[Pw_forum] Relaxation of AlN surface

[Vladlen Zhukov Windows]

 Hi!

   Are you shure that the atomic coordinates  are correct?  In fact,
estimated scf accuracy is too  big   from the very beginning.
Although  I am also novice in PW-calculations, I  relaxed  recently anatase 
very successfully,  so my impression is  that  PW is beautifull  is this 
respect.

----------------------------------------------------------------------
Vladlen P. Zhukov,  chief research associate,
Institute of Solid State Chemistry,
Russian  Academy of Sciences,
Ekaterinburg,
Russia


----- Original Message ----- 
From: "Somesh Kumar Bhattacharya" <somesh.kb at gmail.com>
To: <pw_forum at pwscf.org>
Sent: Tuesday, February 17, 2009 3:08 AM
Subject: [Pw_forum] Relaxation of AlN surface


> Dear All,
>
> I am a new to PWSCF.
>
> I am trying to relax a surface slab of AlN which has 32 atoms.
> However, the system is not achieving convergence.
>
> The input file is  :
>
> &control
>    calculation = 'relax'
>    restart_mode='from_scratch',
>    prefix='AlN',
>    nstep = 100,
>    tprnfor = .true.,
>    etot_conv_thr = 1.d-8,
>    pseudo_dir = '~/QE/espresso-4.0.3/pseudo/',
>    outdir='.'
> /
> &system
>    ibrav=  4, celldm(1) = 11.71623992919922,
>    celldm(3) = 4.513,nat=32, ntyp= 2,
>    ecutwfc =30.0, ecutrho = 400, nspin =1,
> /
> &electrons
>    electron_maxstep=150,
>    conv_thr = 1.D-6,
>    mixing_mode = 'local-TF',
>    mixing_beta = 0.2,
> /
> &ions
>     ion_dynamics='bfgs',
>     phase_space = 'full'
> /
> ATOMIC_SPECIES
> Al  26.98154  Al.pw91-n-van.UPF
> N   14.00674  N.pw91-van_ak.UPF
> ATOMIC_POSITIONS {angstrom}
> Al  1.549999937  4.474454315  14.919999921    1 1 1
> Al  1.549999937  4.474454315  9.919999843     0 0 0
> Al -0.000000015  7.159132936  14.919999921    1 1 1
> Al -0.000000015  7.159132936  9.919999843     0 0 0
> Al  4.649999842  4.474454315  14.919999921    1 1 1
> Al  4.649999842  4.474454315  9.919999843     0 0 0
> Al  3.099999890  7.159132936  14.919999921    1 1 1
> Al  3.099999890  7.159132936  9.919999843     0 0 0
> N   1.549999937  4.474454315  6.818997379     0 0 0
> N   1.549999937  4.474454315 11.778997301     0 0 0
> N  -0.000000015  7.159132936  6.818997379     0 0 0
> N  -0.000000015  7.159132936 11.778997301     0 0 0
> N   4.649999842  4.474454315  6.818997379     0 0 0
> N   4.649999842  4.474454315 11.778997301     0 0 0
> N   3.099999890  7.159132936  6.818997379     0 0 0
> N   3.099999890  7.159132936 11.778997301     0 0 0
> Al  3.099991178  3.579566454  7.439985857     0 0 0
> Al  3.099991178  3.579566454 12.399985779     0 0 0
> Al  1.549991226  6.264245075  7.439985857     0 0 0
> Al  1.549991226  6.264245075 12.399985779     0 0 0
> Al  6.199991083  3.579566454  7.439985857     0 0 0
> Al  6.199991083  3.579566454 12.399985779     0 0 0
> Al  4.649991131  6.264245075  7.439985857     0 0 0
> Al  4.649991131  6.264245075 12.399985779     0 0 0
> N   3.099991178  3.579566454  9.298983315     0 0 0
> N   3.099991178  3.579566454 14.258983237     1 1 1
> N   1.549991226  6.264245075  9.298983315     0 0 0
> N   1.549991226  6.264245075 14.258983237     1 1 1
> N   6.199991083  3.579566454  9.298983315     0 0 0
> N   6.199991083  3.579566454 14.258983237     1 1 1
> N   4.649991131  6.264245075  9.298983315     0 0 0
> N   4.649991131  6.264245075 14.258983237     1 1 1
> K_POINTS {GAMMA}
>
>
> I am allowing only the top two layers to relax.
>
> Using --- grep scf < *.out   ...... the output is the following :
>
>     estimated scf accuracy    <    21.54311123 Ry
>     estimated scf accuracy    <    16.91216138 Ry
>     estimated scf accuracy    <     6.80358058 Ry
>     estimated scf accuracy    <    10.02440462 Ry
>     estimated scf accuracy    <     5.42211905 Ry
>     estimated scf accuracy    <     3.98570225 Ry
>     estimated scf accuracy    <     3.63368556 Ry
>     estimated scf accuracy    <     2.80935163 Ry
>     estimated scf accuracy    <     2.18832175 Ry
>     estimated scf accuracy    <     1.88438498 Ry
>     estimated scf accuracy    <     1.34984265 Ry
>     estimated scf accuracy    <     1.15892961 Ry
>     estimated scf accuracy    <     1.08983405 Ry
>     estimated scf accuracy    <    11.86322500 Ry
>     estimated scf accuracy    <     9.08655092 Ry
>     estimated scf accuracy    <    10.92075279 Ry
>     estimated scf accuracy    <    11.43007849 Ry
>      .................
>
> The system never attain convergence.
>
> Can anyone kindly suggest the possible source of error on my part.
>
> Regards,
> Somesh
> ...............................
> Somesh Kr. Bhattacharya
> Post Doctoral Fellow
> Room No. 263,
> Leonardo Building,
> The Abdus Salam International Centre for Theoretical Physics
> Strada Costiera, 11
> I-34014 Trieste
> Italy
> Phone: +39-040-2240399
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