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SUMMARY:First-Principles Study of Frequency-Dependent Resonant Raman Scatt
 ering - Yannick Gillet\, Université catholique de Louvain
DTSTART:20160427T100000Z
DTEND:20160427T110000Z
UID:TALK65754@talks.cam.ac.uk
CONTACT:Gareth Conduit
DESCRIPTION:A resonance phenomenon appears in the Raman response when the 
 exciting light has frequency close to electronic transitions. Unlike for m
 olecules and for graphene\, the theoretical prediction of such frequency-d
 ependent Raman response of crystalline systems has remained a challenge. I
 ndeed\, many Raman intensity first-principle calculations are nowadays don
 e at vanishing light frequency\, using static Density-Functional Perturbat
 ion Theory\, thus neglecting the frequency dependence and excitonic effect
 s.\n\nDuring this presentation\, I will describe the finite-difference met
 hod we propose to compute frequency-dependent Raman intensities.\n\nRecent
 ly\, we used this methodology for the computation of the first-order frequ
 ency-dependent Raman intensity [1]\, with excitonic effects described by t
 he Bethe-Salpeter equation. We found these to be crucial for the accurate 
 description of the experimental enhancement for laser photon energies arou
 nd the gap.\n\nThis approach can be generalized to the more complex second
 -order Raman intensity\, with phonon losses coming from the entire Brillou
 in zone. Interestingly\, even without excitonic effects\, one is able to c
 apture the main relative changes in the frequency-dependent Raman spectrum
  of silicon at fixed laser frequencies. However\, excitonic effects might 
 affect significantly the intensity of specific modes and also lead to a gl
 obal tenfold increase of absolute intensities.\n\n[1] Y. Gillet\, M. Giant
 omassi\, X. Gonze\, Phys. Rev. B 88\, 094305 (2013).
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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