We published a new paper on the second harmonic generation(SHG) in two-dimensional hexagonal crystals SiC, ZnO and GaN. The SHG is calculated within the so called GW plus Bethe-Salpter formalism, using a real-time implementation proposed by some of us. We found that these system present a large region with a strong SHG before the absorption onset, compatible with laser frequencies available in the market.  This open the possibility to integrate these two dimensional crystals in optoelectronic devices.

Here the reference:

Strong second harmonic generation in SiC, ZnO, GaN two-dimensional hexagonal crystals from first-principles many-body calculations
C. Attaccalite, A. Nguer, E. Cannuccia, M. Grüning
Phys. Chem. Chem. Phys., 17, 9533-9540(2015)