Be_n(n=1～6)团簇吸附H_2的密度泛函研究

采用密度泛函广义梯度近似(GGA)的PW91方法,用全电子基组DNP对Ben(n=2～6)团簇几何结构进行优化,计算了团簇的总能、平均结合能、振动频率、最高已占据轨道能级、最低未占据轨道能级、能隙、垂直电离势和垂直亲和势。在Ben(n=1～6)团簇的顶位、桥位和穴位吸附H2后,进行了吸附物的几何优化和能量计算,得到最佳吸附位,并计算了吸附前后的总态密度和Mulliken电荷布居。结果表明:团簇中Be原子数增多,稳定性增强;吸附H2的吸附能处于0.0061982～0.0089722a.u.之间;随着Be团簇原子数量增加,与H的s-p杂化程度增强;吸附位对应的电荷转移量越大,吸附越牢固。     

H原子在γ-U(100)表面吸附与扩散的密度泛函研究

采用密度泛函理论方法研究了H原子在γ-U(100)表面的吸附和扩散。结果表明：H原子在γ-U(100)表面的最佳吸附位依次为穴位、桥位和顶位,吸附能分别为2.696、2.597和2.017 eV;H原子在γ-U中的最佳间隙位为四面体间隙,其次是八面体间隙,吸附能分别为1.534 eV和0.991 eV;H原子在铀表面以及近表面层的不同吸附位之间的扩散需克服不同的势垒,相比于间隙位,H原子更倾向于在γ-U(100)表面吸附聚集。     

用密度泛函理论研究氚在高温气冷堆核级石墨的吸附与解吸附行为

为研究氚在高温气冷堆核级石墨上的吸附和解吸附行为,本文利用密度泛函理论,采用氢原子代替氚原子的办法,通过理论计算得到了氚在高温气冷堆核级石墨上的结合能,通过模型分析得到了氚在高温气冷堆核级石墨上的吸附、解吸附机理与相应的份额,并得到HTR-10在20年寿期末各部分氚的累积量及事故工况下氚释放量的估计值。本文结果为研究估算高温气冷堆氚释放的机理提供了一条新思路。     

铀的电子能量损失谱密度泛函理论计算及实验研究

采用密度泛函理论计算及实验获取了铀的电子能量损失谱（Electron energy loss spectroscopy,简称EELS）。计算的谱峰位置与实验一致。结合计算得到铀的能带及态密度对计算谱及实验谱特征峰进行分析,结果表明：由于铀的5f电子形成窄带对等离子体振荡贡献较小,6p电子的共振跃迁致使等离子振荡频率降低;实验谱中13．3eV能量损失峰为体等离子体振荡峰,20．3eV能量损失峰为6p能带到费米能级跃迁能量损失峰,27．6eV能量损失峰为两次体等离子振荡吸收峰。     

嵌埋团簇Cu：CaF2膜光学性质的研究

研究了Ｃｕ：ＣａＦ２复合膜的红外光吸收与金属团簇结构之间的关系。结果表明Ｃｕ金属的表面等离子体共振吸收频率明显依赖Ｃｕ团簇的大小。随着团簇尺寸的减小，共振吸收峰发生红移；吸收峰变宽。并且在吸收峰位附近表现出较大的第三级非线性系数，其不电反应速度小于１５０ｆｓ。     

H2O2活化活性炭对U(Ⅵ)的吸附研究

利用H_2O_2对活性炭进行活化,得到了良好的吸附材料(15%-AC),用傅立叶红外(Fourier Transform Infrared spectroscopy,FT-IR)、热重分析(Themiogravimetric Analysis,TGA)、扫描电子显微镜(Scanning Electron Microscope,SEM)和Brunauer-Emmett-Teller (BET)孔径分析等方法测定了活化前后样品。结果表明:经过H_2O_2活化后的活性炭,表面氧化基团增加,形成更多吸附位点,比表面积小幅度减少,但介孔量增加,孔隙率上升。采用静态吸附实验研究了接触时间、pH、固液比、初始浓度、温度、共存阴阳离子等因素对吸附的影响。在最佳条件下(接触时间、pH、固液比、初始浓度、温度分别为90 min、5、8 g·L~(-1)、80 mg·L~(-1)、35℃),吸附性能增加了68%;准二级动力学模型和Langmuir等温吸附模型对吸附行为的拟合效果好,表现为表面均匀且为多基元的吸附行为;15%-AC在共存离子和循环吸附的影响下仍具有良好的吸附性能。实验证明:H_2O_2的活化过程可以有效地提高活性炭对U(Ⅵ)的吸附性能。     

载能钼团簇束与单晶硅碰撞室温下合成二硅化钼

用一种新型磁控溅射气体凝聚团簇源产生Mon^-团簇束,当团簇束分别在偏压为0、1、3、5、10kV的电场中加速后,沉积在室温下的P型Si(111)衬底上,获得Mo／Si(111)薄膜样品。用XRD分析表明,在室温下,偏压≤5kV团簇束沉积和常规磁控溅射沉积获得的Mo／Si(111)样品,其界面均无二硅化钼(MoSi2)生成;偏压=10kV时,团簇束沉积其界面直接有MoSi2生成。对于团簇束沉积,当偏压大于一定值时(在本实验条件下偏压≥3kV),薄膜才开始以Mo(110)择优取向生长。     

锕系金属掺杂硼团簇AnB_(7)(An=Ac、Th、Am、Cm)的理论研究北大核心CSCD

通过金属掺杂,硼团簇可以表现出特殊的结构特征和化学性质。尽管主族金属、过渡金属和镧系金属掺杂的硼团簇已被相继报道,但目前锕系金属掺杂的硼团簇研究相对较少。本工作使用密度泛函理论(DFT)预测了一系列锕系金属掺杂硼团簇AnB_(7)(An=Ac、Th、Am、Cm)。理论计算表明,其能量最低的结构分别为C_(6)v AcB_(7)、C_(2)v ThB_(7)、C_(2)v AmB_(7)和C_(6)v CmB_(7),且均为半夹心构型。在每个AnB_(7)体系中,B_(3)-7具有六个离域的π电子和六个离域的σ电子,均为双重芳香性团簇。成键性质分析表明Am-B和Cm-B键的共价相互作用强于Ac-B和Th-B键。此外,这些硼团簇均非常稳定,且AmB_(7)和CmB_(7)稳定性更高,而共价相互作用是影响AnB_(7)稳定性的重要因素。本工作丰富了锕系金属掺杂的硼团簇的种类,并为设计锕系金属掺杂硼团簇材料提供了理论基础。     

Cu纳米团簇发光性能和结构的研究

利用光致发光谱(Photoluminescence,PL)、X射线吸收精细结构(X-ray Absorption Fine Structure,XAFS)和MALDI-TOF质谱等技术研究了化学还原法合成的Cu金属纳米团簇的发光性能及其结构。PL谱表明随着反应溶液中十二硫醇(C12SH)和2-巯基-5-正丙烷基嘧啶(C7H10N2S,2-mercapto-5-n-propylpyrimidine,MPP)配体比例的增加,Cu纳米团簇主发光峰的波长从618 nm逐渐蓝移到571 nm。质谱的结果说明以MPP作为单一配体时的主要产物为Cu5[MPP]3;而当为MPP与C12SH两种混合配体时,Cu纳米团簇中Cu原子数变小,组成变为Cu4[MPP][C12SH];并且随着C12SH比例增加,Cu4[MPP][C12SH]产物的组成保持不变。XAFS结果则进一步表明随着C12SH比例的增加,Cu纳米团簇的Cu-S键长从0.228 nm缩短到0.224 nm,原子构型从双三角锥结构转变为四面体。综合以上结果,认为Cu纳米团簇的原子数的减少导致团簇的光致发光从618nm蓝移至597 nm;而Cu-S键长的缩短引起Cu(I)-S杂化的HOMO-LUMO带隙增大,从而导致团簇的发光波长进一步从597 nm蓝移至571 nm。     

H原子在Zr(0001)表面吸附的第一性原理研究

结合蒙特卡洛(MC)模拟和第一性原理密度泛函理论(DFT)方法,从Zr-H体系微观结构、吸附概率、吸附能、Mulliken电荷布居数以及电子态密度等方面对H原子在α-Zr(0001)表面的吸附位点和吸附机理等进行计算分析。结果表明:H原子在Zr(0001)表面首先产生物理吸附,然后由物理吸附转变为化学吸附,吸附过程中电荷不断由Zr(0001)表面原子向H原子转移,最后趋于稳定。另外,稳定吸附后的H原子直接与Zr(0001)表面最表层原子生成化学键,且主要由H(s)、Zr(s)和Zr(d)轨道的电子态做贡献。综合分析得到H原子在Zr(0001)表面的吸附位点优先级顺序为密排六方间隙位(hcp位)>面心立方间隙位(fcc位)>桥位(bridge位),顶位(top位)不会产生吸附。     

Reduced partition function ratios of hydrogen species adsorbed on platinum cluster Pt19 studied by density functional theory

Geometry optimization and estimation of H/D reduced partition function ratios (RPFRs) of Pt₁₉–H, Pt₁₉–H⁺, Pt₁₉–H₂, and Pt₁₉–H₂⁺ models of hydrogen species adsorbed on surfaces of metallic platinum particles, were carried out based on the density functional theory. Two types of optimized structures were obtained for Pt₁₉–H and Pt₁₉–H⁺, and three for Pt₁₉–H₂ and Pt₁₉–H₂⁺. Stabilization energy consideration suggested that the most probable structure for Pt₁₉–H and Pt₁₉–H⁺ is the one in which H/H⁺ is bonded to a Pt atom, and that for Pt₁₉–H₂ and Pt₁₉–H₂⁺ is the one in which two H/H⁺s are bonded to two adjacent Pt atoms with no direct bonding between the two H/H⁺s. The value of RPFR obtained for those structures ranged from 3.9303 to 4.4014 at 25 °C. Interaction between two adjacent H–Pt bonds seems to slightly enhance the mutual RPFR values.     

Crystalline and electronic structures of lithium silicates: A density functional theory study

Lithium silicates, such as Li₂SiO₃ and Li₄SiO₄, are considered as favorable candidates for the tritium breeding materials of a deuterium–tritium type nuclear fusion reactor. Their bulk structural and electronic properties are investigated using pseudopotential plane wave (PPW) method within density functional theory (DFT). The optimized crystal structure parameters are well consistent with the experimental results. The results indicate that Li₂SiO₃ and Li₄SiO₄ are insulators with band gaps of about 5.36 and 5.53 eV, respectively. The valence electrons density of state reveal the covalency properties mainly resulting from the overlapping of O 2p and Si 3p orbital electrons in both lithium silicates. The nonbridging O (NBO) atoms and bridging O (BO) atoms of Li₂SiO₃ exhibit significantly different electron distributions. The Si 3s and 3p hybridization is observed in Li₂SiO₃, but not in Li₄SiO₄. The mechanical elastic constants reflected Li₄SiO₄ might be unstable in some degrees.     

Hydrogen and water vapor adsorption on and reaction with uranium

By combining modulated molecular beam scattering, temperature programmed desorption, and atomic force microscopy experiments, the fundamental properties of the interaction of hydrogen and water vapor with uranium at room temperature and above have been investigated. The initial sticking probability, hydride formation probabilities and desorption kinetics for dihydrogen and water vapor on clean uranium have been measured. In addition, saturation coverages for hydrogen and water vapor are determined for an initially clean uranium surface. Atomic force microscopy revealed site-specific initiation of hydride formation for slightly oxidized uranium at grain boundaries. The areal (and hence time) dependence of the hydride formation probability was also observed. The clean uranium surface is passivated significantly by oxidation and carburization. The sticking probabilities for dihydrogen and water vapor are one to two orders of magnitude smaller on oxidized and carbided surfaces. The carbided surface is efficiently produced by reaction of C₆₀ with uranium surfaces between 600 and 800 K.     

Influence on electron energy loss spectroscopy of the niobium-substituted uranium atom: A density functional theory study

We present the electronic structure and electron energy loss spectroscopy (EELS) for uranium, niobium and U3Nb in which uranium is substituted by niobium. Comparing the electronic structures and optical properties for uranium, niobium and U3Nb, we found that when niobium atom replaces uranium atom in the center lattice, density of state (DOS) of U3Nb shifts downward to low energy. Niobium affects DOS forfand d electrons more than that for p and s electrons. U3Nb is similar to uranium for the electronic energy loss spectra.     

Tracks of 30-MeV C60 clusters in yttrium iron garnet studied by scanning force microscopy

Yttrium iron garnet (Y₃Fe₅O₁₂ or YIG), an amorphizable ferrimagnetic insulator, is probably the best studied material with respect to track formation and damage morphology. This paper presents first scanning force microscopy (SFM) of surface damage induced by energetic C₆₀ clusters. YIG single crystals were irradiated at normal incidence with 30-MeV C₆₀ cluster ions (kinetic energy ∼0.04 MeV/u) provided by the tandem accelerator of the Institute of Nuclear Physics in Orsay (IPNO). The SFM topographic images show nano-protrusions on the YIG surface; where each hillock is generated by one C₆₀ cluster. The role of stopping power and deposited energy density is discussed in terms of dimensional analysis of the nanostructures. Hillocks created by C₆₀ clusters are compared with those produced by monatomic ions.     

钨/铜界面处氢原子与空位相互作用的第一性原理计算

钨/铜界面是聚变堆偏滤器的重要连接界面,在高热流密度和强中子辐照下会成为氢同位素渗透滞留的高速通道和捕获陷阱。本文利用第一性原理方法研究了钨/铜界面处氢原子与点缺陷的相互作用,考察了氢原子的滞留行为和空位在界面处的形成行为,分析了氢原子的优先占据位置及氢原子与空位的作用机理。结果表明：在钨/铜界面中,氢原子稳定存在于钨/铜界面中间及铜晶格中;对于空位,界面附近的铜空位不稳定,会自发移动到钨/铜界面的顶端表面,而钨空位相对稳定存在;相比于铜空位,钨空位吸引氢原子的能力更强。氢原子的存在会抑制铜空位的迁移现象,从而可能形成氢泡。     

氢能利用与核能制氢研究开发综述

文章从氢能的资源丰富、热值高、无污染等特点出发叙述了氢能作为一种洁净能源在国民经济（主要为交通用燃料）和国防中广泛的潜在应用，介绍了目前国际上核能制氢的几种主要方法，并展望了核能－氢能系统的发展前景。     

A density functional theory study on the interaction between UO_2~(2+) and the carbamoylphosphoramidic acid ligand for uranium extraction from seawater

Phosphorylurea molecules, which contain both phosphoryl and carbonyl groups, are considered efficient extractants for UO_2~(2+). This study aims to explain the complexation of UO_2~(2+)with carbamoylphosphoramidic acid(CPO), a simple model for phosphorylurea, for ligand design for uranium recovery from seawater using density functional theory calculations, natural bond order analysis,and the quantum theory of atoms in molecules. The results showed that, when CPO acts as a monodentate ligand, the affinity of phosphoryl for UO_2~(2+)is stronger than that of carbonyl, and CPO coordinates with UO_2~(2+)through the phosphoryl oxygen atom. When CPO serves as a bidentate ligand, both the phosphoryl and carbonyl oxygen atoms connect to UO_2~(2+), and the U–O(carbonyl) bond plays a more important role than the U–O(phosphoryl) bond in the interaction between UO_2~(2+)and CPO. This paradox may be caused by the significant charge transfer from the U–O(carbonyl) p bond orbital to the C–N σ antibond orbital of the bidentate CPO. The NH spacer between the phosphoryl and carbonyl groups could ensure the delocalization of the electron system of the molecule. The bidentate binding motif is favored by entropy and opposed by enthalpy, while the monodentate binding motif is favored by enthalpy and opposed by entropy. Ultimately, the bidentate binding motif is more favorable than the monodentate one. As expected, the interaction between UO_2~(2+)and the deprotonated CPO is stronger than that between UO_2~(2+)and the neutral CPO. Comparing the interaction between UO_2~(2+)and CPO with that between UO_2~(2+)and Nphenylcarbamoylphosphoramidic acid(Ph CPO), formed by replacing one hydrogen atom from the terminal nitrogen atom of CPO with a phenyl group, the phenyl substituent at the terminal nitrogen atom of Ph CPO shows a slightly negative effect on the interaction between UO_2~(2+)and Ph CPO.     

Structural, electronic, and thermodynamic properties of UN: Systematic density functional calculations

A systematic first-principle study is performed to calculate the lattice parameters, electronic structure, and thermodynamic properties of UN using the local-density approximation (LDA)+U and the generalized gradient approximation (GGA)+U formalisms. To properly describe the strong correlation in the U 5f electrons, we optimized the U parameter in calculating the total energy, lattice parameters, and bulk modulus at the nonmagnetic (NM), ferromagnetic (FM), and antiferromagnetic (AFM) configurations. Our results show that by choosing the Hubbard U around 2 eV within the GGA+U approach, it is promising to correctly and consistently describe the above mentioned properties of UN. The localization behavior of 5f electrons is found to be stronger than that of UC and our electronic analysis indicates that the effective charge of UN can be represented as U^1.71+N^1.71−. As for the thermodynamic study, the phonon dispersion illustrates the stability of UN and we further predict the lattice vibration energy, thermal expansion, and specific heat by utilizing the quasiharmonic approximation. Our calculated specific heat is well consistent with experiments.