Second-order nonlinear optical susceptibilities and refractive indices of organic crystals from a multiscale numerical simulation approach

The performance of a simple multiscale approach to rapidly screen the second-order nonlinear optical (NLO) susceptibilities [χ ⁽²⁾] as well as the refractive indices of organic crystals solely from the knowledge of their crystal structure is demonstrated. The method combines first principles calculations of the molecular properties with a classical electrostatic interactions scheme to account for the crystal environment effects. The calculated values reproduce closely the measured χ ⁽²⁾ response for 10 organic crystals, including ionic crystalline salts, covering a χ ⁽²⁾ range from 10 to 600 pm V ^-1. The agreement between calculations and measurements is also excellent in the case of the refractive indices. Moreover, the method allows to analyze the relationship between the macroscopic responses [χ ⁽²⁾] and the molecular first hyperpolarizabilities, highlighting the effects of crystal packing and chromophore density as well as the role played by the crystal dressing field.