First-principles study of electronic structures and nonlinear optical properties ofAMoO3(IO3) (A = Li, Rb and Cs) crystals

Abstract

First-principles studies of the geometric structures, electronic structures and second-ordernonlinear optical properties of polar alkali metal–Mo(VI)–iodate compounds (AMoO3(IO3) (A = Li, Rb and Cs)) have been performed within density functional theory and the independentparticle approximation. Our results indicate that, for these compounds, due to thesimilarity in their anionic groups, the electronic structures and the prominent features ofthe frequency dependent second-order nonlinear optical susceptibilities are similar,especially for the isostructural Rb and Cs compounds. Also, the calculated SHG coefficientsof these compounds are large, which confirms the high response in experimental SHGmeasurements. By comparing the absolute magnitude of the SHG coefficients, the orderLiMoO3(IO3) > RbMoO3(IO3) > CsMoO3(IO3) is clearly established in the low photon energy range. Further analyses based onthe spectral and spatial decomposition of the SHG coefficients reveal that themain sources of the SHG properties of these compounds are from the distortedMoO6 andIO3 − groups, and can be mainly attributed to the electronic transition from the nonbonding O 2pstates (i.e. the lone-pair electrons of O atoms) to the Mo 4d and some I 5p states. It isnoticeable that in these compounds, due to the difference in ion size and coordinateenvironment, the contributions of alkali metals to the SHG processes are very different: forlarge cations, such as Rb and Cs, they can be neglected, while for the very small Li, theyshould be included.