圆柱体骰子最终面朝向概率的研究

下落物体的最终静止状态取决于物体的几何特征、运动状态、材料特性等多种因素.本文以圆柱体骰子为研究对象,基于动力学模型,探究了圆柱体骰子初始速度、角速度、高度、质量以及恢复系数等因素对骰子落地后最终面朝向的影响,并探讨了使圆柱体骰子每一面最终朝向概率相等时应具有的几何特征和物理条件.本文结果可为此类研究提供思路和借鉴.     

A strategy of enhancing the photoactivity of TiO2 containing nonmetal and transition metal dopants

An effective structural codoping approach is proposed to modify the photoelectrochemical （PEC） properties of anatase TiO2 by being doped with nonmetal （N or/and C） and transition metal （Re） elements. The electronic structures and for- mation energies of different doped systems are investigated using spin-polarized density functional theory. We find that （C, Re） doped TiO2, with a low formation energy and a large binding energy, reduces the band gap to a large extent, thus it could contribute to the significant enhancement of the photocatalytic activity in the visible-light region. It should be pointed out that, to be successful, the proper proportion of the dopants C and Re should be controlled, so that reasonable PEC properties can be achieved.     

Van der Waals heterostructure of phosphorene and hexagonal boron nitride: First-principles modeling

We have studied the structural and electronic properties of a hybrid hexagonal boron nitride with phosphorene nanocomposite using ab initio density functional calculations. It is found that the interaction between the hexagonal boron nitride and phosphorene is dominated by the weak van der Waals interaction, with their own intrinsic electronic properties preserved. Furthermore, the band gap of the nanocomposite is dependent on the interfacial distance. Our results could shed light on the design of new devices based on van der Waals heterostructure.     

First-principles modeling hydrogenation of bilayered boron nitride

We have investigated the structural and electronic characteristics of hydrogenated boron-nitride bilayer(H–BNBN–H) using first-principles calculations. The results show that hydrogenation can significantly reduce the energy gap of the BN–BN into the visible-light region. Interestingly, the electric field induced by the interface dipoles helps to promote the formation of well-separated electron–hole pairs, as demonstrated by the charge distribution of the VBM and CBM.Moreover, the applied bias voltage on the vertical direction of the bilayer could modulate the band gap, resulting in transition from semiconductor to metal. We conclude that H–BNBN–H could improve the solar energy conversion efficiency, which may provide a new way for tuning the electronic devices to meet different environments and demands.     

分子动力学模拟粒子在表面上的俘获过程

采用分子动力学方法研究了粒子在金属衬底上的俘获过程。发现粒子垂直入射时,俘获概率随入射能量的增加而减小,而45°入射时,俘获概率表现出非单调行为,这些结果与实验观察相一致。同时还研究了俘获概率对入射角的依赖。     

Modulating the properties of monolayer C_2N: A promising metal-free photocatalyst for water splitting

Photocatalytic water splitting has gained increasing attention, since it utilizes renewable resources, such as water and solar energy, to produce hydrogen. Using the first-principles density functional theory, we investigate the properties of the single layer C_2N which was successfully synthesized. We reveal that monolayer C_2N has a substantial direct band gap of 2.45 eV. To regulate its band gap, four different nonmetal elements(B, O, P, and S) on the cation and anion sites are considered. Among them, B-doped N site is the most effective one, with the lowest formation energy and a band gap of 2.01 eV. P-doped N site is the next, with a band gap of 2.08 eV, though its formation energy is higher. The band alignments with respect to the water redox levels show that, for these two dopings, the thermodynamic criterion for the overall water splitting is satisfied. We therefore predict that B-or P-doped C_2N, with an appropriate band gap and an optimal band-edge position, would be a promising photocatalyst for visible-light water splitting.