放射性碘分子在Cu2O表面的吸附:第一性原理密度泛函研究

采用第一性原理密度泛函计算方法和周期性平板模型系统研究了放射性碘分子在Cu₂O三个低指数表面的吸附行为。通过计算若干平衡吸附构型的结构参数和吸附能评估了不同特征吸附位的作用。构型优化计算表明所选晶面存在适度的结构弛豫。计算结果表明,与Cu₂O（110）表面相比,Cu₂O（100）和（111）晶面表现出更高的碘分子吸附反应活性。其中,表面氧原子位（O_S）和配位未饱和铜原子位（Cu_CUS）分别为Cu₂O（100）和（111）晶面的能量最优吸附位点。此外,针对几种典型吸附结构计算分析了其电子结构信息,以进一步阐明吸附体系之间的相互作用机理。     

First-Principles Study on Electronic and Optical Properties of Graphene-Like Boron Phosphide Sheets

Two-dimensional semiconducting materials with moderate band gap and high carrier mobil-ity have a wide range of applications for electronics and optoelectronics in nanoscale. On the basis of first-principles calculations, we perform a comprehensive study on the electronics and optical properties of graphene-like boron phosphide (BP) sheets. The global structure search and first-principles based molecular dynamic simulation indicate that two-dimensional BP sheet has a graphene-like global minimum structure with high stability. BP monolayer is semiconductor with a direct band gap of 1.37 eV, which reduces with the number of layers. Moreover, the band gaps of BP sheets are insensitive to the applied uniaxial strain.= The calculated mobility of electrons in BP monolayer is as high as 10⁶ cm²/(V·s). Lastly, the MoS₂/BP van der Waals heterobilayers are investigated for photovoltaic applications, and their power conversion efficiencies are estimated to be in the range of 17.7%－19.7%. This study implies the potential applications of graphene-like BP sheets for electronic and optoelectronic devices in nanoscale.     

Nucleation of Boron-Nitrogen on Transition Metal Surface: A First-Principles Investigation

Boron nitrogen (BN) monolayer has attracted considerable attention because of their successful incorporation with graphene based nanodevices. However, many important aspects of the growth mechanisms are still not well explored. Using density functional theory (DFT) calculations, we found that Cu(111) surface is more suitable to be used as a substrate to grow BN monolayer compared with Ni(111) surface. Moreover, we explored that one-dimensional (1D) BN chain configuration is dominant to the two-dimensional (2D) BN ring formation from one pair to five BN pairs deposited on Cu(111) surface. Energetically stable structure transformation of BN monolayer from 1D BN chain to 2D BN ring occurs when the number of pairs is n>5. It is suggested that, as the number of BN pairs increases the energetically stable structures achieve.     

First-Principles Study of Field Emission from Zigzag Graphene Nanoribbons Terminated with Ether Groups

Field emission properties of zigzag graphene nanoribbons terminated with C-O-C ether groups (including cyclic and alternative ether groups at edge, denoted as ZGNR-CE and ZGNR-AE) are studied by adopting a self-consistent method based on density functional theory calculation. The results show that the field emissions of these two nanoribbons are dominated by states around Brillouin zone center and close to Fermi level. Because of lower work function, the ZGNR-CE can produce much stronger emission current than recon-structed zigzag graphene nanoribbon. The ZGNR-AE has nearly completely spin-polarized emission current, although its emission current is not strong enough. It is also found that under the lower E-field, the uniaxial strain can effectively modulate their emission currents but the spin polarization of ZGNR-AE keeps unchanged with the varied strain. The under-lying mechanisms are revealed by combining the analyses of their work functions and bandstructures with edge dipole model.     

第一性原理研究富勒烯衍生物PCBM的近边X射线吸收精细结构谱

富勒烯衍生物^{[6, 6]}-苯基-C₆₁-丁酸甲酯(PCBM)在有机聚合物太阳能电池的电子输运方面扮演着非常重要的角色.利用密度泛函理论计算了PCBM的近边X射线吸收精细结构谱及未占据分子轨道.通过对比计算得到的PCBM分子中不等价碳原子的谱线总和,将该分子的主要共振吸收峰进行了标定.我们分析了第一个π^*共振吸收峰高能区右肩吸收峰的来源,并确定了该吸收峰主要来自于C₆₀笼子中碳原子能量较高的未占据分子轨道的跃迁.     

First-Principles Study of La Doping Effects on the Electronic Structures and Photocatalytic Properties of Anatase TiO2

The effects of doping concentration, position and oxygen vacancy defect on the stability, electronic and optical properties of La-doped anatase TiO₂ have been investigated based on DFT+U method. The calculations indicated that the doping concentration and sites of La affected the stability and band gap of La-doped TiO₂ significantly due to the lattice distortion, which obey the ionic Pauling’s rules and crystal field theories; moreover, the simulated adsorption spectrum shows an obviously increase in the photocatalysis properties, which are in good agreement with recently experimental measurements. The oxygen vacancy defect will enhance the structural stability and the adsorption of visible light in La-doped TiO₂ system, which is important in photocatalytic application.     

Magnetism and Sound Velocities of Iron Carbide （Fe3C） under Pressure

The elastic property and sound velocity of FeaC under high pressure are investigated by using the spin-polarized generalized gradient approximation within density-functional theory. It is found that the magnetic phase transition from the ground ferromagnetic （FM） state to the nonmagnetic （NM） state occurs at ～73 GPa. Based on the predicted Hugoniot of Fe3C, we calculate the sound velocities of FM-Fe3C and NM-Fe3C from elastic constants. Compared with pure iron, NM-FeaC provides a better match of compressional and shear sound velocities with the seismic data of the inner core, supporting carbon as one of the light elements in the inner core.     

First-Principles Microkinetic Study of Methanol Synthesis on Cu(221) and ZnCu(221) Surfaces

First-principle based microkinetic simulations are performed to investigate methanol synthesis from CO and CO₂ on Cu(221) and CuZn(221) surfaces. It is found that regardless of surface structure, the carbon consumption rate follows the order:CO hydrogenation > CO/CO₂ hydrogenation > CO₂ hydrogenation. The superior CO hydrogenation activity mainly arises from the lower barriers of elementary reactions than CO₂ hydrogenation. Compared to Cu(221), the introduction of Zn greatly lowers the activity of methanol synthesis, in particularly for CO hydrogenation. For a mixed CO/CO₂ hydrogenation, CO acts as the carbon source on Cu(221) while both CO and CO₂ contribute to carbon conversion on CuZn(221). The degree of rate control studies show that the key steps that determine the reaction activity of CO/CO₂ hydrogenation are HCO and HCOO hydrogenation on Cu(221), instead of HCOOH hydrogenation on CuZn(221). The present work highlights the effect of the Zn doping and feed gas composition on methanol synthesis.     

Aun(n=2-9)团簇与乙醇分子相互作用的第一性原理研究

利用密度泛函理论研究了Au_n(n=2-9)团簇吸附一个乙醇分子的结构和电子性质. 研究结果表明: Au_n(n=2-9)团簇的最稳定构型为二维平面结构, Au6团簇最稳定; 吸附过程是通过金团簇上一个特定的金原子与乙醇分子中氧原子相互作用完成, 形成了20种稳定构型; 金原子的配位数对吸附作用影响明显; 作为吸附主体的金团簇和被吸附的乙醇分子在吸附前后构型无明显变化, 它们之间为弱相互作用.     

Experimental and Theoretical Study of Reactions between Manganese Oxide Cluster Cations and Hydrogen Sulfide

Manganese oxide cluster cations Mnm180n＋ were prepared by laser ablation and reacted with hydrogen sulfide （H2S） in a fast flow reactor under thermal collision conditions. A time-of-flight mass spectrometer was used to detect the cluster distributions before and after the interactions with H2S. The experiments suggest that oxygen-for-sulfur （O/S） ex- change reaction to release water took place in the reactor for most of the manganese oxide cluster cations： MnmlSOn＋＋H2S→Mnm18On-1S＋＋H218O. Density functional theory cal- culations were performed for reaction mechanisms of Mn202＋＋H2S, Mn203＋＋H2S, and Mn204＋＋H2S. The computational results indicate these O/S exchange reactions are both thermodynamically and kinetically favorable, thus in good agreement with the experimental observations. The O/S exchange reactions identified in this gas-phase cluster study parallel similar behavior of related condensed phase reaction systems.     

A First-Principles Study of C3N Nanostructures: Control and Engineering of the Electronic and Magnetic Properties of Nanosheets,Tubes and Ribbons

Using first-principles calculations we systematically investigate the atomic, electronic and magnetic properties of novel two-dimensional materials (2DM) with a stoichiometry C₃N which has recently been synthesized. We investigate how the number of layers affect the electronic properties by considering monolayer, bilayer and trilayer structures, with different stacking of the layers. We find that a transition from semiconducting to metallic character occurs which could offer potential applications in future nanoelectronic devices. We also study the affect of width of C₃N nanoribbons, as well as the radius and length of C₃N nanotubes, on the atomic, electronic and magnetic properties. Our results show that these properties can be modified depending on these dimensions, and depend markedly on the nature of the edge states. Functionalization of the nanostructures by the adsorption of H adatoms is found induce metallic, half-metallic, semiconducting and ferromagnetic behavior, which offers an approach to tailor the properties, as can the application of strain. Our calculations give insight into this new family of C₃N nanostructures, which reveal unusual electronic and magnetic properties, and may have great potential in applications such as sensors, electronics and optoelectronic at the nanoscale.     

碱金属原子掺杂BDC60分子中整流特性第一性原理研究

利用第一性密度泛函理论和非平衡格林函数相结合的方法,研究了碱金属原子掺杂对BDC60 分子电子输运性质的影响. 计算结果表明,在极低偏压下碱金属掺杂的BDC60分子能够表现出非常优良的整流性能,同时也展示出显著的负微分电阻行为. 根据透射谱和前线分子轨道及其空间分布随外加偏压的变化等方面的分析,系统地讨论了整流以及负微分电阻行为产生的内在机理. 我们的研究有助于BDC60 分子在未来低偏压整流和负微分电阻分子器件中的应用.     

Adsorption and Decomposition of NH3 on Ni/Pt(111) and Ni/WC(001) Surfaces: A First-Principles Study

Density functional theory was used to study the NH₃ behavior on Ni monolayer covered Pt(111) and WC(001). The electronic structure of the surfaces, and the adsorption and decomposition of NH₃ were calculated and compared. Ni atoms in the monolayer behave different from that in Ni(111). More dz2 electrons of Ni in monolayer covered systems were shifted to other regions compared to Ni(111), charge density depletion on this orbital is crucial to NH₃ adsorption. NH₃ binds more stable on Ni/Pt(111) and Ni/WC(001) than on Ni(111), the energy barriers of the first N-H bond scission were evidently lower on Ni/Pt(111) and Ni/WC(001) than on Ni(111), these are significant to NH₃ decomposition. N recombination is the rate-limiting step, high reaction barrier implies that N₂ is produced only at high temperatures. Although WC has similar properties to Pt, differences of the electronic structure and catalytic activities are observed for Ni/Pt(111) and Ni/WC(001), the energy barrier for the rate-determined step increases on Ni/WC(001) instead of decreasing on Ni/Pt(111) when compared to Ni(111). To design cheaper and better catalysts, reducing the N recombination barrier by modifying Ni/WC(001) is a critical question to be solved.     

碱性介质中CO对甲醇在PtAu(111)和Pt(111)表面氧化生成甲酸的影响的第一性原理研究

采用密度泛函理论计算研究了碱性介质中甲醇在清洁的PtAu(111)和Pt(111)表面、及有CO存在的PtAu(111)和Pt(111)表面的氧化。计算结果表明,在碱性介质中,预吸附的CO促进了甲醇在PtAu(111)和Pt(111)表面氧化的每一步反应,这与其在Au(111)表面的作用相似。究其原因,是由于CO的吸附增强了OH的稳定性和碱性,从而增强了OH夺取氢原子的能力。     

过渡金属掺杂SnO2的电子结构与磁性

采用密度泛函理论及赝势平面波方法, 对未掺杂SnO2以及过渡金属V、Cr、Mn掺杂SnO2的超原胞体系进行了几何优化, 计算了晶格常数、电子结构与磁学性质. 结果表明, 6.25%与12.5%两种掺杂浓度时, 体系的电子自旋和磁学性质没有发生很大的变化; 相对于未掺杂SnO2, 过渡金属掺杂后SnO2中O原子有向过渡金属移动的趋势, 并使得O与掺杂金属之间键长变短; 在V和Cr掺杂后, SnO2具有半金属性质, 而Mn掺杂SnO2没有发现上述性质. 6.25%与12.5%的杂质浓度对自旋和磁矩影响不大, 掺杂产生的磁矩主要来自于过渡金属3d电子态, 且磁矩的大小与过渡金属的电子排布有关. V、Cr、Mn掺杂SnO2后的总磁矩分别为0.94μB、2.02μB、3.00μB. 磁矩主要来源于过渡金属3d轨道的自旋极化, 当O原子出现负磁矩的时候, 还有很小一部分磁矩来源于临近过渡金属的Sn原子.     

单层石墨相氮化碳负载Pt4团簇吸附O2的第一性理论研究

采用第一性原理密度泛函理论结合周期性平板模型模拟研究了Pt₄团簇吸附单层石墨相氮化碳(g-C₃N₄)的几何结构和电子性质,以及氧气在其表面上的吸附行为。同时,对比分析了氧气在纯净的石墨相氮化碳和Pt₄团簇上的吸附行为。计算结果表明, Pt₄团簇吸附在3-s-三嗪环石墨相氮化碳表面,并与四个边缘氮原子成键,形成两个六元环时为最稳定构型。Pt₄团簇倾向于吸附在三嗪环石墨相氮化碳的空位并与邻近三个氮原子成键。由于Pt与N原子较强的杂化作用,以及金属与底物之间较多电子转移增强了Pt₄团簇吸附g-C₃N₄的稳定性。另外,对比分析了氧气在纯净的g-C₃N₄和金属吸附的g-C₃N₄上吸附行为,发现金属原子的加入促进了电子转移,同时拉长了O―O键长。Pt₄吸附3-s-三嗪环g-C₃N₄比Pt₄吸附三嗪环g-C₃N₄表现出微弱的优势,表现出明显的基底扭曲以及较大的吸附能。这些结果表明,化学吸附通过调节电子结构和表面性质增强催化性能的较好方法。     

过渡金属掺杂SnO_2的电子结构与磁性

采用密度泛函理论及赝势平面波方法,对未掺杂SnO_2以及过渡金属V、Cr、Mn掺杂SnO_2的超原胞体系进行了几何优化,计算了晶格常数、电子结构与磁学性质.结果表明,6.25%与12.5%两种掺杂浓度时,体系的电子自旋和磁学性质没有发生很大的变化;相对于未掺杂SnO_2,过渡金属掺杂后SnO_2中O原子有向过渡金属移动的趋势,并使得O与掺杂金属之间键长变短;在V和Cr掺杂后,SnO_2具有半金属性质,而Mn掺杂SnO_2没有发现上述性质.6.25%与12.5%的杂质浓度对自旋和磁矩影响不大,掺杂产生的磁矩主要来自于过渡金属3d电子态,且磁矩的大小与过渡金属的电子排布有关.V、Cr、Mn掺杂SnO_2后的总磁矩分别为0.94μ_B、2.0μ_B、3.00μ_B.磁矩主要来源于过渡金属3d轨道的自旋极化,当O原子出现负磁矩的时候,还有很小一部分磁矩来源于临近过渡金属的Sn原子.     

Theoretical Study on Molecular Structures of Methylaluminoxane Nanotubes

Density functional theory was used to optimize structures of different methylaluminoxane nanotubes with general formula [(AlOMe)₂]_n, [(AlOMe)₃]_n and [(AlOMe)₄]_n cycle unit, where n ranges from 1 to 10. To explore the stability of nanotubes, the binding energies and total energies are calculated. The results indicate that [(AlOMe)₃]_n and [(AlOMe)₄]_n have the stable structure of nanotubes. When n is 3, they have the most stable structure in all systems. Moreover, [(Al₅O₅)]_n and [(Al₇O₇)]_n are also considered, but their dimers have irregular and distorted structures. So [(Al₅O₅)]_n and [(Al₇O₇)]_n nanotubes are impossible to exist.     

Experimental and Theoretical Study of Deprotonation of DNA Adenine Cation Radical

Among all the DNA components, extremely redox-active guanine (G) and adenine (A) bases are subject to facile loss of an electron and form cation radicals (G^+· and A^+·) when exposed to irradiation or radical oxidants. The subsequent deprotonation of G^+· and A^+· can invoke DNA damage or interrupt hole transfer in DNA. However, compared with intensive reports for G^+·, studies on the deprotonation of A^+· are still limited at present. Herein, we investigate the deprotonation behavior of A^+· by time-resolved laser flash photolysis. The deprotonation product of A(N₆-H)^· is observed and the deprotonation rate constant, (2.0±0.1)×10⁷ s^-1, is obtained at room temperature. Further, the deprotonation rate constants of A^+· are measured at temperatures varying from 280 K to 300 K, from which the activation energy for the N₆-H deprotonation is determined to be (17.1±1.0) kJ/mol by Arrhenius equation. In addition, by incorporating the aqueous solvent effect, we perform density functional theory calculations for A^+· deprotonation in free base and in duplex DNA. Together with experimental results, the deprotonation mechanisms of A^+· in free base and in duplex DNA are revealed, which are of fundamental importance for understanding the oxidative DNA damage and designing DNA-based electrochemical devices.     

First-Principles Study of Aziridinium Lead Iodide Perovskite for Photovoltaics

The long-term stability remains one of the main challenges for the commercialization of the rapidly developing hybrid organic-inorganic perovskite solar cells. Herein, we investigate the electronic and optical properties of the recently reported hybrid halide perovskite (CH₂)₂NH₂PbI₃ (AZPbI₃), which exhibits a much better stability than the popular halide perovskites CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃, by using density functional theory (DFT). We find that AZPbI₃ possesses a band gap of 1.31 eV, ideal for single-junction solar cells, and its optical absorption is comparable with those of the popular CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃ materials in the whole visible-light region. In addition, the conductivity of AZPbI₃ can be tuned from efficient p-type to n-type, depending on the growth conditions. Besides, the charge-carrier mobilities and lifetimes are unlikely hampered by deep transition energy levels, which have higher formation energies in AZPbI₃ according to our calculations. Overall, we suggest that the perovskite AZPbI₃ is an excellent candidate as a stable high-performance photovoltaic absorber material.