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# Quantum theory

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#1
Shimin Cao, Jiaojiao Zhou, Xuan Wei, Shu-Guang Cheng
Massless charge carriers in gate potential modulate graphene quantum well transport in a same way that electromagnetic wave propagates in optical fibers. Recent experiment by Kim {\it et al} (Nat. Phys. 12 1022) reports the valley symmetry preserved transport in graphene carrier guider. Based on a tight-binding model, the valley resolved transport coefficients are calculated with the method of scattering matrix theory. For a straight potential well, valley resolved conductance is quantized with value $2n+1$ multiply $2e^2/h$ with integer $n$...
January 19, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
#2
Klaas A Zachariasse, Attila Demeter, Sergey I Druzhinin
With 4-fluoro-N,N-dimethylaniline (DMA4F) only a single fluorescence from a locally excited (LE) state is observed, irrespective of solvent polarity, temperature, and excitation wavelength. The relatively small excited state dipole moment μe = 7.3 D confirms the identification as LE. The single exponential fluorescence decays in the nonpolar n-hexane (2.04 ns) and in the strongly polar acetonitrile (5.73 ns) are a further support. Similar results are obtained with 4-chloro-N,N-dimethylaniline (DMA4Cl), having a chlorobenzene subgroup, a somewhat better electron acceptor than the fluorobenzene moiety in DMA4F...
January 18, 2017: Journal of Physical Chemistry. A
#3
Weon-Kyu Koh, Naveen Kumar Dandu, Andrew F Fidler, Victor I Klimov, Jeffrey M Pietryga, Svetlana V Kilina
We demonstrate controlled synthesis of discrete two-dimensional (2D) PbSe nanoplatelets (NPLs), with measureable photoluminescence, via oriented attachment directed by quantum dot (QD) surface chemistry. Halide passivation is critical to the growth of these (100) face-dominated NPLs, as corroborated by density functional theory studies. PbCl2 moieties attached to the (111) and (110) of small nanocrystals form interparticle bridges, aligning the QDs and leading to attachment. We find that a 2D bridging network is energetically favored over a 3D network, driving the formation of NPLs...
January 18, 2017: Journal of the American Chemical Society
#4
Gregory R Medders, Ethan C Alguire, Amber Jain, Joseph E Subotnik
We employ surface hopping trajectories to model the short-time dynamics of gas phase and partially solvated 4-(N,N-dimethylamino)benzonitrile (DMABN), a dual fluorescent molecule that is known to undergo a nonadiabatic transition through a conical intersection. To compare theory vs. time-resolved fluorescence measurements, we calculate the mixed quantum-classical density matrix and the ensemble averaged transition dipole moment. We introduce a diabatization scheme based on the oscillator strength to convert the TDDFT adiabatic states into diabatic states of La and Lb character...
January 18, 2017: Journal of Physical Chemistry. A
#5
M Hyla
Network-forming As2(S/Se)m nanoclusters are employed to recognize expected variations in a vicinity of some remarkable compositions in binary As-Se/S glassy systems accepted as signatures of optimally constrained intermediate topological phases in earlier temperature-modulated differential scanning calorimetry experiments. The ab initio quantum chemical calculations performed using the cation-interlinking network cluster approach show similar oscillating character in tendency to local chemical decomposition but obvious step-like behavior in preference to global phase separation on boundary chemical compounds (pure chalcogen and stoichiometric arsenic chalcogenides)...
December 2017: Nanoscale Research Letters
#6
Ying-Chen Duan, Yong Wu, Jun-Ling Jin, Dong-Mei Gu, Yun Geng, Min Zhang, Zhongmin Su
The case that aggregation brings a huge influence on the structure and fluorescent property of 5-(4-(1,2,2-triphenylvinyl)phenyl)thiophene-2-carbaldehyde (P4TA) was detailedly investigated here by employing both quantum mechanics and molecular mechanics. Besides the isolated molecule, the aggregated molecule both in water and crystal state was studied by focusing on the comparison of photoelectronic properties, including the geometrical and electronic structures at ground and excited states, emission and internal conversation properties...
January 17, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
#7
Priyanka Garg, Indrani Choudhuri, Arup Mahata, Biswarup Pathak
Stanene is a quantum spin Hall insulator and a promising material for electronic and optoelectronic devices. Density functional theory (DFT) calculations are performed to study the band gap opening in stanene by elemental mono-doping (B, N) and co-doping (B-N). Different patterned B-N co-doping is studied to change the electronic properties of stanene. A patterned B-N co-doping opens the band gap in stanene and its semiconducting nature persists under strain. Molecular dynamics (MD) simulations are performed to confirm the thermal stability of such a doped system...
January 17, 2017: Physical Chemistry Chemical Physics: PCCP
#8
REVIEW
Yongho Kim, Binh Khanh Mai, Sumin Park
High-valent Cu and Fe species, which are generated from dioxygen activation in metalloenzymes, carry out the functionalization of strong C-H bonds. Understanding the atomic details of the catalytic mechanism has long been one of the main objectives of bioinorganic chemistry. Large H/D kinetic isotope effects (KIEs) were observed in the C-H activation by high-valent non-heme Cu or Fe complexes in enzymes and their synthetic models. The H/D KIE depends significantly on the transition state properties, such as structure, energies, frequencies, and shape of the potential energy surface, when the tunneling effect is large...
January 16, 2017: Journal of Biological Inorganic Chemistry: JBIC
#9
Michael Kühn, Sergei Lebedkin, Florian Weigend, Andreas Eichhöfer
The optical properties of four isostructural trinuclear chalcogenolato bridged metal complexes [Cu2Sn(SPh)6(PPh3)2], [Cu2Sn(SePh)6(PPh3)2], [Ag2Sn(SPh)6(PPh3)2] and [Cu2Ti(SPh)6(PPh3)2] have been investigated by absorption and photoluminescence spectroscopy and time-dependent density functional theory (TDDFT) calculations. All copper-tin compounds demonstrate near-infrared (NIR) phosphorescence at ∼900-1100 nm in the solid state at low temperature, which is nearly absent at ambient temperature. Stokes shifts of these emissions are found to be unusually large with values of about 1...
January 16, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
#10
Sharmistha Karmakar, Ayan Datta
Direct dynamics calculation using canonical variational transtition state theory (CVT) inclusive of small curvature tunneling (SCT) reveals the influential role of quantum mechanical tunneling (QMT) for 2,2a,5,7b-tetrahydro-1H-cyclobuta[e]indene derivatives (2a-2j) in governing their product selectivity. 2a-2j follow two distinct reaction channels namely 6pi-electrocyclization (2-->3) and [1, 5]H-sigmatropic shift (2-->4) amongst which the activation barrier is higher for [1, 5]H-shift (2-->4) thereby favoring the kinetically controlled product (3a-3j) as anticipated...
January 16, 2017: Journal of Organic Chemistry
#11
Sandeep Mavadia, Virginia Frey, Jarrah Sastrawan, Stephen Dona, Michael J Biercuk
The wide-ranging adoption of quantum technologies requires practical, high-performance advances in our ability to maintain quantum coherence while facing the challenge of state collapse under measurement. Here we use techniques from control theory and machine learning to predict the future evolution of a qubit's state; we deploy this information to suppress stochastic, semiclassical decoherence, even when access to measurements is limited. First, we implement a time-division multiplexed approach, interleaving measurement periods with periods of unsupervised but stabilised operation during which qubits are available, for example, in quantum information experiments...
January 16, 2017: Nature Communications
#12
Jin-Jin Ding, Yao Wang, Hou-Dao Zhang, Rui-Xue Xu, Xiao Zheng, YiJing Yan
We revisit Caldeira-Leggett's quantum master equation representing mixed quantum-classical theory, but with limited applications. Proposed is a Fokker-Planck quantum master equation theory, with a generic bi-exponential correlation function description on semiclassical Brownian oscillators' environments. The new theory has caustic terms that bridge between the quantum description on primary systems and the semiclassical or quasi-classical description on environments. Various parametrization schemes, both analytical and numerical, for the generic bi-exponential environment bath correlation functions are proposed and scrutinized...
January 14, 2017: Journal of Chemical Physics
#13
J Rehacek, M Paúr, B Stoklasa, Z Hradil, L L Sánchez-Soto
We establish the conditions to attain the ultimate resolution predicted by quantum estimation theory for the case of two incoherent point sources using a linear imaging system. The solution is closely related to the spatial symmetries of the detection scheme. In particular, for real symmetric point spread functions, any complete set of projections with definite parity achieves the goal.
January 15, 2017: Optics Letters
#14
R M Sullenberger, S M Redmond, D Crompton, A M Stolyarov, W D Herzog
We report a photothermal modulation of Mie scattering (PMMS) method that enables concurrent spatial and spectral discrimination of individual micron-sized particles. This approach provides a direct measurement of the "fingerprint" infrared absorption spectrum with the spatial resolution of visible light. Trace quantities (tens of picograms) of material were deposited onto an infrared-transparent substrate and simultaneously illuminated by a wavelength-tunable intensity-modulated quantum cascade pump laser and a continuous-wave 532 nm probe laser...
January 15, 2017: Optics Letters
#15
Atsushi Kobayashi, Ryuya Arata, Tomohiro Ogawa, Masaki Yoshida, Masako Kato
Two luminescent pyrazine-bridged dinuclear Cu(I) complexes, namely, [{Cu(PPh3)2(H2O)}(μ-MeOpyz){Cu(PPh3)2(CH3CN)}](BF4)2 and [{Cu(PPh3)2(H2O)}(μ-MeOpyz){Cu(PPh3)2(H2O)}](BF4)2 (H2O-Cu2-AN and H2O-Cu2-H2O; PPh3 = triphenylphosphine, MeOpyz = 2-methoxypyrazine), were successfully synthesized and characterized by single-crystal X-ray diffraction and luminescence measurements. X-ray analysis revealed that the water molecules are coordinated to both Cu(I) ions to form almost the same P2N1O1 coordination structure in H2O-Cu2-H2O, whereas one of the two Cu ions in H2O-Cu2-AN was coordinated by acetonitrile instead of water to form a different P2N2 coordination environment...
January 12, 2017: Inorganic Chemistry
#16
Arjen J de Haas, Jos Oomens, Jordy Bouwman
Energetic processing of gaseous polycyclic aromatic hydrocarbons (PAHs) plays a pivotal role in the chemistries of inter- and circumstellar environments, certain planetary atmospheres, and also in the chemistry of combustion and soot formation. Although the precursor PAH species have been extensively characterized, the products from these gaseous breakdown reactions have received far less attention. It has been particularly challenging to accurately determine their molecular structure in gas-phase experiments, where comparisons against theoretical modeling are best made...
January 12, 2017: Physical Chemistry Chemical Physics: PCCP
#17
Igor Goychuk
Can the statistical properties of single-electron transfer events be correctly predicted within a common equilibrium ensemble description? This fundamental in nanoworld question of ergodic behavior is scrutinized within a very basic semi-classical curve-crossing problem. It is shown that in the limit of non-adiabatic electron transfer (weak tunneling) well-described by the Marcus-Levich-Dogonadze (MLD) rate the answer is yes. However, in the limit of the so-called solvent-controlled adiabatic electron transfer, a profound breaking of ergodicity occurs...
January 12, 2017: Physical Chemistry Chemical Physics: PCCP
#18
Ashok Kodigala, Thomas Lepetit, Qing Gu, Babak Bahari, Yeshaiahu Fainman, Boubacar Kanté
In 1929, only three years after the advent of quantum mechanics, von Neumann and Wigner showed that Schrödinger's equation can have bound states above the continuum threshold. These peculiar states, called bound states in the continuum (BICs), manifest themselves as resonances that do not decay. For several decades afterwards the idea lay dormant, regarded primarily as a mathematical curiosity. In 1977, Herrick and Stillinger revived interest in BICs when they suggested that BICs could be observed in semiconductor superlattices...
January 11, 2017: Nature
#19
E M Kendirlik, S Sirt, S B Kalkan, N Ofek, V Umansky, A Siddiki
Since the experimental realization of the integer quantum Hall effect in a two-dimensional electron system, the interrelation between the conductance quantization and the topological properties of the system has been investigated. Assuming that the two-dimensional electron system is described by a Bloch Hamiltonian, system is insulating in the bulk of sample throughout the quantum Hall plateau due to a magnetic field induced energy gap. Meanwhile, the system is conducting at the edges resembling a 2+1 dimensional topological insulator without time-reversal symmetry...
January 10, 2017: Nature Communications
#20
Gyeongjin Lee, Junwoo Kim, So Young Kim, Dong Eon Kim, Taiha Joo
Coherent nuclear wave packet motions in an electronic excited state of a molecule have been measured directly by time-resolved spontaneous fluorescence with an unprecedented time resolution by employing two photon absorption excitation and fluorescence upconversion by noncollinear sum frequency generation. With estimated time resolution of ~25 fs, we were able to record wave packet motions of vibrational modes up to 1600 cm1 for coumarin 153 in ethanol. Two-color transient absorption at 13 fs time resolution has been measured to confirm the result...
January 10, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
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