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 <[email protected]>: > 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 <[email protected]> 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 <[email protected]>: >> >>> On Tue, Jul 28, 2015 at 5:26 PM, anyy zsj <[email protected]> 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 >>>> [email protected] >>>> 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 >>> [email protected] >>> http://pwscf.org/mailman/listinfo/pw_forum >>> >> >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> 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 > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum >
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