3750000000000002   0.2500000000000000   0.3906091167327304
  O   0.3750000000000002   0.0000000000000001   0.0000000000000003 0 0 0
  O   0.3750000000000001  -0.0000000000000002   0.1562436466930924 0 0 0
  O   0.3750000000000003   0.0000000000000001   0.3124872933861844
  O   0.1250000000000001   0.2499999999999999   0.2343654700396383 0 0 0
  O   0.1250000000000001   0.2500000000000001   0.0781218233465462 0 0 0
  O   0.1250000000000001   0.2500000000000000   0.3906091167327304
  O   0.6250000000000002  -0.0000000000000001   0.0000000000000003 0 0 0
  O   0.6250000000000002  -0.0000000000000001   0.1562436466930924 0 0 0
  O   0.6250000000000002   0.0000000000000000   0.3124872933861844
  O   0.8750000000000002   0.2499999999999998   0.2343654700396384 0 0 0
  O   0.8750000000000002   0.2499999999999998   0.0781218233465463 0 0 0
  O   0.8750000000000002   0.2499999999999999   0.3906091167327304
  O   0.8750000000000002  -0.0000000000000001   0.0000000000000003 0 0 0
  O   0.8750000000000001  -0.0000000000000001   0.1562436466930924 0 0 0
  O   0.8750000000000004   0.0000000000000000   0.3124872933861845
  O   0.6250000000000002   0.2499999999999999   0.2343654700396384 0 0 0
  O   0.6250000000000002   0.2500000000000002   0.0781218233465463 0 0 0
  O   0.6250000000000002   0.2500000000000001   0.3906091167327304
  O   0.1250000000000000   0.4999999999999999   0.0000000000000003 0 0 0
  O   0.1250000000000000   0.5000000000000001   0.1562436466930923 0 0 0
  O   0.1250000000000001   0.5000000000000001   0.3124872933861844
  O   0.3750000000000002   0.7500000000000000   0.2343654700396384 0 0 0
  O   0.3750000000000002   0.7499999999999999   0.0781218233465463 0 0 0
  O   0.3750000000000002   0.7500000000000000   0.3906091167327304
  O   0.3750000000000002   0.5000000000000001   0.0000000000000002 0 0 0
  O   0.3750000000000001   0.4999999999999999   0.1562436466930924 0 0 0
  O   0.3750000000000004   0.5000000000000001   0.3124872933861843
  O   0.1250000000000001   0.7500000000000000   0.2343654700396383 0 0 0
  O   0.1250000000000001   0.7500000000000001   0.0781218233465462 0 0 0
  O   0.1250000000000001   0.7500000000000002   0.3906091167327304
  O   0.6250000000000003   0.4999999999999999   0.0000000000000002 0 0 0
  O   0.6250000000000001   0.5000000000000001   0.1562436466930923 0 0 0
  O   0.6250000000000003   0.5000000000000001   0.3124872933861844
  O   0.8750000000000002   0.7500000000000000   0.2343654700396384 0 0 0
  O   0.8750000000000002   0.7499999999999999   0.0781218233465463 0 0 0
  O   0.8750000000000002   0.7500000000000001   0.3906091167327304
  O   0.8750000000000002   0.5000000000000001   0.0000000000000002 0 0 0
  O   0.8750000000000000   0.4999999999999999   0.1562436466930924 0 0 0
  O   0.8750000000000006   0.5000000000000001   0.3124872933861844
  O   0.6250000000000002   0.7500000000000001   0.2343654700396384 0 0 0
  O   0.6250000000000002   0.7500000000000001   0.0781218233465462 0 0 0
  O   0.6250000000000002   0.7500000000000002   0.3906091167327305
 Ce   0.0000000000000000  -0.0000000000000000   0.0781218233465463 0 0 0
 Ce   0.0000000000000000  -0.0000000000000000   0.2343654700396383 0 0 0
 Ce   0.0000000000000001  -0.0000000000000001   0.3906091167327305
 Ce   0.2500000000000002   0.2500000000000000   0.0000000000000002 0 0 0
 Ce   0.2500000000000002   0.2499999999999999   0.3124872933861844
 Ce   0.2500000000000002   0.2500000000000001   0.1562436466930924 0 0 0
 Ce   0.5000000000000001   0.0000000000000000   0.0781218233465463 0 0 0
 Ce   0.5000000000000001   0.0000000000000000   0.2343654700396384 0 0 0
 Ce   0.5000000000000001  -0.0000000000000001   0.3906091167327304
 Ce   0.7500000000000003   0.2500000000000001   0.0000000000000002 0 0 0
 Ce   0.7500000000000003   0.2499999999999999   0.3124872933861844
 Ce   0.7500000000000003   0.2500000000000001   0.1562436466930924 0 0 0
 Ce   0.0000000000000000   0.5000000000000001   0.0781218233465463 0 0 0
 Ce   0.0000000000000000   0.5000000000000001   0.2343654700396383 0 0 0
 Ce   0.0000000000000001   0.4999999999999999   0.3906091167327304
 Ce   0.2500000000000001   0.7500000000000001   0.0000000000000001 0 0 0
 Ce   0.2500000000000001   0.7500000000000000   0.3124872933861844
 Ce   0.2500000000000001   0.7500000000000001   0.1562436466930923 0 0 0
 Ce   0.5000000000000000   0.5000000000000000   0.0781218233465463 0 0 0
 Ce   0.5000000000000002   0.5000000000000001   0.2343654700396384 0 0 0
 Ce   0.5000000000000002   0.5000000000000000   0.3906091167327304
 Ce   0.7500000000000002   0.7500000000000001   0.0000000000000001 0 0 0
 Ce   0.7500000000000002   0.7500000000000000   0.3124872933861844
 Ce   0.7500000000000002   0.7500000000000001   0.1562436466930923 0 0 0

K_POINTS automatic
1 1 1 1 1 1

CELL_PARAMETERS Bohr
   20.556138517348749     0.000000000000002    -0.000000000000004
    0.000000000000000    14.535384940627280     0.000000000000002
   -0.000000000000000    -0.000000000000000    46.515123169068765

====================================================================

SCF in each DFGS iteration converges in about 200-300 steps. 
My main problem is final section of the output:

======================
.
.
.
atom   71 type  2   force =     0.00000009   -0.00000005   -0.00000464
     atom   72 type  2   force =    -0.00000004    0.00000118    0.00769631

     Total force =     0.000043     Total SCF correction =     0.000001


     entering subroutine stress ...


     negative rho (up, down):  7.323E-04 7.323E-04
          total   stress  (Ry/bohr**3)                   (kbar)     P=  -24.51
  -0.00007691   0.00000000  -0.00000000        -11.31      0.00     -0.00
   0.00000000  -0.00032173   0.00000000          0.00    -47.33      0.00
  -0.00000000   0.00000000  -0.00010117         -0.00      0.00    -14.88


     bfgs converged in  19 scf cycles and  18 bfgs steps
     (criteria: energy <  1.0E-09, force <  1.0E-04)

     End of BFGS Geometry Optimization
.
.
==================================

As you see final stress is -24.51 kbar ??????!!!!!!!!!!!!!!
As you know, for slab, we don't used "vc-relax", and only optimize ions positions. What should I do to reduce the stress on the slab?
 


Regards

David Foster
Ph.D. Student of Chemistry



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