Theoretical Prediction of Monolayer BeP₂O₄H₄ with Excellent Nonlinear‐Optical Properties in Deep‐Ultraviolet Range

Most 2D nonlinear optical (NLO) materials do not have an ultrawide bandgap, therefore, they are unsuitable for working in the deep‐ultraviolet spectral range (< 200 nm). Herein, the theoretical prediction of an excellent monolayer BeP 2 O 4 H 4 (ML‐BPOH) is reported. DFT analyses suggest a low cleavage energy (≈45 meV per atom) from a naturally existed bulk‐BPOH material, indicating feasible exfoliation. This novel 2D material exhibits excellent properties including an ultrawide bandgap ( E g ) of 7.84 eV, and a strong second‐order nonlinear susceptibility ( = 0.43 pm V −1 ), which is comparable to that of benchmark bulk‐KBBF crystal ( d 16 = 0.45 pm V −1 ). The wide bandgap and large SHG effect of ML‐BPOH are mainly derived from the (PO 2 H 2 ) − tetrahedron. Notably, ML‐BPOH exhibits an outstanding 50% variation in d sheet under minor stress stimuli (±3%) due to rotation of structurally rigid (PO 2 H 2 ) − tetrahedron. This indicates significant potential for application in material deformation monitoring.