Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
186,207
result(s) for
"Molecular structure"
Sort by:
Atomic and molecular structure
Learn about the atom, what it is, the people responsible for helping us understand it, and how it affects us in the world today.
Book
Boosting triplet self-trapped exciton emission in Te(IV)-doped Cs2SnCl6 perovskite variants
Perovskite variants have attracted wide interest because of the lead-free nature and strong self-trapped exciton (STE) emission. Divalent Sn(II) in CsSnX
3
perovskites is easily oxidized to tetravalent Sn(IV), and the resulted Cs
2
SnCl
6
vacancy-ordered perovskite variant exhibits poor photoluminescence property although it has a direct band gap. Controllable doping is an effective strategy to regulate the optical properties of Cs
2
SnX
6
. Herein, combining the first principles calculation and spectral analysis, we attempted to understand the luminescence mechanism of Te
4+
-doped Cs
2
SnCl
6
lead-free perovskite variants. The chemical potential and defect formation energy are calculated to confirm theoretically the feasible substitutability of tetravalent Te
4+
ions in Cs
2
SnCl
6
lattices for the Sn-site. Through analysis of the absorption, emission/excitation, and time-resolved photoluminescence (PL) spectroscopy, the intense green-yellow emission in Te
4+
:Cs
2
SnCl
6
was considered to originate from the triplet Te(IV) ion
3
P
1
→
1
S
0
STE recombination. Temperature-dependent PL spectra demonstrated the strong electron-phonon coupling that inducing an evident lattice distortion to produce STEs. We further calculated the electronic band structure and molecular orbital levels to reveal the underlying photophysical process. These results will shed light on the doping modulated luminescence properties in stable lead-free Cs
2
MX
6
vacancy-ordered perovskite variants and be helpful to understand the optical properties and physical processes of doped perovskite variants.
Journal Article
Molecules
\"Molecules may be minuscule, but life wouldn't exist without them! This approachable look at an important chemistry topic takes young scientists on a tour of the world at the atomic level. They'll learn how atoms combine to form molecules and about some familiar and vital molecules, such as carbon dioxide. Thought-provoking fact boxes offer even more interesting information, while useful diagrams help learners visualize the amazing processes of nature\"-- Provided by publisher.
Book
Atomic basis functions for molecular electronic structure calculations
Electronic structure methods for accurate calculation of molecular properties have a high cost that grows steeply with the problem size; therefore, it is helpful to have the underlying atomic basis functions that are less in number but of higher quality. Following our earlier work (Laikov in Chem Phys Lett 416:116, 2005. https://doi.org/10.1016/j.cplett.2005.09.046) where general correlation-consistent basis sets are defined, for any atom, as solutions of purely atomic functional minimization problems, and which are shown to work well for chemical bonding in molecules, we take a further step here and define a new kind of atomic polarization functionals, whose minimization yields additional sets of diffuse functions that help to calculate better molecular electron affinities, polarizabilities, and intermolecular dispersion interactions. Analytical representations by generally contracted Gaussian functions of up to microhartree numerical accuracy grades are developed for atoms hydrogen through nobelium within the four-component Dirac–Coulomb theory and its scalar-relativistic approximation, and also for hydrogen through krypton in the nonrelativistic case. The convergence of correlation energy with the basis set size is studied, and complete-basis-set extrapolation formulas are developed.
Journal Article
Tertiary orientation structures enhance the piezoelectricity of MXene/PVDF nanocomposite
With the increasing demand for flexible piezoelectric sensor components, research on polyvinylidene fluoride (PVDF) based piezoelectric polymers is mounting up. However, the low dipole polarization and disordered polarization direction presented in PVDF hinder further improvement of piezoelectric properties. Here, we constructed an oriented tertiary structure, consisting of molecular chains, crystalline region, and MXene sheets, in MXene/PVDF nanocomposite via a temperature-pressure dual-field regulation method. The highly oriented PVDF molecular chains form approximately 90% of the β phase. In addition, the crystalline region structure with long-range orientation achieves out of plane polarization orientation. The parallel orientation arrangement of MXene effectively enhances the piezoelectric performances of the nanocomposite, and the current output of the device increases by nearly 23 times. This high output device is used to monitor exercise action, exploring the potential applications in wearable electronics.
Journal Article
Molecular Asymmetry and Optical Cycling: Laser Cooling Asymmetric Top Molecules
We present a practical roadmap to achieve optical cycling and laser cooling of asymmetric top molecules (ATMs). Our theoretical analysis describes how reduced molecular symmetry, as compared to diatomic and symmetric nonlinear molecules, plays a role in photon scattering. We present methods to circumvent limitations on rapid photon cycling in these systems. We calculate vibrational branching ratios for a diverse set of asymmetric top molecules and find that many species within a broad class of molecules can be effectively cooled with a manageable number of lasers. We also describe methods to achieve rotationally closed optical cycles in ATMs. Despite significant structural complexity, laser cooling can be made effective by using extensions of the current techniques for linear molecules. Potential scientific impacts of laser-cooled ATMs span frontiers in controlled chemistry, quantum simulation, and searches for physics beyond the Standard Model.
Journal Article
Structural Characterization and Molecular Model Construction of Lignite: A Case of Xianfeng Coal
The object of the study is lignite. Analytical testing techniques, such as elemental analysis, 13C nuclear magnetic resonance (13C NMR) spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM), were used to acquire information on the structural parameters of lignite. The aromaticity of Xianfeng lignite is 43.57%, and the aromatic carbon structure is mainly naphthalene and anthracene/phenanthrene. The aliphatic carbon structure is dominated by cycloalkanes, alkyl side chains, and hydrogenated aromatics. Oxygen is mainly present in ether oxygen, carboxyl, and carbonyl groups. Nitrogen is mainly in the form of pyrrole nitrogen and quaternary nitrogen. Sulfur is mainly thiophene sulfur. According to the analysis results, the molecular structure model of XF lignite was constructed. The molecular formula is C184H172O39N6S2. The 2D structure was converted to a 3D structure using computer simulation software and optimized. The optimized model has a remarkable stereoconfiguration, and the aromatic lamellae are irregularly arranged in space. The aromatic rings were mainly connected by methylene, hypomethylene, methoxy, and aliphatic rings. In addition, the simulated 13C NMR spectra are in good agreement with the experimental spectra. This shows the rationality of the 3D chemical structure model.
Journal Article