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
