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/
