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Quantum theory

Giacomo Lovat, Bonnie Choi, Daniel W Paley, Michael L Steigerwald, Latha Venkataraman, Xavier Roy
Fabricating nanoscopic devices capable of manipulating and processing single units of charge is an essential step towards creating functional devices where quantum effects dominate transport characteristics. The archetypal single-electron transistor comprises a small conducting or semiconducting island separated from two metallic reservoirs by insulating barriers. By enabling the transfer of a well-defined number of charge carriers between the island and the reservoirs, such a device may enable discrete single-electron operations...
August 14, 2017: Nature Nanotechnology
Marek Cigáň, Miroslav Horváth, Juraj Filo, Klaudia Jakusová, Jana Donovalová, Vladimír Garaj, Anton Gáplovský
The water sensing properties of two efficient two-component fluorescent "turn-on" chemo-sensors based on the 7-dialkylaminocoumarin oxime acid-base equilibrium were investigated. Interestingly, although simple frontier orbital analysis predicts an intramolecular photoinduced electron transfer quenching pathway in conjugated oximates, TD-DFT (Time-dependent density functional theory) quantum chemical calculations support non-radiative dark S₁ excited state deactivation as a fluorescence quenching mechanism...
August 12, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
V R Shaginyan, V A Stephanovich, A Z Msezane, G S Japaridze, K G Popov
We show that a quantum phase transition, generating flat bands and altering Fermi surface topology, is a primary reason for the exotic behavior of the overdoped high-temperature superconductors represented by La2-xSrxCuO4, whose superconductivity features differ from what is predicted by the classical Bardeen-Cooper-Schrieffer theory. This observation can open avenues for chemical preparation of high-Tc materials. We demonstrate that (1) at temperature T = 0, the superfluid density ns turns out to be considerably smaller than the total electron density; (2) the critical temperature Tc is controlled by ns rather than by doping, and is a linear function of the ns; (3) at T > Tc the resistivity ρ(T) varies linearly with temperature, ρ(T) ∝ αT, where α diminishes with Tc → 0, whereas in the normal (non superconducting) region induced by overdoping, Tc = 0, and ρ(T) ∝ T(2)...
August 14, 2017: Physical Chemistry Chemical Physics: PCCP
Ekadashi Pradhan, Alex Brown
The minimum energy structures, i.e., trans-HONO, cis-HONO, HNO2, and OH + NO, as well as the corresponding transition states, i.e., TStrans↔cis, TS1,2H-shift, and TS1,3H-shift, on the ground state potential energy surface (PES) of HONO have been characterized at the CCSD(T)-F12/cc-pVTZ-F12 level of theory. Using the same level of theory, a six-dimensional (6D) PES, encompassing the trans- and cis-isomers as well as the associated transition state, is fit in a sum-of-products form using neural network exponential fitting functions...
August 14, 2017: Physical Chemistry Chemical Physics: PCCP
Ramin Ekhteiari Salmas, Yusuf Serhat Is, Serdar Durdagi, Matthias Stein, Mine Yurtsever
The dopamine D2 Receptor (D2R) is a member of the G-Protein Coupled Receptor (GPCR) family and plays a critical role in neurotransmission activities in the human brain. Dysfunction in dopamine receptor signaling may lead to mental health illnesses such as schizophrenia and Parkinson's disease. D2R is the target protein of the commonly used anti-psychotic drugs such as risperidone, clozapine, aripiprazole, olanzapine, ziprasidone and quetiapine. Due to their significant side effects and nonselective profiles, the discovery of novel drugs has become a challenge for researchers working in this field...
August 14, 2017: Journal of Biomolecular Structure & Dynamics
Sara Moa, Fahmi Himo
Secondary alcohol dehydrogenase from Thermoanaerobacter brockii (TbSADH) is a Zn- and NADP-dependent enzyme that catalyses the reversible transformation of secondary alcohols into ketones. It is of potential biocatalytic interest as it can be used in the synthesis of chiral alcohols by asymmetric reduction of ketones. In this paper, density functional theory calculations are employed to elucidate the origins of the enantioselectivity of TbSADH using a large model of the active site and considering two different substrates, 2-butanol and 3-hexanol...
July 24, 2017: Journal of Inorganic Biochemistry
Masaki Shimizu, Daiki Ryuse, Takumi Kinoshita
[1]Benzogermolo[3,2-b]indoles, [1]benzogermolo[3,2-b]-benzofuran, [1]benzogermolo[3,2-b]benzothiophene, and [1]benzo-germolo[3,2-b]benzothiophene-S,S-dioxide were synthesized from the corresponding 3-bromo-2-(2-bromophenyl)benzoheteroles and characterized. A comparison of the absorption spectra of the Ph2Ge- and Ph2Si-bridged 2-phenylindoles reveals that the Ge-bridge has the effect of slightly widening the HOMO-LUMO energy gap of the bridged 2-phenylindole π-system with regard to the Si-bridged system. Replacement of the indole ring by benzofuran or benzothiophene rings induces blue-shifts in the absorption spectrum, while the absorption spectrum of the benzothiophene-S,S-dioxide derivative was red-shifted with respect to the indole derivative...
August 11, 2017: Chemistry: a European Journal
Frank Neese
Quantum chemistry can be used as a powerful link between theory and experiment for studying reactions in all areas of catalysis. The key feature of this approach is the combination of quantum chemistry with a range of high-level spectroscopic methods. This allows for conclusions to be reached that neither theory nor experiment would have been able to obtain in isolation.
August 11, 2017: Angewandte Chemie
Francesco Silvio Gentile, Simone Salustro, Mauro Causà, Alessandro Erba, Philippe Carbonniére, Roberto Dovesi
The VN3H defect in diamond (a vacancy surrounded by three nitrogen and one carbon atoms, the latter being saturated by a hydrogen atom) is investigated quantum-mechanically by use of a periodic supercell approach, an all-electron Gaussian-type basis set, "hybrid" functionals of density functional theory, and the Crystal program. Three fully optimized structural models (supercells containing 32, 64, and 128 atoms) are considered to investigate the effect of defect concentration. The electronic configuration of the defect is reported along with a description of its structural features...
August 11, 2017: Physical Chemistry Chemical Physics: PCCP
Zongyuan Liu, Carl O Trindle, Quanli Gu, Wei Wu, Peifeng Su
The neutral and cationic forms of tryptamine-water dimer present a variety of noncovalent interactions. To characterize these interactions, a series of complementary methods, including the quantum theory of atoms in molecules, noncovalent interaction plots, natural bond orbital analysis, and energy decomposition analysis, were used. For the first time, the existence of the three intermolecular H-bonds in the conformer-locked tryptamine-water dimer A-H2O are identified, highlighting a single water's role as one proton donor and two proton acceptors as it binds to tryptamine...
August 11, 2017: Physical Chemistry Chemical Physics: PCCP
Silvio J Prado, Gilmar Eugenio Marques, Augusto Alcalde
In this work we show calculation of optimized efficiencies of intermediate band solar cells (IBSC) based on Mn-doped II-VI CdTe/CdMnTe coupled quantum dot (QD) structures. We focus our attention on the combined effects of geometrical and Mn-doping parameters on the optical properties and solar cell efficiency. In the framework of k . p theory, we accomplished detailed calculations of electronic structure, transition energies, optical selection rules and their corresponding intra- and interband oscillator strengths...
August 11, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Jeff P Thompson, Isaac C Sanchez
We investigate the system-size dependence of the thermodynamic properties of ionic fluids under periodic boundary conditions. Following an approach previously developed in the context of quantum Monte Carlo simulations of many-electron systems, we show that the leading-order finite-size artifact in the Coulomb energy per particle of a classical fluid of N structureless ions at given density and temperature is simply -kBT(2N)(-1). Analytical approximations for the periodicity-induced size dependence of the excess thermodynamic properties of the fluid in the weak-coupling regime are obtained within the linearized Debye-Hückel theory...
December 7, 2016: Journal of Chemical Physics
Shigenori Tanaka
Correlational and thermodynamic properties of homogeneous electron liquids at finite temperatures are theoretically analyzed in terms of dielectric response formalism with the hypernetted-chain (HNC) approximation and its modified version. The static structure factor and the local-field correction to describe the strong Coulomb-coupling effects beyond the random-phase approximation are self-consistently calculated through solution to integral equations in the paramagnetic (spin unpolarized) and ferromagnetic (spin polarized) states...
December 7, 2016: Journal of Chemical Physics
Biplab Bhattacharyya, Alka Sharma, Bhavesh Sinha, Kunjal Shah, Suhas Jejurikar, T D Senguttuvan, Sudhir Husale
We report the experimental observation of variable range hopping conduction in focused-ion-beam (FIB) fabricated ultra-narrow nanowires of topological insulator (Bi2Se3). The value of the exponent (d + 1)(-1) in the hopping equation was extracted as [Formula: see text]for different widths of nanowires, which is the proof of the presence of Efros-Shklovskii hopping transport mechanism in a strongly disordered system. High localization lengths (0.5 nm, 20 nm) were calculated for the devices. A careful analysis of the temperature dependent fluctuations present in the magnetoresistance curves, using the standard Universal Conductance Fluctuation theory, indicates the presence of 2D topological surface states...
August 10, 2017: Scientific Reports
Peng Liu, Qiong Wang, Meixing Niu, Dunyou Wang
Combining multi-level quantum mechanics theories and molecular mechanics with an explicit water model, we investigated the ring opening process of guanine damage by hydroxyl radical in aqueous solution. The detailed, atomic-level ring-opening mechanism along the reaction pathway was revealed in aqueous solution at the CCSD(T)/MM levels of theory. The potentials of mean force in aqueous solution were calculated at both the DFT/MM and CCSD(T)/MM levels of the theory. Our study found that the aqueous solution has a significant effect on this reaction in solution...
August 10, 2017: Scientific Reports
R Narayanan, H Yamada, B C Marin, A Zaretski, P R Bandaru
The theories to describe the rate at which electrochemical reactions proceed, to date, do not consider explicitly the dimensionality or the discreteness and occupancy of the energy levels of the electrodes. We show experimentally that such quantum mechanical aspects are important for dimensionally confined nanostructured materials and yield unusual variation of the kinetic rate constants with applied voltage in single-layer graphene. The observed divergence from conventional electrokinetics was ascribed to the linear energy dispersion as well as a nonzero density of states at the Dirac point in the graphene...
August 14, 2017: Journal of Physical Chemistry Letters
Saya Ito, Nobuyuki Kurita, Hidekazu Tanaka, Seiko Ohira-Kawamura, Kenji Nakajima, Shinichi Itoh, Keitaro Kuwahara, Kazuhisa Kakurai
A spin-1/2 triangular-lattice Heisenberg antiferromagnet (TLHAF) is a prototypical frustrated quantum magnet, which exhibits remarkable quantum many-body effects that arise from the synergy between spin frustration and quantum fluctuation. The ground-state properties of a spin-1/2 TLHAF are theoretically well understood. However, the theoretical consensus regarding the magnetic excitations is limited. The experimental study of the magnetic excitations in spin-1/2 TLHAFs has also been limited. Here we show the structure of magnetic excitations in the spin-1/2 TLHAF Ba3CoSb2O9 investigated by inelastic neutron scattering...
August 10, 2017: Nature Communications
Jakob Petersen, Eli Pollak
Attosecond ionization experiments have not resolved the question: ``What is the tunneling time?''. Different definitions of tunneling time lead to different results.Secondly, a zero tunneling time for a material particle suggests that the non-relativistic theory includes speeds greater than the speed of light. Chemical reactions, occurring via tunneling, should then not be considered in terms of a non-relativistic quantum theory calling into question quantum dynamics computations on tunneling reactions. To answer these questions, we define a new experimentally measurable paradigm - the tunneling flight time - and show that it vanishes for scattering through an Eckart or a square barrier, irrespective of barrier length or height, generalizing the Hartman effect...
August 9, 2017: Journal of Physical Chemistry Letters
Anders M N Niklasson
Extended Lagrangian Born-Oppenheimer molecular dynamics [A. M. N. Niklasson, Phys. Rev. Lett. 100, 123004 (2008)] is formulated for general Hohenberg-Kohn density-functional theory and compared with the extended Lagrangian framework of first principles molecular dynamics by Car and Parrinello [Phys. Rev. Lett. 55, 2471 (1985)]. It is shown how extended Lagrangian Born-Oppenheimer molecular dynamics overcomes several shortcomings of regular, direct Born-Oppenheimer molecular dynamics, while improving or maintaining important features of Car-Parrinello simulations...
August 7, 2017: Journal of Chemical Physics
Roman Čurík, Chris H Greene
Inelastic low-energy (0-1 eV) collisions of electrons with HeH(+) cations are treated theoretically, with a focus on the rovibrational excitation and dissociative recombination (DR) channels. In an application of ab initio multichannel quantum defect theory, the description of both processes is based on the Born-Oppenheimer quantum defects. The quantum defects were determined using the R-matrix approach in two different frames of reference: the center-of-charge and the center-of-mass frames. The results obtained in the two reference systems, after implementing the Fano-Jungen style rovibrational frame-transformation technique, show differences in the rate of convergence for these two different frames of reference...
August 7, 2017: Journal of Chemical Physics
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