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CATEGORIES:Theory of Condensed Matter
SUMMARY:First-Principles Study of Frequency-Dependent Reso
nant Raman Scattering - Yannick Gillet\, Universit
é catholique de Louvain
DTSTART;TZID=Europe/London:20160427T110000
DTEND;TZID=Europe/London:20160427T120000
UID:TALK65754AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/65754
DESCRIPTION:A resonance phenomenon appears in the Raman respon
se when the exciting light has frequency close to
electronic transitions. Unlike for molecules and f
or graphene\, the theoretical prediction of such f
requency-dependent Raman response of crystalline s
ystems has remained a challenge. Indeed\, many Ram
an intensity first-principle calculations are nowa
days done at vanishing light frequency\, using sta
tic Density-Functional Perturbation Theory\, thus
neglecting the frequency dependence and excitonic
effects.\n\nDuring this presentation\, I will desc
ribe the finite-difference method we propose to co
mpute frequency-dependent Raman intensities.\n\nRe
cently\, we used this methodology for the computat
ion of the first-order frequency-dependent Raman i
ntensity [1]\, with excitonic effects described by
the Bethe-Salpeter equation. We found these to be
crucial for the accurate description of the exper
imental enhancement for laser photon energies arou
nd the gap.\n\nThis approach can be generalized to
the more complex second-order Raman intensity\, w
ith phonon losses coming from the entire Brillouin
zone. Interestingly\, even without excitonic effe
cts\, one is able to capture the main relative cha
nges in the frequency-dependent Raman spectrum of
silicon at fixed laser frequencies. However\, exci
tonic effects might affect significantly the inten
sity of specific modes and also lead to a global t
enfold increase of absolute intensities.\n\n[1] Y.
Gillet\, M. Giantomassi\, X. Gonze\, Phys. Rev. B
88\, 094305 (2013).
LOCATION:TCM Seminar Room\, Cavendish Laboratory
CONTACT:Gareth Conduit
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