title: First-principles study of the dynamical and nonlinear optical properties of urea single crystals.
abstract: Raman and infrared spectra of urea single crystals have been calculated using the density functional theory. This allowed us to assign the remaining experimental low-frequency phonon modes. Then, we have determined the sign of the second-harmonic nonlinear optical susceptibility coefficient in urea to be negative, clarifying a long debate in the literature. Finally, we computed for the first time the electro-optic coefficients of urea. We found that the electronic and ionic contributions have a similar order of magnitude and an opposite sign, yielding a smaller value than that expected, and necessitating further experimental clarifications.
authors.affiliation: Physique Théorique des Matériaux, Université de Liège, B-5, 4000 Sart-Tilman, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Hermet
authors.forename: Ph
authors.initials: P
authors.lastname: Ghosez