Phononic effects and nonlocality contributions to second harmonic generation in NiO

Abstract

We present a method for calculating second harmonic generation on a purely ab initio basis in NiO, both for the (001) surface and for the bulk. We go beyond the electric dipole approximation and we incorporate magnetic dipoles and electric quadrupoles in our results. A full detailed symmetry analysis of these contributions is given. Then we calculate phononic contributions to the second order susceptibility tensor for the bulk within the frozen phonon approximation. It is shown that transient lattice distortions can lead to a second harmonic signal, even in centrosymmetric materials like NiO. The second order susceptibility tensor is calculated from first principles, including nonlocalities in two different ways: (i) with phononic contributions on a time averaged way and (ii) with a time resolved single optical phonon at the $\ensuremath{\Gamma}$ point. Furthermore the effects of electronic redistribution prior to the probe pulse are given.