Ab initio calculations on the borate nonlinear optical crystal BaAlBO3F2

BaAlBO3F2 (BABF) crystal is a recently developed borate nonlinear optical crystal. However, re-examination has revealed a different space group from that previously measured. Since the newly and previously measured structures are very similar, their structural stabilities are compared by the plane-wave pseudopotential method, and the calculations confirm the correctness of the recent measurement. Furthermore, the electronic structures and the linear and nonlinear optical properties of BABF are theoretically studied. The calculated linear refractive indices and birefringence are in good agreement with the available experimental results, but the calculated second harmonic generation coefficient is much smaller than the experimental value, suggesting that this value should be remeasured. In order to elucidate the mechanism of the optical properties in BABF, a real-space atom-cutting technique is used to analyze the contributions of the respective ionic group. Finally, the comparison of optical effects for se...