Dear Lorenzo,<br>Thanks for your reply.<br>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.<br>
<br>Is the non-diagonalised matrix is printed elsewhere?<br><br>regards<br><br><div class="gmail_quote">On Tue, Dec 1, 2009 at 1:14 PM, Lorenzo Paulatto <span dir="ltr"><<a href="mailto:paulatto@sissa.it">paulatto@sissa.it</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im">Quoting Bipul Rakshit <<a href="mailto:bipulrr@gmail.com">bipulrr@gmail.com</a>>:<br>
> The calculation is finished with the following lines<br>
><br>
> * End of self-consistent calculation<br>
> Convergence has been achieved<br>
> Stopping because representation 4 is not done*<br>
><br>
> But in LaMnO3.dyn2 or in the output file, no where it is giving me<br>
> frequencies.<br>
> So can anybody tell me how to get the frequencies of only first three modes,<br>
> rather than calculating all 60 modes?<br>
> What I have to modify in my input file?<br>
<br>
<br>
</div>Dear Bipul,<br>
it is not possible to compute the frequency of a single mode; each<br>
mode gives you a line of the dynamical matrix; the matrix is then<br>
diagonalized and each eigenvalue correspond to a frequency. If you<br>
only compute the modes corresponding to the first atom you can still<br>
compute the frequency belonging to the first atom ***but*** under the<br>
approximation that all the other atoms have infinite masses; i.e. a<br>
mass much larger than the first one.<br>
<br>
This clearly is **not** your case, as Lanthanium is 2.5 times heavier<br>
than Manganese and almost 9 times heavier than Oxygen. Nevertheless,<br>
I'll give you the procedure as reference, but don't be tempted to use<br>
it in your case, unless you really know what you're doing.<br>
<br>
After computing the first 3 mode you have the first 3 lines of the<br>
dynamical matrix. You can take the 3x3 minor of the the matrix (first<br>
3 rows and first 3 columns) and diagonalize it by hand (using octave,<br>
matlab or whatever software you prefer). The eigenvalues are the<br>
frequencies you are looking for in the said approximation. They are in<br>
Rydberg atomic units, you can get cm-1 multiplying by 109737.<br>
<br>
best regards.<br>
<br>
<br>
--<br>
Lorenzo Paulatto (MS)<br>
SISSA & Democritos<br>
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</blockquote></div><br><br clear="all"><br>-- <br>Dr. Bipul Rakshit<br>Research Associate,<br>S N Bose Centre for Basic Sciences,<br>Salt Lake,<br>Kolkata 700 098<br>India<br>