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

[Stefano Baroni]

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
> >>
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> >
> >---
> >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
> >
> >
> >
> >
> >
> >
>
>
>
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---
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






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