[Pw_forum] Relaxation of AlN surface
Somesh Kumar Bhattacharya
somesh.kb at gmail.com
Tue Feb 17 13:44:20 CET 2009
Dear Prof. Eyvaz,
Thanks a lot for your suggestion. I have introduced the key words
occupations etc. and the system is achieving convergence.
To comment on some suggestions on a denser grid, the system is
attaining convergence for GAMMA point only. Though I would like to
test the k-point sampling.
Moreover, Giuseppe Mattioli's suggestion seems more plausible to me as
it is known that the intragap states arising from the dangling bonds
will affect the energy gap. However, for III-V and II-VI
semiconductors the passivation by ordinary hydrogen is not enough as
explained by Chelikowsky et. al. I have worked earlier on CdTe and
othe II-VI semiconductor clusters and have found the same. In
accordance with the paper and from my past experience, the best result
is obtained by the use of fictitious hydrogen atom (H*) where Z for H*
is different than 1. A usual choice is H* (Z=1.5) for cation and
H*(Z=0.5) for anion in case of II-VI materials and H* (Z=1.25) and H*
(Z=0.75) for cations and anions respectively for III-V materials.
Regards,
Somesh
On Tue, Feb 17, 2009 at 12:03 AM, Eyvaz Isaev <eyvaz_isaev at yahoo.com> wrote:
> 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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>
>
>
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--
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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