On Wed, Oct 31, 2012 at 6:14 PM, david furman <sirok4 at gmail.com> wrote:
> Hi all, > > I sucsessfully calculated equation of state for CaF2 by varying celldm(1) > in a loop. > then fitting the EV data to murnaghan EOS to get a parabola like plot. > > Now I try to calculate EV data for CaTiO3 (Pnma space group) by the same > method. > But, no matter how large the celldm(1) is (keeping the b/a and c/a fixed), > the energy still goes down instead of going up, with no parabola like > behavior. > I assume this is wrong, because when distances between atoms are large > (expansion of unit cell), this state should be higher > in energy than the equilibrium volume state, just like when compressing > the unitcell the energy goes up because of repulsion. > > Can anybody tell me why is this happening ? Could it be a bug ? > Before reaching any excellent conclusion can you provide your input file for system. > > P.S > The pseudopotentials i'm using are all PBE > whether it is NCPP or USPP? > and verified with other systems so they should be OK. > There are 20 atoms in the primitive unit cell. I'm using a 8x8x8 k-point > grid > Have you check your k-point convergence with the total energy? > with 180 Ry cutoff for wavefunction. > It is very large for USPP and check it for both pseudopotential convergence . > I've opened the structure in Xcrysden and it looks OK, no weird things. > > > > -- > > *David Furman* > * > * > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- Thanks and Regards Bramha Prasad Pandey Indian School of Mines(ISM) Dhanbad, INDIA. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121031/e809d02e/attachment.html
