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Computational study of molecular geometries, and vibrational characteristics of two liquid crystalline disubstituted biphenylcyclohexanes using ab-initio methods

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MOLECULAR CRYSTALS AND LIQUID CRYSTALS 2019年第1期682卷 27-43页

作者： Prasad, Seema Ojha, Durga P. Sambalpur Univ Sch Phys Sambalpur 768019 Odisha India

The present article deals with computational study of molecular geometries, electronic properties, and vibrational characteristics using the density functional theory (DFT) and Hartree-Fock methods supplemented with basis set 6-31++G(d.p) at Gaussion-09 program. The Raman and infrared spectra of two liquid crystalline disubstituted biphenylcyclohexanes (BCH RX) of general formula R-C6H10-C6H4-C6H4-X with R: C3H7;X = H (BCH30) and R: C5H11;X = CN (BCH5CN) have been analyzed and vibrations corresponding to particular frequency are assigned in detail. Most of the modes have wavenumbers/frequencies in the expected range, and the error obtained was minimum. Aromatic ring with terminal cyano group confers a positive dielectric anisotropy, and high optical anisotropy. Cyanobiphenyls possess high dielectric anisotropy and good electro-optical characteristics are used to decrease the switching time of liquid crystalline materials. It has been observed that the DFT based calculations consider the different types of interactions between electrons, thus it gives more accuracy as compared to HF method. Further, the electronic properties of the mesogenic compounds have been reported to understand the molecular reactivity, charge transfer, electro-optical, and other molecular properties.

关键词： ab-initio methods electronic properties IR and Raman spectra

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Acetalization of 2-Hydroxybenzaldehyde mechanism using halogen acid catalysts based on ab initio methods

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AIP Conference Proceedings 2017年第1期1904卷 020012-020012页

作者： Muhammad Yusuf Destria Roza Ahmad Kamil Nasution Department of Chemistry State University of Medan Jl. Willem Iskandar Psr V Medan Indonesia

The computational calculation was performed on the acetalization of 2-hydroxybenzaldehyde by using ab initio method. ab initio method is derived directly from theoretical principles with no inclusion of experimental data and this is an approximate quantum mechanical calculation. The aim of this research was to studies the acetalization of 2-hydroxybenzaldehyde mechanism using halogen acid catalysts. Computational calculation which was applied on the acetalization of 2-hydroxybenzaldehyde using halogen acid catalysts provided possible reaction steps. The first step was formation of a labile hemiacetal because it is essentially tetrahedral intermediates containing a leaving group. The second step was formation of a stable acetal. The results of computational calculation of acetalization of 2-hydroxybenzaldehyde provided possible energy change in the each step of the reaction process. A labile hemiacetal showed higher energy (481.04 kJ/mol) than 2-hydroxybenzaldehyde dimethyl acetal (65.32 kJ/mol) and 2-hydroxybenzaldehyde (0 kJ/mol) due to its instability. In general, acetalization of 2-hydroxybenzaldehyde reaction is a reversible reaction. The effect of Lewis acidity on halogen acid catalysts was also studied in this research. Based on the Mulliken charge on the H atom, it is found that HF has the highest Lewis acidity compared to other halogen acids with order HF> HCl> HBr> HI. As a result, HF was the efficient catalysts for acetalization of 2-Hydroxybenzaldehyde.

关键词： Polymers Mulliken charges Chemical elements Catalyst Quantum mechanical calculations ab-initio methods

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Theoretical calculation of the adiabatic electron affinities of the monosubstituted benzaldehyde derivatives

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JOURNAL OF KING SAUD UNIVERSITY SCIENCE 2023年第5期35卷

作者： Safi, Zaki S. Wazzan, Nuha Al Azhar Univ Gaza Fac Sci Dept Chem POB 1277 Gaza Palestine King Abdulaziz Univ Fac Sci Chem Dept POB 4280 Jeddah 21589 Saudi Arabia

In the current study, several computational models were examined to calculate accurate adiabatic electron affinity (AEA) of twelve m- and p-monosubstituted benzaldehyde derivatives. The examined models are as follows: (i) composite high-level ab initio (G3B3, G4, CBS-Q, and CBS-QB3), (ii) Three hybrid DFT approaches (B3LYP, CAM-B3LYP, and wB97XD) with two basis sets (6-31 + G(d,p) and 6-311++G (2df,2p)) and (iii) single point calculation using fifteen DFT approaches with 6-311++G(2df,2p) at the B3LYP/6-31 + G(d,p) geometry. Several statistical descriptors were computed to validate the calculated AEAs based on the available experimental results. Results revealed that G3B3 and CBS-QB3 are the most accurate result, while G4 and CBS-Q methods yield less accurate ones. Also, the wB97XD and CAM-B3LYP in combination with 6-311++G(2df,2p) able to calculate accurate AEAs. Low CPU time single point calculation strategy by using wb97 and wb97X approaches can compute AEAs value as accurately as G3B3 and CBS-QB3 methods. The AEAs of other several monosubstituted benzaldehydes were also predicted by using the wb97, wb97X, and wb97XD. The effect of the nature and position of substituents on the natural spin density and natural charge is also studied and discussed. & COPY;2023 The Author(s). Published by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://***/licenses/by-nc-nd/4.0/).

关键词： Adiabatic electron affinity (AEA) Natural spin densities Benzaldehyde Density Functional Theory ab-initio methods

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Coherence and de-coherence in the Time-Resolved ARPES of realistic materials: An ab-initio perspective

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JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 2022年 257卷

作者： Marini, Andrea Perfetto, Enrico Stefanucci, Gianluca CNR Ist Struttura Mat Via Salaria Km 29-3 I-00016 Monterotondo Italy CNR Div Ultrafast Proc Mat FLASHit Via Salaria Km 29-3 I-00016 Monterotondo Italy European Theoret Spect Facil ETSF Donostia An Sebastian Spain Univ Roma Tor Vergata Dipartimento Fis Via Ric Sci 1 I-00133 Rome Italy INFN Sez Roma Tor Vergata Via Ric Sci 1 I-00133 Rome Italy

Coherence and de-coherence are the most fundamental steps that follow the initial photo-excitation occurring in typical pump-and-probe experiments. Indeed, the initial external laser pulse transfers coherence to the system in terms of creation of multiple electron-hole pairs excitation. The excitation concurs both to the creation of a finite carriers density and to the appearance of induced electromagnetic fields. The two effects, to a very first approximation, can be connected to the simple concepts of populations and oscillations. The dynamics of the system following the initial photo-excitation is, thus, entirely dictated by the interplay between coherence and de-coherence. This interplay and the de-coherence process itself, is due to the correlation effects stimulated by the photo-excitation. Single-particle, like the electron-phonon, and two-particles, like the electron-electron, scattering processes induce a complex dynamics of the electrons that, in turn, makes the description of the correlated and photo-excited system in terms of pure excitonic and/or carriers populations challenging.

关键词： Out-of-equilibrium many-body ab-initio methods Excitons Coherence and de-coherence

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Electronic structure of reduced CeO2(111) surfaces interacting with hydrogen as revealed through electron energy loss spectroscopy in comparison with theoretical investigations

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JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 2022年第0期257卷

作者： Paier, Joachim Nelin, Connie J. Bagus, Paul S. Plucienik, Agata Kuhlenbeck, Helmut Freund, Hans-Joachim Humboldt Univ Inst Chem Unter Linden 6 D-10099 Berlin Germany 6008 Maurys Trail Austin TX 78730 USA Univ North Texas Dept Chem Denton TX 76203 USA Gesellschaft Fritz Haber Inst Max Planck Faradayweg 4-6 D-14195 Berlin Germany

Based on both, ab-initio cluster calculations as well as periodic density functional based loss function calculations, we have assigned the origins of the valence electron excitation regime in electron energy loss spectra of well-ordered ceria films in (111) orientation at various states of reduction as well as after exposing the reduced films to hydrogen from the gas phase (Li et al, Angew. Chem. Int. Ed., 58 (2019) 14686-14693). The explicit calculation of intensity distributions using the dipole approximation allow us to draw conclusions about the nature of oxygen vacancies, which occur upon reduction and how those interact with hydrogen to form hydride *** present study also reports a brief discussion of vibrational excitations of hydrogen loaded ceria and corroborates previous interpretations, based on inelastic neutron scattering.

关键词： Ceria Energy loss spectroscopy Valence electron excitations Vibrational excitations Density functional theory ab-initio methods

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Probing the range of applicability of structure- and energy-adjusted QM/MM link bonds II: Optimized link bond parameters for density functional tight binding approaches

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JOURNAL OF COMPUTATIONAL CHEMISTRY 2022年第11期43卷 746-756页

作者： Gallmetzer, Hans Georg Hofer, Thomas S. Univ Innsbruck Ctr Chem & Biomed Inst Gen Inorgan & Theoret Chem Theoret Chem Div Innrain 80-82 A-6020 Innsbruck Austria

Optimized link bond parameters for the C-alpha-C-beta bond of 22 different capped amino acid model systems have been determined at SCC DFTB/mio (self-consistent charge density functional tight-binding), SCC DFTB/3ob and GFNn-xTB (n = 0, 1, and 2) level in conjunction with the AMBER 99SB, 14SB, and 19B force fields. The resulting parameter sets have been compared to newly calculated reference data obtained via resolution-of-identity 2nd order Moller-Plesset perturbation theory. The data collected in this work suggests that the optimized values in this study provide a more suitable setup of the QM/MM link bonds compared to the use of a single global setting applied to every amino acid fragmented by the QM/MM interface. The results also imply that a transfer of the ideal link bond settings between different levels of theory is not advised. In contrast, virtually identical parameters were obtained in calculations employing different variants of the AMBER force field. Considering the increasing success of tight binding based approaches being inter alia a results of their exceptional accuracy/effort ratio the provided collection of link atoms parameters provides a valuable resource for QM/MM studies of biomacromolecular systems as demonstrated in an exemplary QM/MM MD simulation of the beta-amyloid/Zn2+ complex.

关键词： QM MM link bonds ab-initio methods density functional tight binding semi-empirical amyloid

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Ultrafast dynamics of electrons and phonons: from the two-temperature model to the time-dependent Boltzmann equation

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ADVANCES IN PHYSICS-X 2022年第1期7卷 Article: 2095925页

作者： Caruso, Fabio Novko, Dino Christian Albrechts Univ Kiel Inst Theoret Phys & Astrophys Kiel Germany Inst Phys Zagreb Croatia

The advent of pump-probe spectroscopy techniques paved the way to the exploration of ultrafast dynamics of electrons and phonons in crystalline solids. Following photo-absorption of a pump pulse and the initial electronic thermalization, the dynamics of electronic and vibrational degrees of freedom is dominated by electron-phonon and phonon-phonon scattering processes. The two-temperature model (TTM) and its generalizations provide valuable tools to describe these phenomena and the ensuing coupled dynamics of electrons and phonons. While more sophisticated theoretical approaches are nowadays available, the conceptual and computational simplicity of the TTM makes it the method of choice to model thermalization processes in pump-probe spectroscopy, and it keeps being widely applied in both experimental and theoretical studies. In the domain of ab-initio methods, the time-dependent Boltzmann equation (TDBE) ameliorates many of the shortcomings of the TTM and enables a realistic and parameter-free description of ultrafast phenomena with full momentum resolution. After a pedagogical introduction to the TTM and TDBE, in this manuscript we review their application to the description of ultrafast process in solid-state physics and materials science as well as their theoretical foundation. [GRAPHICS] .

关键词： ab-initio methods ultrafast dynamics electron-phonon coupling carrier thermalization two-temperature model time-dependent boltzmann equation

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A generalized hybrid scheme for multireference methods

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JOURNAL OF CHEMICAL PHYSICS 2021年第20期155卷 204106-204106页

作者： Waigum, A. Black, J. A. Kohn, A. Univ Stuttgart Inst Theoret Chem Pfaffenwaldring 55 D-70569 Stuttgart Germany

A generalization of the hybrid scheme for multireference methods as recently put forward by Saitow and Yanai [J. Chem. Phys. 152, 114111 (2020)] is presented. The hybrid methods are constructed by defining internal and external excitation spaces and evaluating these two subsets of excitations at different levels of theory. New hybrids that use the mix of internally contracted multireference coupled-cluster, unshifted multireference coupled electron pair, and multireference perturbation methods are derived and benchmarked. A new separation of the excitation space, which combines all singles and doubles excitations to the virtual orbitals into the external space, is also presented and tested. In general, the hybrid methods improve upon their non-hybrid parent method and offer a good compromise between computational complexity and numerical accuracy. Published under an exclusive license by AIP Publishing.

关键词： Topics: Potential energy surfaces Perturbation theory ab-initio methods Correlation energy Complete-active space self-consistent field Coupled-cluster methods.

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Ultrafast stimulated resonance Raman signatures of lithium polysulfides for shuttling effect characterization: An ab initio study

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JOURNAL OF CHEMICAL PHYSICS 2021年第17期155卷 174301-174301页

作者： Ren, Hao Wang, Zhengjie Guo, Sibei Guo, Wenyue Tian, Guangjun Tian, Baoling China Univ Petr East China Sch Mat Sci & Engn Qingdao 266580 Shandong Peoples R China Yanshan Univ Sch Sci Key Lab Microstruct Mat Phys Hebei Prov Qinhuangdao 066004 Hebei Peoples R China Qingdao Agr Univ Coll Chem & Pharmaceut Sci Qingdao 266109 Shandong Peoples R China

The shuttling effect is a crucial obstacle to the practical deployment of lithium sulfur batteries (LSBs). This can be ascribed to the generation of lithium polysulfide (LiPS) redox intermediates that are soluble in the electrolyte. The detailed mechanism of the shuttling, including the chemical structures responsible for the loss of effective mass and the dynamics/kinetics of the redox reactions, are not clear so far. To obtain this microscopic information, characterization techniques with high spatial and temporal resolutions are required. Here, we propose that resonance Raman spectroscopy combined with ultrafast broadband pulses is a powerful tool to reveal the mechanism of the shuttling effect. By combining the chemical bond level spatial resolution of resonance Raman and the femtosecond scale temporal resolution of the ultrafast pulses, this novel technique holds the potential of capturing the spectroscopic fingerprints of the LiPS intermediates during the working stages of LSBs. Using ab initio simulations, we show that, in addition to the excitation energy selective enhancement, resonance Raman signals of different LiPS intermediates are also characteristic and distinguishable. These results will facilitate the real-time in situ monitoring of LiPS species and reveal the underlying mechanism of the shuttling effect.

关键词： Topics: Redox reactions Quantum chemical dynamics Resonance Raman spectroscopy Electrolytes ab-initio methods Measurement theory Excitation energies Chemical bonding Stimulated scattering Batteries

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Inhibition of steel corrosion with imidazolium-based compounds - Experimental and theoretical study

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CORROSION SCIENCE 2021年 191卷 109716-109716页

作者： Legut, Dominik Kadzielawa, Andrzej Piotr Panek, Petr Markova, Kristyna Vanova, Petra Konecna, Katerina Langova, Sarka VSB Tech Univ Ostrava IT4Innovat 17 Listopadu 2172-15 Ostrava 70800 Czech Republic Uniwersytet Jagiellonski Instyut Fizyki Teoretycznej Ul Lojasiewicza 11 PL-30348 Krakow Poland VSB Tech Univ Ostrava Fac Mat Sci & Technol 17 Listopadu 2172-15 Ostrava 70800 Czech Republic VSB Tech Univ Ostrava Inst Environm Technol 17 Listopadu 2172-15 Ostrava 70800 Czech Republic

This work aims to investigate the corrosion inhibition of the mild steel in the 1 M HCl solution by 1-octyl-3-methylimidazolium hydrogen sulphate 1-butyl-3-methylimidazolium hydrogen sulphate, and 1-octyl-3-methylimidazolium chloride, using electrochemical, weight loss, and surface analysis methods as well as the full quantummechanical treatment. Polarization measurements prove that studied compounds are mixed-type inhibitors with a predominantly anodic reaction. The inhibition efficiency obtained from the polarization curves is about 80-92% for all of the 1-octyl-3-methylimidazolium salts with a concentration higher than 0.005 mol/l, while it is much lower for 1-butyl-3-methylimidazolium hydrogen sulphate. The values measured in the weight loss experiments (after seven days) are to some extent higher (reaching up to 98% efficiency). Furthermore, we have shown that the influence of the alkyl chain length on the inhibition efficiency is much larger than that of the anion type. Furthermore, we obtain a realistic model of a single molecule on iron surface Fe(110) by applying the Density Functional Theory calculations. We use the state-of-the-art computational approach, including the meta-GGA strongly-constrained and appropriately normed semilocal density functional to model the electronic structure properties of both free and bounded-to-surface molecules of 1-butyl-, 1-hexyl-, and 1-octyl-3-methylimizadolium bromide, chloride, and hydrogen sulphate. From the calculations we extract, the HOMO/LUMO gap, hardness, electronegativity, and charge transfer of electrons from/to molecules-in-question. It supports the experimental findings and explains the influence of the alkyl chain length and the functional group on the inhibition process.

关键词： Imidazolium-based compounds Corrosion inhibition Polarization curve Electrochemical impedance spectroscopy Steel Density functional theory Electronic structure ab-initio methods

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