Calculating the Dielectric Function of metals - Units trouble

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Discussion Overview

The discussion revolves around the calculation of the dielectric function of metals, specifically using the Lorentz-Drude model as referenced in a paper by Rakic et al. Participants are addressing issues related to unit conversions and the proper interpretation of parameters in the context of MATLAB programming.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion regarding the units of the permittivity function, questioning whether ε(w) is unitless.
  • Another participant asserts that ε_r is indeed unitless and suggests that both ω and Γ have the same units as Ω_p, implying that the quotient should also be unitless.
  • A participant mentions using eV for ω and highlights a potential inconsistency in the definitions provided in the paper, particularly regarding the relationship between Ω_p and ω.
  • There is a suggestion that dividing by ħ may not be necessary, but this remains contested among participants.
  • One participant indicates that they are obtaining incorrect graphs and seeks clarification on the necessary unit conversions for the parameters involved.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct approach to unit conversions and the interpretation of parameters. There are competing views on whether to divide by ħ and how to properly align the units of ω and Ω_p.

Contextual Notes

Participants express uncertainty regarding the definitions and units used in the referenced paper, particularly in relation to the plasma frequency and its implications for the calculations being performed.

zellwwf
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Hello everyone here!

See i got my hands on this paper:
Optical properties of metallic films for vertical-cavity optoelectronic devices
by Rakic et al.

A simple google search of the title will give you access to the paper.
Now, i am writing the function in MATLAB to calculate the permittivity based on the Lorentz-Drude model mentioned in the paper.
The paper however doesn't help with the units. It's my fault i know.. i should know my units. But I've tried a lot of stuff and nothing seems to work.. i am getting weird graphs that don't look anything like the ones in the paper. Not even close. I rewrote the MATLAB function a number of times and i don't think it's that. i think its in the units.

Here is what i need help with:
I believe that ε(w) is unitless. Correct me here if i am wrong.
(i will be using silver as an example here)
Plasma Frequency of silver is 9.01 (see ref) eV.
\omega_p* \hbar = 9.01 eV
And if i am not wrong in formulas (1) (2) (3), he references [
itex]\omega_p[/itex], so i automatically divided 9.01 by Hbar (in Ev.S units), but that would give inconsistent results with a Unitless permittivity. It would give units of: s^{-2}.eV^{-2} for the permittivity function he mentions.

so let's check what have i done:
1) Feed 9.01 into the formula where wp is. Wrong Graph.
2) Feed 9.01/Hbar into the formula where wp is. Wrong Graph again.

Can someone tell me what are the units for the formula (1,2,3) in the ref? and what kind of normalizations or unit conversions i have to do in order to put the data from Tables 1, 2 (ref) to make it work?
If i am getting anything wrong, tell me please.
 
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Yes, the ##\epsilon_r## he defines is unitless.
Apart from this, I don't understand your problem: both ##\omega## and ##\Gamma## have the same units as ##\Omega_p## so that the whole quotient is unitless, as it should be.
The question is rather: What units are you using for ##\omega##?
 
I am using eV, in other words.. i am running a loop from 0.01 ev to 1 ev. Feeding 0.01 to the function.
But \Omega_p is defined as \sqrt{f}\omega_p, where omega is in Hz, not eV, as i noted in table 2, in table 2 he says that the value 9.01 is hbar times plasma freq.

Should i divide by hbar? but still that gave me a wrong graph.
I you need, i can send you my results.

If i divided by hbar, that means Omega is not in eV anymore, it's in Hz, which means it the units won't cancel out.
 
Last edited:
No matter what you think he may write. If your ##\omega## is in eV, ##\Omega_p## has to be in eV, too.
 
I agree... so i shouldnt' divide by hbar?
 

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