Si掺杂金红石TiO2光学特性的第一性原理研究

TiO2是一种重要的n型金属氧化物半导体功能材料。近年来的实验与理论研究表明,运用杂质掺入来减小TiO2禁带宽度是提高其活性的一种有效办法。本文运用基于局域密度泛函和赝势的第一性原理方法,从理论上研究了Si掺杂金红石相TiO2的电子结构和光学特性。通过能带结构、态密度及电荷布居的分析发现,Si原子的引入使Si-Ti的键长发生明显的变化,近邻氧原子有靠近硅原子的趋势而近邻钛原子有远离硅原子的趋势。半导体禁带宽度没有明显变化,但是禁带中产生了一个杂质能级,该杂质能级主要是由Si的3p电子和Ti的3d电子杂化引起的。因此,Si掺杂能使材料的宏观特性表现为电子激发能量减小,材料活性增强,响应可见光范围达到480nm左右。     

A coherent three-dimensional Fermi surface in a high-transition-temperature superconductor

All conventional metals are known to possess a three-dimensional Fermi surface, which is the locus in reciprocal space of the long-lived electronic excitations that govern their electronic properties at low temperatures. These excitations should have well-defined momenta with components in all three dimensions. The high-transition-temperature (high-T(c)) copper oxide superconductors have unusual, highly two-dimensional properties above the superconducting transition. This, coupled with a lack of unambiguous evidence for a three-dimensional Fermi surface, has led to many new and exotic models for the underlying electronic ground state. Here we report the observation of polar angular magnetoresistance oscillations in the overdoped superconductor Tl2Ba2CuO6+delta in high magnetic fields, which firmly establishes the existence of a coherent three-dimensional Fermi surface. Analysis of the oscillations reveals that at certain symmetry points, however, this surface is strictly two-dimensional. This striking form of the Fermi surface topography, long-predicted by electronic band structure calculations, provides a natural explanation for a wide range of anisotropic properties both in the normal and superconducting states. Our data reveal that, despite their extreme electrical anisotropy, the high-T(c) materials at high doping levels can be understood within a framework of conventional three-dimensional metal physics.     

UC-PBG结构分析及在雷达系统中的应用

光子晶体又称光子带隙,是指具有一定光子带隙的人造周期性电介质结构,其理论依据来源于电子能带理论(半导体中的电子存在禁带),人们对光子带隙结构在微波工程中的应用给予了特别的关注,PBG结构的材料在微波集成电路的应用中造就了许多新型器件。经过近年的发展,又派生出新型单平面紧凑型光子带隙结构,在军用和民用方面有极大的应用价值,该文对UC-PBG结构在雷达系统中的应用展开分析。     

Si掺杂金红石TiO2光学特性的第一性原理研究

TiO2是一种重要的n型金属氧化物半导体功能材料。近年来的实验与理论研究表明,运用杂质掺入来减小TiO2禁带宽度是提高其活性的一种有效办法。本文运用基于局域密度泛函和赝势的第一性原理方法,从理论上研究了Si掺杂金红石相TiO2的电子结构和光学特性。通过能带结构、态密度及电荷布居的分析发现,Si原子的引入使Si-Ti的键长发生明显的变化,近邻氧原子有靠近硅原子的趋势而近邻钛原子有远离硅原子的趋势。半导体禁带宽度没有明显变化,但是禁带中产生了一个杂质能级,该杂质能级主要是由Si的3p电子和Ti的3d电子杂化引起的。因此,Si掺杂能使材料的宏观特性表现为电子激发能量减小,材料活性增强,响应可见光范围达到480nm左右。     

掺杂硫化铅体系的电子性质研究

基于密度泛函理论和广义梯度近似,对掺杂PbS体系进行了电子性质的第一性原理计算. 首先,对恒定掺杂浓度(6.25%)时3种替换杂质(Cd、Sn、Sb)不同掺杂位置的形成能进行比较分析,得到了最稳定的掺杂结构. 然后,计算不同掺杂体系的能带结构,能带结构发生了平移,带隙随掺杂原子序数单调递减. 最后,研究掺杂前后光学性质,光学性质的显著变化出现在Sb掺杂的PbS体系中,主要包括介电光谱下杂质峰的出现、相关红移现象以及掺杂后吸收谱能带边缘的拓展. 同时,Cd掺杂PbS介电光谱的反射峰最小.     

Challenges in band alignment between semiconducting materials:A case of rutile and anatase TiO_2

This topical review focuses on the recently active debate on the band alignment between two polymorphs of TiO_2,rutile and anatase.A summary is given to the popular methods for measurement and calculation of band alignment between materials.We point out,through examination of recently experimental and theoretical reports,that the outstanding discrepancy in the band alignment between two Ti02 phases is attributed to factors that influence band alignment rather than needs a definite answer of which band alignment is right.According to an important factor,the presence of an interface,a new classification of band alignment is proposed as the coupled and intrinsic band alignments.This classification indeed reveals that the rutile/anatase interface can qualitatively change the type of their band alignment.However,further systematic information of the interface and other factors that influence band alignment will be needed to better understand changes in energy bands of materials.The results obtained from discussion of the band alignment between rutile and anatase may also work for the band alignment between other semiconductors.     

Zn掺杂MoS2的构型、电子结构及电催化析氢性能的理论研究

采用密度泛函理论(DFT)方法对二硫化钼(MoS₂)完整表面和不同掺杂浓度下过渡金属Zn原子掺杂MoS₂表面(Zn-MoS₂)的构型、电子结构及其电催化析氢性能进行了研究.研究结果表明:与MoS₂完整表面相比,Zn掺杂单层MoS₂的氢吸附吉布斯自由能(-0.09 eV)明显减小,接近理想值(约0 eV),表现出优异的析氢催化反应性能.电子结构研究结果表明:Zn掺杂MoS₂表面后,体系费米能级附近出现了Zn-3d轨道的带隙态,这表明有效调控了MoS₂催化材料的电子结构.在费米能级附近还出现了与Zn原子相邻的S原子的3p轨道的新电子态,可有效增强S-3p轨道和H-1s轨道的重叠,从而提高吸附氢的性能、优化电催化析氢性能.进一步对不同Zn掺杂浓度下Zn-MoS₂体系的研究结果表明提高Zn掺杂浓度仍能保持优异的电催化析氢反应性能.该文通过引入不同Zn掺杂浓度的方法,对MoS₂电催化剂的电子结构进行调控,从而有效提升电催化析氢反应性能.     

TiH_2电子结构和导电性的第一原理计算

采用基于密度泛函理论的全势全电子线性缀加平面波方法,对储氢材料TiH2的电子结构进行了理论分析.计算得到的能带结构和态密度表明该化合物具有金属性的特点,但是Ti—H键有明显的共价键特征.因此可以理解其导电性小于金属Ti,这与实验观测符合得很好.     

氢键、氢桥键、氢配位键的关系

讨论了氢桥键、氢键、氢配位键的共同特征，指出了氢键、氢桥键、氢配位键都是氢键，氢桥是氢键作用过程的基本形式，氢键、氢桥键、氢配位键是桥氢受两端基团作用力不同而引起的不同的氢键作用结果．并用氢桥键理论解释了一些物质的结构和性质     

A superconductor to superfluid phase transition in liquid metallic hydrogen

Although hydrogen is the simplest of atoms, it does not form the simplest of solids or liquids. Quantum effects in these phases are considerable (a consequence of the light proton mass) and they have a demonstrable and often puzzling influence on many physical properties, including spatial order. To date, the structure of dense hydrogen remains experimentally elusive. Recent studies of the melting curve of hydrogen indicate that at high (but experimentally accessible) pressures, compressed hydrogen will adopt a liquid state, even at low temperatures. In reaching this phase, hydrogen is also projected to pass through an insulator-to-metal transition. This raises the possibility of new state of matter: a near ground-state liquid metal, and its ordered states in the quantum domain. Ordered quantum fluids are traditionally categorized as superconductors or superfluids; these respective systems feature dissipationless electrical currents or mass flow. Here we report a topological analysis of the projected phase of liquid metallic hydrogen, finding that it may represent a new type of ordered quantum fluid. Specifically, we show that liquid metallic hydrogen cannot be categorized exclusively as a superconductor or superfluid. We predict that, in the presence of a magnetic field, liquid metallic hydrogen will exhibit several phase transitions to ordered states, ranging from superconductors to superfluids.     

化学物质的颜色和电子跃迁

本文根据量子理论,主要从电子跃迁(d-d跃迁、分子轨道跃迁、电荷跃迁和能带跃迁等)的角度,探讨了过渡金属离子及其化合物、有机分子、金属、合金、半导体、矿石、宝石及其它某些无机物呈现颜色的机理,     

Sb掺SnO2的光电性质研究

基于密度泛函理论,我们研究了掺杂浓度为12.5%时Sb掺杂SnO₂的电子结构和光学性质,包括能带结构、态密度、介电函数和光学吸收谱。掺杂后的SnO₂材料的导电性得到了明显的增强,具有了半金属的性质;费米能级处能带细化,介电常数和光学吸收谱具有对应关系,光学吸收谱峰值发生了蓝移。     

Pt掺杂锐钛矿型TiO2电子结构和光学性质第一性原理研究

为了研究Pt掺杂对锐钛矿型TiO2电子结构和光学性质的影响,本文采用基于密度泛函理论的平面波超软赝势方法,对未掺杂和Pt掺杂锐钛矿型TiO2的电子结构和光学性质做第一性原理计算。得到了掺杂前后的品格结构常数、结合能电子态密度分布、能带结构、介电函数虚部、光吸收系数等性质,定性地分析了掺杂前后能带结构和光学性质的变化。研究结果表明,Pt掺杂锐钛矿型TiO2带隙中能产生新的能带,而且能带位置明显下移,掺杂后不但能使TiO2的吸收带产生红移,而且在可见光区具有较大的吸收系数,表现出较高的光催化活性,理论与实验基本吻合。     

聚螺戊二烯及其衍生物的理论研究

用ＳＣＦ－ＣＮＤＯ／２－ＣＯ方法对聚螺戊二烯及其取代衍生物的电子结构进行了研究，目的在于探讨螺环共轭高分子体系电子结构的特点，以及不同电子性质的取代基对聚螺戊二烯衍生物的高聚物电子特性的影响，计算结果表明取代基对带隔影响不大，而且也不能使主链结构变化，但体系的电离势和电子亲和势的变化与取代基的电子特性有关。     

Controlled properties of perovskite oxide films by engineering oxygen octahedral rotation

Complex perovskite oxides exhibit extremely rich physical properties in terms of magnetism, electrical transport, and electrical polarization characteristics due to the competition and coupling of many degrees of freedom. The B-site ions and O ions in perovskite form six-coordinated octahedral units, which are connected at a common vertex toward the basic framework of the perovskite oxide, providing a crucial platform to tailor physical properties. The rotation or distortion of the oxygen octahedra will tip the competing balance, leading to many emergent ground states. To further clarify the subtle relationship between emergent properties and oxide octahedral behavior, this article reviews the structure of perovskite oxides, the characterization methods of oxygen octahedral rotation and the response of transport, electrical polarization and magnetism of several typical perovskite heterostructures to oxygen octahedral rotation modes. With knowledge of how to manipulate the octahedral rotation behavior and regulate the physical properties of perovskite oxides, rationally designing the sample manufacturing process can effectively guide the development and application of novel electronic functional materials and devices.     

基于Fe/Ni共掺杂CdS的电子结构和光学性质

利用第一性原理计算方法，研究Fe/Ni单（共）掺杂对CdS几何结构、电子结构和光学性质的影响. 结果表明，Fe/Ni单（共）掺杂使带隙发生窄化，（Fe，Ni）共掺杂使带隙中出现更多的杂质能级，这些杂质能级主要来自Fe 3d态、Ni 3d态和S 3p态电子相互间的杂化作用; （Fe，Ni）共掺杂远大于单掺杂CdS的光吸收强度，（Fe，Ni）共掺杂的协同作用可大幅度提高CdS对可见光的响应能力和光催化活性.     

基于Fe/Ni共掺杂CdS的电子结构和光学性质

利用第一性原理计算方法，研究Fe/Ni单（共）掺杂对CdS几何结构、电子结构和光学性质的影响. 结果表明，Fe/Ni单（共）掺杂使带隙发生窄化，（Fe，Ni）共掺杂使带隙中出现更多的杂质能级，这些杂质能级主要来自Fe 3d态、Ni 3d态和S 3p态电子相互间的杂化作用; （Fe，Ni）共掺杂远大于单掺杂CdS的光吸收强度，（Fe，Ni）共掺杂的协同作用可大幅度提高CdS对可见光的响应能力和光催化活性.     

Role of intrinsic dipole on photocatalytic water splitting for Janus MoSSe/nitrides heterostructure:A first-principles study

Searching for visible-infrared solar utilization for photocatalytic water splitting is highly desirable,since most of solar energy is distributed the visible-infrared region.However,it is difficult for a pure system to satisfy both band gap and band edge conditions for water splitting in visible-infrared region.Herein,heterostructure consisting of Janus MoSSe and nitrides XN (X=Al,Ga) is proposed,and the structural and electronic properties are systematically studied by the firstprinciples calculations.It shows that the AA-stacking heterostructure is more stable than other stacking.The calculated electronic property shows that MoSSe/AIN heterostructures have indirect band gaps in the range of 1.00eV-1.68eV,while MoSSe/GaN heterostructures are always direct semiconductors with band gaps of0.8 eV-1.51 eV.Interestingly,despite the band gaps of MoSSe/XN heterostructures being smaller than 1.23 eV,the band edge positions are always suitable for water splitting,suggesting good activity of these heterostructures in visible-infrared region.This special behavior mainly originates from the intrinsic dipole with the electrons of VBM and CBM distributed on two opposite layers,producing an electrostatic potential difference between the layers.This electrostatic potential difference,acting as an auxiliary booster for photoinduced carriers,can effectively reduce the band gap required for water splitting in visible-infrared region.In addition,the band edge position can be further adjusted by strains,leading to higher reactivity for water splitting.Our findings strongly suggest that this novel Janus MoSSe/XN heterostructure can offer exciting opportunities for designing visible-infrared photocatalysis for water splitting.     

不同氧化锆相的稳定性及电子结构的第一性原理研究

通过密度泛函理论计算了不同氧化锆相的晶体结构参数,在所有晶相模型结构优化的基础上,分析了在一般温度和压力下不同晶相稳定程度不同的原因。使用3种不同的泛函计算了不同晶相的电子能带结构和态密度电荷差分密度,发现在氧化锆高温稳定相体系中,由于强关联电子的相互作用增强,传统密度泛函理论的广义梯度近似平面波超软赝势泛函及其修正的Hubbard U方法都会严重低估能带带隙,因此所得各层能带位置不准确,而使用B3LYP杂化泛函计算的结果则可以很好地与已有实验结果相吻合。结合杂化泛函计算出的态密度和差分密度数据,在理论上从电子间相互作用的角度解释了氧化锆不同晶相的稳定性、导电性及光吸收性能。     

激发态对C60价电荷密度的影响

为发展sp3s*紧束缚模型，用于计算笼状纳米结构的电子结构．具体考虑了s*激发态对C60电子结构的影响．计算了C60团簇的能带结构和电子几率密度．计算的能隙值1．893eV与实验值符合得很好．同时，计算的结果也能对价带和导带进行很好的描述．