Theoretical Prediction of Monolayer BeP 2 O 4 H 4 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 ( d b u l k e f f $d_{bulk}^{eff}$ = 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.