Molecular hydrogen physisorption on boron-nitride nanotubes probed by second harmonic generation

Abstract

We present ab initio calculations to investigate second harmonic generation (SHG) response of single wall zigzag pristine boron-nitride nanotubes (BNNTs) and BNNTs modified by the molecular hydrogen adsorption. Calculations have been performed using density functional theory (DFT) within the local-density approximation (LDA) together with the GW Green function method to determine the band gap. A length gauge approach has been used to calculate the nonlinear optical response with the scissors correction to obtain the nonlinear susceptibility ${\ensuremath{\chi}}^{zzz}(\ensuremath{-}2\ensuremath{\omega};\ensuremath{\omega},\ensuremath{\omega})$ of the zigzag BNNTs. We have found that, contrary to reports in the literature, the (5,0) and (9,0) BNNTs have a nonvanishing SHG response. We have also found that SHG intensity decreases with the increase of the molecular hydrogen coverage.