[Pw_forum] intraband transitions in eps.x code

[Stefano Baroni]

Olga: I know nothing about eps.x, but my solid-state textbook says that only inter-band transitions contribute to the optical absorption coefficient (because of selection rules, electromagnetic radiation only couples electronic states with a same wavevector). Maybe, part of the code (or of its documentation) refers to the general dielectric function, eps(q,omega), whereas some other parts only calculate eps(q=0,omega). The latter is relevant for optical transitions (and, as said, does not contain contributions from intra-band transitions). The former does have contributions from intraband transition (only in metals, though), but it is not relevant for optical transitions (it is for other spectroscopies, such as eels). The former note on the relevance of interband transitions (if any) only for metals is due to the Pauli principle which forbids transition to an accupied state. Hope this helps - Stefano PS: would you mind completeing your signature with your current scientific affiliation? thanks

On Apr 23, 2010, at 7:34 AM, Olga Sedelnikova wrote:

> Dear All,
> The equation for complex dielectric function used in eps.x code contains intra and interband transitions. From the other hand, the matrix elemt acconts only for interband transitions.
> My question is
> Wither will the intraband transitions affect on the results of eps.x calculations?
> 
> Thank you
> 
> Olga Sedelnikova
> 
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

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