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