Simulation of Inelastic Electron Tunnelling Spectroscopy on Different Contact Structures in 4,4＇-Biphenyldithiol Molecular Junctions

A first-principles computational method is developed to study the inelastic electron tunnelling spectroscopy （IETS） of 4,4＇-biphenyldithiol molecular junction with three different contact structures between the molecule and electrodes in the nonresonant regime. The obtained distinct IETS can be used to resolve the geometrical structure of the molecular junction. The computational results demonstrate that the IETS has certain selection rule for vibrational modes, where the longitudinal modes with the same direction as the tunnelling current have greatest contribution to the IETS. The thermal effect on the IETS is also displayed.     

有机分子电子输运性质的计算与分析

从第一性原理出发,采用杂化的密度泛函理论和弹性散射格林函数法,计算有机分子4,4'-二巯基二苯醚分子的电子结构并研究其电子输运性质.计算结果表明,电场对分子系统电子结构有明显的影响,电流、电导表现为非线性变化,与不考虑电场作用时相比,更为接近实验结果.     

分子线电子输运特性的第一性原理研究

从第一性原理出发,利用密度泛函理论研究了SH-C8H16-SH分子和金表面的相互作用,并利用分子前线轨道理论和微扰理论定量地确定了该相互作用能常数,然后,利用弹性散射格林函数方法研究了该分子与金表面形成的分子线的伏-安特性.研究结果表明,当含有硫氢官能团的有机分子化学吸附于金表面时,硫原子将与金原子形成以共价键为主的混和键,此时,扩展的分子轨道使分子线的电导呈现出欧姆特性,而对于局域的分子轨道,电子的输运只能通过隧道效应来实现.对分子线伏-安特性的计算结果显示,在零偏压附近,存在一个电流禁区,随着偏压的增加,分子线的电导呈现出平台特征.     

异构二芳基乙烯分子结低偏压电导机制的第一性原理研究

本文用结合密度泛函理论的非平衡格林函数方法研究了具有开环和闭环两种同分异构体的二芳基乙烯衍生物分子的结构-特性关系. 该功能分子通过末端的吡啶基团连接到取向沿(111)方向的金电极. 计算结果表明，异构体分子结的不同低偏压电导主要是由于它们具有不同的电子结构. 两种构型分子结的低偏压导电都主要来自于电子隧穿最低未占据分子轨道(LUMO). 由于具有扩展的单双键交替共轭结构，闭环构型分子具有更好的导电通道. 通过计算分子结在平衡状态下的电子转移，可发现更多电子转移到闭环构型分子，导致了其LUMO能量更靠近费米能级，从而有利于低偏压下的导电性能. 结果有助于理解二芳基乙烯分子及其衍生物分子的低偏压电导机制，也为设计更高性能的同类分子开关提供理论依据.     

Current spin polarization of a platform molecule with compression effect

Using the first-principles method, the spin-dependent transport properties of a novel platform molecule containing a freestanding molecular wire is investigated by simulating the spin-polarized scanning tunneling microscope experiment with Ni tip and Au substrate electrodes. Transport calculations show that the total current increases as the tip gradually approaches to the substrate, which is consistent with the conductance obtained from previous experiment. More interestingly, the spin polarization (SP) of current modulated by compression effect has the completely opposite trend to the total current. Transmission analyses reveal that the reduction of SP of current with compression process originates from the promotion of spin-down electron channel, which is controlled by deforming the molecule wire. In addition, the density of states shows that the SP of current is directly affected by the organic-ferromagnetic spinterface. The weak orbital hybridization between the Ni tip and propynyl of molecule results in high interfacial SP, whereas the breaking of the C $\equiv$ C triple of propynyl in favor of the Ni-C-C bond induces the strong orbital hybridization and restrains the interfacial SP. This work proposes a new way to control and design the SP of current through organic-ferromagnetic spinterface using functional molecular platform.     

Spin-excited states and rectification in an organic spin rectifier

Spin-excited states in an asymmetric magnetic organic co-oligomer diode are investigated theoretically. The results demonstrate that the structural asymmetry of the co-oligomer is modulated by the spin-excited states, which is embodied in the wave functions of the eigenstates as well as the spin density wave. By calculating the transport property, a robust spin-current rectification concomitant with a charge-current rectification is observed in all spin-excited states. However, the current through the diode is suppressed distinctly by the spin-excited states, while the rectification ratios may be reduced or enhanced depending on the bias and the excited spins. The intrinsic mechanism is analyzed from the spin-dependent trans- mission combined with the change of molecular eigenstates under bias. Finally, the temperature-induced spin excitation is simulated. Significant rectification behavior is obtained even at room temperature.     

D-A型二噻吩并磷杂茂衍生物分子的双光子吸收性质

在密度泛函理论理论水平上,采用响应理论方法计算了一系列2,6-donor-acceptor 二噻吩并磷杂茂衍生物分子的单、双光子吸收性质. 理论计算结果表明该系列分子都具有较大的双光子吸收截面,并且分子中心的磷原子无论被氧化还是金属配合,其双光子吸收截面几乎保持不变. 此外,还考虑了溶剂效应对分子光学性质的影响,研究表明分子能级发生了溶剂化蓝移,并且分子的单光子和双光子吸收性质随着溶剂极性表现出非单调变化.     

Theoretical verification of intermolecular hydrogen bond induced thermally activated delayed fluorescence in SOBF-Ome

Thermally activated delayed fluorescence (TADF) molecules have attracted great attention as high efficient luminescent materials. Most of TADF molecules possess small energy gap between the first singlet excited state (S₁) and the first triplet excited state (T₁) to favor the up-conversion from T₁ to S₁. In this paper, a new TADF generation mechanism is revealed based on theoretical simulation. By systematic study of the light-emitting properties of SOBF-OMe in both toluene and in aggregation state, we find that the single SOBF-OMe could not realize TADF emission due to large energy gap as well as small up-conversion rates between S₁ and T₁. Through analysis of dimers, we find that dimers with intermolecular hydrogen bond (H-bond) are responsible for the generation of TADF, since smaller energy gap between S₁ and T₁ is found and the emission wavelength is in good agreement with experimental counterpart. The emission properties of SOBF-H are also studied for comparison, which reflect the important role of H-bond. Our theoretical results agree ith experimental results well and confirm the mechanism of H-bond induced TADF.     

The theoretical studies on the two-photon absorption properties of symmetric l,4-bis{2-[4-(2-aryl)phenyl]vinyl}-2,5-bisdialkoxybenzenes

<正>On the level of the time-dependent hybrid density functional theory,the one- and two-photon absorption properties of a series of symmetric 4-bis{2-[4-(2-aryl) phenyl]vinyl}-2,5-bisdialkoxybenzenes are studied respectively utilizing the analytic response theory and the few-state model methods.The calculated results show that the planarity of the geometrical structure plays a great role in enhancing the linear and nonlinear optical abilities of the molecule.However the effect of the length of the chain linked to theπ-centre on the optical property is very little.For the investigated compounds,the A-π-A type charge-transfer molecules display more superior one- and two-photon absorption characteristics than the D-π-D type ones.Furthermore,the two-photon absorption results by use of few-state model are generally consistent with those by analytic response theory,demonstrating the reliability of the few-state model for evaluating the two-photon absorption cross section.The numerical simulations are in good agreement in tendency with the available experimental measurements.     

(E,E)-1,4-双{2''-[5''-(B,B-二甲基苯硼)-2-噻吩基]乙烯基}-苯分子双光子吸收特性的理论研究

在密度泛函水平上,利用响应函数方法,研究了分子的单光子和双光子吸收特性.计算出了该分子在低能量范围内的最大双光子吸收截面为6.47×10-47 cm4 s/photon,与实验符合的较好.研究结果表明该分子具有较强的双光子吸收特性,是较好的双光子吸收材料.