Prediction of unexpected B n P n structures: promising materials for non-linear optical devices and photocatalytic activities.

In the present work, a modern method of crystal structure prediction, namely USPEX conjugated with density functional theory (DFT) calculations, was used to predict the new stable structures of B n P n ( n = 12, 24) clusters. Since B 12 N 12 and B 24 N 24 fullerenes have been synthesized experimentally, it motivated us to explore the structural prediction of B 12 P 12 and B 24 P 24 clusters. All new structures were predicted to be energetically favorable with negative binding energy in the range from -4.7 to -4.8 eV per atom, suggesting good experimental feasibility for the synthesis of these structures. Our search for the most stable structure of B n P n clusters led us to classify the predicted structures into two completely distinct structures such as α-B n P n and β-B n P n phases. In α-B n P n , each phosphorus atom is doped into a boron atom, whereas B atoms form a B n unit. On the other hand, each boron atom in the β-phase was bonded to a phosphorus atom to make a fullerene-like cage structure. Besides, theoretical simulations determined that α-B n P n structures, especially α-B 24 P 24 , show superior oxidation resistance and also, both α-B n P n and β-B n P n exhibit better thermal stability; the upper limit temperature that structures can tolerance is 900 K. The electronic properties of new compounds illustrate a higher degree of absorption in the UV and visible-region with the absorption coefficient larger than 10 5 cm -1 , which suggests a wide range of opportunities for advanced optoelectronic applications. The β-B n P n phase has suitable band alignments in the visible-light excitation region, which will produce enhanced photocatalytic activities. On the other hand, α-B n P n structures with modest band gap exhibit large second hyperpolarizability, which are anticipated to have excellent potential as second-order non-linear optical (NLO) materials.