[Pw_forum] negative value of polarization and Z* for Pb in Tetragonal PbTiO3 and discrepancy

Wed Jul 9 22:03:24 CEST 2008

Hi,

In addition to Stefano's comment I would recommend check your input file by means of XCrysDen  in order to see whether you have correct structure. At this time it seems to be incorrect. 

Besides, use lower convergence threshold, conv_thr=1d-8, 1e-6 looks quite high.

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 Wed, 7/9/08, Stefano Baroni <baroni at sissa.it> wrote:
From: Stefano Baroni <baroni at sissa.it>
Subject: Re: [Pw_forum] negative value of polarization and Z* for Pb in Tetragonal PbTiO3 and discrepancy
To: "sathya subramanyan" <sathya_sheela1985001 at rediffmail.com>, "PWSCF Forum" <pw_forum at pwscf.org>
Date: Wednesday, July 9, 2008, 3:53 AM

what I was suggesting is that YOU perform a convergence test and ley us know ...SB
On Jul 8, 2008, at 6:44 PM, sathya subramanyan wrote:
   Dear Sir,
             I have checked the k -point sampling for the tetragonal PbTiO3 and I hope that the k-point sampling is alright. I am giving below the input file for your reference. Pl, let me know if anything is wrong in the input.:

    THE I/P FILE FOR TETRAGONAL PbTiO3

 &CONTROL
      calculation  = 'nscf'
      pseudo_dir    = '/home/nbaski/espresso-4.0/pseudo/'
      outdir        = '/home/nbaski/tmp/'
     lberry        = .true.
      gdir          = 3
      nppstr        = 7
 /
 &SYSTEM
      ibrav        = 6
       celldm(1)    = 7.3415
      celldm(3)    = 1.0653
      nat          = 5
      ntyp          = 3
      nbnd          = 22
      ecutwfc      = 30.0
      occupations  = 'fixed'
      degauss      = 0.00
 /
 &ELECTRONS
    conv_thr      = 1e-5
      mixing_beta  = 0.3
 /
 ATOMIC_SPECIES
    Pb  207.2      Pb.vdb.UPF
    Ti    47.867    Ti.vdb.UPF
    O    15.9994  O.vdb.UPF
 ATOMIC_POSITIONS
    Pb    0.00000    0.00000    0.01000
    Ti    0.50000    0.50000    0.53770
    O    0.50000    0.50000    0.11180
    O    0.00000    0.50000    0.61740
    O    0.50000    0.00000    0.61740
 K_POINTS {automatic}
    4 4 7  1 1 1

 Thank you in advance for any help
 SATHYA SHEELA.S
 Grad. Student
 Department of Physics
 National Institute of Technology
 Tiruchirapalli 

 On Fri, 27 Jun 2008 Stefano Baroni wrote :
 >the sum of the all the effective charges should be zero for any  structure, due dynamical charge neutrality (or acoustic sum rule, or  whatever you want to call the fact that a homogeneouse electric field  will not exert a net (and infinite!) force on a crystal. Vioation of  this charge neutrality/acoustic sum rule are often due to numerical  inaccuracy, often inaccurate k-point sampling. you may want to check  the convergence of your calculations with respect to the number of k  points and/or try to calculate the effective charges using linear- response theory. SB
 >
 >On Jun 27, 2008, at 11:51 AM, sathya subramanyan wrote:
 >
 >>
 >>Dear Developers,
 >>                 I am trying to calculate the Berry Phaze  Polarization and effective charge on Pb(with the displacement of . 01*ao) for PbTiO3(tetragonal) but am getting a negative value, using  quantum espresso ver 4.0.
 >>
 >>                 When I run the example 10 for cubic phase the  polarization and the Z* comes out to be alright. But, when I try for  tetragonal phase, I am getting negative ionic phase leading to  negative polarization for Pb.
 >>                 If I compare the out put file for both cubic and  tertragonal phase, to my surprise in the cubic phase the total ionic  phase comes out to be positive (actually, if you sum it is  negative), where as in the case of tetragonal phase the ionic phase  comes out to be negative (but, it is positive if you sum the same  way as for the cubic).
 >>                 I do not understand this differrent summing rule for  different phases. I am attaching both the input and out files for  cubic and tetragonal phases. I would appreciate any useful  suggestions to clear this point.
 >>I am very sorry for the long mail and data files.
 >>
 >>- 620015
 >>India
 >>
 >>_______________________________________________
 >>Pw_forum mailing list
 >>Pw_forum at pwscf.org
 >>http://www.democritos.it/mailman/listinfo/pw_forum
 >
 >---
 >Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  Trieste
 >http://www.sissa.it/~baroni / [+39] 040 3787 406 (tel) -528 (fax) /  stefanobaroni (skype)
 >
 >La morale est une logique de l'action comme la logique est une morale  de la pensée - Jean Piaget
 >
 >Please, if possible, don't  send me MS Word or PowerPoint attachments
 >Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html
 >
 >
 >
 >
 >
 >

 _______________________________________________
Pw_forum mailing list
Pw_forum at pwscf.org
http://www.democritos.it/mailman/listinfo/pw_forum

 ---Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Triestehttp://www.sissa.it/~baroni / [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)
La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget
Please, if possible, don't  send me MS Word or PowerPoint attachmentsWhy? See:  http://www.gnu.org/philosophy/no-word-attachments.html

_______________________________________________
Pw_forum mailing list
Pw_forum at pwscf.org
http://www.democritos.it/mailman/listinfo/pw_forum

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20080709/25151a04/attachment.html>