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 <[email protected]
<mailto:[email protected]>> 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 andRy.
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
[email protected]
http://pwscf.org/mailman/listinfo/pw_forum
_______________________________________________
Pw_forum mailing list
[email protected] <mailto:[email protected]>
http://pwscf.org/mailman/listinfo/pw_forum
_______________________________________________
Pw_forum mailing list
[email protected]
http://pwscf.org/mailman/listinfo/pw_forum
_______________________________________________
Pw_forum mailing list
[email protected]
http://pwscf.org/mailman/listinfo/pw_forum
