[Pw_forum] ev.x problem on bulk modulus

[stefano de gironcoli]

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
>
>
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