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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