[Pw_forum] Regarding raman spectra

[Eduardo Ariel Menendez Proupin]

Hi,
save the data in a file, let's name it archive.dat

call gnuplot with the command of the same name. Inside the gnuplot
terminal,
plot "archive.dat"  using 2:5  with impulses
or
plot "archive.dat"  u 2:5  w i

that will produce a plot of vertical lines. If you want a continuous curve,
you need to write your own program. I know no utility in Quantum ESRESSO to
do that. Any user of Quantum ESPRESSO and similar non-commercial packages
needs to write, and enjoy doing it :-),  some small programs to analize the
output data.

Yoy have asked for a GGA pseudopotential, but take into account that the
PHONON  code calculates the Raman spectra only for LDA and norm conserving
pseudopotentials.

I guess that vdW interaction is important for soft modes, or at least to
have an apropriate strucuture with minimal energy, otherwise there are
imaginary frequencies. Graphene is a famous case where vdW is important.

best regards
Eduardo Menendez Proupin
Departamento de Química Fisica Aplicada
Facultad de Ciencias
Universidad Autónoma de Madrid
28049 Madrid, Spain
Phone: +34 91 497 6706



---------- Mensaje reenviado ----------
From: Kondaiah Samudrala <konda.physics at gmail.com>
To: pw_forum at pwscf.org
Cc:
Date: Mon, 23 Jan 2012 15:45:23 +0530
Subject: [Pw_forum] Regarding raman spectra

   Dear all,
   I get the result of cross section of Raman and IR. The results are:

#  mode   [cm-1]     [THz]      IR           Raman     depol
    1      0.00   -0.0001    0.0000         0.0000    0.7298
    2      0.00    0.0000    0.0000         0.0000    0.4596
    3      0.00    0.0000    0.0000         0.0000    0.3769
    4     72.48    2.1728    0.2093         0.0000    0.7221
    5    181.80    5.4503    0.0000      1725.7832    0.7500
    6    216.89    6.5023    0.0000      2083.4500    0.7500
    7    363.65   10.9021    0.0000     91729.5039    0.2795
    8    396.95   11.9001    0.0000    104976.3780    0.7500
    9    420.27   12.5992    0.0000         0.0000    0.6389
   10    425.05   12.7427    0.0000      1248.5419    0.7500
   11    451.38   13.5321    0.0000    329620.4654    0.3306
   12    460.15   13.7949    0.1942         0.0000    0.3225


   The result of raman data are very well compared with the experimental
result. But I am not able to plot Raman spectrum with this o/p using
XMGRACE.

   Please give me suggetion for plot raman spectra. Here with i attached
direct plot of my trail with xmgrace (2 and 5th colums) .

   What is the meaning of cross section in this calculation?

   Please provide norm conserving pseudopotential for phosphorus using GGA
(PBE or PW91) XC-functional ( Using LDA-CAPZ is already in website).

   Finally, for structural properties semiemperical correction of Vdw
interactions plays very importent role. But, Is there any  influence of
semiemperical  correction  to Vdw interaction on vibrational properties????
.

  I appreciate to all your instructions.

  with regards
  S.Appalakondaiah
  Research Schloar
  University of hyderabad
  Hyderabad
  India

-- 




On leave from: Departamento de Fisica, Facultad de Ciencias, Universidad de
Chile URL: http://fisica.ciencias.uchile.cl/~emenendez

"*Padece, espera y trabaja para gentes que nunca conocerá y que a su vez
padecerán, esperarán y trabajarán para otros, que tampoco serán felices,
pues el hombre ansía siempre una felicidad situada más allá de la porción
que le es otorgada. Pero la grandeza del hombre está precisamente en querer
mejorar lo que es. En imponerse Tareas. En el Reino de los Cielos no hay
grandeza que conquistar, puesto que allá todo es jerarquía establecida,
incógnita despejada, existir sin término, imposibilidad de sacrificio,
reposo y deleite. Por ello, agobiado de penas y de Tareas, hermoso dentro
de su miseria, capaz de amar en medio de las plagas, el hombre puede hallar
su grandeza, su máxima medida en el Reino de este Mundo*".
Alejo Carpentier, El reino de este mundo, (1949).

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