[Pw_forum] Negative charge

Latévi Max LAWSON DAKU Max.Lawson at unige.ch
Thu Nov 15 11:13:34 CET 2012



On 10. 11. 12 08:56, Paolo Giannozzi wrote:
> Usually negative charges tend to disappear, not to increase,
> at large cutoff, but it is hard to say more.


Dear Paolo,

Thanks a lot for reply.

I am still trying to figure out the what is at the origin of this
problem...

I may be missing something in the generated PSPs (Co and Li).
I have attached to this mail the summaries of simple tests made
for validating them, as well as the Li PSP, which actually is a
NC PSP, not an US PSP as I previously wrote. The Co PSP is too
large to be sent to the list; this an USSP with the semicore 3s
and 3p states in the valence.  The results of the tests seem
to be good and the results obtained for the studied crystals
and molecular systems look fine also.

If someone is interested in trying/using these PSPs, they are
avalaibe as a gzipped tar file (PSP.tar.gz) at the following
address

http://dl.free.fr/ft0lYSNFT

Please do not hesitate to report if they do not behave
correctly or if they do.

Thanks for your time and interest,

All the best,
Max

>
> P.
>
> On Nov 8, 2012, at 15:37 , Latévi Max LAWSON DAKU wrote:
>
>> Dear QE users and developers,
>>
>>
>> I am working on a large system, which I would like to characterize
>> in two spin states. The unit cell is made of 324 atoms and there are
>> 1220 electrons. The system is made of transition metal complexes
>> in a polymeric framework; and I am using the PBE GGA and USSPs
>> with nonlinear core corrections, a few of them which I have generated
>> and tested as much as possible.
>>
>> To proceed, I have taken in the USPPs the suggested largest cutoffs,
>> which I have raised to WFNc=70Ry and RHOc=750Ry, for the kinetic
>> energy and charge density, respectively.
>> I ran optimization calculations (vc-relax)  with the total
>> magnetization
>> fixed to the desired values and the Gamma point only. The results
>> obtained for the structures in both spin states seem fine and
>> consistent
>> with available experimental data for similar and isostructural
>> systems.
>> To be sure about the choice made for the k-point sampling, I have
>> restarted the optimizations using a shifted 4x4x4 MP grid (actually
>> only 4 k-points): this did not change the results; this seems fine.
>> So I
>> felt quite confident.
>>
>> As a further test, and before moving to more demanding phonon
>> calculations, I increased the WFNc to 80Ry and RHOc to 950 Ry:
>> the cell parameters slightly increases by less than 1%, and the energy
>> difference between the two phases changes by less than
>> 2% (total energies - quite large values - vary by less than 0.01%).
>> However, for these cutoff values, a negative charge (rho_dwn)
>> appears in one case, with a final value of the order of 1e-4:
>>
>>        Total force =     0.006379     Total SCF correction =
>> 0.000024
>>
>>        entering subroutine stress ...
>>
>>        negative rho (up, down):  0.000E+00 0.302E-03
>>
>> which, if I correctly understand the FAQ entry 6.12, is not harmful
>> at all.
>> I am however worried by the fact that this charge was not produced
>> in the calculations with the lower cutoff values. Did one of you
>> already
>> observe this? Should this be taken as a symptom of something wrong
>> in the calculation setups (USPPs, or WFNc and RHOc values)?
>>
>> Thanks for your time, answers and comments.
>>
>> Best regards,
>> Max
>>
>>
>> -- 
>> Latevi Max LAWSON DAKU
>> Universite de Geneve - Sciences II
>> Quai Ernest-Ansermet 30                            Tel: (41) 22/379
>> 6548
>> CH-1211 Geneve 4                                   Fax: (41) 22/379
>> 6103
>>
>>
>>
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://pwscf.org/mailman/listinfo/pw_forum
> ---
> Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
>
>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>

-- 
Latevi Max LAWSON DAKU
Universite de Geneve - Sciences II
Quai Ernest-Ansermet 30                            Tel: (41) 22/379 6548
CH-1211 Geneve 4                                   Fax: (41) 22/379 6103



-------------- next part --------------
/ ----
| BCC Co
| --
|
|-+ Murnaghan equation of state
|-+ Calculation details, use: ecutrho = 800 Ry; and a 8x8x8 MP grid
|
\ ----


  | 1) Equilibrium lattice parameter
  \ --

  ------------------------
  ecut (Ry)   a (Ang)
  ------------------------
  60          2.861
  70          2.859
  80          2.858
  ------------------------
  Exp.) 2.82 Ang; grown on a GaAs (110) substrate 
  	[Phys. Rev. Lett 62, 2480 (1985)].



  | 2) Bulk modulus 
  \ --

  -------------------------------
  ecut (Ry)   B0 (GPa)
  -------------------------------
  60          155.9
  70          157.5
  80          156.5
  -------------------------------



/ ----
| FCC Co
| --
|
|-+ Murnaghan equation of state
|-+ Calculation details, use: ecutrho = 800 Ry; and a 8x8x8 MP grid
|
\ ----


  | 1) Equilibrium lattice parameter
  \ --

  ------------------------
  ecut (Ry)   a (Ang)
  ------------------------
  60          3.578
  70          3.576
  80          3.575
  ------------------------
  Exp.) 3.545 Ang [X-ray powder JCPDS diffraction files 15.806].



  | 2) Bulk modulus 
  \ --

  -------------------------------
  ecut (Ry)   B0 (GPa)
  -------------------------------
  60          199.2
  70          197.8
  80          198.4
   -------------------------------
  Exp.) 199 GPa [Phys. Rev. B 54, 5 (1996)] 




-------------- next part --------------
/ ----
| BCC Li (no contribution from zero-point motion)
| --
|
|-+ Murnaghan equation of state
|-+ Calculation details, use: a 8x8x8 MP grid
|
\ ----


  1) Equilibrium lattice parameter
     ----


  ------------------------
  ecut (Ry)   a (Ang)
  ------------------------
  20          3.370
  25          3.369
  30          3.371
  35          3.370
  40          3.373
  45          3.375
  50          3.372
  60          3.370
  70          3.369
  80          3.370
  90          3.368
  ------------------------
  Exp.) 3.480 Angstrom at 4 K [Phys. Rev. B 31, 5395 (1985)].



  2) Bulk modulus 
     --

  -------------------------------
  ecut (Ry)   Bulk modulus (kbar)
  -------------------------------
  20          130
  25          131
  30          130
  35          131
  40          129
  45          127
  50          129
  60          131
  70          131
  80          131
  90          132
  -------------------------------
  Exp.) 126.5 kbar at 4 K. See Tab. 3 in [Phys. Rev. B 31, 5395 (1985)].



/ ----
| FCC LiH (no contribution from zero-point motion)
| --
|
|-+ Murnaghan equation of state
|-+ Calculation details, use: a 8x8x8 MP grid
|
\ ----


  1) Equilibrium lattice parameter
     ----

  ------------------------
  ecut (Ry)   a (Ang)
  ------------------------
  60          4.001
  ------------------------
  Exp.) 4.061 Ang. in the T -> 0 K limit [Phys. Rev. B 39, 3351 (1989)].

  NB.) Result similar to the one obtained by Zhang et al. using the 
  PBE GGA and normconserving PSP [J. Phys.: Condens. Matter 19, 425218 (2007)]


  2) Bulk modulus 
     --

  -------------------------------
  ecut (Ry)   Bulk modulus (kbar)
  -------------------------------
  60          389
  -------------------------------
  Exp.) 342.4 kbar in the T -> 0 K limit [Phys. Rev. B 39, 3351 (1989)]. 



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