[Pw_forum] vc -relax converge
Giuseppe Mattioli
giuseppe.mattioli at mlib.ism.cnr.it
Tue Apr 28 12:52:41 CEST 2009
Dear Ali
You have surely your good reasons to work with a 72-atom cell, but have you
think about optimizing your lattice parameters by using a 6-atom cell and then
building a supercell with an O vacancy? This is the best speed-up I can
suggest.
By the way, in a vc-relax calculation you should calculate forces and stress
very accurately. You should decrease conv_thr (=1.0d-9) and insert within the
&control box
etot_conv_thr=1.0E-5,
forc_conv_thr=1.0D-4,
Moreover, in my experience a 4*4*4 k-point mesh is a very robust one for a 72-
atom TiO2 supercell. A 2*2*2 mesh should give reliable and well converged
results.
Finally, give a chance to the vc-bfgs... And don't forget that you should use
some beyond-LDA calculation in order to achieve a good description of reduced
TiO2.
Yours
Giuseppe
On Tuesday 28 April 2009 09:54:43 ali kazempoor wrote:
> Dear all
> I use vc -relax to obtain the optimized lattice constant(tetragonal cell)
> and also the atomic position around O vacancy in TiO2 (2*2*3
> supercell),but after 2 weeks , the pressure slowly goes from -100 kbar to
> -56 kbar( two far from 0.00. The input file is at following: &control
> calculation = 'vc-relax'
> restart_mode='restart',
> prefix='rutile-71atom'
> tstress = .true.
> tprnfor = .true.
> pseudo_dir = './',
> outdir='/ptmp/javad/scratch/'
> nstep=1000,
> dt=70,
> /
> &system
> ibrav= 6 , celldm(1) =17.36,celldm(3)=0.9663585, nat= 71, ntyp= 2,
> ecutwfc =35.0,ecutrho=400
> /
> &electrons
> diagonalization=''
> mixing_mode = 'plain'
> mixing_beta = 0.7
> conv_thr = 1.0d-6
> /
> &IONS
> /
> &CELL
> cell_dynamics = 'damp-w',
> press=00.0
> /
> ATOMIC_SPECIES
> Ti 43.0 Ti.pz-sp-van.UPF
> O 16.0 O.pz-van_ak.UPF
> ATOMIC_POSITIONS crystal
> Ti 0.00000000 0.00000000 0.00000000
> Ti 0.50000000 0.00000000 0.00000000
> Ti 0.00000000 0.50000000 0.00000000
> Ti 0.50000000 0.50000000 0.00000000
> Ti 0.00000000 0.00000000 0.33333333
> Ti 0.50000000 0.00000000 0.33333333
> Ti 0.00000000 0.50000000 0.33333333
> Ti 0.50000000 0.50000000 0.33333333
> Ti 0.00000000 0.00000000 0.66666667
> Ti 0.50000000 0.00000000 0.66666667
> Ti 0.00000000 0.50000000 0.66666667
> Ti 0.50000000 0.50000000 0.66666667
> Ti 0.25000000 0.25000000 0.16666667
> Ti 0.75000000 0.25000000 0.16666667
> Ti 0.25000000 0.75000000 0.16666667
> Ti 0.75000000 0.75000000 0.16666667
> Ti 0.25000000 0.25000000 0.50000000
> Ti 0.75000000 0.25000000 0.50000000
> Ti 0.25000000 0.75000000 0.50000000
> Ti 0.75000000 0.75000000 0.50000000
> Ti 0.25000000 0.25000000 0.83333333
> Ti 0.75000000 0.25000000 0.83333333
> Ti 0.25000000 0.75000000 0.83333333
> Ti 0.75000000 0.75000000 0.83333333
> O 0.65265000 0.15265000 0.00000000
> O 0.15265000 0.65265000 0.00000000
> O 0.65265000 0.65265000 0.00000000
> O 0.15265000 0.15265000 0.33333333
> O 0.65265000 0.15265000 0.33333333
> O 0.15265000 0.65265000 0.33333333
> O 0.65265000 0.65265000 0.33333333
> O 0.15265000 0.15265000 0.66666667
> O 0.65265000 0.15265000 0.66666667
> O 0.15265000 0.65265000 0.66666667
> O 0.65265000 0.65265000 0.66666667
> O 0.34735000 0.34735000 0.00000000
> O 0.84735000 0.34735000 0.00000000
> O 0.34735000 0.84735000 0.00000000
> O 0.84735000 0.84735000 0.00000000
> O 0.34735000 0.34735000 0.33333333
> O 0.84735000 0.34735000 0.33333333
> O 0.34735000 0.84735000 0.33333333
> O 0.84735000 0.84735000 0.33333333
> O 0.34735000 0.34735000 0.66666667
> O 0.84735000 0.34735000 0.66666667
> O 0.34735000 0.84735000 0.66666667
> O 0.84735000 0.84735000 0.66666667
> O 0.40265000 0.09735000 0.16666667
> O 0.90265000 0.09735000 0.16666667
> O 0.40265000 0.59735000 0.16666667
> O 0.90265000 0.59735000 0.16666667
> O 0.40265000 0.09735000 0.50000000
> O 0.90265000 0.09735000 0.50000000
> O 0.40265000 0.59735000 0.50000000
> O 0.90265000 0.59735000 0.50000000
> O 0.40265000 0.09735000 0.83333333
> O 0.90265000 0.09735000 0.83333333
> O 0.40265000 0.59735000 0.83333333
> O 0.90265000 0.59735000 0.83333333
> O 0.09735000 0.40265000 0.16666667
> O 0.59735000 0.40265000 0.16666667
> O 0.09735000 0.90265000 0.16666667
> O 0.59735000 0.90265000 0.16666667
> O 0.09735000 0.40265000 0.50000000
> O 0.59735000 0.40265000 0.50000000
> O 0.09735000 0.90265000 0.50000000
> O 0.59735000 0.90265000 0.50000000
> O 0.09735000 0.40265000 0.83333333
> O 0.59735000 0.40265000 0.83333333
> O 0.09735000 0.90265000 0.83333333
> O 0.59735000 0.90265000 0.83333333
> K_POINTS automatic
> 4 4 4 0 0 0
> Have you any comment to accelerate the convergence?
> Thanks A lt
> Ali KAzempour,Isfahan University of Technology,Physics Dept
>
>
>
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Giuseppe Mattioli
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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