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Quantum theory

Zhaoju Yang, Baile Zhang
Lorentz-violating type-II Weyl fermions, which were missed in Weyl's prediction of nowadays classified type-I Weyl fermions in quantum field theory, have recently been proposed in condensed matter systems. The semimetals hosting type-II Weyl fermions offer a rare platform for realizing many exotic physical phenomena that are different from type-I Weyl systems. Here we construct the acoustic version of a type-II Weyl Hamiltonian by stacking one-dimensional dimerized chains of acoustic resonators. This acoustic type-II Weyl system exhibits distinct features in a finite density of states and unique transport properties of Fermi-arc-like surface states...
November 25, 2016: Physical Review Letters
Denisa Geffertová, Syed Tahir Ali, Veronika Šolínová, Marcela Krečmerová, Antonín Holý, Zdeněk Havlas, Václav Kašička
Capillary electrophoresis (CE) and quantum mechanical density functional theory (DFT) were applied to the investigation of the acid-base and electromigration properties of important compounds: newly synthesized derivatives of 5-azacytosine - analogs of efficient antiviral drug cidofovir. These compounds exhibit a strong antiviral activity and they are considered as potential new antiviral agents. For their characterization and application, it is necessary to know their acid-base properties, particularly the acidity constants (pKa) of their ionogenic groups (the basic N(3) atom of the triazine ring and the acidic phosphonic acid group in the alkyl chain)...
November 29, 2016: Journal of Chromatography. A
Michał Turowski, Urszula Szczepaniak, Thomas Custer, Marcin Gronowski, Robert Kołos
The results of a study devoted to the electronic spectroscopy of gaseous, solid, and cryogenic matrix-isolated methylcyanodiacetylene (CH3 C5 N) are reported. UV absorption and optical phosphorescence spectra of the compound are described here for the first time, and the corresponding vibronic assignments are proposed. UV absorption, studied directly or through the excitation of phosphorescence, revealed the B˜  (1) E--X˜  (1) A1 system, very weak A˜  (1) A2 -X˜  (1) A1 bands, and a strong, broad absorption feature, tentatively identified as D˜  (1) E-X˜  (1) A1 ...
December 5, 2016: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Andrea Zen, Loïc M Roch, Stephen J Cox, Xiao Liang Hu, Sandro Sorella, Dario Alfè, Angelos Michaelides
Clay minerals are ubiquitous in nature, and the manner in which they interact with their surroundings has important industrial and environmental implications. Consequently, a molecular-level understanding of the adsorption of molecules on clay surfaces is crucial. In this regard computer simulations play an important role, yet the accuracy of widely used empirical force fields (FF) and density functional theory (DFT) exchange-correlation functionals is often unclear in adsorption systems dominated by weak interactions...
November 23, 2016: Journal of Physical Chemistry. C, Nanomaterials and Interfaces
Dinh Bao Nguyen, Thanh Danh Nguyen, Sangsoo Kim, Sang-Woo Joo
Spectral differences between cytosine (Cyt) and 5-methylcytosine (5MC) were investigated by means of Raman spectroscopy with a combination of density functional theory (DFT) calculations. Surface-enhanced Raman scattering (SERS) revealed discriminating peaks of 5MC from those of Cyt upon adsorption on gold nanoparticles (AuNPs). Among the notable features, the multiple bands between 850 and 700cm(-1) for the ring-breathing modes of 5MC and Cyt could be correlated well with the simulated spectra based on the DFT calculations of the adsorbates on the gold cluster atoms...
November 9, 2016: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Piotr Tourkine, Pierre Vanhove
The monodromy relations in string theory provide a powerful and elegant formalism to understand some of the deepest properties of tree-level field theory amplitudes, like the color-kinematics duality. This duality has been instrumental in tremendous progress on the computations of loop amplitudes in quantum field theory, but a higher-loop generalization of the monodromy construction was lacking. In this Letter, we extend the monodromy relations to higher loops in open string theory. Our construction, based on a contour deformation argument of the open string diagram integrands, leads to new identities that relate planar and nonplanar topologies in string theory...
November 18, 2016: Physical Review Letters
Siavash Golkar, Dung Xuan Nguyen, Matthew M Roberts, Dam Thanh Son
Fractional quantum Hall liquids exhibit a rich set of excitations, the lowest energy of which are the magnetorotons with dispersion minima at a finite momentum. We propose a theory of the magnetorotons on the quantum Hall plateaux near half filling, namely, at filling fractions ν=N/(2N+1) at large N. The theory involves an infinite number of bosonic fields arising from bosonizing the fluctuations of the shape of the composite Fermi surface. At zero momentum there are O(N) neutral excitations, each carrying a well-defined spin that runs integer values 2,3,…...
November 18, 2016: Physical Review Letters
Michael Schuler, Seth Whitsitt, Louis-Paul Henry, Subir Sachdev, Andreas M Läuchli
The low-energy spectra of many body systems on a torus, of finite size L, are well understood in magnetically ordered and gapped topological phases. However, the spectra at quantum critical points separating such phases are largely unexplored for (2+1)D systems. Using a combination of analytical and numerical techniques, we accurately calculate and analyze the low-energy torus spectrum at an Ising critical point which provides a universal fingerprint of the underlying quantum field theory, with the energy levels given by universal numbers times 1/L...
November 18, 2016: Physical Review Letters
Peter Wittek, Ying-Hsang Liu, Sándor Darányi, Tom Gedeon, Ik Soo Lim
Information foraging connects optimal foraging theory in ecology with how humans search for information. The theory suggests that, following an information scent, the information seeker must optimize the tradeoff between exploration by repeated steps in the search space vs. exploitation, using the resources encountered. We conjecture that this tradeoff characterizes how a user deals with uncertainty and its two aspects, risk and ambiguity in economic theory. Risk is related to the perceived quality of the actually visited patch of information, and can be reduced by exploiting and understanding the patch to a better extent...
2016: Frontiers in Psychology
Eszter Makkos, Andrew Kerridge, Jonathan Austin, Nikolas Kaltsoyannis
Density functional theory (DFT) at the generalised gradient approximation level is employed within the periodic electrostatic embedded cluster method (PEECM) to model the brucite (0001) surface. Three representative studies are then used to demonstrate the reliability of the PEECM for the description of the interactions of various ionic species with the layered Mg(OH)2 structure, and its performance is compared with periodic DFT, an approach known to be challenging for the adsorption of charged species. The adsorption energies of a series of s block cations, including Sr(2+) and Cs(+) which are known to coexist with brucite in nuclear waste storage ponds, are well described by the embedded cluster model, provided that basis sets of triple-zeta quality are employed for the adsorbates...
November 28, 2016: Journal of Chemical Physics
Bennett D Marshall
Equations of state for hydrogen bonding fluids are typically described by two energy scales. A short range highly directional hydrogen bonding energy scale as well as a reference energy scale which accounts for dispersion and orientationally averaged multi-pole attractions. These energy scales are always treated independently. In recent years, extensive first principles quantum mechanics calculations on small water clusters have shown that both hydrogen bond and reference energy scales depend on the number of incident hydrogen bonds of the water molecule...
November 28, 2016: Journal of Chemical Physics
Luca Semeria, Paul Jansen, Frédéric Merkt
The term values of all rotational levels of the (4)He2(+) X(+)  (2)Σu(+) (ν(+)=0) ground vibronic state with rotational quantum number N(+) ≤ 19 have been determined with an accuracy of 8 × 10(-4) cm(-1) (∼25 MHz) by multichannel-quantum-defect-theory-assisted Rydberg spectroscopy of metastable He2(∗). Comparison of these term values with term values recently calculated ab initio by Tung et al. [J. Chem. Phys. 136, 104309 (2012)] reveals discrepancies that rapidly increase with increasing rotational quantum number and reach values of 0...
November 28, 2016: Journal of Chemical Physics
Jin-Jin Ding, Hou-Dao Zhang, Yao Wang, Rui-Xue Xu, Xiao Zheng, YiJing Yan
A unified theory for minimum exponential-term ansatzes on bath correlation functions is proposed for numerically efficient and physically insightful treatments of non-Markovian environment influence on quantum systems. For a general Brownian oscillator bath of frequency Ω and friction ζ, the minimum ansatz results in the correlation function a bi-exponential form, with the effective Ω¯ and friction ζ¯ being temperature dependent and satisfying Ω¯/Ω=(ζ¯/ζ)(1/2)=r¯BO/rBO≤ 1, where r¯BO=ζ¯/(2Ω¯) and rBO=ζ/(2Ω)...
November 28, 2016: Journal of Chemical Physics
Ari T Friberg, Tero Setälä
The coherence theory of random, vector-valued optical fields has been of great research interest in recent years. In this work we formulate the foundations of electromagnetic coherence theory both in the space-time and space-frequency domains, with particular emphasis on various types of optical interferometry. Analyzing statistically stationary, two-component (paraxial) electric fields in the classical and quantum-optical contexts we show fundamental connections between the conventional (polarization) Stokes parameters and the associated two-point (coherence) Stokes parameters...
December 1, 2016: Journal of the Optical Society of America. A, Optics, Image Science, and Vision
Amirul Edham Roslee, Saifful Kamaluddin Muzakir, Jamil Ismail, Mashitah M Yusoff, Rajan Jose
This article addresses the heat capacity of quantum dots (QDs) using density functional theory (DFT). By analyzing the evolution of phonon density of states and heat capacity as CdSe clusters grow from a molecular cluster into larger quantum confined solids, we have shown that their heat capacity does not fit very well with the Debye T(3) model. We observed that the number of phonon modes, which is discrete, increases as the particles grow, and the dispersion relation shows a quadratic behavior in contrast to the bulk solids whose dispersion relation is linear and equal to the sound velocity...
December 1, 2016: Physical Chemistry Chemical Physics: PCCP
Roberto Di Remigio, Maarten T P Beerepoot, Yann Cornaton, Magnus Ringholm, Arnfinn Hykkerud Steindal, Kenneth Ruud, Luca Frediani
The study of high-order absorption properties of molecules is a field of growing importance. Quantum-chemical studies can help design chromophores with desirable characteristics. Given that most experiments are performed in solution, it is important to devise a cost-effective strategy to include solvation effects in quantum-chemical studies of these properties. We here present an open-ended formulation of self-consistent field (SCF) response theory for a molecular solute coupled to a polarizable continuum model (PCM) description of the solvent...
December 1, 2016: Physical Chemistry Chemical Physics: PCCP
Michael E Rudd, Fred Rieke
In human rod-mediated vision, threshold for small, brief flashes rises in proportion to the square root of adapting luminance at all but the lowest and highest adapting intensities. A classical signal detection theory from Rose (1942, 1948) and de Vries (1943) attributed this rise to the perceptual masking of weak flashes by Poisson fluctuations in photon absorptions from the adapting field. However, previous work by Brown and Rudd (1998) demonstrated that the square-root law also holds for suprathreshold brightness judgments, a finding that supports an alternative explanation of the square-root sensitivity changes as a consequence of physiological adaptation (i...
November 1, 2016: Journal of Vision
Yulia B Dudkina, Kirill V Kholin, Tatyana V Gryaznova, Daut R Islamov, Olga N Kataeva, Ildar Kh Rizvanov, Alina I Levitskaya, Olga D Fominykh, Marina Yu Balakina, Oleg G Sinyashin, Yulia H Budnikova
A series of diverse binuclear and mononuclear cyclometalated palladium(ii) complexes of different structure was investigated by electrochemical techniques combined with density functional theory (DFT) calculations. The studies including cyclic and differential pulse voltammetry, X-ray structure analysis and quantum chemical calculations revealed a regularity of the complexes oxidation potential on the metal-metal distance in the complexes: the larger Pd-Pd distance, the higher oxidation potentials. The reduction potentials feature unusually high negative values while no correlation depending on the structure could be observed...
November 30, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
T Stoecklin, A Faure, P Jankowski, S Chefdeville, A Bergeat, C Naulin, S B Morales, M Costes
A joint crossed beam and quantum mechanical investigation of the rotationally inelastic collisions of CO with ortho- and para-D2 molecules is reported. A new 4D potential energy surface (PES) averaged over the ground vibrational states of D2 and CO is used to calculate the rovibrational bound states of the ortho-D2-CO complexes. Close coupling calculations are then performed in the rigid rotor approximation for ortho- and para-D2 colliding with CO for the experimentally investigated transition of CO (j = 0 → 1) and for collision energies ranging from 0...
November 30, 2016: Physical Chemistry Chemical Physics: PCCP
Gabor Paragi, Célia Fonseca Guerra
The guanine nucleobase can self-assemble into tetrameric or ribbon structures on surfaces or in solution. The origin for the occurrence of different aggregation patterns has not been investigated yet. Here, we present a quantum chemical study on the different self-assembled structures of guanine and xanthine using dispersion-corrected density functional theory. Our theoretical investigations explain from an electronic point of view the differences between the experimental findings. With quantitative Kohn-Sham molecular orbital theory and the accompanying energy decomposition analysis, we disclose the hydrogen bonding mechanism within the guanine ribbons and explain the preferred self-assembled structures under different experimental conditions...
November 29, 2016: Chemistry: a European Journal
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