[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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