[Wien] How to calculate Plasma Frequency and Number of effective electrons.

Kulpreet Virdi kulpreet.virdi at cup.uni-muenchen.de
Fri Apr 12 09:17:42 CEST 2013



Hi Zaid, 

yes, one way of identifying the Plasmon (energy) is the
maximum in loss function (electron energy loss plot) however this is not
always correct. The loss function is given by Im [-1/ε] which is equal to
[ε2/(ε1^2+ε2^2)]. In the loss function you would see a maximum when there
is a local minimum of (ε1^2+ε2^2) or a local maximum of ε2. 

The local
maxima of ε2 imply interband transition(s) ; which are often visible in
loss spectrum especially for materials containing transition or heavy
metals. However a minima of (ε1^2+ε2^2) implies a plasmon excitation. 

The
most often used definition of plasmon is when ε2 crosses zero [and a minmum
of ε1^2+ε2^2 ] with a positive slope with respect to the energy axis. For
details you can check either of these 

M. Fox, Optical Properties of
Solids (Oxford University Press,
Oxford, UK, 2010). 

V. Gallegos-Orozco,
R. Martınez-Sanchez, and F. Espinosa-
Magana, Phys. Rev. B 77, 045128
(2008). 

V. J. Keast, A. J. Scott, M. J. Kappers, C. T. Foxon, and C.
J.
Humphreys, Phys. Rev. B 66, 125319 (2002). 

I guess someone else could
help you with the effective number of electrons. 

All the best, 

Kulpreet


On Fri, 12 Apr 2013 12:30:09 +0800, Zaid  wrote:     Respected Wien
Users

 I am inexperience in calculating optical properties May any one
guide me how to calculate Plasmon energy and Number of effective electrons
? After some effort I came to know that the energy associated to highest
peak value in Electron loss plot will be Plasmon energy. While value for No
of effective electrons can be obtained from X KRAM sumrule. Can Any one
confirm this information true ? And which sum rule should be selected ? 


Best Regards M, Zaid   

 
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