Deep‐Ultraviolet Nonlinear‐Optical van‐der‐Waals Beryllium Borates**

Following our ab initio nonlinear optical (NLO) materials design guidelines, in this Letter, we discovered a novel type of structure to realize potential deep-ultraviolet (DUV) NLO performance the classical beryllium borate system. By densely stacking NLO-active layered frameworks, key scheme for structural evolution from (Be2BO3F2) layers KBe2BO3F2 (KBBF) (Be2BO5H3) berborite is illustrated. Based on available experimental results and systematical theoretical evaluation first principles, properties are further obtained as comparable only pratical DUV crystal KBBF. It demonstrated that can achieve phase-matched output with strong effect practically important 177.3 nm 193.7 lasers. Once sizable single crystal, it be applied promising crystal.