Effects of External Field and Nanoribbon Length on the Electronic Structure and Properties of Graphene Nanoribbons

在密度泛函理论(dfT)和含时密度泛函理论(TddfT)的基础上对宽度上含有8个zIgzAg链的石墨烯条带(8-zgnr)的基态和激发态的性质进行了理论研究,着重考察了条带长度及电场的影响.b3lyP杂化泛函的计算结果显示:在基态上,8-zgnr的最低能量态并不具有磁性,随着长度的增加,才会显示出反铁磁的性质.静电场的加入使8-zgnr显示出反铁磁性和半金属性.在激发态上,诱导电子会随着外激光脉冲的变化而发生移动和变化,但是相比而言,α自旋电子更容易被激发而产生较明显的诱导电子密度,而β自旋电子则更容易脱离外激光场的控制而产生非绝热现象.We investigated the ground and excited state electronic properties of finite length zigzag graphene nanoribbons,using time-dependent density functional theory.The ground state of short graphene nanoribbons with eight H atoms on their armchair edges(8-ZGNR) is diamagnetic,and antiferromagnetism can be exhibited with increasing the length of nanoribbons.The antiferromagnetism and half-metallicity can also be shown when a static field is added.When a laser pulse is applied in the excited state,the induced electrons can move and change with the laser pulse.There exist some differences between α- and β-spin electrons.α-Spin electrons can be induced,and show induced charge density more readily.β-Spin electrons can escape the external field control,and show non-adiabatic properties more readily.国家自然科学基金(21103001); 高等学校博士学科点专项科研基金(20113401120004)资助项目~

Two-Photon Absorption Properties of Chromophores of a Few Fluorescent Proteins: a Theoretical Investigation

实验测得的荧光蛋白的单、双光子吸收光谱在低频和高频区域都表现出明显不同的特征。为了揭示这些不同点的起源和研究荧光蛋白的构–效关系,我们详细研究了三种荧光蛋白发色团(一种增强型蓝绿色荧光蛋白的中性发色团和两种红色荧光蛋白的阴离子发色团)的单、双光子吸收特性,分别计算了纯的和振动分辨的电子谱。计算结果表明:光谱线形与计算采用的交换相关密度泛函及谱截面计算所采用的近似关系密切;如果在计算光谱截面时,我们利用长程修正的交换相关泛函CAM-B3LYP来计算几何和电子结构参数,然后把Franck-Condon(FC)效应和包含Herzberg-Teller(HT)效果的电-声耦合效应都考虑进去,理论计算的光谱与实验测定的光谱可以很好地符合;对于两种离子态的发色团,HT电-声耦合效应使得对应于基态到第一激发态跃迁的双光子吸收最强峰相对于单光子吸收的最强峰发生了蓝移,但HT电-声耦合效应对高频的双光子吸收谱没有太大的影响;分子内电荷转移是导致高频区的双光子吸收明显强于单光子吸收的主要原因。The experimentally-measured two-photon absorption(TPA) spectra of fluorescent proteins(FPs) show quite different characteristics with one-photon absorption(OPA) spectra in both the low- and high-frequency regions. To reveal the mechanism that results in the discrepancies between OPA and TPA spectra, and to obtain the fundamental structure–property relationships of FPs, here we conduct a theoretical study of OPA and TPA properties of three FP chromophores, including a neutral chromophore in enhanced cyan fluorescent protein(ECFP) and two anionic FP chromophores in Ds Red2 and Tag RFP.Both the pure electronic and vibrationally-resolved TPA spectra have been calculated. The calculated spectra were found to be highly dependent on the density functional theory exchange-correlation functional used. The experimental spectral lineshapes of vibronic spectra can be well produced when the FranckCondon(FC) scattering and Herzberg-Teller(HT) vibronic coupling effects were taken into account and the structure parameters produced by CAM-B3 LYP were applied in the theoretical calculations. The HT effects affect the low-frequency absorption bands corresponding to the electronic transition from S_0 to S_1 for two anionic chromophores, leading to a blue-shift of the TPA maximum relative to OPA maximum, while the HT effect is insignificant in the higher-frequency region of the TPA spectra. The intramolecular charge-transfer character of higher-lying excited states explains why the TPA spectra in the higher-frequency region are much stronger than those in the low-frequency region.supported by the National Natural Science Foundation of China(21373163,21290193,21573177)~

基于二维材料WX2构建的范德华异质结的结构和性质及应变效应的理论研究

二维材料过渡金属硫属化物（TMDs）,因其优越的物理化学特性及其在光电子器件、光催化等领域的潜在应用价值,得到了人们的广泛关注。基于TMDs材料可以构建具有不同性能的范德华（vdW）异质...国家自然科学基金(21573177)资助项目~

Localized-denisty-matrix method and its application to nano-size systems

published_or_final_versionChemistryDoctoralDoctor of Philosoph

Theoretical investigation of the non-Condon effect on electron transfer:Application to organic semiconductor

随着COndOn近似下各种电子转移理论的不断发展与完善和人们对nOn-COndOn效应在电子转移过程中重要作用认识的逐步深入,已建立了几个理论模型来研究这种效应对电子转移速率的影响.本文主要总结了近两年来我们在nOn-COndOn效应电子转移理论方面的工作,首先阐述了指数型、高斯型以及直线型nOn-COndOn电子转移速率的全量子表达式,然后运用该理论模型以及分子动力学模拟计算了二噻吩四硫富瓦烯(dT-TTf)有机半导体的迁移率.此外,还进一步利用数值模拟详细研究了这三种线型的nOn-COndOn效应在量子尺度上对电子转移速率的影响.The non-Condon effect plays an important role in the process of electron transfer(ET) .Several theoretical models have been proposed to investigate its effect on ET rates.In this paper,we overview a theoretical method for the calculations of the non-Condon ET rate constants proposed by us,and its applications to organic semiconductors.First,full quantum expressions of the non-Condon ET rates are presented with the electronic couplings having exponential,Gaussian and linear dependences in terms of the nuclear coordinates,respectively.The proposed formulas have closed forms in time domain and they thus can be easily applied to multi-mode systems.Then,the driving force dependence of the ET rates involving the non-Condon effect are calculated with use of full quantum mechanical formulas.It is found that these dependences show very different properties from the Marcus one.As an example of applications,the approaches are used to investigate the non-Condon effect on the mobility of the organic semiconductor dithiophene-tetrathiafulvalene(DT-TTF) .The results manifest that the non-Condon effect enhances ET rates compared with the Condon approximation,and static fluctuations of electronic coupling dominates the ET rate in the DT-TTF,which has been confirmed by the molecular dynamics simulation.国家自然科学基金(20833004;21073146)的资

Charge transfer in organic molecules for solar cells: theoretical perspective

National Science Foundation of China [20833004, 21073168, 21073146]; National Key Basic Research Foundation Program of China [2011CB808501, 2007CB815204]This tutorial review primarily illustrates rate theories for charge transfer and separation in organic molecules for solar cells. Starting from the Fermi's golden rule for weak electronic coupling, we display the microcanonical and canonical rates, as well as the relationship with the Marcus formula. The fluctuation effect of bridges on the rate is further emphasized. Then, several rate approaches beyond the perturbation limit are revealed. Finally, we discuss the electronic structure theory for calculations of the electronic coupling and reorganization energy that are two key parameters in charge transfer, and show several applications

Effects of External Field and Nanoribbon Length on the Electronic Structure and Properties of Graphene Nanoribbons

National Natural Science Foundation of China [21103001]; Research Fund for the Doctoral Program of Higher Education of China [20113401120004]We investigated the ground and excited state electronic properties of finite length zigzag graphene nanoribbons, using time-dependent density functional theory. The ground state of short graphene nanoribbons with eight Hatoms on their armchair edges (8-ZGNR) is diamagnetic, and antiferromagnetismcan be exhibited with increasing the length of nanoribbons. The antiferromagnetismand half-metallicity can also be shown when a static field is added. When a laser pulse is applied in the excited state, the induced electrons can move and change with the laser pulse. There exist some differences between alpha- and beta-spin electrons. alpha-Spin electrons can be induced, and show induced charge density more readily. beta-Spin electrons can escape the external field control, and show non-adiabatic properties more readily

Time-Dependent Approach to Resonance Raman Spectra Including Duschinsky Rotation and Herzberg-Teller Effects: Formalism and Its Realistic Applications

National Science Foundation of China [20833003, 21073168]; National Basic Research Program of China [2011CB808501]Efficient quantum dynamical and electronic structure approaches are presented to calculate resonance Raman spectroscopy (RRS) with inclusion of Herzberg-Teller (HT) contribution and mode-mixing (Duschinsky) effect. In the dynamical method, an analytical expression for RRS in the time domain is proposed to avoid summation over the large number of intermediate vibrational states. In the electronic structure calculations, the analytic energy:derivative approaches for the excited states within the time dependent density functional theory (TDDFT), developed by.,us, are adopted to overcome the computational bottleneck of excited state gradient and Hessian calculations In addition; an analytic calculation to the geometrical derivatives of the transition dipole moment, entering the HT term, is also adopted The proposed approaches are implemented to calculate RR spectra. of a few Of conjugated systems, phenoxyl radical, 2-thiopyridone in water, solution, and free base porphyrin. The calculated RR spectra show the evident HT effect in those g-conjugated systems, and their relative intensities are consistent with experimental measurements

Theory and algorithms for the excited states of large molecules and molecular aggregates

This project aims to attack the frontiers of electronic structure calculations on the excited states of large molecules and molecular aggregates by developing novel theoretical and computational methods. The methodology development is especially based on the time-dependent density functional theory (TDDFT) and valence bond (VB) theory, and is expected to be computationally effective and accurate as well. Research works on the following related subjects will be performed: (1) The analytical energy-derivative approaches for electronically excited state within TDDFT will be developed to reduce bypass the computational costs in the calculation of molecular excited-state properties. (2) The ab initio methods for electronically excited state based on VB theory and hybrid TDDFT-VB method will be developed to overcome the limitations of current TDDFT in simulating photophysics and photochemistry. (3) For larger aggregates, neither ab initio methods nor TDDFT is applicable. We intend to build the effective model Hamiltonian by developing novel theoretical and computational methods to calculate the involved microscopic physical parameters from the first-principles methods. The constructed effective Hamiltonian is then used to describe the excitonic states and excitonic dynamics of the natural or artificial photosynthesized systems, organic or inorganic photovoltaic cell. (4) The condensed phase environment is taken into account by combining the developed theories and algorithms based on TDDFT and VB with the polarizable continuum solvent models (PCM), molecular mechanism (MM), classical electrodynamics (ED) or molecular dynamics (MD) theory. (5) Highly efficient software packages will be designed and developed. ? 2013 Science China Press and Springer-Verlag Berlin Heidelberg

Computational Insight on the Working Principles of Zinc Porphyrin Dye-Sensitized Solar Cells

National Science Foundation of China [21073168, 21290193]; National Basic Research Program of China [2011CB808501]A step-by-step theoretical protocol based on the density functional theory (DFT) and time-dependent DFT (TD-DFT) at both the molecular and periodic levels have been performed to study a zinc porphyrin complex (named YDoc) sensitized TiO2 solar cell including dye excitations, electron injection, the regeneration of photooxidized dyes and the effect of electrolyte additives. Our study reveals the possibility of a favorable electron transfer from the excited dye to the semiconductor conduction band (CB) and suggests three possible pathways of the electron injection from the dye to the nanoparticle (TiO2)(38). One is the direct one-step injection by photoexcitation, and the other two are from the different parts of the excited dye to the nanoparticle. The influence of the electrolyte composition on the geometric and electronic features of the dye/TiO2 system has also been studied. It is found that, with the additive of the lithium ion, the energy gap between the LUMO of dye and the TiO2 CB edge increases, which subsequently increases the driving force for the ultrafast excited-state electron injection, contrary to the effect of 4-tert-butylpyridine additive. The computational results of the oxidized dye interacting with I- and I-2(-) reveal that there are a few possible mechanisms for the regeneration of oxidized dye. The effective mechanisms of the regeneration are suggested