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Quantum theory

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https://www.readbyqxmd.com/read/28550814/determination-of-equilibrium-structures-of-bromothymol-blue-revealed-by-using-quantum-chemistry-with-an-aid-of-multivariate-analysis-of-electronic-absorption-spectra
#1
Toru Shimada, Takeshi Hasegawa
The pH dependent chemical structures of bromothymol blue (BTB), which have long been under controversy, are determined by employing a combined technique of multivariate analysis of electronic absorption spectra and quantum chemistry. Principle component analysis (PCA) of the pH dependent spectra apparently reveals that only two chemical species are adequate to fully account for the color changes, with which the spectral decomposition is readily performed by using augmented alternative least-squares (ALS) regression analysis...
May 19, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
https://www.readbyqxmd.com/read/28549214/griffith-criterion-for-nanoscale-stress-singularity-in-brittle-silicon
#2
Takashi Sumigawa, Takahiro Shimada, Shuuhei Tanaka, Hiroki Unno, Naoki Ozaki, Shinsaku Ashida, Takayuki Kitamura
Brittle materials such as silicon fail via the crack nucleation and propagation, which is characterized by the singular stress field formed near the crack tip according to Griffith or fracture mechanics theory. The applicability of these continuum-based theories is, however, uncertain and questionable in nanoscale system due to its extremely small singular stress field of only a few nanometers. Here, we directly characterize the mechanical behavior of a nano-crack via the development of in situ nanomechanical testing using a transmission electron microscope, and demonstrate that Griffith or fracture mechanics theory can be applied to even 4-nm stress singularity despite their continuum-based concept...
May 26, 2017: ACS Nano
https://www.readbyqxmd.com/read/28548848/quantum-mechanical-study-of-the-reaction-mechanism-for-2%C3%AF-2%C3%AF-cycloaddition-of-fluorinated-methylene-groups
#3
Andrew R Motz, Andrew M Herring, Shubham Vyas, C Mark Maupin
Perfluorocyclobutyl polymers are thermally and chemically stable, may be produced without a catalyst via thermal 2π-2π cycloaddition, and can form block structures making them suitable for commercialization of specialty polymers. Thermal 2π-2π cycloaddition is a rare reaction that starts in the singlet state and proceeds through a triplet intermediate forming an energetically stable 4 membered ring in the singlet state. This reaction involves two changes in spin state and thus two spin-crossover transitions...
May 26, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28548847/simulating-the-electronic-circular-dichroism-spectra-of-photo-reversible-peptide-conformations
#4
Hugo Gattuso, Cristina García-Iriepa, Diego Sampedro, Antonio Monari, Marco Marazzi
Electronic circular dichroism (CD) spectroscopy of peptides is one of the most important experimental char-acterization tools to get insights regarding their structure. Nevertheless, even though highly useful, the reliable simulations of CD spectra result in a complex task. Here, we propose a combination of quantum mechanics/molecular mechanics (QM/MM) methods with a semi-empirical Hamiltonian based on the Frankel excitons theory to efficiently describe the behavior of a 27-amino acid α-helical peptide in water...
May 26, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28548672/complex-magnetic-orders-in-small-cobalt-benzene-molecules
#5
J W González, T Alonso-Lanza, F Delgado, F Aguilera-Granja, A Ayuela
Organometallic clusters based on transition metal atoms are interesting because of their possible applications in spintronics and quantum information processing. In addition to the enhanced magnetism at the nanoscale, the organic ligands may provide a natural shield against unwanted magnetic interactions with the matrices required for applications. Here we show that the organic ligands may lead to non-collinear magnetic order as well as the expected quenching of the magnetic moments. We use different density functional theory (DFT) methods to study the experimentally relevant three cobalt atoms surrounded by benzene rings (Co3Bz3)...
May 26, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28548536/inductive-supervised-quantum-learning
#6
Alex Monràs, Gael Sentís, Peter Wittek
In supervised learning, an inductive learning algorithm extracts general rules from observed training instances, then the rules are applied to test instances. We show that this splitting of training and application arises naturally, in the classical setting, from a simple independence requirement with a physical interpretation of being nonsignaling. Thus, two seemingly different definitions of inductive learning happen to coincide. This follows from the properties of classical information that break down in the quantum setup...
May 12, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28548528/typical-relaxation-of-isolated-many-body-systems-which-do-not-thermalize
#7
Ben N Balz, Peter Reimann
We consider isolated many-body quantum systems which do not thermalize; i.e., expectation values approach an (approximately) steady longtime limit which disagrees with the microcanonical prediction of equilibrium statistical mechanics. A general analytical theory is worked out for the typical temporal relaxation behavior in such cases. The main prerequisites are initial conditions which appreciably populate many energy levels and do not give rise to significant spatial inhomogeneities on macroscopic scales...
May 12, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28548518/density-functional-theory-of-the-fractional-quantum-hall-effect
#8
Jianyun Zhao, Manisha Thakurathi, Manish Jain, Diptiman Sen, J K Jain
A conceptual difficulty in formulating the density-functional theory of the fractional quantum Hall effect is that while in the standard approach the Kohn-Sham orbitals are either fully occupied or unoccupied, the physics of the fractional quantum Hall effect calls for fractionally occupied Kohn-Sham orbitals. This has necessitated averaging over an ensemble of Slater determinants to obtain meaningful results. We develop an alternative approach in which we express and minimize the grand canonical potential in terms of the composite fermion variables...
May 12, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28548512/quantum-fluctuations-along-symmetry-crossover-in-a-kondo-correlated-quantum-dot
#9
Meydi Ferrier, Tomonori Arakawa, Tokuro Hata, Ryo Fujiwara, Raphaëlle Delagrange, Richard Deblock, Yoshimichi Teratani, Rui Sakano, Akira Oguri, Kensuke Kobayashi
Universal properties of entangled many-body states are controlled by their symmetry and quantum fluctuations. By the magnetic-field tuning of the spin-orbital degeneracy in a Kondo-correlated quantum dot, we have modified quantum fluctuations to directly measure their influence on the many-body properties along the crossover from SU(4) to SU(2) symmetry of the ground state. High-sensitive current noise measurements combined with the nonequilibrium Fermi liquid theory clarify that the Kondo resonance and electron correlations are enhanced as the fluctuations, measured by the Wilson ratio, increase along the symmetry crossover...
May 12, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28541673/fenton-s-reagent-catalysed-release-of-carbon-monooxide-from-1-3-dihydroxy-acetone
#10
Tumpa Sadhukhan, Dharitri Das, Pratik Kalekar, Vidya Avasare, Sourav Pal
Triose sugar, 1,3-Dihydroxy acetone (DHA) on treatment with Fenton's reagent releases CO under physiological conditions. The release of CO has been demonstrated by myoglobin assay and quantum chemical studies. The mechanistic study has been carried out using B3LYP/6-311++G(d,p), M06-2X/6-311++G(d,p) and CCSD(T)//M06-2X/6-311++G(d,p) level of theories in aqueous medium with dielectric constant of 78.39 by employing polarized continuum model (PCM). The theoretical investigation shows that DHA breaks down completely into two equivalents of CO, one equivalent of CO2 and six equivalents of H2O without formation of toxic metabolites...
May 25, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28540950/multi-level-quantum-mechanics-theories-and-molecular-mechanics-study-of-the-double-inversion-mechanism-of-the-f-ch3i-reaction-in-aqueous-solution
#11
Peng Liu, Jingxue Zhang, Dunyou Wang
A double-inversion mechanism of the F(-) + CH3I reaction was discovered in aqueous solution using combined multi-level quantum mechanics theories and molecular mechanics. The stationary points along the reaction path show very different structures to the ones in the gas phase due to the interactions between the solvent and solute, especially strong hydrogen bonds. An intermediate complex, a minimum on the potential of mean force, was found to serve as a connecting-link between the abstraction-induced inversion transition state and the Walden-inversion transition state...
May 25, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28540941/chiral-differentiation-of-d-and-l-alanine-by-permethylated-%C3%AE-cyclodextrin-irmpd-spectroscopy-and-dft-methods
#12
Sung-Sik Lee, Soojin Park, Yin Hong, Jae-Ung Lee, Jun-Hyeok Kim, Dongkyung Yoon, Xianglei Kong, Sungyul Lee, Han Bin Oh
The gaseous chiral differentiation of alanine by permethylated β-cyclodextrin was studied using IRMPD spectroscopy and density functional theory calculations. The protonated non-covalent complexes of permethylated β-cyclodextrin and d- or l-alanine were mass-selected and investigated by IR laser pulses in the wavelength region of 2650-3800 cm(-1). The remarkably different features of the IRMPD spectra for d- and l-alanine are described, and their origin is elucidated by quantum chemical calculations. We show that the differentiation of the experimentally observed spectral features is the result of different local interactions of d- and l-alanine with permethylated β-cyclodextrin...
May 25, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28540939/rydberg-states-of-alkali-atoms-on-superfluid-helium-nanodroplets-inside-or-outside
#13
Johann V Pototschnig, Florian Lackner, Andreas W Hauser, Wolfgang E Ernst
Electronic excitations of an electron bound to an alkali metal ion inside a droplet of superfluid (4)He are computed via a combination of helium density functional theory and the numerical integration of the Schrödinger equation for a single electron in a modified, He density dependent atomic pseudopotential. The application of a spectral method to the radial part of the valence electron wavefunction allows the computation of highly excited Rydberg states. For low principal quantum numbers, the energy required to push the electron outward is larger than the solvation energy of the ion...
May 25, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28539053/atomic-psychiatry-an-essay
#14
Ian Patrick Paddy Burges Watson
OBJECTIVE: This article aims to address the need to rethink the classification of mental illness and to draw attention to the current use of quantum biology and its likely future use in understanding the nature of mental illness. CONCLUSION: It is desirable to separate out neuroscience and clinical research and to become better acquainted with the concepts of quantum mechanical/quantum biological theory and its contribution to medicine.
May 1, 2017: Australasian Psychiatry: Bulletin of Royal Australian and New Zealand College of Psychiatrists
https://www.readbyqxmd.com/read/28538206/spectroscopic-far-or-terahertz-mid-infrared-and-raman-investigation-thermal-analysis-and-biological-activity-of-piplartine
#15
Anubha Srivastava, T Karthick, B D Joshi, Rashmi Mishra, Poonam Tandon, A P Ayala, Javier Ellena
Research in the field of medicinal plants including Piper species like long pepper (Piper longum L.- Piperaceae) is increasing all over the world due to its use in traditional and Ayurvedic medicine. Piplartine (piperlongumine, 5,6-dihydro-1-[(2E)-1-oxo-3-(3,4,5-trimethoxyphenyl)-2-propenyl]-2(1H)-pyridinone), a biologically active alkaloid/amide was isolated from the phytochemical investigations of Piper species, as long pepper. This alkaloid has cytotoxic, anti-fungal, anti-diabetic, anti-platelet aggregation, anti-tumoral, anxiolytic, anti-depressant, anti-leishmanial, and genotoxic activities, but, its anticancer property is the most promising and has been widely explored...
May 5, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
https://www.readbyqxmd.com/read/28537395/effects-of-alkyl-groups-on-excess-electron-binding-to-small-sized-secondary-amide-clusters-a-combined-experimental-and-computational-study
#16
Toshihiko Maeyama, Takuto Shimamori, Asuka Fujii
Excess-electron binding to dimers and trimers of secondary amide molecules was studied by a combination of photoelectron spectroscopy and theoretical calculations. Vertical detachment energies (VDEs) of the cluster anions were measured in the range of a few hundred meV. We found a tendency for VDE to decline with extension of alkyl side-chains. It was fairly reproduced by results of quantum chemical calculations based on density functional theory. For the optimized structures of the cluster anions, the excess electron is located diffusively around the dangling NH group of the hydrogen-bond acceptor molecule...
May 24, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28537284/laser-desorption-single-conformation-uv-and-ir-spectroscopy-of-the-sulfonamide-drug-sulfanilamide-the-sulfanilamide-water-complex-and-the-sulfanilamide-dimer
#17
Thomas Uhlemann, Sebastian Seidel, Christian W Müller
We have studied the conformational preferences of the sulfonamide drug sulfanilamide, its dimer, and its monohydrated complex through laser desorption single-conformation UV and IR spectroscopy in a molecular beam. Based on potential energy curves for the inversion of the anilinic and the sulfonamide NH2 groups calculated at DFT level, we suggest that the zero-point level wave function of the sulfanilamide monomer is appreciably delocalized over all four conformer wells. The sulfanilamide dimer, and the monohydrated complex each exhibit a single isomer in the molecular beam...
May 24, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28537281/comprehensive-theoretical-study-of-all-1812-c60-isomers
#18
Rebecca Sure, Andreas Hansen, Peter Schwerdtfeger, Stefan Grimme
We investigate all 1812 isomers of the fullerene C60 consistently with high-accuracy quantum chemistry methods. The isomers are optimized at the PBE-D3/def2-TZVP level of theory and their relative energies are obtained at the affordable and accurate hybrid-DFT level PW6B95-D3(ATM)/def2-QZVP. For the first time reliable values for the relative energy distribution among the 1812 isomers (maximum value of 549.1 kcal mol(-1), average value of 189.8 ± 46.8 kcal mol(-1), 1267 isomers in an energy window of 150-250 kcal mol(-1)) are given...
May 24, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28537261/thermoelectric-quantum-oscillations-in-zrsis
#19
Marcin Matusiak, J R Cooper, Dariusz Kaczorowski
Topological semimetals are systems in which conduction and valence bands cross each other and the crossings are protected by topological constraints. These materials provide intriguing tests for fundamental theories, while their unique physical properties promise a wide range of possible applications in low-power spintronics, optoelectronics, quantum computing and green energy harvesting. Here we report our study of the thermoelectric power of single-crystalline ZrSiS that is believed to be a topological nodal-line semimetal...
May 23, 2017: Nature Communications
https://www.readbyqxmd.com/read/28535459/spectra-structure-correlations-of-saturated-and-unsaturated-medium-chain-fatty-acids-near-infrared-and-anharmonic-dft-study-of-hexanoic-acid-and-sorbic-acid
#20
Justyna Grabska, Krzysztof B Beć, Mika Ishigaki, Marek J Wójcik, Yukihiro Ozaki
Quantum chemical reproduction of entire NIR spectra is a new trend, enabled by contemporary advances in the anharmonic approaches. At the same time, recent increase of the importance of NIR spectroscopy of biological samples raises high demand for gaining deeper understanding of NIR spectra of biomolecules, i.e. fatty acids. In this work we investigate saturated and unsaturated medium-chain fatty acids, hexanoic acid and sorbic acid, in the near-infrared region. By employing fully anharmonic density functional theory (DFT) calculations we reproduce the experimental NIR spectra of these systems, including the highly specific spectral features corresponding to the dimerization of fatty acids...
May 13, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
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