染料敏化太阳能电池中具有不同电子给体的吩噻嗪类有机光敏染科的理论研究

采用密度泛函理论和含时密度泛函理论方法计算了2个吩噻嗪类染料及其吸附到TiO2上后分子的基态和激发态光物理性质与热力学参数.结果表明,电子给体的改变虽未明显改变染料的光谱性质(垂直跃迁能和振子强度),但可以改变分子的前线轨道能级,进而影响染料分子的激子结合能Eb及激发态电子注入到半导体TiO2中的驱动力△Gint的大小...     

8-巯基喹啉阴离子的锌配合物及其衍生物的电子光谱性质的含时密度泛函理论研究

采用从头算(ab initio)和密度泛函理论(DFT B3LYP)方法, 对配合物8-巯基喹啉锌Zn(tq)₂及其5种衍生物基态结构进行优化, 用含时密度泛函理论(TD-DFT/B3LYP)及6-31＋G(d)基组计算吸收光谱; 同时用ab initio HF 单激发组态相互作用(CIS)法在6-31G(d)基组上优化其最低激发单重态几何结构, 用含时密度泛函理论计算发射光谱. 结果表明, 电子在基态与激发态间的跃迁, 主要是在配体8-巯基喹啉(tq)环内的电荷转移, 电子从含S的苯硫酚环转移至含N的吡啶环上; 吸收光谱和发射光谱的计算值与实验值基本符合. 该类配合物都是优良的电子传输材料, 改变金属离子和取代基均可以调控发光材料的光谱波段.     

二(2-苯基-8-羟基喹啉)锌及其衍生物的电子光谱性质的含时密度泛函理论研究

采用从头算(ab initio)和密度泛函理论(DFT B3LYP)方法。对二(2-苯基-8-羟基喹啉)锌(Zn(qPh)₂)及其衍生物的基态结构进行优化，同时用ab initio HF单激发组态相互作用(CIS)法在6-31G基组上优化其最低激发单重态几何结构，用含时密度泛函理论(TD-DFT/B3LYP)及6-31G基组计算吸收和发射光谱。计算表明，该类物质电子在基态与激发态间的跃迁，主要是电子云分布由定域化向离域化的转变。吸收及发射光谱的计算值与实验值基本符合。该类化合物的电子亲和能较大，都是优良的电子传输材料，改变中心金属原子对配合物光谱性质影响不大。而羟基氧被硫原子取代后，化合物的吸收光谱产生明显红移。     

Yb、YbO电子激发态的相对论含时密度泛函理论研究

本文用基于精确二分量哈密顿（exact two—component Hamiltonian）的相对论含时密度泛函理论（time-dependent relativistic density functional theory）计算了Yb和YbO的电子激发态,并利用对称性、自然原子轨道对激发态性质和归属进行了详细分析,所得结果支持实验对YbO基态与激发态的指认．     

1,3-二氮杂薁类衍生物电子结构和光谱性质的理论研究

对1,3-二氮杂薁类衍生物采用密度泛函理论(DFT)在B3LYP/6-31G(d)的水平上进行了几何构型的全优化, 在此基础上探讨了分子结构和前线分子轨道能量等性质的变化规律, 采用含时密度泛函理论(TD-DFT)计算了分子的电子跃迁性质, 采用二维平面图和三维立体图来直观表示激发态的性质, 研究分子内电子转移特性. 跃迁密度矩阵的二维等高线图反映了电子-空穴相干性, 三维跃迁密度图反映了跃迁偶极矩的方向和强度, 三维电荷差异密度图说明了激发过程中分子内电子转移性质.     

基于苯并噻二唑和硅芴的一系列红光材料的载流子传输性质及荧光性质(英文)

用密度泛函理论(DFT)方法研究了基于苯并噻二唑和硅芴的一系列聚合物的基态和激发态结构、传输和荧光性质.聚合物的能隙、电离能、电子亲和势、最低激发能以及吸收光谱通过外推法得到.结果表明空穴、电子注入和传输性质受苯并噻唑在硅芴上的位置以及正丁基在噻吩上的位置影响很大.(SiF2-DHTBT1-m)n和(SiF1-DHTBT1-m)n(SiF和DHTBT分别代表硅芴和4,7-二(2-噻吩基)-2,1,3-苯并噻二唑)表现出较好的空穴和电子注入性质,而(SiF1-DHTBT1-o)n和(SiF1-DHTBT1-p)n的电荷注入性质较差.除(SiF1-DHTBT1-o)n外,聚合物的荧光光谱处于红光范围.     

7-甲氧基香豆素-3-甲酰二乙醇胺的电子结构和光谱性质的理论研究

采用密度泛函的B3LYP和单激发组态相互作用(CIS)方法分别对基态和第一、第二单重激发态(S1和S2)结构进行优化,均采用6-31G(d)基组.在优化的基态和第一单重激发态的结构基础上,用含时密度泛函理论(TD-DFT),成功模拟了7-甲氧基香豆素-3-甲酰二乙醇胺的吸收光谱和荧光发射光谱,并用极化连续模型考虑了溶剂的影响.利用前线轨道、电荷密度差(CDD)和态密度(DOS)图分析了电子跃迁的特性.计算结果与实验结果吻合得很好.该量子计算方法对此类化合物的定性和定量研究是有效的.     

荧光素及其衍生物电子结构与光谱性质的理论研究

用ZINDO、从头算和密度泛函理论方法研究荧光素及其衍生物的电子结构和光谱性质.计算结果表明母体双阴离子荧光素分子(1)与单(2)、双(3)取代形成的单阴离子荧光素分子的基态电子结构不同,而且1与2和3的基态和激发态的电子转移方向相反.体系1~3的最大吸收波长依次发生红移,与实验结果相符合.     

[Pt2(P2O5H2)4]4-和[Pt2(P2O4CH4)4]4-基态和激发态性质的理论研究

采用从头计算MP2和CIS方法分别优化等电子双核d8配合物[Pt2(P2O5H2)4]4-和[Pt2(P2O4CH4)4]4-的基态和激发态结构.结果表明基态Pt-Pt距离分别为0.2905和0.2987nm,与实验的0.2925和0.2980nm符合.NBO计算的Pt-Pt键级以及Pt原子间伸缩振动说明Pt-Pt相互作用具有吸引本质.CIS计算揭示电子激发到Pt-Pt的σ(pz)成键轨道使得相互作用增强.保持激发态几何,含时密度泛函理论(TD-DFT)计算的溶液发射分别为449和475nm,与实验值512和510nm接近.     

8-羟基喹啉过渡金属配合物电子光谱和二阶非线性光学性质的 DFT研究

使用含时密度泛函理论(TDDFT)B3LYP方法计算了IB, IIB, VIIIB过渡金属与8-羟基喹啉络合(MQ)后, 配合物的电子光谱以及二阶非线性光学性质. 结果表明, 掺杂过渡金属后, 形成络合物的能隙值减小100～150 kJ/mol, 最大吸收波长红移150～200 nm左右. 电子从基态到激发态的跃迁主要为p→p*, n→p*跃迁, 属于LLCT, MLCT过程. IB的络合物MQ以及VIIIB的络合物MQ3表现出良好的非线性光学性质.     

Electronic and magnetic properties of armchair and zigzag graphene nanoribbons

The electronic properties, band gap, and ionization potential of zigzag and armchair graphene nanoribbons are calculated as a function of the number of carbon atoms in the ribbon employing density functional theory at the B3LYP6-31G* level. In armchair ribbons, the ionization potential and band gap show a gradual decrease with length. For zigzag ribbons, the dependence of the band gap and ionization potential on ribbon length is different depending on whether the ribbon has an unpaired electron or not. It is also found that boron and nitrogen zigzag and armchair doped graphene nanoribbons have a triplet ground state and could be ferromagnetic.     

Communication: A dramatic transition from nonferromagnet to ferromagnet in finite fused-azulene chain

One-dimensional fused-azulene oligomers (n = 2-6) are studied with the effective valence bond as well as density functional theory methods. A nonferromagnetic (closed-shell singlet) to ferromagnetic (triplet) ground state transformation is witnessed with increasing length of oligomers. The computational results are interpreted in terms of spin coupling between the unpaired electrons of two nonbonding molecular orbitals localized, respectively, on the top and bottom chains of the oligomers. The present study provides a theoretical suggestion for understanding the ferromagnetic spin polarizations that has been observed very recently in graphene nanoribbons.     

Spin-spin and spin-orbit interactions in nanographene fragments: a quantum chemistry approach

The relativistic behavior of graphene structures, starting from the fundamental building blocks--the poly-aromatic hydrocarbons (PAHs) along with other PAH nanographenes--is studied to quantify any associated intrinsic magnetism in the triplet (T) state and subsequently in the ground singlet (S) state with account of possible S-T mixture induced by spin-orbit coupling (SOC). We employ a first principle quantum chemical-based approach and density functional theory (DFT) for a systematic treatment of the spin-Hamiltonian by considering both the spin-orbit and spin-spin interactions as dependent on different numbers of benzene rings. We assess these relativistic spin-coupling phenomena in terms of splitting parameters which cause magnetic anisotropy in absence of external perturbations. Possible routes for changes in the couplings in terms of doping and defects are also simulated and discussed. Accounting for the artificial character of the broken-symmetry solutions for strong spin polarization of the so-called "singlet open-shell" ground state in zigzag graphene nanoribbons predicted by spin-unrestricted DFT approaches, we interpolate results from more sophisticated methods for the S-T gaps and spin-orbit coupling (SOC) integrals and find that these spin interactions become weak as function of size and increasing decoupling of electrons at the edges. This leads to reduced electron spin-spin interaction and hence almost negligible intrinsic magnetism in the carbon-based PAHs and carbon nanographene fragments. Our results are in agreement with the fact that direct experimental evidence of edge magnetism in pristine graphene has been reported so far. We support the notion that magnetism in graphene only can be ascribed to structural defects or impurities.     

Quenching of local magnetic moment in oxygen adsorbed graphene nanoribbons

The electronic and magnetic properties of oxidized zigzag and armchair graphene nanoribbons, with hydrogen passivated edges, have been investigated from ab initio pseudopotential calculations within the density functional scheme. The oxygen molecule in its triplet state is adsorbed most stably at the edge of a zigzag nanoribbon. The Stoner metallic behavior of the ferromagnetic nanoribbons and the Slater insulating (ground state) behavior of the antiferromagnetic nanoribbons remain intact upon oxygen adsorption. The formation of a spin-paired C-O bond drastically reduces the local atomic magnetic moment of carbon at the edge of the ferromagnetic zigzag ribbon.     

Electronic and Optical Properties of O-Terminated Armchair Graphene Nanoribbons

The structure, electromagnetic and optical properties of the O-terminated graphene nanorib-bons with armchair edge are studied using first-principles theory. The results show that the O-terminated armchair edge are more stable than the H-terminated ribbons and show metal-lic character. Spin-polarized calculations reveal that the antiferromagnetic state are more stable than the ferromagnetic state. The energy band and density of states analyses show that the O-terminated armchair edge are antiferromagnetic semiconductors. Because of the terminated O atoms, the dielectric function has an evident red shift and the first peak is the strongest with its main contribution derived from the highest valence band. The peaks of the dielectric function, re ection, absorption, energy loss are related to the transition of electrons. Our results suggest that the O-terminated graphene nanoribbons have potential applications in nanoelectronics, opto-electric devices.     

Correlated electron dynamics: how aromaticity can be controlled

In this Article, we show that the aromaticity of a molecule can be turned off by controlling the electron dynamics. We present a controlled switching from the aromatic ground state of benzene to two different nonaromatic states, using a laser pulse. The propagation of the molecular wave function is carried out with the time-dependent configuration interaction method. The laser pulse for switching between the ground and excited states is optimized using optimal control theory. Bond orders and Mulliken charges serve as an aromaticity criterion. The nonaromatic target states exhibit localized bonds and partial charges on the carbon atoms; these localized electrons circulate on an attosecond time scale in the ring system.     

Half-metallicity in undoped and boron doped graphene nanoribbons in the presence of semilocal exchange-correlation interactions

We perform density functional calculations on one-dimensional zigzag edge graphene nanoribbons (ZGNRs) of different widths, with and without edge doping including semilocal exchange correlations. Our study reveals that, although the ground state of edge-passivated (with hydrogen) ZGNRs prefers to be anti-ferromagnetic, the doping of both of the edges with boron atoms stabilizes the system in a ferromagnetic ground state. Both the local and semilocal exchange correlations result in half-metallicity in edge-passivated ZGNRs at a finite cross-ribbon electric field. However, the ZGNR with boron edges shows half-metallic behavior irrespective of the ribbon width even in the absence of electric field and this property sustains for any field strength, opening a huge possibility of applications in spintronics.     

First-principles study of the triwing graphene nanoribbons: junction-dependent electronic structures and electric field modulations

Using first-principles calculations, we investigate the structural, electronic and magnetic properties of triwing zigzag graphene nanoribbons (TW-ZGNRs), as well as the electric field effects on their electronic structures. The TW-ZGNRs have comparable energetic stabilities to the normal ZGNRs and exhibit fascinating junction-dependent electronic properties. With the sp(2) hybridized junctions, the TW-ZGNRs undergo a Peierls distortion and behave as ferromagnetic metals. While the TW-ZGNRs with sp(3) hybridized junctions become semiconductors, which have a ferrimagnetic ground state. An external electric field can further modulate the band structures of semiconducting TW-ZGNRs. The parallel electric field directly moves the flat bands around the Fermi level, while the perpendicular field controls the edge states at the ribbon wings. By these electric field modulations, the band gaps are effectively tuned and half-metallicity can be induced into TW-ZGNRs. Our studies demonstrate that the junctions play an important role in the electronic structures of TW-ZGNRs, which have well-tunable electronic and magnetic properties for potential applications in nanoelectronics and spintronics.     

Gapped ferromagnetic graphene nanoribbons

We theoretically design a graphene-based all-organic ferromagnetic semiconductor by terminating zigzag graphene nanoribbons (ZGNRs) with organic magnets. A large spin-split gap with a 100% spin polarized density of states near the Fermi energy is obtained, which is of potential application in spin transistors. The interactions among electron, spin and lattice degrees of freedom are studied using the first-principles calculations including non-collinear spin orientations. All of the calculations consistently demonstrate that although no d electrons existing, the antiferromagnetic π-π exchange together with the strong electron-lattice interactions between organic magnets and ZGNRs make the ground state ferromagnetic.     

Effects of Edge Oxidation on the Stability and Half‐Metallicity of Graphene Quantum Dots

A comprehensive first‐principles theoretical study of the electronic properties and half‐metallic nature of zigzag edge‐oxidized graphene quantum dots (GQDs) is carried out by using density functional theory (DFT) with the screened exchange hybrid functional of Heyd, Scuseria and Ernzerhof (HSE06). The oxidation schemes include ‐OH, ‐COOH and ‐COO groups. We identify oxidized GQDs whose opposite spins are localized at the two zigzag edges in an antiferromagnetic‐type configuration, showing a spin‐polarized ground state. Oxidized GQDs are more stable than the corresponding fully hydrogenated GQDs. The partially hydroxylated and carboxylated GQDs with the same size exhibit half‐metallic state under almost the same electric‐field intensity whereas fully oxidized GQDs behave as spin‐selective semiconductors. The electric‐field intensity inducing the half metal increases with the length of the partially oxidized GQDs, ranging from M=4 to 7.