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31.
A detailed Hamiltonian analysis for a five-dimensional Stüeckelberg theory with a compact dimension is performed. First, we develop a pure Dirac’s analysis of the theory; we show that after performing the compactification, the theory is reduced to four-dimensional Stüeckelberg theory plus a tower of Kaluza–Klein modes. We develop a complete analysis of the constraints, we fix the gauge and we show that there are present pseudo-Goldstone bosons. Then we quantize the theory by constructing the Dirac brackets. As complementary work, we perform the Faddeev–Jackiw quantization for the theory under study, and we calculate the generalized Faddeev–Jackiw brackets, we show that both the Faddeev–Jackiw and Dirac’s brackets are the same. Finally we discuss some remarks and prospects. 相似文献
32.
Yoan Hidalgo-Rosa Manuel A. Treto-Suárez Eduardo Schott Ximena Zarate Dayán Páez-Hernández 《International journal of quantum chemistry》2020,120(23):e26404
Theoretical elucidation of the turn-off mechanism of the luminescence of a chemosensor based on a metal-organic framework (MOF) [Zn2(OBA)4(BYP)2] (BYP: 4,4′-bipyridine; H2OBA: 4,4′-oxybis[benzoic acid]), selective to nitrobenzene (NB) via quantum chemical computations, is presented. The electronic structure and optical properties of Zn-MOF were investigated through the combination of density functional theory (DFT) and time-dependent DFT methods. Our results indicate that the fluorescence emission is governed by a linker (BPY)-to-linker (OBA) charge transfer (LLCT) involving orbitals π-type. Next, the interaction with the analyte was analyzed, where very interesting results were obtained, that is, the lowest unoccupied molecular orbital is now composed of orbitals from NB, which changes the emissive state of the Zn-MOF. This suggests that the LLCT process is blocked, inducing the fluorescence quenching. Otherwise, the Morokuma-Ziegler energy decomposition and natural orbitals for chemical valence on the Zn-MOF-NB interactions were studied in detail, which illustrate the possible channels of charge transfer between Zn-MOF and NB. Finally, we believe that this proposed methodology can be applied to different chemosensor-analyte systems to evidence the molecular and electronic factors that govern the sensing mechanisms. 相似文献
33.
Xiang‐Wei Liu Cayetana Zarate Ruben Martin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(7):2086-2090
The ability to selectively forge C–heteroatom bonds by C?F scission is typically accomplished by metal catalysts, specialized ligands and/or harsh reaction conditions. Described herein is a base‐mediated defluorosilylation of unactivated C(sp2)?F and C(sp3)?F bonds that obviates the need for metal catalysts. This protocol is characterized by its simplicity, mild reaction conditions, and wide scope, even within the context of late‐stage functionalization, constituting a complementary approach to existing C?Si bond‐forming protocols. 相似文献
34.
We evaluate numerically the free energy of a strong-coupling superconductor with paramagnetic impurities in the model of Shiba and Rusinov. Our work is based on a recent formula for the free energy given by Yamamoto and Nagi. This formula is based on the same fundamental expression as used by Schossmann and Schachinger but without their simplfying approximations. Our results are numerically quite different from the previous ones. It is still concluded, however, that the thermodynamic critical field is very sensitive to the model chosen to describe the scattering. 相似文献
35.
A new synthesis route to obtain high-purity cupric oxide, CuO, using the hydrothermal reaction of copper sulfide and a NaOH solution in an oxygen atmosphere has been developed. The synthesized products showed nanoplatelet-like morphologies with rectangular cross-sections and dimensions at the nanometric scale. Variations in the oxygen partial pressure and synthesis temperature produced changes in size and shape, being found that the proliferation of nanoplatelet structures occurred at 200 °C and 30 bar. 相似文献
36.
Gabriela Castillo-Toraya Mesías Orozco-Ic Eugenia Dzib Ximena Zarate Filiberto Ortíz-Chi Zhong-hua Cui Jorge Barroso Gabriel Merino 《Chemical science》2021,12(19):6699
Among the list of planar tetracoordinate atoms, fluorine is missing. So far, there are no theoretical or experimental reports suggesting their existence. Herein, we introduce the first six combinations (FIn4+, FTl4+, FGaIn3+, FIn2Tl2+, FIn3Tl+, and FInTl3+) whose global minima contain a planar tetracoordinate fluorine. The bonding analyses indicate that the interactions between the fluorine and the peripheral atoms are significantly electrostatic, which is also reflected in the electronic delocalization. As opposed to other planar tetracoordinate systems with carbon, nitrogen, or oxygen atoms, the fluorine in the ptFs does not act as a σ-acceptor, restraining any back-donation. On the other hand, σ-electrons show a diatropic response, which would characterize these clusters as σ-aromatic.The first global minima with a planar tetracoordinate fluorine atom are introduced. Their stabilization depends mainly on subtle ionic interactions and an adequate cavity. 相似文献
37.
In this work, we introduce a new measure for the dispersion of the spectral scale of a Hermitian (self-adjoint) operator acting on a separable infinite-dimensional Hilbert space that we call spectral spread. Then, we obtain some submajorization inequalities involving the spectral spread of self-adjoint operators, that are related to Tao's inequalities for anti-diagonal blocks of positive operators, Kittaneh's commutator inequalities for positive operators and also related to the arithmetic–geometric mean inequality. In turn, these submajorization relations imply inequalities for unitarily invariant norms (in the compact case). 相似文献
38.
Armando A. Morin-Martinez Jessica Arcudia Ximena Zarate Miguel Eduardo Cifuentes-Quintal Gabriel Merino 《Journal of computational chemistry》2023,44(3):248-255
Herein we show a density functional theory-based study performed on two recently predicted polymorphs of the BeH2 monolayer, α-BeH2 and β-BeH2. The α-BeH2 phase possesses an in-plane negative Poisson's ratio (NPR), introducing it into the unique group of auxetic materials. Our assessment delves into the linear-elastic and finite-strain regimes to understand both polymorphs' structural and mechanical responses to deformation. We find that the in-plane NPR is shown to be only parallel to the bonds in α-BeH2 and remains along the uniaxial tensile path. Concomitantly, an out-of-plane transition toward auxetic is also revealed in regions exhibiting conventional Poisson's ratios, making α-BeH2 a bidirectionally auxetic material. While phase transitions in β-BeH2 are triggered at very short strains, α-BeH2 displays excellent elasticity against tension, superior to that of most currently known 2D materials. 相似文献
39.
Yoan Hidalgo-Rosa Manuel A. Treto-Suárez Eduardo Schott Ximena Zarate Dayán Páez-Hernández 《Journal of computational chemistry》2020,41(22):1956-1964
A theoretical procedure, via quantum chemical computations, to elucidate the detection principle of the turn-off luminescence mechanism of an Eu-based Metal-Organic Framework sensor (Eu-MOF) selective to aniline, is accomplished. The energy transfer channels that take place in the Eu-MOF, as well as understanding the luminescence quenching by aniline, were investigated using the well-known and accurate multiconfigurational ab initio methods along with sTD-DFT. Based on multireference calculations, the sensitization pathway from the ligand (antenna) to the lanthanide was assessed in detail, that is, intersystem crossing (ISC) from the S1 to the T1 state of the ligand, with subsequent energy transfer to the 5D0 state of Eu3+. Finally, emission from the 5D0 state to the 7FJ state is clearly evidenced. Otherwise, the interaction of Eu-MOF with aniline produces a mixture of the electronic states of both systems, where molecular orbitals on aniline now appear in the active space. Consequently, a stabilization of the T1 state of the antenna is observed, blocking the energy transfer to the 5D0 state of Eu3+, leading to a non-emissive deactivation. Finally, in this paper, it was demonstrated that the host-guest interactions, which are not taken frequently into account by previous reports, and the employment of high-level theoretical approaches are imperative to raise new concepts that explain the sensing mechanism associated to chemical sensors. 相似文献
40.
Ximena Zarate Eduardo Schott Leonor Alvarado‐Soto Todd C. Sutherland 《International journal of quantum chemistry》2013,113(20):2287-2294
A theoretical study has been carried out on two methoxyphenyl derivatives (tetrakis‐(p‐methoxyphenyl)‐ porphyrin and the Zn‐containing complex), which are the reduced size representation of the alkyl peripheral substituent systems. The aim is to study the electronic interactions on these aromatic cores which is one of the most important properties in discotic liquid crystals. Their face‐to‐face dimeric conformation systems were studied in order to evaluate charge transport properties, by assessing the intermolecular charge transfer integrals “t” in the context of the Marcus electron transfer theory. The intermolecular transfer integral has been calculated from the matrix elements of the Kohn–Sham Hamiltonian including dispersion correction for noncovalent interacting systems. The results indicate that the effect of the Zn center in these porphyrins is nearly negligible and both studied systems can act as electron carriers, which are also seen in the bonding interaction of the LUMO orbitals. © 2013 Wiley Periodicals, Inc. 相似文献