London Dispersion Effects on the Structure and Properties of Nonlinear Optical BiB3O6 Crystal.

a-BiB3O6 (BiBO) is an important nonlinear optical (NLO) material with high efficiency for applications in harmonic generations and quantum technology. Owing to its low symmetry and cooperative Bi3+ lone pair arrangement, it has also exceptional large piezoelectric and electro-optic coefficients and strong anisotropies on other material characteristics.  Previous theoretical calculations on its physical properties often gave confusing results. It is found here that London dispersion (LD) tends to stabilize structures with closer pack  Bi3+ with large polarizabilities, which is ignored in most previous density functional theory (DFT) calculations. Present study shows that without considering the LD effect, the structure of a-BiB3O6 (BiBO) was predicted with an over-estimated (by over 10%) unique b-axis while underestimates a and overestimates c in a less amount. Consequently it is not possible to use the calculated structure to obtain meaningful properties of this important material. By applying a modified post-DFT LD correction, the experimental structure is well reproduced with the theoretical optimized one. Important material property tensors of BiBO crystal are calculated in unprecedented precisions, including: dielectric constants (static and in THz range), elastic and elasto-optic constants, piezoelectric constants, refractive indices, NLO and electro-optic (EO) coefficients.

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