[Wien] Why dielectric function differs by 1 ?

[Rocquefelte]

Dear Liu,

It is related to the Kramers-Kro"nig relation.
Looking at these equations you will see that eps2 is an additive
quantity, while for eps1 you should consider (eps1 - 1) ...

Regards

Xavier



On 06/30/2011 07:47 PM, gbliu wrote:
> Dear all,
>
> I calculated the dielectric function of fcc Au, using a k-mesh
> 15x15x15. After the scf run, my step is as follow:
> 1. x opitc
> 2. Calculate intraband contribution, by setting swith 6 in
> fccAu.injoint file. Then I run "x joint".
> 3. Read the file fccAu.outputjoint, and get the plasma frequencies:
> 9.0075eV for both xx and zz.
> 4. Save a copy of fccAu.joint as *Intra.epsilon*, in which is the data
> of dielectric function from intraband contribution (Drude model).
> 5. Change the swith in fccAu.injoint from 6 to 4. "x joint" to compute
> epsilon.
> 6. "add intraband" set to 0 in fccAu.inkram, then "x kram", save the
> file fccAu.epsilon as *noIntra.epsilon*
> 7. "add intraband" set to 1 in fccAu.inkram, then "x kram" again, save
> the file fccAu.epsilon as *withIntra.epsilon*.
> 8. Then I compare the data in files Intra.epsilon, noIntra.epsilon and
> withIntra.epsilon, I found that:
> Im(withIntra.epsilon) = Im(noIntra.epsilon) + Im(Intra.epsilon)
> But Re(withIntra.epsilon) = Re(noIntra.epsilon) + Re(Intra.epsilon) - 1
>
> So I'm confused why not "Re(withIntra.epsilon) = Re(noIntra.epsilon) +
> Re(Intra.epsilon)" ?
> How does the difference "1" come from?
>
> Can anyone help me ?
>
> Thanks in advance.
>
> ---------fccAu.inop-------
> 99999 1 number of k-points, first k-point
> -5.0 3.0 9999 Emin, Emax for matrix elements, NBvalMAX
> 2 number of choices (columns in *outmat): 2: hex or tetrag. case
> 1 Re xx
> 3 Re zz
> OFF ON/OFF writes MME to unit 4
> --------------------------
>
> -------fccAu.injoint------
> 1 9999 9999 : LOWER,UPPER and (optional) UPPER-VAL BANDINDEX
> 0.0000 0.00100 1.0000 : EMIN DE EMAX FOR ENERGYGRID IN ryd
> eV : output units eV / ryd / cm-1
> *4 * *"first I use 6, then 4" * : SWITCH
> 2 : NUMBER OF COLUMNS
> 0.1 0.1 : BROADENING (FOR DRUDE MODEL - switch 6,7 - ONLY)
> --------------------------
>
> -------fccAu.inkram---------
> 0.1 Gamma: broadening of interband spectrum
> 0.0 energy shift (scissors operator)
> *1 "first I use 0, then 1" * add intraband contributions? yes/no: 1/0
> 9.0075 9.0075 plasma frequencies (from joint, opt 6)
> 0.10 0.10 Gammas for Drude terms
> ------------------------------
> -- 
> Best regards!
>
>                  Liu Guibin
>              Postdoctoral Fellow,
>              Department of Physics,
>              The University of Hong Kong
>              
>
>
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> Wien at zeus.theochem.tuwien.ac.at
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