[Pw_forum] Relaxation of AlN surface

[Eyvaz Isaev]

Dear Somesh,

Looking at your structure by means of XCrysDen have shown you have a slab with vacuum on both sides. Most likely, your system is metallized due to surface states and you should consider it as metallic turning on "occupations" and related keywords. Please have a look at /DOC/INPUT_PW.

Hope this helps.

Bests,
Eyvaz.

-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com


--- On Tue, 2/17/09, Somesh Kumar Bhattacharya <somesh.kb at gmail.com> wrote:

> From: Somesh Kumar Bhattacharya <somesh.kb at gmail.com>
> Subject: [Pw_forum] Relaxation of AlN surface
> To: pw_forum at pwscf.org
> Date: Tuesday, February 17, 2009, 1:08 AM
> 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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