[Pw_forum] convergence for lattice parameter

[funmi ayedun]

Dear All,

Good day all, I am a new user in quantum espresso, I am working on anatase TiO2 (with hexagonal structure) but  I have problem with convergence test  for lattice parameter for TiO2 system.  I have tried to vary celldm 1 from 8.2 to 9.0Bohr but I was unable get a convergence result. Also, I tried to vary celldm 3  from 0.2441 to 1.3441Bohr and  keeping celldm 1 constant, I was unable to get convergence as well. I have my input file below. 

&control
  calculation = 'scf',
  restart_mode='from_scratch',
  prefix='TiO2'
  pseudo_dir='/home/funmilayo/espresso-4.2.1/pseudo',
  outdir='./',
    tprnfor = .true.
  tstress = .true.
/
&system
  ibrav=6, celldm(1)= 8.6808, celldm(3)= 0.7450,
  nat=3, ntyp=2,occupations='smearing', smearing='marzari-vanderbilt', degauss=0.02 
  ecutwfc= 25.0,
/
&electrons
 mixing_beta = 0.7
 diagonalization='davidson'
conv_thr =  1.0d-8
/
ATOMIC_SPECIES
Ti 47.867  Ti.blyp-sp-van_ak.UPF
O  15.994  O.blyp-van_ak.UPF
ATOMIC_POSITIONS
Ti 0.00000000   0.00000000   0.00000000 
O  0.33333333   0.33333333   0.33333333
O  0.80000000   0.20000000   0.50000000
K_POINTS (automatic)
6 6 6  0  0  0

Can anyone please tell me where I have gone wrong.  
Thank you all.


Ayedun Oluwafunmilayo,
PhD student,
Department of Physics,
University of Agriculture,
Abeokuta,
Nigeria.
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