[Pw_forum] Why dielectric function of only interband contribution has the features of intraband?

[gbliu]

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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