Prediction Of Unexpected Bnpn 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 BnPn (n = 12, 24) clusters. Since B12N12 and B24N24 fullerenes have been synthesized experimentally, it motivated us to explore the structural prediction of B12P12 and B24P24 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 BnPn clusters led us to classify the predicted structures into two completely distinct structures such as alpha-BnPn and beta-BnPn phases. In alpha-BnPn, 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 beta-phase was bonded to a phosphorus atom to make a fullerene-like cage structure. Besides, theoretical simulations determined that alpha-BnPn structures, especially alpha-B24P24, show superior oxidation resistance and also, both alpha-BnPn and beta-BnPn 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 beta-BnPn phase has suitable band alignments in the visible-light excitation region, which will produce enhanced photocatalytic activities. On the other hand, alpha-BnPn structures with modest band gap exhibit large second hyperpolarizability, which are anticipated to have excellent potential as second-order non-linear optical (NLO) materials.