BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//talks.cam.ac.uk//v3//EN
BEGIN:VTIMEZONE
TZID:Europe/London
BEGIN:DAYLIGHT
TZOFFSETFROM:+0000
TZOFFSETTO:+0100
TZNAME:BST
DTSTART:19700329T010000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0100
TZOFFSETTO:+0000
TZNAME:GMT
DTSTART:19701025T020000
RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
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
END:VEVENT
END:VCALENDAR