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Riccardo Adami Ugo Boscain Valentina Franceschi Dario Prandi 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2021,38(4):1095-1113
In this paper we show that, for a sub-Laplacian Δ on a 3-dimensional manifold M, no point interaction centered at a point exists. When M is complete w.r.t. the associated sub-Riemannian structure, this means that Δ acting on is essentially self-adjoint in . A particular example is the standard sub-Laplacian on the Heisenberg group. This is in stark contrast with what happens in a Riemannian manifold N, whose associated Laplace-Beltrami operator acting on is never essentially self-adjoint in , if . We then apply this result to the Schrödinger evolution of a thin molecule, i.e., with a vanishing moment of inertia, rotating around its center of mass. 相似文献
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L. G. Kuz'mina I. I. Konstantinov A. V. Churakov 《Molecular Crystals and Liquid Crystals》2018,664(1):95-100
4-methoxyphenyl-4′-n-nonyloxybenzoate have been investigated by single crystal X-ray structural analysis. Crystal packing of the compounds does not represent a precursor of the mesophse although the typical for liquid crystal compounds separation of crystal packing on aromatic and aliphatic areas is observed here. Possible reason for monotropic properties are discussed. 相似文献
5.
Domain-based local pair natural orbital methods within the correlation consistent composite approach
Ab initio composite approaches have been utilized to model and predict main group thermochemistry within 1 kcal mol−1, on average, from well-established reliable experiments, primarily for molecules with less than 30 atoms. For molecules of increasing size and complexity, such as biomolecular complexes, composite methodologies have been limited in their application. Therefore, the domain-based local pair natural orbital (DLPNO) methods have been implemented within the correlation consistent composite approach (ccCA) framework, namely DLPNO-ccCA, to reduce the computational cost (disk space, CPU (central processing unit) time, memory) and predict energetic properties such as enthalpies of formation, noncovalent interactions, and conformation energies for organic biomolecular complexes including one of the largest molecules examined via composite strategies, within 1 kcal mol−1, after calibration with 119 molecules and a set of linear alkanes. © 2019 Wiley Periodicals, Inc. 相似文献
6.
The use of additive correction schemes to obtain structures and vibrational frequencies of increasingly larger molecules is becoming more common. Such approaches, based on the cubic extrapolation formula applied directly to the quantity of interest, have been successfully validated only at the highest levels of computational accuracy: for coupled cluster methods with comparably large basis sets. Here, a systematic validation of geometries and vibrational frequencies is carried out, including more affordable and relevant levels of theory, such as the Møller-Plesset perturbation theory applied with smaller basis sets. Comparisons of such additive schemes against the more rigorous gradient-based extrapolation are presented. The cbs () routine of the open-source quantum-chemistry package Psi4 has been extended for this purpose. The results confirm that geometries and frequencies of covalently bound species obtained with additive correction schemes are in an excellent agreement with the results of gradient-based extrapolations. However, when applied to systems involving noncovalent interactions, the errors due to such schemes are significantly larger. In general, we propose the application of gradient-based extrapolations, as they incur no extra cost compared to additive schemes. 相似文献
7.
In this communication, the study on the effect of Ni2+ substitution on structural, magnetic and electrical transport properties were performed in Pr0.75Na0.25Mn1-xNixO3 (x = 0–0.10) ceramics synthesized using conventional solid-state method. X-ray diffraction patterns showed that all samples were present in single phase and crystallized in orthorhombic structure with Pnma space group. Rietveld refinement analysis revealed unit cell volume slight increase with increase Ni concentration, thereby indicating partial substitution of Ni2+ at Mn3+. The presence majority of Ni2+ states in the compound were confirmed by X-ray photoelectron spectrum. Tolerance factor calculation suggested that Ni substitution exerted no strong effect on structural distortion. For un-doped sample (x = 0), AC susceptibility (χ′) against temperature (T) curve showed paramagnetic (PM)–antiferromagnetic(AFM) behavior at Neel temperature (TN) of approximately 170 K. Furthermore, resistivity (ρ) against temperature (T) curve showed an insulating behavior for the whole measured temperature range. The χ′ against T curve of x = 0 sample showed broad peak at approximately 218 K which was attributed to the onset of charge ordered (CO) state. No such broad peak was observed in Ni-substituted samples which indicated the weakening of CO state. Moreover, χ′ measurements exhibited successful inducement of PM–FM transition with Curie temperature (TC), decreasing from 132 K (x = 0.02) to 92 K (x = 0.08). Electrical resistivity measurement on samples (x = 0.02–0.08) displayed inducement of metal–insulator transition, where transition temperature (TMI) decreased and resistivity increased, with x before re-entrant insulating behavior at x = 0.10. Notably, upturn resistivity was observed below 40 K for x = 0.06 and 0.08 samples. The suppression of CO state and inducement of ferromagnetic-metallic (FMM) state beginning from x = 0.02 sample was attributed to the reduced degree of Jahn–Teller distortion and Coulomb interaction among Mn ions, as well as the presence of ferromagnetic superexchange (FM SE) interaction among Ni2+–O–Mn4+ which improved the alignment charge carrier spins and induced the double-exchange (DE) interaction among Mn3+–O–Mn4+. The decrease in TC and TMI with increased x may be due to the enhanced AFM SE interactions of Mn3+–O–Mn3+, Mn4+–O–Mn4+ and Ni2+–O–Ni2+ which decreased the FM SE interaction of Ni2+–O–Mn4+. Consequently, the effective DE interaction was decreased. In addition, the decreased metallic behavior and re-entrant insulating behavior for x = 0.10 sample was due to the strong AFM interaction between Ni2+ ions which consequently contributed to the suppression of FM SE and DE interactions. The observed upturn resistivity below 40 K for x = 0.06 and 0.08 samples was attributed to the Kondo-like effect which resulted from the interaction between itinerant conduction electron spin and localized spin impurity. 相似文献
8.
Y. T. Angel Wong Vinicius Martins Dr. Bryan E. G. Lucier Prof. Dr. Yining Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(8):1848-1853
Metal–organic frameworks (MOFs) have shown great potential in gas separation and storage, and the design of MOFs for these purposes is an on-going field of research. Solid-state nuclear magnetic resonance (SSNMR) spectroscopy is a valuable technique for characterizing these functional materials. It can provide a wide range of structural and motional insights that are complementary to and/or difficult to access with alternative methods. In this Concept article, the recent advances made in SSNMR investigations of small gas molecules (i.e., carbon dioxide, carbon monoxide, hydrogen gas and light hydrocarbons) adsorbed in MOFs are discussed. These studies demonstrate the breadth of information that can be obtained by SSNMR spectroscopy, such as the number and location of guest adsorption sites, host–guest binding strengths and guest mobility. The knowledge acquired from these experiments yields a powerful tool for progress in MOF development. 相似文献
9.
José R. Mohallem Paulo F. G. Velloso Antonio F. C. Arapiraca 《International journal of quantum chemistry》2019,119(13):e25917
A HD-like (HD: mono-deuterated hydrogen molecule) isotopic dipole moment is proposed as a sensible probe for molecular environments, in particular for electrostatic fields and polarizable (reactive) sites of molecules. Fictitious nuclear masses are chosen in order to yield a rigid dipole with a small appropriate magnitude. Upon subtracting the Born-Oppenheimer energy, the interaction is reduced to field-dipole-like and dipole-polarizability-like terms, the last one being particularly informative since connected to potentially reactive sites. Possible asymmetries of this term appear as signatures of charged sites in the molecule. The field strength and orientation are easily obtained by identifying the minimum field-dipole energy configuration and flipping the dipole from it. Tests with hydrogen, water, benzene, and chlorobenzene molecules confirm the good performance of the method. In an application to test the present models for hydrogen activation by a frustrated Lewis pair, the full potential of the method is assessed. 相似文献
10.
Dr. Chaolu Eerdun Thi Hien Thuy Nguyen Takuya Okayama Satoshi Hisanaga Prof. Dr. Jun-ichiro Setsune 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(22):5777-5786
The hexapyrrole-α,ω-dicarbaldehydes 1 a and 1 b were metallated with CuII, NiII, and PdII to give bimetallic complexes where a pair of 3 N+O four-coordinate metal planes are helically distorted and the central 2,2′-bipyrrole subunit adopts a cis or trans conformation. X-ray crystallographic analysis of the bisCu complex revealed a closed form with a cis-2,2′-bipyrrole subunit and an open form with a trans-2,2′-bipyrrole subunit. The bisPd complexes took a closed form both in the solid state and in solution. They are regarded as single helicates of two turns and the energy barrier for the interchange between an M helix and a P helix was remarkably influenced by the bulky 3,3′-substituent of the central 2,2′-bipyrrole subunit. Although the bisNi complexes adopt a closed form in the solid state, they exist as a homohelical open C2-symmetric form or a heterohelical open Ci-symmetric form in solution. A theoretical study suggested that the closed form of 1 a Pd was stabilized by the Pd–Pd interaction. Compound 1 a Pd was reversibly oxidized by one electron at 0.14 V versus ferrocene/ferrocenium (Fc/Fc+) and this oxidized species showed Vis/NIR absorption bands at λ=767 and 1408 nm. 相似文献