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Influence of Oxygen Vacancy Density on the Polaronic Configuration in Rutile
摘要： Polaronic con?gurations that were introduced by oxygen vacancy in rutile TiO2 crystal have been studied by the DFT + U method. It is found that the building block of TiO6 will expand when extra electron is trapped in the central Ti atom as polaron. With manually adjusting the initial geometry of oxygen vacancy structure, a variety of polaronic con?gurations are obtained after variable-cell relaxation. By calculating different sizes of supercell model, it is found that the most stable con?guration can be in?uenced by the density of oxygen vacancy. With increasing interaction between vacancies, the most stable polaronic con?guration change from small polaronic con?guration to mixed con?guration.
关键词： DFT + U,rutile,electronic structure,oxygen vacancies,polarons
更新于2025-09-10 09:29:36
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Regulating the Optoelectronic Properties of Nickel Dithiolene by the Substituents: A Theoretical Study
摘要： Dithiolene-based complexes show great potential to be applied as materials for organic optoelectronic devices. In this study, we theoretically designed a series of complexes based on nickel dithiolene and its substituted derivatives, the optoelectronic properties of which were comparatively studied by density functional theory (DFT)/time-dependent density functional theory (TD-DFT). The results show that the charge injection property of nickel dithiolene complexes can be significantly improved with introduction of electron-withdrawing groups. The charge transportation property of nickel dithiolene depends on the conjugation degree of the system. The energy gaps between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are determined by the substituents, which makes the maximum absorption wavelength red-shift from the visible to the near-infrared (NIR) region. The electron density difference graph shows that the electron transition from the ground state to the first excited state is assigned to π-π* transition mainly from HOMO to LUMO. The regularity of substituent effect revealed by us in this study will shed light on the application of nickel dithiolenes as potential optoelectronic materials.
关键词： substituents,DFT,nickel dithiolene,optoelectronic properties
更新于2025-09-10 09:29:36
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Numerical Study of a Hybrid Optical DMT/DFT-S QAM Modulation
摘要： A hybrid modulation offers the peak-to-average power ratio (PAPR) robustness of discrete Fourier transform spread (DFT-S) QAM (quadrature amplitude modulation) with the bit rate optimization of discrete multi-tone (DMT) modulation. We examine via simulation under what circumstances this hybrid can increase achievable bit rate. Hybrid PAPR reduction allows us to increase the peak-to-peak voltage at the modulator electrical input to increase the signal mean power at the modulator output. We propose a methodology to identify the optimal driving strategy. We optimize the bit rate for the available spectrum, i.e., the spectral efficiency, taking into account the bandwidth limited nature of the transmitter. The final optimization we propose is the partition of the available spectrum into a lower frequency band for DFT-S QAM and a higher frequency band for DMT. The modulation level of the DFT-S QAM is also optimized. We compare the optimal hybrid performance versus DMT performance for a range of bit rates for a given modulation bandwidth. Improved performance comes at the cost of greater DSP complexity for the hybrid solution. We compare the number of complex multipliers required to implement hybrid versus DMT for both dispersive and non-dispersive systems.
关键词： simulation,DFT-spread,QAM,complexity comparison,frequency optimization,DMT,hybrid
更新于2025-09-10 09:29:36
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Terahertz Time Domain Spectroscopy of Transformer Insulation Paper after Thermal Aging Intervals
摘要： An accelerated thermal aging process was used to simulate the condition of paper insulation in transformer oil-paper systems. Optical parameters of the insulation paper after various aging intervals were analyzed with terahertz time-domain spectroscopy (THz-TDS) over the range 0.1~ 1.8 THz. The result shows that the paper had seven absorption peaks at 0.19, 0.49, 0.82, 1.19, 1.43, 1.53, and 1.74 THz, and density functional theory of B3LYP/6-311G+ (d, p) was used to simulate the molecular dynamics of the repeating component (cellobiose) of the cellulose paper. Theoretical spectra were consistent with experiment, which had absorption peaks at 0.18, 0.82, 1.47, and 1.53 THz in the same frequency range. At the same time, the paper samples after various aging intervals had different refractive indexes, and least squares ?tting revealed a linear relationship between the degree of polymerization and the refractive index of the paper. Hence, this paper demonstrates that THz-TDS could be used to analyze the aging condition of transformer insulation paper and provides the theoretical and experimental basis for detection.
关键词： transformer insulation paper,novel diagnostic technique,molecular dynamics simulation,DFT,terahertz-time-domain spectroscopy
更新于2025-09-10 09:29:36
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Synthesis, spectral characterization (FT-IR and NMR) and DFT (Conformational analysis, molecular structure, HOMO-LUMO, UV-vis, NLO) computational studies on 2,2’-((1E,1’E)-phenazine-2,3 dilbis(azanylylidene))bis(methanyly- lidene))diphenol
摘要： A new Schiff base was synthesized for the first time by the phenazine-2,3-diamine and 2-hydroxy benzaldedye in ethanol (1:1). The structure of Schiff bases was experimentally characterized by using UV-vis, IR, 1H NMR and 13C NMR spectroscopic methods. Further, the synthesized compound was subjected to DFT for better understanding of the molecular architecture and optoelectronic properties. The optimized geometric parameters supported the available experimental values. The Mulliken and MEP analyses are utilized to identify reactive sites of title molecule. The energetic behaviors of compound 3 in hexane, chloroform, methanol solvents and gas phase were examined using by time-dependent DFT (TD-DFT) method by applying the polarizable continuum model (PCM). The calculated ΔE energies exposed that charge transfer takes place within the molecule. In addition to the polarizability and hyperpolarizability have been calculated which exhibit that compounds possess non-linear optical nature.
关键词： Schiff Base,MEP,HOMO-LUMO,DFT,Mulliken Charge
更新于2025-09-10 09:29:36
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Matrix-induced Linear Stark Effect of Single Dibenzoterrylene Molecules in 2,3-Dibromonaphthalene Crystal
摘要： Absorption and fluorescence from single molecules can be tuned by applying an external electric field – a phenomenon known as the Stark effect. A linear Stark effect is associated to a lack of centrosymmetry of the guest in the host matrix. Centrosymmetric guests can display a linear Stark effect in disordered matrixes, but the response of individual guest molecules is often relatively weak and non-uniform, with a broad distribution of the Stark coefficients. Here we introduce a novel single-molecule host-guest system, dibenzoterrylene (DBT) in 2,3-dibromonaphthalene (DBN) crystal. Fluorescent DBT molecules show excellent spectral stability with a large linear Stark effect, of the order of 1.5 GHz/(kVcm -1), corresponding to an electric dipole moment change of around 2 D. Remarkably, when the electric field is aligned with the a crystal axis, nearly all DBT molecules show either positive or negative Stark shifts with similar absolute values. These results are consistent with quantum chemistry calculations. Those indicate that DBT substitutes three DBN molecules along the a axis, giving rise to eight equivalent embedding sites, related by the three glide planes of the orthorhombic crystal. The static dipole moment of DBT molecules is created by host-induced breaking of the inversion symmetry. This new host-guest system is promising for applications that require a high sensitivity of fluorescent emitters to electric fields, for example to probe weak electric fields.
关键词： 2,3-dibromonaphthalene,linear Stark effect,single-molecule spectroscopy,symmetry breaking,DFT,dibenzoterrylene,insertion sites,induced dipole moment
更新于2025-09-10 09:29:36
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Spin-polarized optical properties of half-metallic binary XBi (X?=?Ca, Sr and Ba) compounds in zinc blende and wurtzite phases
摘要： In this work, we aim to study the spin-polarized optical properties of the non-transition metal-based binary compounds XBi (X = Ba, Sr and Ca) in the zinc blende and wurtzite phases. The calculations are performed by the developed full-potential augmented plane wave plus local orbitals (FP-L/APW ? lo) method within the spin density functional theory. We used the Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (PBE-GGA) and the recently modi?ed Becke–Johnson potential (mBJ-GGA) to generate the exchange–correlation potential. The optical constants as the dielectric function, refractive index and extinction coef?cient were calculated and discussed in detail. Our compounds are identi?ed as potential candidates for spintronic applications and high-performance electronic devices, due to their possible half-metallic character. The interband transitions responsible for the structures in the spectra are speci?ed. It is shown that the Bi-p states and (Ca, Sr, Ba)-d states play the major role in optical transitions as initial and ?nal states.
关键词： Ferromagnetism,DFT,Half-metal,Optical properties
更新于2025-09-10 09:29:36
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Encyclopedia of Spectroscopy and Spectrometry || Vibrational CD, Theory and Application to Determination of Absolute Configuration
摘要： Chiral organic molecules are currently of widespread interest to organic chemists and pharmaceutical chemists. Chiral drugs, for example, omeprazole, are of increasing importance in the pharmaceutical industry. Since the two enantiomers of a chiral drug generally possess different pharmaceutical activities, the resolution and clinical testing of both enantiomers is a prerequisite to the development of the optimum drug. The increasing importance of chiral drugs has stimulated the development of improved techniques, especially chromatographic, for the resolution of racemic mixtures of chiral molecules, and of new asymmetric synthesis methods. In addition to synthetic chiral molecules, naturally occurring molecules (‘natural products’), which are invariably chiral and generally enantiomerically enriched, are of increasing interest as drugs, or leads for new drugs. Many natural products have been used in folk medicine for centuries, and such molecules are now receiving increasing attention.
关键词： Vibrational CD,Chiral organic molecules,Absolute configuration,Circular dichroism,Conformational analysis,DFT
更新于2025-09-10 09:29:36
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Highly fluorescent materials derived from ortho-vanillin: Structural, photophysical electrochemical and theoretical studies
摘要： Small-molecule organic fluorophores are highly in demand attributed to their extensive prospective in material and biomedical applications. Particularly, luminescent π-conjugated organic molecules that possess an efficient solid-state emission are excellent candidates for optoelectronic devices. Focusing on high demand of organic fluorophores, we herein report the synthesis of three organic fluorescent materials derived from o-vanillin, viz. an ester (F1), an azine (F2) and an azo dye (F3). Interestingly, F2 exhibited very intense luminescence in its aggregate phase due to the restriction in intra-molecular rotation (RIR), as demonstrated by solution thickening studies. Further, its Single Crystal X-ray Crystallography (SCXRD) study suggested bathochromic shift in fluorescence from solution to solid phase was confirmed by its thin-film emission spectrum, which evidences the formation of J-aggregates. The observed RIR, development of J-aggregates and high conjugation in F2 impart an excellent fluorescence in its aggregated state. Thin films of both F2 and F3 on ITO plates exhibited a bathochromic shift with a deep orange to red photoluminescence on UV excitation. Furthermore, the morphological characterization revealed the presence of clear dense grains in case of F2 and F3, while the DSC analysis indicated phase transitions of all the derivatives. As seen from dielectric measurement studies, the azo dye F3 exhibited the highest dielectric constant among the three derivatives. The electronic and photophysical data based on Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) calculations are in agreement with the experimental results. All the above data clearly advocate that, the synthesized fluorophoric o-vanillin derivatives are excellent candidates for electro-optical devices.
关键词： Fluorophore,Electrochemical,X-ray Crystallography,Aggregation,Dielectric,DFT,Azine
更新于2025-09-10 09:29:36
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Convolution neural network-based time-domain equalizer for DFT-Spread OFDM VLC system
摘要： This paper presents a novel time-domain equalizer for visible light communication (VLC) system using machine learning (ML) method. In this work, we employ discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) as modem scheme and convolution neural network (CNN) as kernel processing unit of equalizer. After estimating channel state information (CSI) from training sequence, the proposed equalizer recovers transmitted symbols according to the estimated CSI. Numerical simulations indicate that the equalizer can significantly enhance bit error rate (BER) performance. For example, when signal-to-noise ratio (SNR) is 20dB and 16/32/64-quadrature amplitude modulation (QAM) is exploited, original BER is about 0.5 while the BER after recovery achieves 10?5, which is much lower than forward error correction (FEC) limit 3.8×10?3. This work promotes the application of ML in VLC domain. To the best of our knowledge, this is the first time a CNN-based equalizer has been explored.
关键词： Machine learning (ML),Discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM),Visible light communication (VLC),Convolution neural network (CNN)
更新于2025-09-10 09:29:36