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Exploring approximate geometries of minimum energy conical intersections by TDDFT calculations
摘要： An approach is proposed to obtain approximate geometries for minimum energy conical intersections between the ground and first excited singlet electronic states (S0/S1-MECIs) using the time-dependent density functional theory (TDDFT). This approach uses the energy shift method to avoid discontinuities on TDDFT potential energy surfaces around conical intersections. It is shown numerically that the approximate S0/S1-MECIs of benzene and naphthalene obtained by this approach qualitatively reproduce the geometries and energies of the S0/S1-MECIs obtained by multireference theories. Moreover, the performance of the present approach when combined with an automated MECI searching method is examined through applications to benzene and naphthalene.
关键词： energy shift method,time dependent density functional theory,gradient projection,single component artificial force induced reaction,conical intersection,global reaction route mapping
更新于2025-09-23 15:23:52
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Structural, energetic and spectroscopic studies of new luminescent complexes based on 2-(2′-hydroxyphenyl)imidazo[1,2- <i>a</i> ]pyridines and 1,2-phenylenediboronic acid
摘要： Three new blue-luminescent complexes of selected imidazo[1,2-a]pyridine derivatives and 1,2-phenylenediboronic acid have been synthesized and structurally characterized using single-crystal X-ray diffraction. Additionally, the crystal structures of two of the (N,O)-donor compounds have been evaluated for the first time. The crystal packing and molecular motifs observed in the studied crystals have been thoroughly analysed, including computational studies, and are also discussed within the context of analogous systems reported in the literature. It appears that the new compounds form different crystal networks with regard to the asymmetric unit content and packing, although some similarities can be found. In all cases a typical centrosymmetric dimer bound via boronic acid groups is formed, characterized by an interaction energy of about -80 kJ mol-1, while the 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine complex and its methoxy derivative form solvate structures, somewhat resembling the previously studied 8-oxyquinolinate analogues. As far as the spectroscopic properties are concerned, the lowest energy excitation observed in the studied complexes is based on the highest occupied molecular orbital–lowest unoccupied molecular orbital transition, and both these molecular orbitals are centred predominantly on the (N,O)-donor species according to the results of time-dependent density functional theory. Thus, the charge transfer observed for the 8-oxyquinolinate equivalents does not occur in these cases. Consequently, the spectroscopic behaviour of the series is very much comparable with that of the parent imidazo[1,2-a]pyridine derivatives, if the excited-state intramolecular proton-transfer process does not take place, as shown by the absorption and emission spectra collected in toluene and acetone solutions. Complexation causes a reduction in the Stokes shift compared with the respective (N,O)-donor molecules.
关键词： periodic calculations,TDDFT,UV–Vis spectroscopy,X-ray diffraction,time-dependent density functional theory,spectroscopic properties,luminescent boron complexes,transferred aspherical atom model (TAAM) refinement
更新于2025-09-23 15:22:29
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Impact of Organic Spacers on the Carrier Dynamics in 2D Hybrid Lead-Halide Perovskites
摘要： We have carried out non-adiabatic molecular dynamics simulations combined with time-dependent density functional theory calculations to compare the properties of the two-dimensional (2D) (BA)2(MA)Pb2I7 and three-dimensional (3D) MAPbI3 (where MA = methylammonium and BA = butylammonium) materials. We evaluate the different impacts that the 2D-confined spacer layer of butylammonium cations and the 3D-confined methylammonium cations have on the charge carrier dynamics in the two systems. Our results indicate that while both the MA+ and BA+ cations play important roles in determining the carrier dynamics, the BA+ cations exhibit stronger non-adiabatic couplings with the 2D perovskite framework. The consequence is a faster hot-carrier decay rate in 2D (BA)2(MA)Pb2I7 than in 3D MAPbI3. Thus, tuning of the functional groups of the organic spacer cations in order to reduce the vibronic couplings between the cations and the Pb-I framework can offer the opportunity to slow down the hot-carrier relaxations and increase the carrier lifetimes in 2D lead-halide perovskites.
关键词： carrier dynamics,2D hybrid lead-halide perovskites,time-dependent density functional theory,non-adiabatic molecular dynamics,organic spacers
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Field emission patterns from carbon nanotubes calculated by time-dependent density functional theory
摘要： We calculated the field emission patterns of various types of carbon nanotubes (CNTs). Regarding the near field regime, emission patterns of CNTs and hydrogen terminated CNTs (H-CNTs) well corresponds to the atoms located in the tube tip. We also found different focusing features; a focused-type and an unfocused-type. The beams from armchair (5,5) and (6,6) types are focused, while the beam from zigzag (9,0) types are unfocused.
关键词： field emission,carbon nanotubes,emission pattern,time dependent density functional theory,first principle calculation,ab initio calculation
更新于2025-09-23 15:21:21
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Theoretical study of Da??Aa?2a????a??A/Da????a??Aa?2a????a??A triphenylamine and quinoline derivatives as sensitizers for dye-sensitized solar cells
摘要： We have designed four dyes based on D–A0–p–A/D–p–A0–p–A triphenylamine and quinoline derivatives for dye-sensitized solar cells (DSSCs) and studied their optoelectronic properties as well as the e?ects of the introduction of alkoxy groups and thiophene group on these properties. The geometries, single point energy, charge population, electrostatic potential (ESP) distribution, dipole moments, frontier molecular orbitals (FMOs) and HOMO–LUMO energy gaps of the dyes were discussed to study the electronic properties of dyes based on density functional theory (DFT). And the absorption spectra, light harvesting e?ciency (LHE), hole–electron distribution, charge transfer amount from HOMO to LUMO (QCT), D index, HCT index, Sm index and exciton binding energy (Ecoul) were discussed to investigate the optical and charge-transfer properties of dyes by time-dependent density functional theory (TD-DFT). The calculated results show that all the dyes follow the energy level matching principle and have broadened absorption bands at visible region. Besides, the introduction of alkoxy groups into triarylamine donors and thiophene groups into conjugated bridges can obviously improve the stability and optoelectronic properties of dyes. It is shown that the dye D4, which has had alkoxy groups as well as thiophene groups introduced and possesses a D–p–A0–p–A con?guration, has the optimal optoelectronic properties and can be used as an ideal dye sensitizer.
关键词： alkoxy groups,thiophene group,density functional theory,dye-sensitized solar cells,D–A0–p–A/D–p–A0–p–A,triphenylamine,quinoline derivatives,time-dependent density functional theory,optoelectronic properties
更新于2025-09-23 15:21:01
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Osmium sensitizer with enhanced spin-orbit coupling for panchromatic dye-sensitized solar cells
摘要： Low-lying triplet metal-to-ligand charge transfer (3MLCT) transitions of osmium complexes induced by spin-orbit coupling (SOC) is promising to extend photocurrent response when applied to dye-sensitized solar cells. In this study, we present a newly designed osmium complex (coded CYC-33O), incorporating a 2-thiohexyl-3,4-ethylenedioxythiophene functionalized bipyridyl ancillary ligand to red-shift the absorption and enhance the absorbance of both singlet and triplet MLCT transitions. Time-dependent density functional theory (TDDFT) calculations clearly signify the reinforced 1MLCT and 3MLCT transitions of CYC-33O mainly originate from osmium to 4,4',4"-tricarboxy-2,2':6',2"-terpyridine anchoring ligand, advantaging the heterogeneous electron transfer between CYC-33O and TiO2. The device sensitized with CYC-33O exhibits the panchromatic conversion beyond 1000 nm, yielding the photocurrent density of 19.38 mA cm–2 which is much higher than those of the cells based on the ruthenium analogue (CYC-33R) and model osmium complex (Os-3) sensitizers.
关键词： dye-sensitized solar cell,triplet metal-to-ligand charge transfer (3MLCT),ruthenium complex,spin-orbit coupling (SOC),osmium complex,time-dependent density functional theory (TDDFT)
更新于2025-09-23 15:21:01
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Theoretical study on nonlinear optical properties of N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole
摘要： The first-, second- and third-order nonlinear optical properties of N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole in gas phase employing sum-over-states (SOS) method have been calculated for the first time. The ground state molecular structure of N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole was obtained by the geometrical optimizations based on the B3LYP/6-31+G(d) level. The energy of excited states and transition dipole moments between different excited states were obtained by using the time-dependent density functional theory (TDDFT) based on the CAM-B3LYP/Sadlej POL level. Charge transfer during electron excitation was analyzed based on hole and electron distributions. Our calculations showed that the N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole has good nonlinear optical properties and its nonlinear optical properties arise from charge-transfer excitation and local excitation but charge transfer plays the leading role.
关键词： N-(6-hydroxyhexyl)-5-nitroazophenyl carbazole,the time-dependent density functional theory (TDDFT),charge transfer,sum-over-states (SOS) method,nonlinear optical properties
更新于2025-09-19 17:15:36
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Many-body States Description of Single-molecule Electroluminescence Driven by Scanning Tunneling Microscope
摘要： Electron transport and optical properties of a single molecule in contact with conductive materials have attracted considerable attention owing to their scientific importance and potential applications. With recent progresses of experimental techniques, especially by the virtue of scanning tunneling microscope (STM)-induced light emission, where the tunneling current of the STM is used as an atomic-scale source for induction of light emission from a single molecule, it becomes possible to investigate single-molecule properties at sub-nanometer spacial resolution. Despite extensive experimental studies, the microscopic mechanism of electronic excitation of a single molecule in STM-induced light emission is yet to be clarified. Here we present a formulation of single-molecule electroluminescence driven by electron transfer between a molecule and metal electrodes based on a many-body state representation of the molecule. The effects of intra-molecular Coulomb interaction on conductance and luminescence spectra are investigated using the nonequilibrium Hubbard Green's function technique combined with first-principles calculations. We compare simulation results with experimental data and find that the intra-molecular Coulomb interaction is crucial for reproducing recent experiments for a single phthalocyanine molecule. The developed theory provides a unified description of both electron-transport and optical properties of a single molecule in contact with metal electrodes driven out of equilibrium, and thereby it contributes to a microscopic understanding of optoelectronic conversion in single molecules on solid surfaces and in nanometer-scale junctions.
关键词： Single molecule luminescence,exciton formation,nonequilibrium Hubbard Green's function technique,time-dependent density functional theory (TDDFT),scanning tunneling microscope-induced light emission,Vibronic interaction
更新于2025-09-19 17:15:36
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Soft Lattice and Defect Covalency Rationalize Tolerance of ?2a??CsPbI3 Perovskite Solar Cells to Native Defects
摘要： Although all-inorganic lead halide perovskite solar cells have shown tremendous improvement over the past few years, they are still inferior to the hybrid organic-inorganic perovskites in the solar power conversion efficiency. Recently, a conceptually new β-CsPbI3 perovskite has demonstrated an impressive 18.4% efficiency combined with good thermodynamic stability at ambient conditions. We use ab initio non-adiabatic molecular dynamics to show that native point defects in β-CsPbI3 are generally benign for nonradiative charge recombination, regardless of whether they introduce shallow or deep trap states. Moreover, formation of new covalently bound species in the presence of defects slows down the recombination. These results indicate that halide perovskites do not follow the simple models used to explain defect-mediated charge recombination in the conventional semiconductors. The strong tolerance of electron-hole recombination against defects arises due to the softness of the perovskite lattice, which permits separation of electrons and holes upon defect formation, and allows only low-frequency vibrations to couple to the electronic subsystem. Both factors decrease significantly the non-adiabatic coupling and slow down the dissipation of electronic energy to heat. We suggest that a halide-rich synthesis environment may further improve the efficiency, and propose that strong defect tolerance is general to metal halide perovskites because they exhibit much lower bulk moduli compared to the conventional semiconductors used in photovoltaic, photocatalytic, electrocatalytic, lasing, light-emitting, detecting and other opto-electronic devices.
关键词： Electron-phonon coupling,Nonradiative recombination,All-inorganic perovskites,Time-dependent density functional theory,Defects
更新于2025-09-19 17:13:59
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[IEEE 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Ottawa, ON, Canada (2019.7.8-2019.7.12)] 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Numerical Analysis of Quantum Plasmonic Metasuraface by Time-Dependent Density Functional Theory
摘要： We theoretically investigate optical properties of a quantum plasmonic metasurface composed of metallic nanoparticles that are arranged in a two-dimensional matrix form with a sub-nanometer gap. We employ a time-dependent density functional theory approach to calculate optical properties of the metasurface. They show characteristic features at gap distance smaller than 0.4 nm due to the tunneling currents that flow through the gaps.
关键词： optical properties,tunneling currents,time-dependent density functional theory,quantum plasmonic metasurface
更新于2025-09-12 10:27:22