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 >
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