[Pw_forum] Pw_forum Digest, Vol 49, Issue 33

[Eduardo Ariel Menendez Proupin]

Hi Gui-Bin

To avoid intraband contribution it is not enough to use intrasmear=0, you
also need to set occupations='fixed' in the PW calculations, at least for
the nscf one. The following reads in the manual of epsilon.

\emph{intrasmear} is the broadening parameter for the intraband, i.e. metal
Drude like term (again in eV),
the intraband contribution is calculated only if a Gaussian broadening or
tetrahedron method it's been
applied in PW calculations.


On the other hand, it seems from the epsi plot,  that the Wien calculation
considers automatically a larger number of bands. You must set manually the
parameter nbnd in the  nscf calculations, and increase it until the
dielectric function is converged. Check specially the convergence of epsr.
nbnd determine the number of transitions (the peaks) observed in epsri. High
energy transitions contribute in shifting the low energy values of epsr, as
you can see looking at the Kramers-Kronig relations.

Best wishes
Eduardo


"
>
> Today's Topics:
>
>   1. Why dielectric function of only interband contribution has
>      the features of intraband? (gbliu)
>
>
> ---------- Mensaje reenviado ----------
> From: gbliu <goodluck_1982 at 163.com>
> To: PWSCF Forum <pw_forum at pwscf.org>
> Date: Wed, 13 Jul 2011 01:04:28 +0800
> Subject: [Pw_forum] Why dielectric function of only interband contribution
> has the features of intraband?
> **
> Dear PW users,
>
>     I calculated the dielectric function of (3,3) Carbon nanotube (CNT).
> However, the results for only interband contribution has the features of
> intraband contribution! Attached figures show the results of parallel
> polarization compared with wien2k (a FP-LAPW software). Using "intrasmear =
> 0", the direct result of epsi.dat should gives out only interband
> contributions, while epsr.dat is added by  "omega_p^2/omega^2" to get the
> interband contributions only.  And omega_p is obtained as *3.5679eV* by
> fitting the difference of data with intrasmear=0 and intrasmear=0.1 using
> Drude model  "\epsilon_{intra}=1- omega_p^2/(omega^2+i*omega*intrasmear)".
> How to understand this?
>
>     Another problem is, fitted omega_p = 3.5679eV. This is far from the
> result given by wien2k, 24.5eV!  Which one is more reasonable? And why?
>
>    Can anyone help me?  Thanks in advance!
>
> Best wishes,
>
> Liu Gui-Bin
> Dept. of Physics, The University of Hong Kong
>
> ---------------input file for epsilon.x----------
>  &inputpp
>    outdir='./work'
>    prefix='cnt33'
>    calculation='eps'
> /
> &energy_grid
>    smeartype='gauss'
>    intersmear=0.1d0
>    intrasmear=0d0
>    wmax=30d0
>    wmin=0d0
>    nw=2000
>    shift=0d0
> /
> ----------------------------------------------------------
>
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>
>


-- 


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

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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