[Pw_forum] ev.x gives wrong results

[Paolo Giannozzi]

On Tue, Jul 28, 2015 at 5:26 PM, anyy zsj <zsjanyy at gmail.com> wrote:


>    1.4989396432   -6.0466776328
>    1.5430233198   -6.0795705718
>    1.5879629631   -6.0993455319
>    1.6804430727   -5.9859764266
> The first column is volume and the second energy with Ry. After ev.x I
> input Ang, noncubic, 4, it gives me a results of 0.40 for minimal volume.
> It is certainly wrong.
>

of course it is: ev.x assumes that the input data corresponds to a physical
EOS. Your data isn't physical: the volume is way too small

>
> Another example for the below data:
> 10.1      -48.570860572794118
> 10.3      -49.368013045588235
> 10.5      -49.714550792647060
> 10.7      -49.667482497058820
> 10.9      -49.305953287500003
> The first column is lattice constant with angstrom and the second energy
> with Ry.
>
After ev.x I input Ang, sc, 4, it gives me 10.50369, while I get a
> different value 10.57517 by fitting to the formula in PRB 28,5480 (1983)
> of Murnaghan's equation.:
> http://gilgamesh.cheme.cmu.edu/doc/software/jacapo/appendices/appendix-eos.html
>


sure that the first column is in angstrom and not a.u.? This is what I get
assuming it is in a.u.:

 # equation of state: murnaghan.        chisq = 0.5402D-05
# a0 = 10.5740 a.u., k0 =13776 kbar, dk0 =  4.17 d2k0 =  0.000 emin =
-49.73649
# a0 =  5.59554 Ang, k0 =1377.7 GPa,  V0 = ******* (a.u.)^3,  V0 =175.197
A^3

note the small value of the |chi|^2 (chisq) of the fit

Paolo

I have tested many groups of data but the discrepancy is there for those
> large lattice parameters. Does ev.x use another equation or something else
> I have missing? Thank you very much.
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>


-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150728/f3925b58/attachment.html>