A time-dependent density functional theory investigation of plasmon resonances of linear Au atomic chains

We report theoretical studies on the plasmon resonances in linear Au atomic chains by using ab initio time- dependent density functional theory. The dipole responses are investigated each as a function of chain length. They converge into a single resonance in the longitudinal mode but split into two transverse modes. As the chain length increases, the longitudinal plasmon mode is redshifted in energy while the transverse modes shift in the opposite direction （blueshifts）. In addition, the energy gap between the two transverse modes reduces with chain length increasing. We find that there are unique characteristics, different from those of other metallic chains. These characteristics are crucial to atomic-scale engineering of single-molecule sensing, optical spectroscopy, and so on.

Theoretical investigation on the excited state intramolecular proton transfer in Me_2N substituted flavonoid by the time-dependent density functional theory method

Time-dependent density functional theory（TDDFT） method is used to investigate the details of the excited state intramolecular proton transfer（ESIPT） process and the mechanism for temperature effect on the Enol＊/Keto＊emission ratio for the Me2N-substited flavonoid（MNF） compound. The geometric structures of the S0 and S1 states are denoted as the Enol, Enol＊, and Keto＊. In addition, the absorption and fluorescence peaks are also calculated. It is noted that the calculated large Stokes shift is in good agreement with the experimental result. Furthermore, our results confirm that the ESIPT process happens upon photoexcitation, which is distinctly monitored by the formation and disappearance of the characteristic peaks of infrared（IR） spectra involved in the proton transfer and in the potential energy curves. Besides, the calculations of highest occupied molecular orbital（HOMO） and lowest unoccupied molecular orbital（LUMO） reveal that the electronegativity change of proton acceptor due to the intramolecular charge redistribution in the S1 state induces the ESIPT. Moreover, the thermodynamic calculation for the MNF shows that the Enol＊/Keto＊emission ratio decreasing with temperature increasing arises from the barrier lowering of ESIPT.

Theoretical Study on the Optical Properties for 2,7- and 3,6-Linked Carbazole Trimers by Time-dependent Density Functional Theory

Electronic properties, such as HOMO and LUMO energies, band gaps, ionization potential （IP） and electron affinity （EA） of 2,7- and 3,6-1inked carbazole trimers, two conjugated oligomcrs with different linkages of carbazole, were studicd by the density functional theory with Becke-Lee-Young-Parr composite exchange correlation functional （B3LYP）. The absorption spectra of these compounds were also investigated by time-dependent density functional theory （TD-DFT） with 6-3 IG＊ basis set. The calculated results indicated that the HOMO and LUMO of the 2,7- and 3,6-1inked carbazole trimers are both slightly destabilized on going from methyl substitution to sec-butyl substitution. Both IP and EA exhibit their good hole-transporting but poor electronaccepting ability. The presence of alkyl groups on the nitrogen atoms does not affect the intra-chain electronic delocalization along the molecular frame. Thus no significant effect on the band gap and absorption spectra of compounds has been found.

Time-dependent density functional theoretical studies on the photo-induced dynamics of an HCI molecule encapsulated in C60 under femtosecond laser pulses

By using first-principles simulations based on time-dependent density functional theory, the chemical reaction of an HCl molecule encapsulated in C60 induced by femtosecond laser pulses is observed. The H atom starts to leave the Cl atom and is reflected by the C60 wall. The coherent nuclear dynamic behaviors of bond breakage and recombination of the HCl molecule occurring in both polarized parallel and perpendicular to the H-Cl bond axis are investigated. The radial oscillation is also found in the two polarization directions of the laser pulse. The relaxation time of the H-Cl bond lengths in transverse polarization is slow in comparison with that in longitudinal polarization. Those results are important for studying the dynamics of the chemical bond at an atomic level.

Time-dependent density functional theory for quantum transport

电子设备的快速的小型化在量运输激发研究兴趣。最近，时间依赖者量运输成为了一个重要研究话题。这里，我们在时间依赖者的发展考察最近的进步为包括理论基础和数字算法的量运输的密度功能的理论。特别地，还原剂单人赛电子密度矩阵基于运动的层次方程，它能从 Liouville-von Neumann 方程被导出，在细节被考察。数字实现被讨论，现实主义的设备的模拟结果将被给。

Time-dependent density-functional theory for open electronic systems

Time-dependent density-functional theory(TDDFT)has been successfully applied to predict excited-state properties of isolated and periodic systems.However,it cannot address a system coupled to an environment or whose number of electrons is not conserved.To tackle these problems,TDDFT needs to be extended to accommodate open systems.This paper provides a comprehensive account of the recent developments of TDDFT for open systems(TDDFT-OS),including both theoretical and practical aspects.The practicality and accuracy of a latest TDDFT-OS method is demonstrated with two numerical examples:the time-dependent electron transport through a series of quasi-one-dimensional atomic chains,and the real-time electronic dynamics on a two-dimensional graphene surface.The advancement of TDDFT-OS may lead to promising applications in various fields of chemistry,including energy conversion and heterogeneous catalysis.

Chiroptical properties of artemisinin and artemether investigated using time-dependent density functional theory

Chiroptical properties including electronic circular dichroism（ECD） and optical rotatory dispersion（ORD） of artemisinin and artemether have been fully studied using quantum-chemical calculation based on time-dependent density functional theory.Both theoretical ECD and ORD of these two compounds were in good match with the experimental data.ECD spectrum of artemether could be totally attributed to the peroxide group,and that of artemisinin was an overlay of contribution from δ-lactone and peroxide moieties,which leading to a positive maximum at 260 nm.Our results showed that peroxide group could produce a broad ECD band in the far-UV region originated from electron transitions of HOMO →LUMO,HOMO-1 →LUMO and HOMO-2 →LUMO in the case of artemether.This work provided a theoretical interpretation of the ECD behavior of peroxide bond.

Studies on Optical Properties of Si220 Nanoclusters viaTime-dependent Density Functional Theory Calculations

The optical properties of bare and hydrogen passivated Si220 nanoclusters（NCs） in four typical motifs（i.e.,bulk-like, onion-like, bucky-diamond and icosahedral motifs） were studied via time-dependent density functionaltheory（TD-DFT） calculations. The calculation results show that there is a significant blue shift in the optical absorp-tion spectra when the Si NCs are passivated with hydrogen. A strong absorption peak in the visible light region ap-years for the hydrogenated bulk-like, onion-like and bucky-diamond Si NCs.

Effective Maxwell Equations from Time-dependent Density Functional Theory

The behavior of interacting electrons in a perfect crystal under macroscopic external electric and magnetic fields is studied. Effective Maxwell equations for the macroscopic electric and magnetic fields are derived starting from time-dependent density functional theory. Effective permittivity and permeability coefficients are obtained.

Time-dependent relativistic density functional study of Yb and YbO

The low-lying electronic states of Yb and YbO are investigated by using time-dependent relativistic density functional theory,which is based on the newly developed exact two-component Hamiltonian resulting from symmetrized elimination of the small component.The nature of the excited states is analyzed by using the full molecular symmetry.The calculated results support the previous experimental assignment of the ground and excited states of YbO.

Microscopic mechanism of plasmon-mediated photocatalytic H_(2) splitting on Ag-Au alloy chain

Alloy nanostructures supporting localized surface plasmon resonances has been widely used as efficient photocatalysts,but the microscopic mechanism of alloy compositions enhancing the catalytic efficiency is still unclear.By using time-dependent density functional theory(TDDFT),we analyze the real-time reaction processes of plasmon-mediated H_(2) splitting on linear Ag-Au alloy chains when exposed to femtosecond laser pulses.It is found that H_(2) splitting rate depends on the position and proportion of Au atoms in alloy chains,which indicates that specially designed Ag-Au alloy is more likely to induce the reaction than pure Ag chain.Especially,more electrons directly transfer from the alloy chain to the anti-bonding state of H_(2),thereby accelerating the H_(2) splitting reaction.These results establish a theoretical foundation for comprehending the microscopic mechanism of plasmon-induced chemical reaction on the alloy nanostructures.

Plasmon-induced nonlinear response on gold nanoclusters

The plasmon-induced nonlinear response has attracted great attention in micro-nano optics and optoelectronics applications,yet the underlying microscopic mechanism remains elusive.In this study,the nonlinear response of gold nanoclusters when exposed to a femtosecond laser pulse was investigated using time-dependent density functional theory.It was observed that the third-order tunneling current was augmented in plasmonic dimers,owing to a greater number of electrons in the dimer being excited from occupied to unoccupied states.These findings provide profound theoretical insights and enable the realization of accurate regulation and control of nonlinear effects induced by plasmons at the atomic level.

基于密度泛函理论的沙林毒剂近红外光谱研究

近红外光谱涵盖了有机分子中C—H,N—H和O—H等含氢基团的倍频和合频产生的光谱,提供了分子的结构、组成、状态等信息,是研究有机物含氢基团振动的重要方法,常用于食品、农作物等的定性定量分析。生化领域内所研究对象也都含有氢基团,这些含氢基团吸收频率特征性强,受分子内外环境影响小,近红外光谱特性更稳定,故可用于化学战剂和危险化学品检测。沙林是一种神经性化学毒剂,研究其结构、化学特性及光谱性质时,为保证安全,实验中常用模拟剂样品代替测试,但目前尚无公允的沙林毒剂近红外模拟剂。采用密度泛函理论(DFT),基于Gaussian程序包,利用B3LYP/def2-SVP对沙林分子进行基态结构优化,计算了沙林分子的精细结构和分子基频振动模式,引入广义二阶微扰理论(GVPT2)建立了模拟生化毒剂近红外光谱的理论模型,得到近红外振动峰与主要振动模式,由倍频(Overtones)和合频(Combination Bands)振动绘制得到近红外光谱。对沙林在近红外区域内的含氢基团进行解析,对其特征峰进行指认,得到沙林分子在1150、1362和1500 nm处的三个特征峰及其振动模式,其中1150 nm峰是由多个倍频和合频的组合振动贡献产生;1362 nm是一个较宽的吸收振动峰,主要由分子中与C原子相连的原子合频和其他的非C,H原子产生的倍频或合频引起的;1500 nm位置的近红外振动峰主要由C8相关的振动模式贡献产生。通过密度泛函理论建立沙林的近红外光谱理论模型,通过实验验证了其理论模型的可行性,为寻找其近红外光谱模拟剂提供理论支撑。

Plasmonic hybridization properties in polyenes octatetraene molecules based on theoretical computation

Relationship of plasmonic properties of multiple clusters to molecular interactions and properties of a single cluster or molecule have become increasingly important due to the continuous emergence of molecular and cluster devices or systems.A hybrid phenomenon similar to plasmonic nanoparticle hybridization exists between two molecules with plasmon excitation modes.We use linear-response time-dependent density functional theory,real-time propagation time-dependent density functional theory,the plasmonicity index,and transition contribution maps(TCMs)to identify the plasmon excitation modes for the linear polyenes octatetraene with–OH and–NH_(2)groups and analyze the hybridization characteristics using charge transitions.The results show that molecular plasmon hybridization exists when the two molecules are coupled.The TCM analysis shows that the plasmon modes and hybridization result from collective and single-particle excitation.The plasmon mode is stronger,and the individual properties of the molecules are maintained after coupling when there is extra charge depose in the molecules because the electrons are moving in the molecules.This study provides new insights into the molecular plasmon hybridization of coupled molecules.

A theoretical study of fragmentation dynamics of water dimer by proton impact

To investigate the collision processes of proton with the water dimer(H_(2)O)_(2)at 50 e V,the time-dependent density functional theory coupled with molecular dynamics nonadiabatically is applied.Six specific collision orientations with various impact parameters are considered.The reaction channels,the mass distribution and the fragmentation mass spectrum are explored.Among all launched samples,the probability of the channel of non-charge transfer scattering and charge transfer scattering is about 80%,hinting that the probability of fragmentation is about 20%.The reaction channel of proton exchange process 2 is taken as an example to exhibit the detailed microscopic dynamics of the collision process by inspecting the positions,the respective distance,the number of loss of electrons and the evolution of the electron density.The study of the mass distribution and the fragmentation mass spectrum shows that among all possible fragments,the fragment with mass 36 has the highest relative abundance of 65%.The relative abundances of fragments with masses 1,35,and 34are 20%,13%,and 1.5%,respectively.For the total electron capture cross section,the present calculations agree with the available measurements and calculations over the energy range from 50 e V to 12 ke V.

Effects of π-conjugation-substitution on ESIPT process for oxazoline-substituted hydroxyfluorenes

Excited-state intramolecular proton transfer(ESIPT) molecules are broadly applied to UV absorbers, fluorescence sensing, and lighting materials. In previous work, the fluorescence colors of oxazoline-substituted hydroxyfluorenes and hydroxylated benzoxazole were diversified by adding the π-conjugation. There is intriguing that the mechanism of diversified fluorescence colors induced by ESIPT. Here, the density functional theory(DFT) and time-dependent DFT(TDDFT)are advised to identify the effects of π-conjugation on ESIPT and photophysical properties. The stabilized geometrical configurations, frontier molecular orbitals(FMOs) isosurfaces, and O–H stretching vibration frequency analysis demonstrate that PT processes are more active in S1state. Constructing the minimum energy pathways of ESIPT processes, we find that the calculated peak of enol and keto fluorescence of naphthoxazole(NO–OH) is distinctly bathochromic-shift relative to the oxazoline-substituted hydroxyfluorenes(Oxa–OH) configuration when adding π-conjugation-substitution, and it means that π-conjugation-substitution can diversify the fluorescence color. We hope our studies can establish new channels to devise the ESIPT-based molecules.

High-order harmonic generation of the cyclo[18]carbon molecule irradiated by circularly polarized laser pulse

High-order harmonic generation of the cyclo[18]carbon(C_(18) ) molecule under few-cycle circularly polarized laser pulse is studied by time-dependent density functional theory. Compared with the harmonic emission of the ring molecule C_(6)H_(6) having similar ionization potential, the C_(18) molecule has higher efficiency and cutoff energy than C_(6)H_(6) with the same laser field parameters. Further researches indicate that the harmonic efficiency and cutoff energy of the C_(18) molecule increase gradually with the increase of the laser intensity of the driving laser or decrease of the wavelength, both are larger than those of the C_(6)H_(6) molecule. Through the analysis of the time-dependent evolution of the electronic wave packets, it is also found that the higher efficiency of harmonic generation can be attributed to the larger spatial scale of the C_(18) molecule,which leads to a greater chance for the ionized electrons from one atom to recombine with others of the parent molecule.Selecting the suitable driving laser pulse, it is demonstrated that high-order harmonic generation in the C_(18) molecule has a wide range of applications in producing circularly polarized isolated attosecond pulse.

酞菁基态和激发态的计算

采用DFT方法在B3LYP/6-31G水平上得到了H2Pc(酞菁)的优化结构,并在此基础上采用TDDFT方法计算了激发态.通过与H2P(卟吩)、H2Pz(四氮卟吩)和H2TBP(四苯并卟啉)的比较,研究了苯并取代以及氮杂取代对H2Pc的分子轨道和激发态的影响,上述取代效应使得H2Pc的HOMO-1(132b1u)和HOMO-3(130b1u)轨道发生了翻转,氮杂取代的影响尤其明显.这两种取代都使得Q带振子强度增大,在这四种化合物中,H2Pc的振子强度最大.TDDFT计算结果与实验值符合得较好.

密度泛函理论及其数值方法新进展

综述了密度泛函理论及其数值方法的最新进展。密度泛函理论的发展以寻找合适的交换相关近似为主线 ,从最初的局域密度近似、广义梯度近似到现在的非局域泛函、自相互作用修正 ,多种泛函形式的相继出现使得密度泛函理论可以提供越来越精确的计算结果。除了交换相关近似的发展 ,近年来密度泛函理论向含时理论、相对论等方面的扩展也很活跃。另外 ,在密度泛函理论体系发展的同时 ,相应的数值计算方法的发展也非常迅速。从古老的有限差分、有限元到新兴的小波分析都被用来实现密度泛函理论的数值计算。与此同时 ,线性标度的密度泛函理论算法日趋成熟 ,使得通过密度泛函理论研究诸如生物大分子之类的体系成为可能。随着密度泛函理论本身及其数值方法的发展 ,它的应用也越来越广泛 ,一些新的应用领域和研究方向不断涌现。

密度泛函理论的若干进展

密度泛函理论 (DFT)作为处理非均匀相互作用多粒子体系的近似方法已经在计算凝聚态物理、计算材料科学和计算量子化学诸多领域取得巨大成功并获得广泛应用。然而它也存在一些被广泛关注的弱点或困难。例如关于激发态问题 ,强关联问题和处理大原子数复杂体系方面的困难。本文将针对DFT在以上三方面的问题 ,评述近年来的主要努力和进展。着重介绍最近发展的含时间密度泛函理论 (TDDFT) ,它有可能发展成为处理激发态问题的标准方法。关于强电子关联体系的处理 ,主要介绍LDA以外的新发展 ,包括LDA ++方法和计及动力学平均场理论的LDA +DMFT方法。最后 ,评述DFT框架内的线性标度Order N算法的物理基础和主要策略。该算法将在处理大原子数复杂体系问题上发挥重要作用。