[Pw_forum] ev.x problem on bulk modulus

[Xiao]

Dear Stefano,
The fcc unit cell isn’t it 4 atoms per cell? Actually I have tried to set the braves lattice to sc with same input. And it shows me a more better result.
But for Pd, it can be easily find that it’s fcc structure.
Maybe I misunderstand something. Please correct me.
Thank you again!

xiao 

> On 20 Apr 2015, at 23:20, stefano de gironcoli <degironc at sissa.it> wrote:
> 
> Dear Xiao,
>    there is a factor of 4 in the volume per unit-cell between sc and fcc. just geometry.
>    I don't really know what you have calculated but the energy one should feed to ev.x is the energy per unit cell as you have used in the pw.x calculation. So if in the ev.x input you say that your cell is fcc then you should use the energy computed with the fcc unit cell (1 Pd atom per cell). If your energy was computed in the sc unit cell (that has 4 Pd atoms in the unit cell) then you should specify sc in the ev.x input. just be consistent. 
> 
> stefano
> 
> On 20/04/2015 22:31, Xiao wrote:
>> Dear Stefano,
>> Yes! I used a fcc unit cell. It should have a factor 4. Thank you!!!
>> But can you explain why there is a 4 times relation between fcc and sc?
>> I don’t really understand why it happens.
>> 
>> best
>> xiao
>>> On 20 Apr 2015, at 22:09, stefano de gironcoli <degironc at sissa.it <mailto:degironc at sissa.it>> wrote:
>>> 
>>> Dear Xiao,
>>>   are you using the fcc unit cell (1 atom/cell) or the SC one (4 atoms/cell) ?
>>>   that would make a factor of 4 in your bulk modulus.
>>> stefano
>>> 
>>> On 20/04/2015 21:34, 杨潇 wrote:
>>>> Dear All,
>>>> 
>>>> Sorry for my mistake of previous email! It should be Ry I used.
>>>> 
>>>> As I am using the ev.x to fitting EOS on Pd. I got the wrong bulk modulus. Here is my procedure. Please  help me check what’s wrong with my fitting? 
>>>> input data in Å and Ry.
>>>> 
>>>> 3.7351  -1.455513098
>>>> 3.8129  -1.5041846
>>>> 3.8907  -1.527184909
>>>> 3.9685  -1.530334715
>>>> 4.0463  -1.51819883
>>>> 4.1241  -1.4945274
>>>> 
>>>>      Lattice parameter or Volume are in (au, Ang) > Ang
>>>>      Assuming Angstrom
>>>>      Enter type of bravais lattice (fcc, bcc, sc, noncubic) > fcc
>>>>      Enter type of equation of state :
>>>>      1=birch1, 2=birch2, 3=keane, 4=murnaghan > 2
>>>> then I get the output file like below:
>>>> 
>>>> # equation of state: birch 3rd order.  chisq = 0.3034D-10
>>>> # a0 =  7.4514 a.u., k0 = 6726 kbar, dk0 =  5.51 d2k0 = -0.001 emin =   -1.53118
>>>> # a0 =  3.94309 Ang, k0 = 672.7 GPa,  V0 = 103.430 (a.u.)^3,  V0 = 15.327 A^3 
>>>> 
>>>> #########################################################################
>>>> # Lat.Par       E_calc        E_fit       E_diff    Pressure      Enthalpy
>>>> # Ang             Ry           Ry            Ry        GPa           Ry
>>>> #########################################################################
>>>>   3.73510      -1.45551      -1.45551     0.00000     170.75       -0.43510
>>>>   3.81290      -1.50418      -1.50418    -0.00000      89.34       -0.93621
>>>>   3.89070      -1.52718      -1.52719     0.00001      30.14       -1.32358
>>>>   3.96850      -1.53033      -1.53033    -0.00001     -12.29       -1.61843
>>>>   4.04630      -1.51820      -1.51820     0.00001     -42.10       -1.83804
>>>>   4.12410      -1.49453      -1.49453    -0.00000     -62.42       -1.99662
>>>> ~                                                                           
>>>> The k0 here is 672.7GPa, it should be 180GPa more or less. And I fitted same data with another software, it gives me 167GPa.
>>>> 
>>>> So Please Help Me What’s Wrong With My Fitting?
>>>> 
>>>> Thank you!!!
>>>> 
>>>> best
>>>> xiao
>>>> 
>>>> 
>>>> _______________________________________________
>>>> Pw_forum mailing list
>>>> Pw_forum at pwscf.org <mailto:Pw_forum at pwscf.org>
>>>> http://pwscf.org/mailman/listinfo/pw_forum <http://pwscf.org/mailman/listinfo/pw_forum>
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org <mailto:Pw_forum at pwscf.org>
>>> http://pwscf.org/mailman/listinfo/pw_forum <http://pwscf.org/mailman/listinfo/pw_forum>
>> 
>> 
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org <mailto:Pw_forum at pwscf.org>
>> http://pwscf.org/mailman/listinfo/pw_forum <http://pwscf.org/mailman/listinfo/pw_forum>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150421/2bbc43c1/attachment.html>