[Pw_forum] ev.x gives wrong results

Wed Jul 29 17:52:05 CEST 2015

ev.x enforces a lower (1) and an upper (15) bound on the derivative of the
bulk modulus. I don't remember where they come from, but I am quite sure
that dK0/dP ranges between 4 and 6 and never becomes negative or very large

Paolo

On Wed, Jul 29, 2015 at 5:24 PM, anyy zsj <zsjanyy at gmail.com> wrote:

> similar but not the same. The fitting parameter for V0 is 1165.10028469
> A^3, Bulk modulus is 808.33GPa and its derivative is -31.54200148. The
> derivative is very different.
>
> On Wed, Jul 29, 2015 at 11:03 AM, Paolo Giannozzi <p.giannozzi at gmail.com>
> wrote:
>
>> 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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>>>>>>>>> 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
>>>>>>>>
>>>>>>>> _______________________________________________
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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
>>>>>> 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
>>>> 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
>> 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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