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Quantum theory

Seyyed Hossein Asadpour, Hamid Reza Hamedi, Mahmoud Jafari
This paper hints at the Goos-Hänchen shift properties of a cavity containing an ensemble of atoms using a four-level atomic system involving a Rydberg state. By means of the stationary phase theory and density matrix formalism in quantum optics, we study theoretically the Goos-Hänchen shifts in both reflected and transmitted light beams. It is realized that as a result of the interaction between Rydberg and excited states in such a four-level atom-light coupling scheme the maximum positive and negative Goos-Hänchen shifts can be obtained in reflected and transmitted light beams owning to the effect of the Rydberg electromagnetically induced transparency (EIT) or Rydberg electromagnetically induced absorption...
May 20, 2018: Applied Optics
Quan-De Wang, Zi-Wu Liu
Alkenes are important ingredients of realistic fuels and are also critical intermediates during the combustion of a series of other fuels including alkanes, cycloalkanes and biofules. To provide insights into the combustion behavior of alkenes, detailed quantum chemical studies for crucial reactions are desired. Hydrogen abstractions of alkenes play a very important role in determining the reactivity of fuel molecules. This work is motivated by previous experimental and modeling evidences that current literature rate coefficients for the abstraction reactions of alkenes are still in need of refinement and/or re-determination...
May 23, 2018: Journal of Physical Chemistry. A
Lee Belding, Matt Guest, Richard Le Sueur, Travis Dudding
The synthesis of cyclopropenium-substituted amino compounds and analysis of their photophysical properties is described. Systematic structural modifications of these derivatives lead to measurable and predictable changes in molar extinction coefficients, quantum yields, and Stokes shifts. Using time-dependent density functional theory (TD-DFT) calculations, the origin of these trends was traced to internal charge transfer (ICT) coupled with ensuing structural reorganization. The latter involving inward gearing of the cyclopropenium ring and twisting of the peri-NMe2 group into co-planarity with the naphtha-lene ring systems...
May 23, 2018: Journal of Organic Chemistry
Sarah Keller, Alessandro Prescimone, Henk Bolink, Michele Sessolo, Giulia Longo, Laura Martínez-Sarti, José M Junquera-Hernández, Edwin C Constable, Enrique Ortí, Catherine E Housecroft
Heteroleptic [Cu(P^P)(N^N)][PF6] complexes, where N^N is a halo-substituted 2,2'-bipyridine (bpy) and P^P is either bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) have been synthesized and investigated. To stabilize the tetrahedral geometry of the copper(i) complexes, the steric demands of the bpy ligands have been increased by introducing 6- or 6,6'-halo-substituents in 6,6'-dichloro-2,2'-bipyridine (6,6'-Cl2bpy), 6-bromo-2,2'-bipyridine (6-Brbpy) and 6,6'-dibromo-2,2'-bipyridine (6,6'-Br2bpy)...
May 23, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Jianguang Feng, Hongzhou Dong, Beili Pang, Feifei Shao, ChunKai Zhang, Liyan Yu, Lifeng Dong
The effects of four heteroatoms (B, N, P, and S) with three doping patterns on graphene quantum dots (GQDs) are systematically investigated using time-dependent density functional theory (TD-DFT). The absorption spectra and HOMO-LUMO gaps are quantitatively analyzed to study the correlations between the optical properties and heteroatom doping of doped GQDs. Heteroatom doping can endow GQDs with various new optical and structural properties, depending on the dopants and doping configurations. Compared with the absorption spectra of pristine GQD, both N and S surface doping demonstrate a slight blue shift, whereas B and P doping lead to a blue shift for edge-doped GQDs with heteroatoms in a pentatomic ring...
May 23, 2018: Physical Chemistry Chemical Physics: PCCP
Hongfei Zhu, Yu-An Tan, Liehuang Zhu, Xianmin Wang, Quanxin Zhang, Yuanzhang Li
With the development of wireless sensor networks, IoT devices are crucial for the Smart City; these devices change people's lives such as e-payment and e-voting systems. However, in these two systems, the state-of-art authentication protocols based on traditional number theory cannot defeat a quantum computer attack. In order to protect user privacy and guarantee trustworthy of big data, we propose a new identity-based blind signature scheme based on number theorem research unit lattice, this scheme mainly uses a rejection sampling theorem instead of constructing a trapdoor...
May 22, 2018: Sensors
Jeremy O Richardson
Transition-state theory is one of the most successful theories in chemistry. Not only does it provide a simple formula for computing the rate of a reaction but it defines our understanding of how a chemical reaction occurs - by overcoming an energy barrier. However, the theory is based on classical assumptions and ignores several quantum effects which can be important for certain reactions, particularly those involving hydrogen transfer at low temperatures. We are developing a more general quantum version of transition-state theory which reveals how quantum tunnelling and nonadiabatic effects can strongly affect the rate...
May 30, 2018: Chimia
Xiang Liu, Wenjian Kuang, Haibing Ni, Zhi Tao, Qianqian Huang, Jing Chen, Qingquan Liu, Jianhua Chang, Wei Lei
Although recent breakthroughs in reported graphene-based phototransistors with embedded quantum dots (QDs) have definitely been astonishing, there are still some obstacles in their practical use with regard to their electrical and optical performances. We show that through optimization of the vertical graphene nanoribbon (GNR)/QD/IGZO heterostructure and the ultrahigh efficiency of CsPbBr3 QDs, it is possible to significantly increase the on/off ratio (>103), the subthreshold slope (S.S., 0.9 V dec-1), the device's field effect mobility (μFET, 13 cm-1 V-1 S-1) and other electrical properties...
May 22, 2018: Nanoscale
Matthew Reichert, Hugo Defienne, Jason W Fleischer
Entangled states of light are essential for quantum technologies and fundamental tests of physics. Current systems rely on entanglement in 2D degrees of freedom, e.g., polarization states. Increasing the dimensionality provides exponential speed-up of quantum computation, enhances the channel capacity and security of quantum communication protocols, and enables quantum imaging; unfortunately, characterizing high-dimensional entanglement of even bipartite quantum states remains prohibitively time-consuming. Here, we develop and experimentally demonstrate a new theory of camera detection that leverages the massive parallelization inherent in an array of pixels...
May 21, 2018: Scientific Reports
Hai Xiao, Hyeyoung Shin, William A Goddard
The oxygen evolution reaction (OER) is critical to solar production of fuels, but the reaction mechanism underlying the performance for a best OER catalyst, Fe-doped NiOOH [(Ni,Fe)OOH], remains highly controversial. We used grand canonical quantum mechanics to predict the OER mechanisms including kinetics and thus overpotentials as a function of Fe content in (Ni,Fe)OOH catalysts. We find that density functional theory (DFT) without exact exchange predicts that addition of Fe does not reduce the overpotential much...
May 21, 2018: Proceedings of the National Academy of Sciences of the United States of America
Tuhin Shuvra Basu, Simon Diesch, Elke Scheer
We have fabricated organically capped stable luminescent silicon nanocrystals with narrow size distribution by a novel, high yield and easy to implement technique. We demonstrate transport measurements of individual silicon nanocrystals by scanning tunnelling microscopy at a low temperature in a double-barrier tunnel junction arrangement in which we observed pronounced single electron tunnelling effects. The tunnelling spectroscopy of these nanocrystals with different diameters reveals quantum confinement induced bandgap modifications...
May 21, 2018: Nanoscale
Erik Donovan Hedegård, Ulf Ryde
The lytic polysaccharide monooxygenases (LPMOs) are copper metalloenzymes that can enhance polysaccharide depolymerization through an oxidative mechanism and hence boost generation of biofuel from e.g. cellulose. By employing density functional theory in a combination of quantum mechanics and molecular mechanics (QM/MM), we report a complete description of the molecular mechanism of LPMOs. The QM/MM scheme allows us to describe all reaction steps with a detailed protein environment and we show that this is necessary...
April 21, 2018: Chemical Science
Jamal Sakhr, John M Nieminen
Two decades ago, Wang and Ong, [Phys. Rev. A 55, 1522 (1997)]10.1103/PhysRevA.55.1522 hypothesized that the local box-counting dimension of a discrete quantum spectrum should depend exclusively on the nearest-neighbor spacing distribution (NNSD) of the spectrum. In this Rapid Communication, we validate their hypothesis by deriving an explicit formula for the local box-counting dimension of a countably-infinite discrete quantum spectrum. This formula expresses the local box-counting dimension of a spectrum in terms of single and double integrals of the NNSD of the spectrum...
March 2018: Physical Review. E
S V Batalov, A G Shagalov, L Friedland
Controlling the state of a Bose-Einstein condensate driven by a chirped frequency perturbation in a one-dimensional anharmonic trapping potential is discussed. By identifying four characteristic time scales in this chirped-driven problem, three dimensionless parameters P_{1,2,3} are defined describing the driving strength, the anharmonicity of the trapping potential, and the strength of the particles interaction, respectively. As the driving frequency passes the linear resonance in the problem, and depending on the location in the P_{1,2,3} parameter space, the system may exhibit two very different evolutions, i...
March 2018: Physical Review. E
Hyosub Kim, YeJe Park, Kyungtae Kim, H-S Sim, Jaewook Ahn
Dynamics of large complex systems, such as relaxation towards equilibrium in classical statistical mechanics, often obeys a master equation that captures essential information from the complexities. Here, we find that thermalization of an isolated many-body quantum state can be described by a master equation. We observe sudden quench dynamics of quantum Ising-like models implemented in our quantum simulator, defect-free single-atom tweezers in conjunction with Rydberg-atom interaction. Saturation of their local observables, a thermalization signature, obeys a master equation experimentally constructed by monitoring the occupation probabilities of prequench states and imposing the principle of the detailed balance...
May 4, 2018: Physical Review Letters
Tran Dieu Hang, Minh Tho Nguyen
(Abstract) Interaction, dissociation and dehydrogenation reactions of water monomer and dimer with pure and mixed tetrameric silicon clusters Si3X with X = Si, Be, Mg, Ca were investigated using high accuracy quantum chemical calculations. While geometries were optimized using the DFT/B3LYP functional with the aug-cc-pVTZ basis set, reaction energy profiles were constructed making use of the coupled-cluster theory with extrapolation to complete basis set, CCSD(T)/CBS. Cleavage of the O-H bond in water dimer is found to be more favored than that of water monomer in the reaction with Si4...
May 18, 2018: Journal of Physical Chemistry. A
Minghua Zhang, Jiyong Fu, A C Dias, Fanyao Qu
We present a theory to address the photoluminescence (PL) intensity and valley polarization (VP) dynamics in monolayer WSe$_2$, under the impact of excitonic dark states of both excitons and biexcitons. We find that the PL intensity of all excitonic channels including intravalley exciton (X$_{\rm b}$), intravalley biexciton (XX$_{\rm k,k}$) and intervalley biexciton (XX$_{\rm k,k^\prime}$) in particular for the {XX$_{\rm k,k}$} PL is enhanced by laser excitation fluence. In addition, our results indicate the anomalous temperature dependence of PL, i...
May 18, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Erika N Bentz, Rosana Maria Lobayan, Henar Martinez, Pilar Redondo, Antonio Largo
A computational kinetics study of the antioxidant activity of tryptamine toward HO● and HOO● radicals in water at 298 K has been carried out. Density functional methods have been employed for the quantum chemical calculations and conventional transition state theory was used for rate constants evaluation. Different mechanisms have been considered: radical adduct formation (RAF), single electron transfer (SET), and hydrogen atom transfer (HAT). For the reaction of tryptamine with the hydroxyl radical nearly all channels are diffusion controlled, and the overall rate constant is very high, 6...
May 18, 2018: Journal of Physical Chemistry. B
Daniel G A Smith, Lori A Burns, Dominic A Sirianni, Daniel R Nascimento, Ashutosh Kumar, Andrew M James, Jeffrey B Schriber, Tianyuan Zhang, Boyi Zhang, Adam S Abbott, Eric J Berquist, Marvin H Lechner, Leonardo A Cunha, Alexander G Heide, Jonathan M Waldrop, Tyler Y Takeshita, Asem Alenaizan, Daniel Neuhauser, Rollin A King, Andrew C Simmonett, Justin M Turney, Henry F Schaefer, Francesco A Evangelista, A Eugene DePrince, T Daniel Crawford, Konrad Patkowski, C David Sherrill
Psi4NumPy demonstrates the use of efficient computational kernels from the open-source Psi4 program through the popular NumPy library for linear algebra in Python to facilitate the rapid development of clear, understandable Python computer code for new quantum chemical methods, while maintaining a relatively low execution time. Using these tools, reference implementations have been created for a number of methods, including self-consistent field (SCF), SCF response, many-body perturbation theory, coupled-cluster theory, configuration interaction, and symmetry-adapted perturbation theory...
May 17, 2018: Journal of Chemical Theory and Computation
Hikaru Yanai, Pedro Almendros, Saori Takahashi, Carlos Lázaro-Milla, Benito Alcaide, Takashi Matsumoto
Phosphorus 1,3- and 1,4-carbabetaines with 'P(+)-C-C(-)' and 'P(+)-C-C-C(-)' structures, in which the carbanion moiety was significantly stabilised by two triflyl groups, were synthesised. Through their crystal structures, it was suggested that attractive interactions between the anionic and cationic moieties were negligibly weak. This point was corroborated by Natural Bond Orbital (NBO) and Bader's Quantum Theory of Atoms in Molecules (QTAIM) analyses. In contrast, the same analysis of known 1,3-carbabetaine equivalent depicted as 'P(+)-C-C=C-O(-)' resonance structure revealed pronounced charge-transfer bonding between the anionic and cationic atoms...
May 17, 2018: Chemistry, An Asian Journal
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