[Pw_forum] ev.x gives wrong results

Wed Jul 29 17:03:49 CEST 2015

Which parameters do you obtain for V0 (equilibrium volume), K0 (bulk
modulus), dK0/dP?

Paolo

On Wed, Jul 29, 2015 at 4:13 PM, anyy zsj <zsjanyy at gmail.com> wrote:

> Thank you. But there is still a discrepancy for the following data set:
> 10.3      -54.420098694852939
> 10.4      -54.716135146323531
> 10.5      -54.894109787500000
> 10.7      -53.873787839705884
> modified ev.x gives 10.46368, while the fitting is 10.52255.
>
>
> On Wed, Jul 29, 2015 at 4:23 AM, Paolo Giannozzi <p.giannozzi at gmail.com>
> wrote:
>
>> Funny: one of the parameters of the fit is good for small unit cells, but
>> too small for larger cells. In line 162 of PW/tools/ev.f90, replace
>>       deltapar(1) = 0.1d0
>> with something larger:
>>       deltapar(1) = 1.0d0
>> should be sufficient. Thank you for noticing this
>>
>> Paolo
>>
>> On Tue, Jul 28, 2015 at 6:06 PM, anyy zsj <zsjanyy at gmail.com> wrote:
>>
>>> 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.
>>>>>>>
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>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
>>>>>> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>>>>>> Phone +39-0432-558216, fax +39-0432-558222
>>>>>>
>>>>>> _______________________________________________
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>>>>>> Pw_forum at pwscf.org
>>>>>> http://pwscf.org/mailman/listinfo/pw_forum
>>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> 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
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>>>>
>>>
>>>
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>>
>>
>>
>> --
>> 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
>>
>
>
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-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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