The structures and stabilities of gold clusters with up to 14 atoms have been determined by density-functional theory. The structure optimizations and frequency analysis are performed with the Perdew-Wang 1991 gradient-corrected functional combined with the effective core potential and corresponding valence basis set (LANL2DZ). The turnover point from two-dimensional to three-dimensional geometry for gold clusters occurs at Au12. The energetic and electronic properties of the small gold clusters are strongly dependent on sizes and structures, which are in good agreement with experiment and other theoretical calculations. The even-odd oscillation in cluster stability and electronic properties predicted that the clusters with even numbers of atoms were more stable than the neighboring clusters with odd numbers of atoms. The stability and electronic structure properties of gold clusters are also characterized by the maximum hardness principle of chemical reactivity and minimum polarizability principle.
The family of bulk metal phosphorus trichalcogenides (APX3, A = M(II), M(I)(0.5)M(III)(0.5); X = S, Se; M(I), M(II), and M(III) represent Group-I, Group-II, and Group-III metals, respectively) has attracted great attentions because such materials not only own magnetic and ferroelectric properties, but also exhibit excellent properties in hydrogen storage and lithium battery because of the layered structures. Many layered materials have been exfoliated into two-dimensional (2D) materials, and they show distinct electronic properties compared with their bulks. Here we present a systematical study of single-layer metal phosphorus trichalcogenides by density functional theory calculations. The results show that the single layer metal phosphorus trichalcogenides have very low formation energies, which indicates that the exfoliation of single layer APX3 should not be difficult. The family of single layer metal phosphorus trichalcogenides exhibits a large range of band gaps from 1.77 to 3.94 eV, and the electronic structures are greatly affected by the metal or the chalcogenide atoms. The calculated band edges of metal phosphorus trichalcogenides further reveal that single-layer ZnPSe3, CdPSe3, Ag0.5Sc0.5PSe3, and Ag0.5In0.5PX3 (X = S and Se) have both suitable band gaps for visible-light driving and sufficient over-potentials for water splitting. More fascinatingly, single-layer Ag0.5Sc0.5PSe3 is a direct band gap semiconductor, and the calculated optical absorption further convinces that such materials own outstanding properties for light absorption. Such results demonstrate that the single layer metal phosphorus trichalcogenides own high stability, versatile electronic properties, and high optical absorption, thus such materials have great chances to be high efficient photocatalysts for water-splitting.
Two-dimensional materials with higher carrier mobility are promising materials for applications in the nanoelectronics and photocatalysis. In this paper, we have explored the stabilities, structures, electronic properties, carrier mobility and optical properties of few-layer PbX (X = S, Se, Te) by first-principle calculations. Theoretical results show that the band gaps of PbX could be modulated by the thickness, changing from 1.65 eV (1.26 eV, 1.26 eV) of monolayer to 0.98 eV (0.76 eV, 0.97 eV) of tri-layer for PbS (PbSe, PbTe). Most importantly, the bi-layer PbS has an extremely high electron carrier mobility of 252 000 cm 2 V -1 s -1 and the hole carrier mobility of mono-or tri-layer PbTe could obtains a value of 16 000 cm 2 V -1 s -1 , predicating the possible wide applications of few-layer PbXs in novel electronic devices. The strong adsorptions of light of PbXs also indicate their potential implications in solar cell.
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