Calculating the Dielectric Function of metals - Units trouble

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SUMMARY

The forum discussion centers on calculating the dielectric function of metals, specifically using the Lorentz-Drude model in MATLAB, as outlined in the paper "Optical properties of metallic films for vertical-cavity optoelectronic devices" by Rakic et al. The user is struggling with unit conversions, particularly regarding the plasma frequency of silver, which is 9.01 eV. The confusion arises from the need to maintain unit consistency between the permittivity function and the variables used in the calculations, particularly the relationship between energy units (eV) and frequency units (Hz).

PREREQUISITES
  • Understanding of the Lorentz-Drude model for permittivity calculations
  • Familiarity with MATLAB programming for numerical simulations
  • Knowledge of plasma frequency and its significance in optical properties
  • Basic grasp of unit conversions between energy (eV) and frequency (Hz)
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  • Learn MATLAB functions for handling unit conversions and numerical analysis
  • Study the relationship between energy (eV) and frequency (Hz) in physical equations
  • Explore common pitfalls in unit conversions in optical property calculations
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This discussion is beneficial for physicists, materials scientists, and engineers working on optical properties of metals, particularly those involved in computational modeling and simulations in MATLAB.

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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