Dr. Claudio Attaccalite, Institut Neel, CNRS, Grenoble
We present a real-time approach to study nonlinear optical properties in Condensed Matter systems that is especially suitable for crystalline solids. The equation of motions and the coupling of the electrons with the external electric field are derived from the Berry phase formulation of the dynamical polarization. Many-body effects are introduced by adding single-particle operators to the independent-particle Hamiltonian. Specifically we include crystal local field effects, renormalization of the energy levels and excitonic effects. The approach is validated by calculating the second and third harmonic generation of bulk semiconductors. Finally we present second-harmonic generation spectrum of h-BN or MoS2 monolayers and we show that correlation effects double the signal intensity at the excitonic resonances with respect to the contribution from independent electronic transitions.
 Nonlinear optics from an ab-initio approach by means of the dynamical Berry phase: Application to second-and third-harmonic generation in semiconductors, C Attaccalite, M Grüning, Phys. Rev. B 88 (23), 235113 (2013)
 Second harmonic generation in h-BN and MoS2 monolayers: Role of electron-hole interaction, M. Grüning and C. Attaccalite, Phys. Rev. B 89, 081102(R) (2014)