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<div class="moz-cite-prefix">Dear Eduardo,<br>
I don't know whether the code can perform what you want.<br>
I think that with some coding one can instruct the code to
compute only the irreducible representations (all of them)
corresponding to a given symmetry (for a low symmetry system not
much to gain from this, I'm afraid).<br>
Alternatively one can only move a few atoms (in all directions)
and if the mode that is searched is localized on those atoms a
reasonable approximation for its frequency can be obtained. This
might be appropriate to study vibrational modes of a light
adsorbate on a heavy substrate, and maybe in some other particular
situations.<br>
I don't know how last_irr works but I think it's more a way to
break a long calculation in many smaller chunks rather than a way
to perform partial calculations. The code has no way to know which
pattern you would be interested in. <br>
<br>
stefano<br>
<br>
On 24/12/2015 12:54, Eduardo Menendez wrote:<br>
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Hi everybody,<br>
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Let me insist with a question I posted two days ago.<br>
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I interpret from the manual that one can compute a few phonon
irreducible representations. If this means that one can
compute a few phonon frequencies for a big system that could
be useful to do short convergence tests. I guess these
frequencies are true for a high symmetry system, but for a low
symmetry system I do not know (should I ) how the irreducible
representations can be determined before diagonalizing the
full dynamical matrix. I have mad a test using last_irr = 10 ,
and then last_irr = 14, and I get different frequencies. Maybe
I do something wrong, or maybe I just do not understand the
goal of "last_irr" keyword. I appreciate that someone kindly
clarifies this issue. <br>
<br>
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<div>Best regards<br>
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<div>Eduardo<br>
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Date: Tue, 22 Dec 2015 14:48:45 -0300<br>
Subject: [Pw_forum] a few frequencies in PHONON
calculation<br>
<div>Hi, <br>
I have one doubt about the PHONON code. Is it
possible to compute just a few phonon
frequencies using the PHONON keywords last_irr,
ldiag ? For example, using <br>
<br>
last_irr = 10,<br>
ldiag=.true.,,<br>
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may one find the frequencies of just the first
irreducible representations ?<br>
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Thank you, <br>
<br>
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<div>Eduardo Menendez Proupin<br>
Departamento de Fisica, Facultad de
Ciencias, Universidad de Chile <br>
URL: <a moz-do-not-send="true"
href="http://www.gnm.cl/emenendez"
target="_blank">http://www.gnm.cl/emenendez</a></div>
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