[Pw_forum] ev.x gives wrong results

[anyy zsj]

This data set is actual calculated because I use a large supercell:
10.1      -48.570860572794118
10.3      -49.368013045588235
10.5      -49.714550792647060
10.7      -49.667482497058820
10.9      -49.305953287500003
But the fitting results are not compatible.

2015-07-28 12:01 GMT-04:00 Paolo Giannozzi <p.giannozzi at gmail.com>:

> Please show me a set of data *produced by actual calculations* that ev.x
> doesn't fit properly
>
> paolo
>
> On Tue, Jul 28, 2015 at 5:51 PM, anyy zsj <zsjanyy at gmail.com> wrote:
>
>> Thank you very much!
>> Sure it is angstrom. My concern is that with the same data, ev.x and the
>> manual fitting give different results as shown above. So I believe
>> something is there.
>> The discrepancy is gone if I use a small lattice parameter. For example,
>> if I scale the data by 1/3, both of them give the same results. So what's
>> going on?
>>
>> 2015-07-28 11:44 GMT-04:00 Paolo Giannozzi <p.giannozzi at gmail.com>:
>>
>>> 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
>>>
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
>>> http://pwscf.org/mailman/listinfo/pw_forum
>>>
>>
>>
>> _______________________________________________
>> 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
>
> _______________________________________________
> 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/20150728/7ba743f5/attachment.html>