sir i am using quantum espresso 4.3 version i want to study the phase transition of yitrium nitride(yn) first by doing scf calculation at 0k i found a phase transition of B1 to B2 transition at 137 gpa for this i used a 14*14*14 kpoints mesh and convergence achived for scf is 10^-9 i used GGA psudo potentials of pbe type avalable in code of espresso website for y and n but when i did the calculation for phonon dispersion B2 stucter instablity (negative frequency ) in phonon spectrum continues upto 500 gpa why ? for this i used 4*4*4* mesh q points for dyanamical matrices i have incresed further but nothing results
On Sat, May 28, 2011 at 9:36 PM, Stefano de Gironcoli <degironc at sissa.it>wrote: > Dear Bhabya Sahoo, > > your very stingy use of punctuation make quite difficult (at least for > me) to follow your request... > Take your time and try to make you clear providing more detailed > information about your system, what is your aim, what is the problem, what > are the tests you have done. > No one is going to spend more time in thinking about your problem than > you do in explaining it. > > Please provide your affiliation. > > stefano > - > Stefano de Gironcoli, SISSA and DEMOCRITOS > > > On 05/28/2011 05:46 PM, bhabya sahoo wrote: > > i am using quantum espresso static calculation obeys thermdyanamic stability > transition from B1 to B2 transition at 138 gpa so ihave used 24 24 24 > kpoint grid for phonon in B2 phase is calculated 4 4 4 grid by linear > response calculation but why the instability (negative frequency in phonon ) > upto 450 gpa i have used pbe psudo potentials also the lattice constant is > exact for experimental data > can metastability have negative frequency so why this occures > optimisation is ok > other problem why free energy is not coming for unstable phase for qha code > in quantum espresso > replay immidiate if u have solution > On Sat, May 28, 2011 at 5:38 PM, bhabya sahoo <bdslipun at gmail.com> > <bdslipun at gmail.com> wrote: > > > sir > i used to calculate the phonon calculation on a 4*4*4 grid in cscl phase > but the unstability persists upto 500 gpa > but it is the thermodyanamic stability after 140 gpa kpoints 24*24*24 > what may be reseon i donot know > please help me > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.orghttp://www.democritos.it/mailman/listinfo/pw_forum > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110528/da419bf8/attachment.htm
