Dear Lorenzo, Thanks for your reply. One more thing I want to ask is that, after computing first 3 modes using nrapp, where do i find the dynamical matrix? Because in LaMnO3.dyn2 file is empty, after the calculation is finished.
Is the non-diagonalised matrix is printed elsewhere? regards On Tue, Dec 1, 2009 at 1:14 PM, Lorenzo Paulatto <paulatto at sissa.it> wrote: > Quoting Bipul Rakshit <bipulrr at gmail.com>: > > The calculation is finished with the following lines > > > > * End of self-consistent calculation > > Convergence has been achieved > > Stopping because representation 4 is not done* > > > > But in LaMnO3.dyn2 or in the output file, no where it is giving me > > frequencies. > > So can anybody tell me how to get the frequencies of only first three > modes, > > rather than calculating all 60 modes? > > What I have to modify in my input file? > > > Dear Bipul, > it is not possible to compute the frequency of a single mode; each > mode gives you a line of the dynamical matrix; the matrix is then > diagonalized and each eigenvalue correspond to a frequency. If you > only compute the modes corresponding to the first atom you can still > compute the frequency belonging to the first atom ***but*** under the > approximation that all the other atoms have infinite masses; i.e. a > mass much larger than the first one. > > This clearly is **not** your case, as Lanthanium is 2.5 times heavier > than Manganese and almost 9 times heavier than Oxygen. Nevertheless, > I'll give you the procedure as reference, but don't be tempted to use > it in your case, unless you really know what you're doing. > > After computing the first 3 mode you have the first 3 lines of the > dynamical matrix. You can take the 3x3 minor of the the matrix (first > 3 rows and first 3 columns) and diagonalize it by hand (using octave, > matlab or whatever software you prefer). The eigenvalues are the > frequencies you are looking for in the said approximation. They are in > Rydberg atomic units, you can get cm-1 multiplying by 109737. > > best regards. > > > -- > Lorenzo Paulatto (MS) > SISSA & Democritos > > > > > > > > > > ---------------------------------------------------------------- > SISSA Webmail https://webmail.sissa.it/ > Powered by Horde http://www.horde.org/ > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- Dr. Bipul Rakshit Research Associate, S N Bose Centre for Basic Sciences, Salt Lake, Kolkata 700 098 India -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20091201/b2283e9d/attachment.htm
