WorldWideScience

Sample records for critical quantum chemical

  1. Quantum criticality.

    Science.gov (United States)

    Coleman, Piers; Schofield, Andrew J

    2005-01-20

    As we mark the centenary of Albert Einstein's seminal contribution to both quantum mechanics and special relativity, we approach another anniversary--that of Einstein's foundation of the quantum theory of solids. But 100 years on, the same experimental measurement that puzzled Einstein and his contemporaries is forcing us to question our understanding of how quantum matter transforms at ultra-low temperatures.

  2. Quantum Criticality

    Science.gov (United States)

    Drummond, P. D.; Chaturvedi, S.; Dechoum, K.; Comey, J.

    2001-02-01

    We investigate the theory of quantum fluctuations in non-equilibrium systems having large crit­ical fluctuations. This allows us to treat the limits imposed by nonlinearities to quantum squeezing and noise reduction, and also to envisage future tests of quantum theory in regions of macroscopic quantum fluctuations. A long-term objective of this research is to identify suitable physical sys­tems in which macroscopic 'Schrödinger cat'-like behaviour may be observed. We investigate two systems in particular of much current experimental interest, namely the degenerate parametric oscillator near threshold, and the evaporatively cooled (BEC). We compare the results obtained in the positive-P representation, as a fully quantum mechanical calculation, with the truncated Wigner phase space equation, also known as semi-classical theory. We show when these results agree and differ in calculations taken beyond the linearized approximation. In the region where the largest quantum fluctuations and Schrödinger cat-like behaviour might be expected, we find that the quantum predictions correspond very closely to the semi-classical theory. Nature abhors observing a Schrödinger cat. -Pacs: 03.65.Bz

  3. CRITIC2: A program for real-space analysis of quantum chemical interactions in solids

    Science.gov (United States)

    Otero-de-la-Roza, A.; Johnson, Erin R.; Luaña, Víctor

    2014-03-01

    We present CRITIC2, a program for the analysis of quantum-mechanical atomic and molecular interactions in periodic solids. This code, a greatly improved version of the previous CRITIC program (Otero-de-la Roza et al., 2009), can: (i) find critical points of the electron density and related scalar fields such as the electron localization function (ELF), Laplacian, … (ii) integrate atomic properties in the framework of Bader’s Atoms-in-Molecules theory (QTAIM), (iii) visualize non-covalent interactions in crystals using the non-covalent interactions (NCI) index, (iv) generate relevant graphical representations including lines, planes, gradient paths, contour plots, atomic basins, … and (v) perform transformations between file formats describing scalar fields and crystal structures. CRITIC2 can interface with the output produced by a variety of electronic structure programs including WIEN2k, elk, PI, abinit, Quantum ESPRESSO, VASP, Gaussian, and, in general, any other code capable of writing the scalar field under study to a three-dimensional grid. CRITIC2 is parallelized, completely documented (including illustrative test cases) and publicly available under the GNU General Public License. Catalogue identifier: AECB_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECB_v2_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: yes No. of lines in distributed program, including test data, etc.: 11686949 No. of bytes in distributed program, including test data, etc.: 337020731 Distribution format: tar.gz Programming language: Fortran 77 and 90. Computer: Workstations. Operating system: Unix, GNU/Linux. Has the code been vectorized or parallelized?: Shared-memory parallelization can be used for most tasks. Classification: 7.3. Catalogue identifier of previous version: AECB_v1_0 Journal reference of previous version: Comput. Phys. Comm. 180 (2009) 157 Nature of problem: Analysis of quantum-chemical

  4. Unconventional Quantum Critical Points

    OpenAIRE

    Xu, Cenke

    2012-01-01

    In this paper we review the theory of unconventional quantum critical points that are beyond the Landau's paradigm. Three types of unconventional quantum critical points will be discussed: (1). The transition between topological order and semiclassical spin ordered phase; (2). The transition between topological order and valence bond solid phase; (3). The direct second order transition between different competing orders. We focus on the field theory and universality class of these unconventio...

  5. Frustration and quantum criticality

    Science.gov (United States)

    Vojta, Matthias

    2018-06-01

    This review article is devoted to the interplay between frustrated magnetism and quantum critical phenomena, covering both theoretical concepts and ideas as well as recent experimental developments in correlated-electron materials. The first part deals with local-moment magnetism in Mott insulators and the second part with frustration in metallic systems. In both cases, frustration can either induce exotic phases accompanied by exotic quantum critical points or lead to conventional ordering with unconventional crossover phenomena. In addition, the competition of multiple phases inherent to frustrated systems can lead to multi-criticality.

  6. Frustration and quantum criticality.

    Science.gov (United States)

    Vojta, Matthias

    2018-03-15

    This review article is devoted to the interplay between frustrated magnetism and quantum critical phenomena, covering both theoretical concepts and ideas as well as recent experimental developments in correlated-electron materials. The first part deals with local-moment magnetism in Mott insulators and the second part with frustration in metallic systems. In both cases, frustration can either induce exotic phases accompanied by exotic quantum critical points or lead to conventional ordering with unconventional crossover phenomena. In addition, the competition of multiple phases inherent to frustrated systems can lead to multi-criticality. © 2018 IOP Publishing Ltd.

  7. Quantum indistinguishability in chemical reactions.

    Science.gov (United States)

    Fisher, Matthew P A; Radzihovsky, Leo

    2018-05-15

    Quantum indistinguishability plays a crucial role in many low-energy physical phenomena, from quantum fluids to molecular spectroscopy. It is, however, typically ignored in most high-temperature processes, particularly for ionic coordinates, implicitly assumed to be distinguishable, incoherent, and thus well approximated classically. We explore enzymatic chemical reactions involving small symmetric molecules and argue that in many situations a full quantum treatment of collective nuclear degrees of freedom is essential. Supported by several physical arguments, we conjecture a "quantum dynamical selection" (QDS) rule for small symmetric molecules that precludes chemical processes that involve direct transitions from orbitally nonsymmetric molecular states. As we propose and discuss, the implications of the QDS rule include ( i ) a differential chemical reactivity of para- and orthohydrogen, ( ii ) a mechanism for inducing intermolecular quantum entanglement of nuclear spins, ( iii ) a mass-independent isotope fractionation mechanism, ( iv ) an explanation of the enhanced chemical activity of "reactive oxygen species", ( v ) illuminating the importance of ortho-water molecules in modulating the quantum dynamics of liquid water, and ( vi ) providing the critical quantum-to-biochemical linkage in the nuclear spin model of the (putative) quantum brain, among others.

  8. APS Quantum Critical Higgs

    CERN Document Server

    Bellazzini, Brando; Hubisz, Jay; Lee, Seung J.; Serra, Javi; Terning, John

    2016-01-01

    The appearance of the light Higgs boson at the LHC is difficult to explain, particularly in light of naturalness arguments in quantum field theory. However light scalars can appear in condensed matter systems when parameters (like the amount of doping) are tuned to a critical point. At zero temperature these quantum critical points are directly analogous to the finely tuned standard model. In this paper we explore a class of models with a Higgs near a quantum critical point that exhibits non-mean-field behavior. We discuss the parametrization of the effects of a Higgs emerging from such a critical point in terms of form factors, and present two simple realistic scenarios based on either generalized free fields or a 5D dual in AdS space. For both of these models we consider the processes $gg\\to ZZ$ and $gg\\to hh$, which can be used to gain information about the Higgs scaling dimension and IR transition scale from the experimental data.

  9. Quantum Critical Higgs

    Science.gov (United States)

    Bellazzini, Brando; Csáki, Csaba; Hubisz, Jay; Lee, Seung J.; Serra, Javi; Terning, John

    2016-10-01

    The appearance of the light Higgs boson at the LHC is difficult to explain, particularly in light of naturalness arguments in quantum field theory. However, light scalars can appear in condensed matter systems when parameters (like the amount of doping) are tuned to a critical point. At zero temperature these quantum critical points are directly analogous to the finely tuned standard model. In this paper, we explore a class of models with a Higgs near a quantum critical point that exhibits non-mean-field behavior. We discuss the parametrization of the effects of a Higgs emerging from such a critical point in terms of form factors, and present two simple realistic scenarios based on either generalized free fields or a 5D dual in anti-de Sitter space. For both of these models, we consider the processes g g →Z Z and g g →h h , which can be used to gain information about the Higgs scaling dimension and IR transition scale from the experimental data.

  10. Quantum critical Hall exponents

    CERN Document Server

    Lütken, C A

    2014-01-01

    We investigate a finite size "double scaling" hypothesis using data from an experiment on a quantum Hall system with short range disorder [1-3]. For Hall bars of width w at temperature T the scaling form is w(-mu)T(-kappa), where the critical exponent mu approximate to 0.23 we extract from the data is comparable to the multi-fractal exponent alpha(0) - 2 obtained from the Chalker-Coddington (CC) model [4]. We also use the data to find the approximate location (in the resistivity plane) of seven quantum critical points, all of which closely agree with the predictions derived long ago from the modular symmetry of a toroidal sigma-model with m matter fields [5]. The value nu(8) = 2.60513 ... of the localisation exponent obtained from the m = 8 model is in excellent agreement with the best available numerical value nu(num) = 2.607 +/- 0.004 derived from the CC-model [6]. Existing experimental data appear to favour the m = 9 model, suggesting that the quantum Hall system is not in the same universality class as th...

  11. Accurate quantum chemical calculations

    Science.gov (United States)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.

    1989-01-01

    An important goal of quantum chemical calculations is to provide an understanding of chemical bonding and molecular electronic structure. A second goal, the prediction of energy differences to chemical accuracy, has been much harder to attain. First, the computational resources required to achieve such accuracy are very large, and second, it is not straightforward to demonstrate that an apparently accurate result, in terms of agreement with experiment, does not result from a cancellation of errors. Recent advances in electronic structure methodology, coupled with the power of vector supercomputers, have made it possible to solve a number of electronic structure problems exactly using the full configuration interaction (FCI) method within a subspace of the complete Hilbert space. These exact results can be used to benchmark approximate techniques that are applicable to a wider range of chemical and physical problems. The methodology of many-electron quantum chemistry is reviewed. Methods are considered in detail for performing FCI calculations. The application of FCI methods to several three-electron problems in molecular physics are discussed. A number of benchmark applications of FCI wave functions are described. Atomic basis sets and the development of improved methods for handling very large basis sets are discussed: these are then applied to a number of chemical and spectroscopic problems; to transition metals; and to problems involving potential energy surfaces. Although the experiences described give considerable grounds for optimism about the general ability to perform accurate calculations, there are several problems that have proved less tractable, at least with current computer resources, and these and possible solutions are discussed.

  12. Quantum critical environment assisted quantum magnetometer

    Science.gov (United States)

    Jaseem, Noufal; Omkar, S.; Shaji, Anil

    2018-04-01

    A central qubit coupled to an Ising ring of N qubits, operating close to a critical point is investigated as a potential precision quantum magnetometer for estimating an applied transverse magnetic field. We compute the quantum Fisher information for the central, probe qubit with the Ising chain initialized in its ground state or in a thermal state. The non-unitary evolution of the central qubit due to its interaction with the surrounding Ising ring enhances the accuracy of the magnetic field measurement. Near the critical point of the ring, Heisenberg-like scaling of the precision in estimating the magnetic field is obtained when the ring is initialized in its ground state. However, for finite temperatures, the Heisenberg scaling is limited to lower ranges of N values.

  13. Quantum criticality and black holes

    International Nuclear Information System (INIS)

    Sachdev, Subir; Mueller, Markus

    2009-01-01

    Many condensed matter experiments explore the finite temperature dynamics of systems near quantum critical points. Often, there are no well-defined quasiparticle excitations, and so quantum kinetic equations do not describe the transport properties completely. The theory shows that the transport coefficients are not proportional to a mean free scattering time (as is the case in the Boltzmann theory of quasiparticles), but are completely determined by the absolute temperature and by equilibrium thermodynamic observables. Recently, explicit solutions of this quantum critical dynamics have become possible via the anti-de Sitter/conformal field theory duality discovered in string theory. This shows that the quantum critical theory provides a holographic description of the quantum theory of black holes in a negatively curved anti-de Sitter space, and relates its transport coefficients to properties of the Hawking radiation from the black hole. We review how insights from this connection have led to new results for experimental systems: (i) the vicinity of the superfluid-insulator transition in the presence of an applied magnetic field, and its possible application to measurements of the Nernst effect in the cuprates, (ii) the magnetohydrodynamics of the plasma of Dirac electrons in graphene and the prediction of a hydrodynamic cyclotron resonance.

  14. Fermion-induced quantum critical points.

    Science.gov (United States)

    Li, Zi-Xiang; Jiang, Yi-Fan; Jian, Shao-Kai; Yao, Hong

    2017-08-22

    A unified theory of quantum critical points beyond the conventional Landau-Ginzburg-Wilson paradigm remains unknown. According to Landau cubic criterion, phase transitions should be first-order when cubic terms of order parameters are allowed by symmetry in the Landau-Ginzburg free energy. Here, from renormalization group analysis, we show that second-order quantum phase transitions can occur at such putatively first-order transitions in interacting two-dimensional Dirac semimetals. As such type of Landau-forbidden quantum critical points are induced by gapless fermions, we call them fermion-induced quantum critical points. We further introduce a microscopic model of SU(N) fermions on the honeycomb lattice featuring a transition between Dirac semimetals and Kekule valence bond solids. Remarkably, our large-scale sign-problem-free Majorana quantum Monte Carlo simulations show convincing evidences of a fermion-induced quantum critical points for N = 2, 3, 4, 5 and 6, consistent with the renormalization group analysis. We finally discuss possible experimental realizations of the fermion-induced quantum critical points in graphene and graphene-like materials.Quantum phase transitions are governed by Landau-Ginzburg theory and the exceptions are rare. Here, Li et al. propose a type of Landau-forbidden quantum critical points induced by gapless fermions in two-dimensional Dirac semimetals.

  15. Dynamics of quantum discord in a quantum critical environment

    International Nuclear Information System (INIS)

    Xi Zhengjun; Li Yongming; Lu Xiaoming; Sun Zhe

    2011-01-01

    We study the dynamics of quantum discord (QD) of two qubits independently coupled to an Ising spin chain in a transverse field, which exhibits a quantum phase transition. For this model, we drive the corresponding Kraus operators, obtain the analytic results of QD and compare the dynamics of QD with the dynamics of relative entropy of entanglement nearby the critical point. It is shown that the impact of the quantum criticality environment on QD can be concentrated in a very narrow region nearby the critical point, so it supplies an efficient way to detect the critical points. In the vicinity of the critical point, the evolution of QD is shown to be more complicated than that of entanglement. Furthermore, we find that separable states can also be used to reflect the quantum criticality of the environment.

  16. Quantum criticality among entangled spin chains

    Science.gov (United States)

    Blanc, N.; Trinh, J.; Dong, L.; Bai, X.; Aczel, A. A.; Mourigal, M.; Balents, L.; Siegrist, T.; Ramirez, A. P.

    2018-03-01

    An important challenge in magnetism is the unambiguous identification of a quantum spin liquid1,2, of potential importance for quantum computing. In such a material, the magnetic spins should be fluctuating in the quantum regime, instead of frozen in a classical long-range-ordered state. While this requirement dictates systems3,4 wherein classical order is suppressed by a frustrating lattice5, an ideal system would allow tuning of quantum fluctuations by an external parameter. Conventional three-dimensional antiferromagnets can be tuned through a quantum critical point—a region of highly fluctuating spins—by an applied magnetic field. Such systems suffer from a weak specific-heat peak at the quantum critical point, with little entropy available for quantum fluctuations6. Here we study a different type of antiferromagnet, comprised of weakly coupled antiferromagnetic spin-1/2 chains as realized in the molecular salt K2PbCu(NO2)6. Across the temperature-magnetic field boundary between three-dimensional order and the paramagnetic phase, the specific heat exhibits a large peak whose magnitude approaches a value suggestive of the spinon Sommerfeld coefficient of isolated quantum spin chains. These results demonstrate an alternative approach for producing quantum matter via a magnetic-field-induced shift of entropy from one-dimensional short-range order to a three-dimensional quantum critical point.

  17. Controlling superconductivity by tunable quantum critical points.

    Science.gov (United States)

    Seo, S; Park, E; Bauer, E D; Ronning, F; Kim, J N; Shim, J-H; Thompson, J D; Park, Tuson

    2015-03-04

    The heavy fermion compound CeRhIn5 is a rare example where a quantum critical point, hidden by a dome of superconductivity, has been explicitly revealed and found to have a local nature. The lack of additional examples of local types of quantum critical points associated with superconductivity, however, has made it difficult to unravel the role of quantum fluctuations in forming Cooper pairs. Here, we show the precise control of superconductivity by tunable quantum critical points in CeRhIn5. Slight tin-substitution for indium in CeRhIn5 shifts its antiferromagnetic quantum critical point from 2.3 GPa to 1.3 GPa and induces a residual impurity scattering 300 times larger than that of pure CeRhIn5, which should be sufficient to preclude superconductivity. Nevertheless, superconductivity occurs at the quantum critical point of the tin-doped metal. These results underline that fluctuations from the antiferromagnetic quantum criticality promote unconventional superconductivity in CeRhIn5.

  18. Interplay of quantum and classical fluctuations near quantum critical points

    International Nuclear Information System (INIS)

    Continentino, Mucio Amado

    2011-01-01

    For a system near a quantum critical point (QCP), above its lower critical dimension d L , there is in general a critical line of second-order phase transitions that separates the broken symmetry phase at finite temperatures from the disordered phase. The phase transitions along this line are governed by thermal critical exponents that are different from those associated with the quantum critical point. We point out that, if the effective dimension of the QCP, d eff = d + z (d is the Euclidean dimension of the system and z the dynamic quantum critical exponent) is above its upper critical dimension d c there is an intermingle of classical (thermal) and quantum critical fluctuations near the QCP. This is due to the breakdown of the generalized scaling relation ψ = νz between the shift exponent ψ of the critical line and the crossover exponent νz, for d + z > d c by a dangerous irrelevant interaction. This phenomenon has clear experimental consequences, like the suppression of the amplitude of classical critical fluctuations near the line of finite temperature phase transitions as the critical temperature is reduced approaching the QCP. (author)

  19. Spotlighting quantum critical points via quantum correlations at finite temperatures

    International Nuclear Information System (INIS)

    Werlang, T.; Ribeiro, G. A. P.; Rigolin, Gustavo

    2011-01-01

    We extend the program initiated by T. Werlang et al. [Phys. Rev. Lett. 105, 095702 (2010)] in several directions. Firstly, we investigate how useful quantum correlations, such as entanglement and quantum discord, are in the detection of critical points of quantum phase transitions when the system is at finite temperatures. For that purpose we study several thermalized spin models in the thermodynamic limit, namely, the XXZ model, the XY model, and the Ising model, all of which with an external magnetic field. We compare the ability of quantum discord, entanglement, and some thermodynamic quantities to spotlight the quantum critical points for several different temperatures. Secondly, for some models we go beyond nearest neighbors and also study the behavior of entanglement and quantum discord for second nearest neighbors around the critical point at finite temperature. Finally, we furnish a more quantitative description of how good all these quantities are in spotlighting critical points of quantum phase transitions at finite T, bridging the gap between experimental data and those theoretical descriptions solely based on the unattainable absolute zero assumption.

  20. A magnetically induced quantum critical point in holography

    NARCIS (Netherlands)

    Gursoy, U.; Gnecchi, A.; Toldo, C.; Papadoulaki, O.

    We investigate quantum critical points in a 2+1 dimensional gauge theory at finite chemical potential χ and magnetic field B. The gravity dual is based on 4D NN = 2 Fayet-Iliopoulos gauged supergravity and the solutions we consider — that are constructed analytically — are extremal, dyonic,

  1. Detecting quantum critical points using bipartite fluctuations.

    Science.gov (United States)

    Rachel, Stephan; Laflorencie, Nicolas; Song, H Francis; Le Hur, Karyn

    2012-03-16

    We show that the concept of bipartite fluctuations F provides a very efficient tool to detect quantum phase transitions in strongly correlated systems. Using state-of-the-art numerical techniques complemented with analytical arguments, we investigate paradigmatic examples for both quantum spins and bosons. As compared to the von Neumann entanglement entropy, we observe that F allows us to find quantum critical points with much better accuracy in one dimension. We further demonstrate that F can be successfully applied to the detection of quantum criticality in higher dimensions with no prior knowledge of the universality class of the transition. Promising approaches to experimentally access fluctuations are discussed for quantum antiferromagnets and cold gases.

  2. Criticality and entanglement in random quantum systems

    International Nuclear Information System (INIS)

    Refael, G; Moore, J E

    2009-01-01

    We review studies of entanglement entropy in systems with quenched randomness, concentrating on universal behavior at strongly random quantum critical points. The disorder-averaged entanglement entropy provides insight into the quantum criticality of these systems and an understanding of their relationship to non-random ('pure') quantum criticality. The entanglement near many such critical points in one dimension shows a logarithmic divergence in subsystem size, similar to that in the pure case but with a different universal coefficient. Such universal coefficients are examples of universal critical amplitudes in a random system. Possible measurements are reviewed along with the one-particle entanglement scaling at certain Anderson localization transitions. We also comment briefly on higher dimensions and challenges for the future.

  3. Quench dynamics across quantum critical points

    International Nuclear Information System (INIS)

    Sengupta, K.; Powell, Stephen; Sachdev, Subir

    2004-01-01

    We study the quantum dynamics of a number of model systems as their coupling constants are changed rapidly across a quantum critical point. The primary motivation is provided by the recent experiments of Greiner et al. [Nature (London) 415, 39 (2002)] who studied the response of a Mott insulator of ultracold atoms in an optical lattice to a strong potential gradient. In a previous work, it had been argued that the resonant response observed at a critical potential gradient could be understood by proximity to an Ising quantum critical point describing the onset of density wave order. Here we obtain numerical results on the evolution of the density wave order as the potential gradient is scanned across the quantum critical point. This is supplemented by studies of the integrable quantum Ising spin chain in a transverse field, where we obtain exact results for the evolution of the Ising order correlations under a time-dependent transverse field. We also study the evolution of transverse superfluid order in the three-dimensional case. In all cases, the order parameter is best enhanced in the vicinity of the quantum critical point

  4. Fermion-induced quantum critical points

    OpenAIRE

    Li, Zi-Xiang; Jiang, Yi-Fan; Jian, Shao-Kai; Yao, Hong

    2017-01-01

    A unified theory of quantum critical points beyond the conventional Landau?Ginzburg?Wilson paradigm remains unknown. According to Landau cubic criterion, phase transitions should be first-order when cubic terms of order parameters are allowed by symmetry in the Landau?Ginzburg free energy. Here, from renormalization group analysis, we show that second-order quantum phase transitions can occur at such putatively first-order transitions in interacting two-dimensional Dirac semimetals. As such t...

  5. Critical behaviors of gravity under quantum perturbations

    Directory of Open Access Journals (Sweden)

    ZHANG Hongsheng

    2014-02-01

    Full Text Available Phase transition and critical phenomenon is a very interesting topic in thermodynamics and statistical mechanics. Gravity is believed to have deep and inherent relation to thermodynamics. Near the critical point,the perturbation becomes significant. Thus for ordinary matter (governed by interactions besides gravity the critical behavior will become very different if we ignore the perturbations around the critical point,such as mean field theory. We find that the critical exponents for RN-AdS spacetime keep the same values even when we consider the full quantum perturbations. This indicates a key difference between gravity and ordinary thermodynamic system.

  6. Dynamical Response near Quantum Critical Points.

    Science.gov (United States)

    Lucas, Andrew; Gazit, Snir; Podolsky, Daniel; Witczak-Krempa, William

    2017-02-03

    We study high-frequency response functions, notably the optical conductivity, in the vicinity of quantum critical points (QCPs) by allowing for both detuning from the critical coupling and finite temperature. We consider general dimensions and dynamical exponents. This leads to a unified understanding of sum rules. In systems with emergent Lorentz invariance, powerful methods from quantum field theory allow us to fix the high-frequency response in terms of universal coefficients. We test our predictions analytically in the large-N O(N) model and using the gauge-gravity duality and numerically via quantum Monte Carlo simulations on a lattice model hosting the interacting superfluid-insulator QCP. In superfluid phases, interacting Goldstone bosons qualitatively change the high-frequency optical conductivity and the corresponding sum rule.

  7. Critical Kondo destruction and the violation of the quantum-to-classical mapping of quantum criticality

    International Nuclear Information System (INIS)

    Kirchner, Stefan; Si Qimiao

    2009-01-01

    Antiferromagnetic heavy fermion metals close to their quantum critical points display a richness in their physical properties unanticipated by the traditional approach to quantum criticality, which describes the critical properties solely in terms of fluctuations of the order parameter. This has led to the question as to how the Kondo effect gets destroyed as the system undergoes a phase change. In one approach to the problem, Kondo lattice systems are studied through a self-consistent Bose-Fermi Kondo model within the extended dynamical mean field theory. The quantum phase transition of the Kondo lattice is thus mapped onto that of a sub-Ohmic Bose-Fermi Kondo model. In the present article we address some aspects of the failure of the standard order-parameter functional for the Kondo-destroying quantum critical point of the Bose-Fermi Kondo model.

  8. Universal signatures of fractionalized quantum critical points.

    Science.gov (United States)

    Isakov, Sergei V; Melko, Roger G; Hastings, Matthew B

    2012-01-13

    Ground states of certain materials can support exotic excitations with a charge equal to a fraction of the fundamental electron charge. The condensation of these fractionalized particles has been predicted to drive unusual quantum phase transitions. Through numerical and theoretical analysis of a physical model of interacting lattice bosons, we establish the existence of such an exotic critical point, called XY*. We measure a highly nonclassical critical exponent η = 1.493 and construct a universal scaling function of winding number distributions that directly demonstrates the distinct topological sectors of an emergent Z(2) gauge field. The universal quantities used to establish this exotic transition can be used to detect other fractionalized quantum critical points in future model and material systems.

  9. molecular dynamics simulations and quantum chemical calculations

    African Journals Online (AJOL)

    ABSTRACT. The molecular dynamic (MD) simulation and quantum chemical calculations for the adsorption of [2-(2-Henicos-10- .... electronic properties of molecule clusters, surfaces and ... The local reactivity was analyzed by determining the.

  10. Dynamic trapping near a quantum critical point

    Science.gov (United States)

    Kolodrubetz, Michael; Katz, Emanuel; Polkovnikov, Anatoli

    2015-02-01

    The study of dynamics in closed quantum systems has been revitalized by the emergence of experimental systems that are well-isolated from their environment. In this paper, we consider the closed-system dynamics of an archetypal model: spins driven across a second-order quantum critical point, which are traditionally described by the Kibble-Zurek mechanism. Imbuing the driving field with Newtonian dynamics, we find that the full closed system exhibits a robust new phenomenon—dynamic critical trapping—in which the system is self-trapped near the critical point due to efficient absorption of field kinetic energy by heating the quantum spins. We quantify limits in which this phenomenon can be observed and generalize these results by developing a Kibble-Zurek scaling theory that incorporates the dynamic field. Our findings can potentially be interesting in the context of early universe physics, where the role of the driving field is played by the inflaton or a modulus field.

  11. Quantum chemical studies of estrogenic compounds

    Science.gov (United States)

    Quantum chemical methods are potent tools to provide information on the chemical structure and electronic properties of organic molecules. Modern computational chemistry methods have provided a great deal of insight into the binding of estrogenic compounds to estrogenic receptors (ER), an important ...

  12. Deconfined Quantum Critical Points: Symmetries and Dualities

    Directory of Open Access Journals (Sweden)

    Chong Wang

    2017-09-01

    Full Text Available The deconfined quantum critical point (QCP, separating the Néel and valence bond solid phases in a 2D antiferromagnet, was proposed as an example of (2+1D criticality fundamentally different from standard Landau-Ginzburg-Wilson-Fisher criticality. In this work, we present multiple equivalent descriptions of deconfined QCPs, and use these to address the possibility of enlarged emergent symmetries in the low-energy limit. The easy-plane deconfined QCP, besides its previously discussed self-duality, is dual to N_{f}=2 fermionic quantum electrodynamics, which has its own self-duality and hence may have an O(4×Z_{2}^{T} symmetry. We propose several dualities for the deconfined QCP with SU(2 spin symmetry which together make natural the emergence of a previously suggested SO(5 symmetry rotating the Néel and valence bond solid orders. These emergent symmetries are implemented anomalously. The associated infrared theories can also be viewed as surface descriptions of (3+1D topological paramagnets, giving further insight into the dualities. We describe a number of numerical tests of these dualities. We also discuss the possibility of “pseudocritical” behavior for deconfined critical points, and the meaning of the dualities and emergent symmetries in such a scenario.

  13. Quantum criticality of one-dimensional multicomponent Fermi gas with strongly attractive interaction

    International Nuclear Information System (INIS)

    He, Peng; Jiang, Yuzhu; Guan, Xiwen; He, Jinyu

    2015-01-01

    Quantum criticality of strongly attractive Fermi gas with SU(3) symmetry in one dimension is studied via the thermodynamic Bethe ansatz (TBA) equations. The phase transitions driven by the chemical potential μ, effective magnetic field H 1 , H 2 (chemical potential biases) are analyzed at the quantum criticality. The phase diagram and critical fields are analytically determined by the TBA equations in the zero temperature limit. High accurate equations of state, scaling functions are also obtained analytically for the strong interacting gases. The dynamic exponent z=2 and correlation length exponent ν=1/2 read off the universal scaling form. It turns out that the quantum criticality of the three-component gases involves a sudden change of density of states of one cluster state, two or three cluster states. In general, this method can be adapted to deal with the quantum criticality of multicomponent Fermi gases with SU(N) symmetry. (paper)

  14. Quantum mechanical tunneling in chemical physics

    CERN Document Server

    Nakamura, Hiroki

    2016-01-01

    Quantum mechanical tunneling plays important roles in a wide range of natural sciences, from nuclear and solid-state physics to proton transfer and chemical reactions in chemistry and biology. Responding to the need for further understanding of multidimensional tunneling, the authors have recently developed practical methods that can be applied to multidimensional systems. Quantum Mechanical Tunneling in Chemical Physics presents basic theories, as well as original ones developed by the authors. It also provides methodologies and numerical applications to real molecular systems. The book offers information so readers can understand the basic concepts and dynamics of multidimensional tunneling phenomena and use the described methods for various molecular spectroscopy and chemical dynamics problems. The text focuses on three tunneling phenomena: (1) energy splitting, or tunneling splitting, in symmetric double well potential, (2) decay of metastable state through tunneling, and (3) tunneling effects in chemical...

  15. Effective and fundamental quantum fields at criticality

    Energy Technology Data Exchange (ETDEWEB)

    Scherer, Michael

    2010-10-28

    We employ Wetterich's approach to functional renormalization as a suitable method to investigate universal phenomena in non-perturbative quantum field theories both qualitatively and quantitatively. Therefore we derive and investigate flow equations for a class of chiral Yukawa models with and without gauge bosons and reveal fixed-point mechanisms. In four dimensions chiral Yukawa systems serve as toy models for the standard model Higgs sector and show signatures of asymptotically safe fixed points by a balancing of bosonic and fermionic contributions. In the approximations investigated this renders the theory fundamental and solves the triviality problem. Further, we obtain predictions for the Higgs mass and even for the top mass of our toy model. In three dimensions we compute the critical exponents which define new universality classes and provide benchmark values for systems of strongly correlated chiral fermions. In a Yukawa system of non-relativistic two-component fermions a fixed point dominates the renormalization flow giving rise to universality in the BCS-BEC crossover. We push the functional renormalization method to a quantitative level and we compute the critical temperature and the single-particle gap with a considerable precision for the whole crossover. Finally, we provide further evidence for the asymptotic safety scenario in quantum gravity by confirming the existence of an ultraviolet fixed point under inclusion of a curvature-ghost coupling. (orig.)

  16. Effective and fundamental quantum fields at criticality

    International Nuclear Information System (INIS)

    Scherer, Michael

    2010-01-01

    We employ Wetterich's approach to functional renormalization as a suitable method to investigate universal phenomena in non-perturbative quantum field theories both qualitatively and quantitatively. Therefore we derive and investigate flow equations for a class of chiral Yukawa models with and without gauge bosons and reveal fixed-point mechanisms. In four dimensions chiral Yukawa systems serve as toy models for the standard model Higgs sector and show signatures of asymptotically safe fixed points by a balancing of bosonic and fermionic contributions. In the approximations investigated this renders the theory fundamental and solves the triviality problem. Further, we obtain predictions for the Higgs mass and even for the top mass of our toy model. In three dimensions we compute the critical exponents which define new universality classes and provide benchmark values for systems of strongly correlated chiral fermions. In a Yukawa system of non-relativistic two-component fermions a fixed point dominates the renormalization flow giving rise to universality in the BCS-BEC crossover. We push the functional renormalization method to a quantitative level and we compute the critical temperature and the single-particle gap with a considerable precision for the whole crossover. Finally, we provide further evidence for the asymptotic safety scenario in quantum gravity by confirming the existence of an ultraviolet fixed point under inclusion of a curvature-ghost coupling. (orig.)

  17. Detection of quantum critical points by a probe qubit.

    Science.gov (United States)

    Zhang, Jingfu; Peng, Xinhua; Rajendran, Nageswaran; Suter, Dieter

    2008-03-14

    Quantum phase transitions occur when the ground state of a quantum system undergoes a qualitative change when an external control parameter reaches a critical value. Here, we demonstrate a technique for studying quantum systems undergoing a phase transition by coupling the system to a probe qubit. It uses directly the increased sensibility of the quantum system to perturbations when it is close to a critical point. Using an NMR quantum simulator, we demonstrate this measurement technique for two different types of quantum phase transitions in an Ising spin chain.

  18. New quantum criticality revealed under pressure

    International Nuclear Information System (INIS)

    Watanabe, Shinji; Miyake, Kazumasa

    2017-01-01

    Unconventional quantum critical phenomena observed in Yb-based periodic crystals such as YbRh_2Si_2 and β-YbAlB_4 have been one of the central issues in strongly correlated electron systems. The common criticality has been discovered in the quasicrystal Yb_1_5Au_5_1Al_3_4, which surprisingly persists under pressure at least up to P = 1.5 GPa. The T/H scaling where the magnetic susceptibility can be expressed as a single scaling function of the ratio of the temperature T to the magnetic field H has been discovered in the quasicrystal, which is essentially the same as that observed in β-YbAlB_4. Recently, the T/H scaling as well as the common criticality has also been observed even in the approximant crystal Yb_1_4Au_5_1Al_3_5 under pressure. The theory of critical Yb-valence fluctuation gives a natural explanation for these striking phenomena in a unified way. (author)

  19. Quantum critical scaling of fidelity in BCS-like model

    International Nuclear Information System (INIS)

    Adamski, Mariusz; Jedrzejewski, Janusz; Krokhmalskii, Taras

    2013-01-01

    We study scaling of the ground-state fidelity in neighborhoods of quantum critical points in a model of interacting spinful fermions—a BCS-like model. Due to the exact diagonalizability of the model, in one and higher dimensions, scaling of the ground-state fidelity can be analyzed numerically with great accuracy, not only for small systems but also for macroscopic ones, together with the crossover region between them. Additionally, in the one-dimensional case we have been able to derive a number of analytical formulas for fidelity and show that they accurately fit our numerical results; these results are reported in the paper. Besides regular critical points and their neighborhoods, where well-known scaling laws are obeyed, there is the multicritical point and critical points in its proximity where anomalous scaling behavior is found. We also consider scaling of fidelity in neighborhoods of critical points where fidelity oscillates strongly as the system size or the chemical potential is varied. Our results for a one-dimensional version of a BCS-like model are compared with those obtained recently by Rams and Damski in similar studies of a quantum spin chain—an anisotropic XY model in a transverse magnetic field. (paper)

  20. Quantum mechanical facets of chemical bonds

    International Nuclear Information System (INIS)

    Daudel, R.

    1976-01-01

    To define the concept of bond is both a central problem of quantum chemistry and a difficult one. The concept of bond appeared little by little in the mind of chemists from empirical observations. From the wave-mechanical viewpoint it is not an observable. Therefore there is no precise operator associated with that concept. As a consequence there is not a unique approach to the idea of chemical bond. This is why it is preferred to present various quantum mechanical facets, e.g. the energetic facet, the density facet, the partitioning facet and the functional facet, of that important concept. (Auth.)

  1. Quantum field theory and critical phenomena

    CERN Document Server

    Zinn-Justin, Jean

    1996-01-01

    Over the last twenty years quantum field theory has become not only the framework for the discussion of all fundamental interactions except gravity, but also for the understanding of second-order phase transitions in statistical mechanics. This advanced text is based on graduate courses and summer schools given by the author over a number of years. It approaches the subject in terms of path and functional intergrals, adopting a Euclidean metric and using the language of partition and correlation functions. Renormalization and the renormalization group are examined, as are critical phenomena and the role of instantons. Changes for this edition 1. Extensive revision to eliminate a few bugs that had survived the second edition and (mainly) to improve the pedagogical presentation, as a result of experience gathered by lecturing. 2. Additional new topics; holomorphic or coherent state path integral; functional integral and representation of the field theory S-matrix in the holomorphic formalis; non-relativistic li...

  2. Quantum critical dynamics for a prototype class of insulating antiferromagnets

    Science.gov (United States)

    Wu, Jianda; Yang, Wang; Wu, Congjun; Si, Qimiao

    2018-06-01

    Quantum criticality is a fundamental organizing principle for studying strongly correlated systems. Nevertheless, understanding quantum critical dynamics at nonzero temperatures is a major challenge of condensed-matter physics due to the intricate interplay between quantum and thermal fluctuations. The recent experiments with the quantum spin dimer material TlCuCl3 provide an unprecedented opportunity to test the theories of quantum criticality. We investigate the nonzero-temperature quantum critical spin dynamics by employing an effective O (N ) field theory. The on-shell mass and the damping rate of quantum critical spin excitations as functions of temperature are calculated based on the renormalized coupling strength and are in excellent agreement with experiment observations. Their T lnT dependence is predicted to be dominant at very low temperatures, which will be tested in future experiments. Our work provides confidence that quantum criticality as a theoretical framework, which is being considered in so many different contexts of condensed-matter physics and beyond, is indeed grounded in materials and experiments accurately. It is also expected to motivate further experimental investigations on the applicability of the field theory to related quantum critical systems.

  3. Quantum phase transition and critical phenomena

    International Nuclear Information System (INIS)

    Dutta, A.; Chakrabarti, B.K.

    1998-01-01

    We intend to describe briefly the generic features associated with the zero temperature transition in quantum mechanical systems. We elucidate the discussion of the introductory section using the very common example of Ising model in a transverse field. We discuss the method of fermionisation for one dimensional systems. The quantum-classical correspondence is discussed using Suzuki-Trotter method. We then introduce the quantum rotor model and discuss its spherical limit. We finally discuss novel features arising due to the presence of quenched randomness in the quantum Ising and rotor systems. (author)

  4. Characteristic signatures of quantum criticality driven by geometrical frustration.

    Science.gov (United States)

    Tokiwa, Yoshifumi; Stingl, Christian; Kim, Moo-Sung; Takabatake, Toshiro; Gegenwart, Philipp

    2015-04-01

    Geometrical frustration describes situations where interactions are incompatible with the lattice geometry and stabilizes exotic phases such as spin liquids. Whether geometrical frustration of magnetic interactions in metals can induce unconventional quantum critical points is an active area of research. We focus on the hexagonal heavy fermion metal CeRhSn, where the Kondo ions are located on distorted kagome planes stacked along the c axis. Low-temperature specific heat, thermal expansion, and magnetic Grüneisen parameter measurements prove a zero-field quantum critical point. The linear thermal expansion, which measures the initial uniaxial pressure derivative of the entropy, displays a striking anisotropy. Critical and noncritical behaviors along and perpendicular to the kagome planes, respectively, prove that quantum criticality is driven be geometrical frustration. We also discovered a spin flop-type metamagnetic crossover. This excludes an itinerant scenario and suggests that quantum criticality is related to local moments in a spin liquid-like state.

  5. Universal Postquench Prethermalization at a Quantum Critical Point

    Science.gov (United States)

    Gagel, Pia; Orth, Peter P.; Schmalian, Jörg

    2014-11-01

    We consider an open system near a quantum critical point that is suddenly moved towards the critical point. The bath-dominated diffusive nonequilibrium dynamics after the quench is shown to follow scaling behavior, governed by a critical exponent that emerges in addition to the known equilibrium critical exponents. We determine this exponent and show that it describes universal prethermalized coarsening dynamics of the order parameter in an intermediate time regime. Implications of this quantum critical prethermalization are: (i) a power law rise of order and correlations after an initial collapse of the equilibrium state and (ii) a crossover to thermalization that occurs arbitrarily late for sufficiently shallow quenches.

  6. Critical examination of logical formulations in quantum theory. Statistical inference and Hilbertian distance between quantum states

    International Nuclear Information System (INIS)

    Hadjisawas, Nicolas.

    1982-01-01

    After a critical study of the logical quantum mechanics formulations of Jauch and Piron, classical and quantum versions of statistical inference are studied. In order to do this, the significance of the Jaynes and Kulback principles (maximum likelihood, least squares principles) is revealed from the theorems established. In the quantum mechanics inference problem, a ''distance'' between states is defined. This concept is used to solve the quantum equivalent of the classical problem studied by Kulback. The ''projection postulate'' proposition is subsequently deduced [fr

  7. Quantum uncertainty in critical systems with three spins interaction

    International Nuclear Information System (INIS)

    Carrijo, Thiago M; Avelar, Ardiley T; Céleri, Lucas C

    2015-01-01

    In this article we consider two spin-1/2 chains described, respectively, by the thermodynamic limit of the XY model with the usual two site interaction, and an extension of this model (without taking the thermodynamics limit), called XYT, were a three site interaction term is presented. To investigate the critical behaviour of such systems we employ tools from quantum information theory. Specifically, we show that the local quantum uncertainty, a quantity introduced in order to quantify the minimum quantum share of the variance of a local measurement, can be used to indicate quantum phase transitions presented by these models at zero temperature. Due to the connection of this quantity with the quantum Fisher information, the results presented here may be relevant for quantum metrology and quantum thermodynamics. (paper)

  8. Quantum dynamics of fast chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Light, J.C. [Univ. of Chicago, IL (United States)

    1993-12-01

    The aims of this research are to explore, develop, and apply theoretical methods for the evaluation of the dynamics of gas phase collision processes, primarily chemical reactions. The primary theoretical tools developed for this work have been quantum scattering theory, both in time dependent and time independent forms. Over the past several years, the authors have developed and applied methods for the direct quantum evaluation of thermal rate constants, applying these to the evaluation of the hydrogen isotopic exchange reactions, applied wave packet propagation techniques to the dissociation of Rydberg H{sub 3}, incorporated optical potentials into the evaluation of thermal rate constants, evaluated the use of optical potentials for state-to-state reaction probability evaluations, and, most recently, have developed quantum approaches for electronically non-adiabatic reactions which may be applied to simplify calculations of reactive, but electronically adiabatic systems. Evaluation of the thermal rate constants and the dissociation of H{sub 3} were reported last year, and have now been published.

  9. New Type of Quantum Criticality in the Pyrochlore Iridates

    Directory of Open Access Journals (Sweden)

    Lucile Savary

    2014-11-01

    Full Text Available Magnetic fluctuations and electrons couple in intriguing ways in the vicinity of zero-temperature phase transitions—quantum critical points—in conducting materials. Quantum criticality is implicated in non-Fermi liquid behavior of diverse materials and in the formation of unconventional superconductors. Here, we uncover an entirely new type of quantum critical point describing the onset of antiferromagnetism in a nodal semimetal engendered by the combination of strong spin-orbit coupling and electron correlations, and which is predicted to occur in the iridium oxide pyrochlores. We formulate and solve a field theory for this quantum critical point by renormalization group techniques and show that electrons and antiferromagnetic fluctuations are strongly coupled and that both these excitations are modified in an essential way. This quantum critical point has many novel features, including strong emergent spatial anisotropy, a vital role for Coulomb interactions, and highly unconventional critical exponents. Our theory motivates and informs experiments on pyrochlore iridates and constitutes a singular realistic example of a nontrivial quantum critical point with gapless fermions in three dimensions.

  10. Quantum theories of the early universe - a critical appraisal

    International Nuclear Information System (INIS)

    Hu, B.L.

    1988-01-01

    A critical appraisal of certain general problems in the study of quantum processes in curved space as applied to the construction of theories of the early universe is presented. Outstanding issues in different cosmological models and the degree of success of different quantum processes in addressing these issues are summarized. (author)

  11. Vector boson excitations near deconfined quantum critical points.

    Science.gov (United States)

    Huh, Yejin; Strack, Philipp; Sachdev, Subir

    2013-10-18

    We show that the Néel states of two-dimensional antiferromagnets have low energy vector boson excitations in the vicinity of deconfined quantum critical points. We compute the universal damping of these excitations arising from spin-wave emission. Detection of such a vector boson will demonstrate the existence of emergent topological gauge excitations in a quantum spin system.

  12. Quantum mechanical calculations to chemical accuracy

    Science.gov (United States)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1991-01-01

    The accuracy of current molecular-structure calculations is illustrated with examples of quantum mechanical solutions for chemical problems. Two approaches are considered: (1) the coupled-cluster singles and doubles (CCSD) with a perturbational estimate of the contribution of connected triple excitations, or CCDS(T); and (2) the multireference configuration-interaction (MRCI) approach to the correlation problem. The MRCI approach gains greater applicability by means of size-extensive modifications such as the averaged-coupled pair functional approach. The examples of solutions to chemical problems include those for C-H bond energies, the vibrational frequencies of O3, identifying the ground state of Al2 and Si2, and the Lewis-Rayleigh afterglow and the Hermann IR system of N2. Accurate molecular-wave functions can be derived from a combination of basis-set saturation studies and full configuration-interaction calculations.

  13. Quantum critical scaling and fluctuations in Kondo lattice materials

    Science.gov (United States)

    Yang, Yi-feng; Pines, David; Lonzarich, Gilbert

    2017-01-01

    We propose a phenomenological framework for three classes of Kondo lattice materials that incorporates the interplay between the fluctuations associated with the antiferromagnetic quantum critical point and those produced by the hybridization quantum critical point that marks the end of local moment behavior. We show that these fluctuations give rise to two distinct regions of quantum critical scaling: Hybridization fluctuations are responsible for the logarithmic scaling in the density of states of the heavy electron Kondo liquid that emerges below the coherence temperature T∗, whereas the unconventional power law scaling in the resistivity that emerges at lower temperatures below TQC may reflect the combined effects of hybridization and antiferromagnetic quantum critical fluctuations. Our framework is supported by experimental measurements on CeCoIn5, CeRhIn5, and other heavy electron materials. PMID:28559308

  14. A critical quantum chemical and experimental study of the potentiality of direct labeling of the CN group with [99mTc(CO)3]+ or [186/188Re(CO)3]+ in CN containing biomolecules

    International Nuclear Information System (INIS)

    Safi, Benasser; Mertens, John; Kersemans, Ken; Geerlings, Paul

    2008-01-01

    Introduction: It was determined recently that [ 99m Tc(OH 2 ) 2 (X - )(CO 3 ) 3 ] could strongly bind to the CN group, allowing direct labeling of CN in vitamin B 12 despite the presence of a benzimidazole group. The aim of this paper was to perform a critical study of this potentiality, coupling quantum chemical calculations to experimental evidence. Methods: Computational methods: Within the density functional theory calculations, the 6-31+G** basis set (C, H, O, N atoms) and the LANL2DZ basis set (Tc,Re) were used. Stability calculations of the [RCNM(CO) 3 ] + ) (M=Tc,Re) complexes were performed with the Gaussian 03 suite of programs, while for the evaluation of relative stability substitution reactions were used. Radiochemistry: Vitamin B 12 , 4-hydroxy-benzylcyanide and 4-methoxy-benzonitrile were labeled at 100 deg. C during 30 min. High-performance liquid chromatography analysis was performed using radioactive and UV detection. Results: Computational methods: The influence of different ligands on the stability yielded a sequence: imidazole>tBuCN>NH 3 ∼CH 3 CN>HCN (mimicking the best CoCN)>H 2 O. The transmetalation reaction indicates that all ligands prefer Re to Tc. The preference for the nitrogen atom of imidazole to the cyanide nitrogen atom for complex formation with [Tc(CO) 3 (H 2 O) 3 ] + is interpreted in terms of the hard and soft acid and base properties principle. Radiochemistry: 4-Hydroxy-benzylcyanide and 4-methoxy-benzonitrile did not show any labeling. An excess of acetonitrile did not inhibit the labeling of vitamin B 12 as expected if the CN group should be involved, indicating that the labeling occurs on a stronger complexing group present like benzimidazole. Conclusion: Both theory and experiments prove that [CN-Tc(CO) 3 (H 2 O) (2-x) L x ] + complexes are weak and that in vitamin B 12 most probably the benzimidazole group is involved

  15. Quantum criticality in Einstein-Maxwell-dilaton gravity

    International Nuclear Information System (INIS)

    Wen, Wen-Yu

    2012-01-01

    We investigate the quantum Lifshitz criticality in a general background of Einstein-Maxwell-dilaton gravity. In particular, we demonstrate the existence of critical point with dynamic critical exponent z by tuning a nonminimal coupling to its critical value. We also study the effect of nonminimal coupling and exponent z to the Efimov states and holographic RG flow in the overcritical region. We have found that the nonminimal coupling increases the instability for a probe scalar to condensate and its back reaction is discussed. At last, we give a quantum mechanics treatment to a solvable system with z=2, and comment for generic z>2.

  16. On foundational and geometric critical aspects of quantum electrodynamics

    International Nuclear Information System (INIS)

    Prugovecki, E.

    1994-01-01

    The foundational difficulties encountered by the conventional formulation of quantum electrodynamics, and the criticism by Dirac Schwinger, Rohrlich, and others, aimed at some of the physical and mathematical premises underlying that formulation, are reviewed and discussed. The basic failings of the conventional methods of quantization of the electromagnetic field are pointed out, especially with regard to the issue of local (anti) commutativity of quantum fields as an embodiment of relativistic microcausality. A brief description is given of a recently advanced new type of approach to quantum electrodynamics, and to quantum field theory in general, which is epistemically based on intrinsically quantum ideas about the physical nature of spacetime, and is mathematically based on a fiber theoretical formulation of quantum geometries, aimed in part at removing the aforementioned difficulties and inconsistencies. It is shown that these ideas can be traced to a conceptualization of spacetime outlined by Einstein in the last edition of his well-known semipopular exposition of relativity theory. 57 refs

  17. Phenomenon of quantum low temperature limit of chemical reaction rates

    International Nuclear Information System (INIS)

    Gol'danskij, V.I.

    1975-01-01

    The influence of quantum-mechanical effects on one of the fundamental laws of chemical kinetics - the Arrhenius law - is considered. Criteria characterising the limits of the low-temperature region where the extent of quantum-mechanical tunnelling transitions exceeds exponentially the transitions over the barrier are quoted. Studies of the low-temperature tunnelling of electrons and hydrogen atoms are briefly mentioned and the history of research on low-temperature radiation-induced solid-phase polymerisation, the development of which led to the discovery of the phenomenon of the low-temperature quantum-mechanical limit for the rates of chemical reactions in relation to the formaldehyde polymerisation reaction, is briefly considered. The results of experiments using low-inertia calorimeters, whereby it is possible to determine directly the average time (tau 0 ) required to add one new link to the polymer chain of formaldehyde during its polymerisation by radiation and during postpolymerisation and to establish that below 80K the increase of tau 0 slows down and that at T approximately equal to 10-4K the time tau 0 reaches a plateau (tau 0 approximately equals 0.01s), are described. Possible explanations of the observed low-temperature limit for the rate of a chemical reaction are critically examined and a semiquantitative explanation is given for this phenomenon, which may be particularly common in combined electronic-confirmational transitions in complex biological molecules and may play a definite role in chemical and biological evolution (cold prehistory of life)

  18. Phenomenon of quantum low temperature limit of chemical reaction rates

    Energy Technology Data Exchange (ETDEWEB)

    Gol' danskii, V I [AN SSSR, Moscow. Inst. Khimicheskoj Fiziki

    1975-12-01

    The influence of quantum-mechanical effects on one of the fundamental laws of chemical kinetics - the Arrhenius Law - is considered. Criteria characterising the limits of the low-temperature region where the extent of quantum-mechanical tunnelling transitions exceeds exponentially the transitions over the barrier are quoted. Studies of the low-temperature tunnelling of electrons and hydrogen atoms are briefly mentioned and the history of research on low-temperature radiation-induced solid-phase polymerization, the development of which led to the discovery of the phenomenon of the low-temperature quantum-mechanical limit for the rates of chemical reactions in relation to the formaldehyde polymerization reaction, is briefly considered. The results of experiments using low-inertia calorimeters, whereby it is possible to determine directly the average time (tau/sub 0/) required to add one new link to the polymer chain of formaldehyde during its polymerization by radiation and during postpolymerization and to establish that below 80K the increase of tau/sub 0/ slows down and that at T approximately equal to 10-4K the time tau/sub 0/ reaches a plateau (tau/sub 0/ approximately equals 0.01s), are described. Possible explanations of the observed low-temperature limit for the rate of a chemical reaction are critically examined and a semiquantitative explanation is given for this phenomenon, which may be particularly common in combined electronic-confirmational transitions in complex biological molecules and may play a definite role in chemical and biological evolution (cold prehistory of life).

  19. Itinerant density instability at classical and quantum critical points

    Science.gov (United States)

    Feng, Yejun; van Wezel, Jasper; Flicker, Felix; Wang, Jiyang; Silevitch, D. M.; Littlewood, P. B.; Rosenbaum, T. F.

    2015-03-01

    Itinerant density waves are model systems for studying quantum critical behavior. In both the model spin- and charge-density-wave systems Cr and NbSe2, it is possible to drive a continuous quantum phase transition with critical pressures below 10 GPa. Using x-ray diffraction techniques, we are able to directly track the evolution of the ordering wave vector Q across the pressure-temperature phase diagram. We find a non-monotonic dependence of Q on pressure. Using a Landau-Ginsburg theoretical framework developed by McMillan for CDWs, we evaluate the importance of the physical terms in driving the formation of ordered states at both the thermal and quantum phase transitions. We find that the itinerant instability is the deciding factor for the emergent order, which is further influenced by the critical fluctuations in both the thermal and quantum limits.

  20. Complex Chemical Reaction Networks from Heuristics-Aided Quantum Chemistry.

    Science.gov (United States)

    Rappoport, Dmitrij; Galvin, Cooper J; Zubarev, Dmitry Yu; Aspuru-Guzik, Alán

    2014-03-11

    While structures and reactivities of many small molecules can be computed efficiently and accurately using quantum chemical methods, heuristic approaches remain essential for modeling complex structures and large-scale chemical systems. Here, we present a heuristics-aided quantum chemical methodology applicable to complex chemical reaction networks such as those arising in cell metabolism and prebiotic chemistry. Chemical heuristics offer an expedient way of traversing high-dimensional reactive potential energy surfaces and are combined here with quantum chemical structure optimizations, which yield the structures and energies of the reaction intermediates and products. Application of heuristics-aided quantum chemical methodology to the formose reaction reproduces the experimentally observed reaction products, major reaction pathways, and autocatalytic cycles.

  1. Chemical Reactivity as Described by Quantum Chemical Methods

    Directory of Open Access Journals (Sweden)

    F. De Proft

    2002-04-01

    Full Text Available Abstract: Density Functional Theory is situated within the evolution of Quantum Chemistry as a facilitator of computations and a provider of new, chemical insights. The importance of the latter branch of DFT, conceptual DFT is highlighted following Parr's dictum "to calculate a molecule is not to understand it". An overview is given of the most important reactivity descriptors and the principles they are couched in. Examples are given on the evolution of the structure-property-wave function triangle which can be considered as the central paradigm of molecular quantum chemistry to (for many purposes a structure-property-density triangle. Both kinetic as well as thermodynamic aspects can be included when further linking reactivity to the property vertex. In the field of organic chemistry, the ab initio calculation of functional group properties and their use in studies on acidity and basicity is discussed together with the use of DFT descriptors to study the kinetics of SN2 reactions and the regioselectivity in Diels Alder reactions. Similarity in reactivity is illustrated via a study on peptide isosteres. In the field of inorganic chemistry non empirical studies of adsorption of small molecules in zeolite cages are discussed providing Henry constants and separation constants, the latter in remarkable good agreement with experiments. Possible refinements in a conceptual DFT context are presented. Finally an example from biochemistry is discussed : the influence of point mutations on the catalytic activity of subtilisin.

  2. Characterization of heterocyclic rings through quantum chemical topology.

    Science.gov (United States)

    Griffiths, Mark Z; Popelier, Paul L A

    2013-07-22

    Five-membered rings are found in a myriad of molecules important in a wide range of areas such as catalysis, nutrition, and drug and agrochemical design. Systematic insight into their largely unexplored chemical space benefits from first principle calculations presented here. This study comprehensively investigates a grand total of 764 different rings, all geometry optimized at the B3LYP/6-311+G(2d,p) level, from the perspective of Quantum Chemical Topology (QCT). For the first time, a 3D space of local topological properties was introduced, in order to characterize rings compactly. This space is called RCP space, after the so-called ring critical point. This space is analogous to BCP space, named after the bond critical point, which compactly and successfully characterizes a chemical bond. The relative positions of the rings in RCP space are determined by the nature of the ring scaffold, such as the heteroatoms within the ring or the number of π-bonds. The summed atomic QCT charges of the five ring atoms revealed five features (number and type of heteroatom, number of π-bonds, substituent and substitution site) that dictate a ring's net charge. Each feature independently contributes toward a ring's net charge. Each substituent has its own distinct and systematic effect on the ring's net charge, irrespective of the ring scaffold. Therefore, this work proves the possibility of designing a ring with specific properties by fine-tuning it through manipulation of these five features.

  3. Quantum critical matter. Quantum phase transitions with multiple dynamics and Weyl superconductors

    International Nuclear Information System (INIS)

    Meng, Tobias

    2012-01-01

    In this PhD thesis, the physics of quantum critical matter and exotic quantum state close to quantum phase transitions is investigated. We will focus on three different examples that highlight some of the interesting phenomena related to quantum phase transitions. Firstly, we discuss the physics of quantum phase transitions in quantum wires as a function of an external gate voltage when new subbands are activated. We find that at these transitions, strong correlations lead to the formation of an impenetrable gas of polarons, and identify criteria for possible instabilities in the spin- and charge sectors of the model. Our analysis is based on the combination of exact resummations, renormalization group techniques and Luttinger liquid approaches. Secondly, we turn to the physics of multiple divergent time scales close to a quantum critical point. Using an appropriately generalized renormalization group approach, we identify that the presence of multiple dynamics at a quantum phase transition can lead to the emergence of new critical scaling exponents and thus to the breakdown of the usual scaling schemes. We calculate the critical behavior of various thermodynamic properties and detail how unusual physics can arise. It is hoped that these results might be helpful for the interpretation of experimental scaling puzzles close to quantum critical points. Thirdly, we turn to the physics of topological transitions, and more precisely the physics of Weyl superconductors. The latter are the superconducting variant of the topologically non-trivial Weyl semimetals, and emerge at the quantum phase transition between a topological superconductor and a normal insulator upon perturbing the transition with a time reversal symmetry breaking perturbation, such as magnetism. We characterize the topological properties of Weyl superconductors and establish a topological phase diagram for a particular realization in heterostructures. We discuss the physics of vortices in Weyl

  4. Random walks, critical phenomena, and triviality in quantum field theory

    International Nuclear Information System (INIS)

    Fernandez, R.; Froehlich, J.; Sokal, A.D.

    1992-01-01

    The subject of this book is equilibrium statistical mechanics - in particular the theory of critical phenomena - and quantum field theory. A general review of the theory of critical phenomena in spin systems, field theories, and random-walk and random-surface models is presented. Among the more technical topics treated in this book, the central theme is the use of random-walk representations as a tool to derive correlation inequalities. The consequences of these inequalities for critical-exponent theory and the triviality question in quantum field theory are expounded in detail. The book contains some previously unpublished results. It addresses both the researcher and the graduate student in modern statistical mechanics and quantum field theory. (orig.)

  5. Universal post-quench prethermalization at a quantum critical point

    Science.gov (United States)

    Orth, Peter P.; Gagel, Pia; Schmalian, Joerg

    2015-03-01

    We consider an open system near a quantum critical point that is suddenly moved towards the critical point. The bath-dominated diffusive non-equilibrium dynamics after the quench is shown to follow scaling behavior, governed by a critical exponent that emerges in addition to the known equilibrium critical exponents. We determine this exponent and show that it describes universal prethermalized coarsening dynamics of the order parameter in an intermediate time regime. Implications of this quantum critical prethermalization are a powerlaw rise of order and correlations after an initial collapse of the equilibrium state and a crossover to thermalization that occurs arbitrarily late for sufficiently shallow quenches. [1] P. Gagel, P. P. Orth, J. Schmalian, Phys.Rev. Lett. (in press) arXiv:1406.6387

  6. Chemical dosimetry system for criticality accidents.

    Science.gov (United States)

    Miljanić, Saveta; Ilijas, Boris

    2004-01-01

    Ruder Bosković Institute (RBI) criticality dosimetry system consists of a chemical dosimetry system for measuring the total (neutron + gamma) dose, and a thermoluminescent (TL) dosimetry system for a separate determination of the gamma ray component. The use of the chemical dosemeter solution chlorobenzene-ethanol-trimethylpentane (CET) is based on the radiolytic formation of hydrochloric acid, which protonates a pH indicator, thymolsulphonphthalein. The high molar absorptivity of its red form at 552 nm is responsible for a high sensitivity of the system: doses in the range 0.2-15 Gy can be measured. The dosemeter has been designed as a glass ampoule filled with the CET solution and inserted into a pen-shaped plastic holder. For dose determinations, a newly constructed optoelectronic reader has been used. The RBI team took part in the International Intercomparison of Criticality Accident Dosimetry Systems at the SILENE Reactor, Valduc, June 2002, with the CET dosimetry system. For gamma ray dose determination TLD-700 TL detectors were used. The results obtained with CET dosemeter show very good agreement with the reference values.

  7. Chemical applications of molecular quantum theory

    International Nuclear Information System (INIS)

    Ungemach, S.R.

    1977-09-01

    Molecular systems of chemical interest are investigated with the aid of molecular quantum theory. The self-consistent field (SCF) method is used to predict the molecular structures of ClF 2 , ClF 4 and Cl 3 radicals, and the ions ClF 2 + , ClF 2 - , ClF 4 + and ClF 4 - . The ClF 2 and Cl 3 radicals are predicted to be bent with bond angles of 145.2 0 and 158.6 0 , respectively, while the ions ClF 2 + and ClF 2 - are predicted to be bent with a bond angle of 97.4 0 and linear, respectively. The geometry predictions for the ClF 4 radical and the ClF 4 + ion are found to be notably basis set dependent. The ClF 4 - ion is predicted to be square-planar. Multi-configuration self-consistent field (MCSCF) calculations have yielded the dipole moment function for the 1 sigma + state of HI, which qualitatively confirms the experimental finding that the dipole derivative at R/sub e/ is negative. The 2 sigma + F + H 2 potential energy surface is studied extensively with the configuration interaction (CI) method. The most complete calculations yield an activation energy of 2.74 kcal/mole and an exothermicity of 30.0 kcal/mole. The production of a potential energy surface of ''chemical accuracy'' for this system is found to be more difficult than previously believed. The simplest hydrophobic model, the water-methane system, is studied with the SCF method in order to determine the nature and magnitude of the interaction. The most favorable geometric arrangement corresponds to an attraction of 0.5 kcal/mole

  8. Chemical sensors based on quantum cascade lasers

    Science.gov (United States)

    Tittel, Frank K.; Kosterev, Anatoliy A.; Rochat, Michel; Beck, Mattias; Faist, Jerome

    2002-09-01

    There is an increasing need in many chemical sensing applications ranging from industrial process control to environmental science and medical diagnostics for fast, sensitive, and selective gas detection based on laser spectroscopy. The recent availability of novel pulsed and cw quantum cascade distributed feedback (QC-DFB) lasers as mid-infrared spectroscopic sources address this need. A number of spectroscopic techniques have been demonstrated. For example, the authors have employed QC-DFB lasers for the monitoring and quantification of several trace gases and isotopic species in ambient air at ppmv and ppbv levels by means of direct absorption, wavelength modulation, cavity enhanced and cavity ringdown spectroscopy. In this work, pulsed thermoelectrically cooled QC-DFB lasers operating at ~15.6 μm were characterized for spectroscopic gas sensing applications. A new method for wavelength scanning based on the repetition rate modulation was developed. A non-wavelength-selective pyroelectric detector was incorporated in the gas sensor giving an advantage of room-temperature operation and low cost. Absorption lines of CO2 and H2O were observed in ambient air providing information about the concentration of these species.

  9. Field-induced magnetic instability and quantum criticality in the antiferromagnet CeCu2Ge2.

    Science.gov (United States)

    Liu, Yi; Xie, Donghua; Wang, Xiaoying; Zhu, Kangwei; Yang, Ruilong

    2016-01-13

    The magnetic quantum criticality in strongly correlated electron systems has been considered to be closely related with the occurrence of unconventional superconductivity. Control parameters such as magnetic field, pressure or chemical doping are frequently used to externally tune the quantum phase transition for a deeper understanding. Here we report the research of a field-induced quantum phase transition using conventional bulk physical property measurements in the archetypal antiferromagnet CeCu2Ge2, which becomes superconductive under a pressure of about 10 GPa with Tc ~ 0.64 K. We offer strong evidence that short-range dynamic correlations start appearing above a magnetic field of about 5 T. Our demonstrations of the magnetic instability and the field-induced quantum phase transition are crucial for the quantum criticality, which may open a new route in experimental investigations of the quantum phase transition in heavy-fermion systems.

  10. Black holes as critical point of quantum phase transition.

    Science.gov (United States)

    Dvali, Gia; Gomez, Cesar

    We reformulate the quantum black hole portrait in the language of modern condensed matter physics. We show that black holes can be understood as a graviton Bose-Einstein condensate at the critical point of a quantum phase transition, identical to what has been observed in systems of cold atoms. The Bogoliubov modes that become degenerate and nearly gapless at this point are the holographic quantum degrees of freedom responsible for the black hole entropy and the information storage. They have no (semi)classical counterparts and become inaccessible in this limit. These findings indicate a deep connection between the seemingly remote systems and suggest a new quantum foundation of holography. They also open an intriguing possibility of simulating black hole information processing in table-top labs.

  11. Quantum critical phenomena and conformal invariance

    International Nuclear Information System (INIS)

    Zhe Chang.

    1995-05-01

    We show that the Abelian bosonization of continuum limit of the 1D Hubbard model corresponds to the 2D explicitly conformal invariant Gaussian model at weak coupling limit. A universality argument is used to extend the equivalence to an entire segment of the critical line of the strongly correlated electron system. An integral equation satisfied by the mapping function between critical lines of the 1D Hubbard model and 2D Gaussian model is obtained and then solved in some limiting cases. By making use of the fact that the free Hubbard system reduces to four fermions and each of them is related to a c = 1/2 conformal field theory, we present exactly the partition function of the Hubbard model on a finite 1D lattice. (author). 16 refs

  12. Universal postquench coarsening and aging at a quantum critical point

    Science.gov (United States)

    Gagel, Pia; Orth, Peter P.; Schmalian, Jörg

    2015-09-01

    The nonequilibrium dynamics of a system that is located in the vicinity of a quantum critical point is affected by the critical slowing down of order-parameter correlations with the potential for novel out-of-equilibrium universality. After a quantum quench, i.e., a sudden change of a parameter in the Hamiltonian, such a system is expected to almost instantly fall out of equilibrium and undergo aging dynamics, i.e., dynamics that depends on the time passed since the quench. Investigating the quantum dynamics of an N -component φ4 model coupled to an external bath, we determine this universal aging and demonstrate that the system undergoes a coarsening, governed by a critical exponent that is unrelated to the equilibrium exponents of the system. We analyze this behavior in the large-N limit, which is complementary to our earlier renormalization-group analysis, allowing in particular the direct investigation of the order-parameter dynamics in the symmetry-broken phase and at the upper critical dimension. By connecting the long-time limit of fluctuations and response, we introduce a distribution function that shows that the system remains nonthermal and exhibits quantum coherence even on long time scales.

  13. Metatheoretical critics on current trends in Quantum Mechanics

    Directory of Open Access Journals (Sweden)

    Carlos C. Aranda

    2014-06-01

    Full Text Available Is our purpose in this article to review several approaches to modern problems in quantum mechanics from a critical point of view using the approximation of the traditional mathematical thinking. Nevertheless we point out several natural questions that arise in abstract mathematical reasoning.

  14. Electron self-trapping at quantum and classical critical points

    NARCIS (Netherlands)

    Auslender, M.I.; Katsnelson, M.I.

    2006-01-01

    Using Feynman path integral technique estimations of the ground state energy have been found for a conduction electron interacting with order parameter fluctuations near quantum critical points. In some cases only singular perturbation theory in the coupling constant emerges for the electron ground

  15. Critical current in the Integral Quantum Hall Effect

    International Nuclear Information System (INIS)

    Kostadinov, I.Z.

    1985-11-01

    A multiparticle theory of the Integral Quantum Hall Effect (IQHE) was constructed operating with pairs wave function as an order parameter. The IQHE is described with bosonic macroscopic states while the fractional QHE with fermionic ones. The calculation of the critical current and Hall conductivity temperature dependence is presented. (author)

  16. Reggeon quantum mechanics: a critical discussion

    International Nuclear Information System (INIS)

    Ciafaloni, M.; Le Bellac, M.; Rossi, G.C.

    1977-01-01

    The quantum-mechanical problem of reggeon field theory in zero transverse dimensions is re-examined in order to set up a precise mathematical framework for the case μ=α(0)-1>0. The authors establish a Hamiltonian formulation in a Hilbert space for μ 2 (0, infinity) space. It is proved that the S-matrix and the pomeron Green functions, at fixed rapidity Y and triple-pomeron coupling lambda not equal to 0, have a spectral decomposition and are analytic in μ for -infinity 0, most of the qualitative results found by previous authors are confirmed and in particular the tunnelling shift [approximately exp(-μ 2 /2lambda 2 )] setting the scale for the asymptotic behaviour in Y. In the classical limit of lambda/μ small it is found that the action, for μ>0, develops a singularity in Y at some value Ysub(c). Arguements are given to show that for Y approximately Ysub(c) perturbation theory breaks shown. Most of these results are shown to be stable against the addition of a small quartic coupling of the simplest type [lambda'(anti psipsi) 2 ] up to the 'magic' value lambda'=lambda 2 /μ. The existence of a level crossing at this value is confirmed by an analytic continuation in lambda'. (Auth.)

  17. Metallic magnets without inversion symmetry and antiferromagnetic quantum critical points

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, I.A.

    2006-07-01

    This thesis focusses on two classes of systems that exhibit non-Fermi liquid behaviour in experiments: we investigated aspects of chiral ferromagnets and of antiferromagnetic metals close to a quantum critical point. In chiral ferromagnets, the absence of inversion symmetry makes spin-orbit coupling possible, which leads to a helical modulation of the ferromagnetically ordered state. We studied the motion of electrons in the magnetically ordered state of a metal without inversion symmetry by calculating their generic band-structure. We found that spin-orbit coupling, although weak, has a profound effect on the shape of the Fermi surface: On a large portion of the Fermi surface the electron motion parallel to the helix practically stops. Signatures of this effect can be expected to show up in measurements of the anomalous Hall effect. Recent neutron scattering experiments uncovered the existence of a peculiar kind of partial order in a region of the phase diagram adjacent to the ordered state of the chiral ferromagnet MnSi. Starting from the premise that this partially ordered state is a thermodynamically distinct phase, we investigated an extended Ginzburg-Landau theory for chiral ferromagnets. In a certain parameter regime of the Ginzburg-Landau theory we identified crystalline phases that are reminiscent of the so-called blue phases in liquid crystals. Many antiferromagnetic heavy-fermion systems can be tuned into a regime where they exhibit non-Fermi liquid exponents in the temperature dependence of thermodynamic quantities such as the specific heat capacity; this behaviour could be due to a quantum critical point. If the quantum critical behaviour is field-induced, the external field does not only suppress antiferromagnetism but also induces spin precession and thereby influences the dynamics of the order parameter. We investigated the quantum critical behavior of clean antiferromagnetic metals subject to a static, spatially uniform external magnetic field. We

  18. Quantum critical spin-2 chain with emergent SU(3) symmetry.

    Science.gov (United States)

    Chen, Pochung; Xue, Zhi-Long; McCulloch, I P; Chung, Ming-Chiang; Huang, Chao-Chun; Yip, S-K

    2015-04-10

    We study the quantum critical phase of an SU(2) symmetric spin-2 chain obtained from spin-2 bosons in a one-dimensional lattice. We obtain the scaling of the finite-size energies and entanglement entropy by exact diagonalization and density-matrix renormalization group methods. From the numerical results of the energy spectra, central charge, and scaling dimension we identify the conformal field theory describing the whole critical phase to be the SU(3)_{1} Wess-Zumino-Witten model. We find that, while the Hamiltonian is only SU(2) invariant, in this critical phase there is an emergent SU(3) symmetry in the thermodynamic limit.

  19. Quantum critical singularities in two-dimensional metallic XY ferromagnets

    Science.gov (United States)

    Varma, Chandra M.; Gannon, W. J.; Aronson, M. C.; Rodriguez-Rivera, J. A.; Qiu, Y.

    2018-02-01

    An important problem in contemporary physics concerns quantum-critical fluctuations in metals. A scaling function for the momentum, frequency, temperature, and magnetic field dependence of the correlation function near a 2D-ferromagnetic quantum-critical point (QCP) is constructed, and its singularities are determined by comparing to the recent calculations of the correlation functions of the dissipative quantum XY model (DQXY). The calculations are motivated by the measured properties of the metallic compound YFe2Al10 , which is a realization of the DQXY model in 2D. The frequency, temperature, and magnetic field dependence of the scaling function as well as the singularities measured in the experiments are given by the theory without adjustable exponents. The same model is applicable to the superconductor-insulator transitions, classes of metallic AFM-QCPs, and as fluctuations of the loop-current ordered state in hole-doped cuprates. The results presented here lend credence to the solution found for the 2D-DQXY model and its applications in understanding quantum-critical properties of diverse systems.

  20. Characterization of the critical submanifolds in quantum ensemble control landscapes

    International Nuclear Information System (INIS)

    Wu Rebing; Rabitz, Herschel; Hsieh, Michael

    2008-01-01

    The quantum control landscape is defined as the functional that maps the control variables to the expectation values of an observable over the ensemble of quantum systems. Analyzing the topology of such landscapes is important for understanding the origins of the increasing number of laboratory successes in the optimal control of quantum processes. This paper proposes a simple scheme to compute the characteristics of the critical topology of the quantum ensemble control landscapes showing that the set of disjoint critical submanifolds one-to-one corresponds to a finite number of contingency tables that solely depend on the degeneracy structure of the eigenvalues of the initial system density matrix and the observable whose expectation value is to be maximized. The landscape characteristics can be calculated as functions of the table entries, including the dimensions and the numbers of positive and negative eigenvalues of the Hessian quadratic form of each of the connected components of the critical submanifolds. Typical examples are given to illustrate the effectiveness of this method

  1. Quantum Triple Point and Quantum Critical End Points in Metallic Magnets.

    Science.gov (United States)

    Belitz, D; Kirkpatrick, T R

    2017-12-29

    In low-temperature metallic magnets, ferromagnetic (FM) and antiferromagnetic (AFM) orders can exist, adjacent to one another or concurrently, in the phase diagram of a single system. We show that universal quantum effects qualitatively alter the known phase diagrams for classical magnets. They shrink the region of concurrent FM and AFM order, change various transitions from second to first order, and, in the presence of a magnetic field, lead to either a quantum triple point where the FM, AFM, and paramagnetic phases all coexist or a quantum critical end point.

  2. Entanglement dynamics in critical random quantum Ising chain with perturbations

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Yichen, E-mail: ychuang@caltech.edu

    2017-05-15

    We simulate the entanglement dynamics in a critical random quantum Ising chain with generic perturbations using the time-evolving block decimation algorithm. Starting from a product state, we observe super-logarithmic growth of entanglement entropy with time. The numerical result is consistent with the analytical prediction of Vosk and Altman using a real-space renormalization group technique. - Highlights: • We study the dynamical quantum phase transition between many-body localized phases. • We simulate the dynamics of a very long random spin chain with matrix product states. • We observe numerically super-logarithmic growth of entanglement entropy with time.

  3. Superconductivity versus quantum criticality: Effects of thermal fluctuations

    Science.gov (United States)

    Wang, Huajia; Wang, Yuxuan; Torroba, Gonzalo

    2018-02-01

    We study the interplay between superconductivity and non-Fermi liquid behavior of a Fermi surface coupled to a massless SU(N ) matrix boson near the quantum critical point. The presence of thermal infrared singularities in both the fermionic self-energy and the gap equation invalidates the Eliashberg approximation, and makes the quantum-critical pairing problem qualitatively different from that at zero temperature. Taking the large N limit, we solve the gap equation beyond the Eliashberg approximation, and obtain the superconducting temperature Tc as a function of N . Our results show an anomalous scaling between the zero-temperature gap and Tc. For N greater than a critical value, we find that Tc vanishes with a Berezinskii-Kosterlitz-Thouless scaling behavior, and the system retains non-Fermi liquid behavior down to zero temperature. This confirms and extends previous renormalization-group analyses done at T =0 , and provides a controlled example of a naked quantum critical point. We discuss the crucial role of thermal fluctuations in relating our results with earlier work where superconductivity always develops due to the special role of the first Matsubara frequency.

  4. Quantum Critical “Opalescence” around Metal-Insulator Transitions

    Science.gov (United States)

    Misawa, Takahiro; Yamaji, Youhei; Imada, Masatoshi

    2006-08-01

    Divergent carrier-density fluctuations equivalent to the critical opalescence of gas-liquid transition emerge around a metal-insulator critical point at a finite temperature. In contrast to the gas-liquid transitions, however, the critical temperatures can be lowered to zero, which offers a challenging quantum phase transition. We present a microscopic description of such quantum critical phenomena in two dimensions. The conventional scheme of phase transitions by Ginzburg, Landau, and Wilson is violated because of its topological nature. It offers a clear insight into the criticalities of metal-insulator transitions (MIT) associated with Mott or charge-order transitions. Fermi degeneracy involving the diverging density fluctuations generates emergent phenomena near the endpoint of the first-order MIT and must shed new light on remarkable phenomena found in correlated metals such as unconventional cuprate superconductors. It indeed accounts for the otherwise puzzling criticality of the Mott transition recently discovered in an organic conductor. We propose to accurately measure enhanced dielectric fluctuations at small wave numbers.

  5. Quantum chemical calculations of using density functional theory ...

    Indian Academy of Sciences (India)

    K RACKESH JAWAHER

    2018-02-15

    Feb 15, 2018 ... Quantum chemical calculations have been employed to study the molecular effects produced by. Cr2O3/SnO2 optimised structure. ... are exploited in solar cells [2], high-capacity lithium– storage [3], solid-state chemical ..... bond distance of metal–oxygen is positively (0.5 Е) deviated to oxygen–oxygen ...

  6. Thermal conductivity at a disordered quantum critical point

    International Nuclear Information System (INIS)

    Hartnoll, Sean A.; Ramirez, David M.; Santos, Jorge E.

    2016-01-01

    Strongly disordered and strongly interacting quantum critical points are difficult to access with conventional field theoretic methods. They are, however, both experimentally important and theoretically interesting. In particular, they are expected to realize universal incoherent transport. Such disordered quantum critical theories have recently been constructed holographically by deforming a CFT by marginally relevant disorder. In this paper we find additional disordered fixed points via relevant disordered deformations of a holographic CFT. Using recently developed methods in holographic transport, we characterize the thermal conductivity in both sets of theories in 1+1 dimensions. The thermal conductivity is found to tend to a constant at low temperatures in one class of fixed points, and to scale as T"0"."3 in the other. Furthermore, in all cases the thermal conductivity exhibits discrete scale invariance, with logarithmic in temperature oscillations superimposed on the low temperature scaling behavior. At no point do we use the replica trick.

  7. Critical indices for the Yukawa2 quantum field theory

    International Nuclear Information System (INIS)

    Bonetto, F.

    1997-01-01

    The understanding of the Yukawa 2 quantum field theory is still incomplete if the fermionic mass is much smaller than the coupling. We analyze the Schwinger functions for small coupling uniformly in the mass and we find that the asymptotic behavior of the two-point Schwinger function is anomalous and described by two critical indices, related to the renormalization of the mass and of the wave function. The indices are explicitly computed by convergent series in the coupling. (orig.)

  8. Entanglement entropy of 2D conformal quantum critical points: hearing the shape of a quantum drum.

    Science.gov (United States)

    Fradkin, Eduardo; Moore, Joel E

    2006-08-04

    The entanglement entropy of a pure quantum state of a bipartite system A union or logical sumB is defined as the von Neumann entropy of the reduced density matrix obtained by tracing over one of the two parts. In one dimension, the entanglement of critical ground states diverges logarithmically in the subsystem size, with a universal coefficient that for conformally invariant critical points is related to the central charge of the conformal field theory. We find that the entanglement entropy of a standard class of z=2 conformal quantum critical points in two spatial dimensions, in addition to a nonuniversal "area law" contribution linear in the size of the AB boundary, generically has a universal logarithmically divergent correction, which is completely determined by the geometry of the partition and by the central charge of the field theory that describes the critical wave function.

  9. Critical reflections on the Chemical Leasing concept

    NARCIS (Netherlands)

    Lozano, Rodrigo; Carpenter, Angela; Lozano, Francisco J.

    Chemical Leasing has been developed as a collaborative business model to complement the two main approaches (policy initiatives and scientific/ technological) used to foster green chemistry and sustainable chemistry. Chemical Leasing is based on using chemicals more efficiently, reducing waste, and

  10. Anomalous quantum critical spin dynamics in YFe2Al10

    Science.gov (United States)

    Huang, K.; Tan, C.; Zhang, J.; Ding, Z.; MacLaughlin, D. E.; Bernal, O. O.; Ho, P.-C.; Baines, C.; Wu, L. S.; Aronson, M. C.; Shu, L.

    2018-04-01

    We report results of a muon spin relaxation (μ SR ) study of YFe2Al10 , a quasi-two-dimensional (2D) nearly ferromagnetic metal in which unconventional quantum critical behavior is observed. No static Fe2 + magnetism, with or without long-range order, is found down to 19 mK. The dynamic muon spin relaxation rate λ exhibits power-law divergences in temperature and magnetic field, the latter for fields that are too weak to affect the electronic spin dynamics directly. We attribute this to the proportionality of λ (ωμ,T ) to the dynamic structure factor S (ωμ,T ) , where ωμ≈105-107s-1 is the muon Zeeman frequency. These results suggest critical divergences of S (ωμ,T ) in both temperature and frequency. Power-law scaling and a 2D dissipative quantum XY model both yield forms for S (ω ,T ) that agree with neutron scattering data (ω ≈1012s-1 ). Extrapolation to μ SR frequencies agrees semiquantitatively with the observed temperature dependence of λ (ωμ,T ) , but predicts frequency independence for ωμ≪T , in extreme disagreement with experiment. We conclude that the quantum critical spin dynamics of YFe2Al10 is not well understood at low frequencies.

  11. Entropy Flow Through Near-Critical Quantum Junctions

    Science.gov (United States)

    Friedan, Daniel

    2017-05-01

    This is the continuation of Friedan (J Stat Phys, 2017. doi: 10.1007/s10955-017-1752-8). Elementary formulas are derived for the flow of entropy through a circuit junction in a near-critical quantum circuit close to equilibrium, based on the structure of the energy-momentum tensor at the junction. The entropic admittance of a near-critical junction in a bulk-critical circuit is expressed in terms of commutators of the chiral entropy currents. The entropic admittance at low frequency, divided by the frequency, gives the change of the junction entropy with temperature—the entropic "capacitance". As an example, and as a check on the formalism, the entropic admittance is calculated explicitly for junctions in bulk-critical quantum Ising circuits (free fermions, massless in the bulk), in terms of the reflection matrix of the junction. The half-bit of information capacity per end of critical Ising wire is re-derived by integrating the entropic "capacitance" with respect to temperature, from T=0 to T=∞.

  12. Isomorphism of critical and off-critical operator spaces in two-dimensional quantum field theory

    Energy Technology Data Exchange (ETDEWEB)

    Delfino, G. [International School of Advanced Studies (SISSA), Trieste (Italy)]|[INFN sezione di Trieste (Italy); Niccoli, G. [Univ. de Cergy-Pontoise (France). LPTM

    2007-12-15

    For the simplest quantum field theory originating from a non-trivial fixed point of the renormalization group, the Lee-Yang model, we show that the operator space determined by the particle dynamics in the massive phase and that prescribed by conformal symmetry at criticality coincide. (orig.)

  13. Defect production in nonlinear quench across a quantum critical point.

    Science.gov (United States)

    Sen, Diptiman; Sengupta, K; Mondal, Shreyoshi

    2008-07-04

    We show that the defect density n, for a slow nonlinear power-law quench with a rate tau(-1) and an exponent alpha>0, which takes the system through a critical point characterized by correlation length and dynamical critical exponents nu and z, scales as n approximately tau(-alphanud/(alphaznu+1)) [n approximately (alphag((alpha-1)/alpha)/tau)(nud/(znu+1))] if the quench takes the system across the critical point at time t=0 [t=t(0) not = 0], where g is a nonuniversal constant and d is the system dimension. These scaling laws constitute the first theoretical results for defect production in nonlinear quenches across quantum critical points and reproduce their well-known counterpart for a linear quench (alpha=1) as a special case. We supplement our results with numerical studies of well-known models and suggest experiments to test our theory.

  14. Quantum Chemical Approach to Estimating the Thermodynamics of Metabolic Reactions

    OpenAIRE

    Adrian Jinich; Dmitrij Rappoport; Ian Dunn; Benjamin Sanchez-Lengeling; Roberto Olivares-Amaya; Elad Noor; Arren Bar Even; Alán Aspuru-Guzik

    2014-01-01

    Thermodynamics plays an increasingly important role in modeling and engineering metabolism. We present the first nonempirical computational method for estimating standard Gibbs reaction energies of metabolic reactions based on quantum chemistry, which can help fill in the gaps in the existing thermodynamic data. When applied to a test set of reactions from core metabolism, the quantum chemical approach is comparable in accuracy to group contribution methods for isomerization and group transfe...

  15. Critical technologies: The role of chemistry and chemical engineering

    International Nuclear Information System (INIS)

    1992-01-01

    The purpose of this report is to identify and illustrate key contributions of chemical and chemical engineering research to the development of technologies that have been deemed critical to the economy, security, and well-being of our nation. The report surveys a wide range of vital technologies that are heavily reliant or even critically dependent on chemical or chemical engineering research. Examples were taken from the fields of materials, manufacturing, energy, transportation, public health, information and communications, and the environment. While loosely following the structure of the critical technologies report of the NCTP, our committee decided on a different approach, that of using examples backed up by extensive illustrations

  16. Quantum correlation approach to criticality in the XX spin chain with multiple interaction

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, W.W., E-mail: weien.cheng@gmail.com [Institute of Signal Processing and Transmission, Nanjing University of Posts and Telecommunication, Nanjing 210003 (China); Department of Physics, Hubei Normal University, Huangshi 435002 (China); Key Lab of Broadband Wireless Communication and Sensor Network Technology, Ministry of Education (China); Shan, C.J. [Department of Physics, Hubei Normal University, Huangshi 435002 (China); Sheng, Y.B.; Gong, L.Y.; Zhao, S.M. [Institute of Signal Processing and Transmission, Nanjing University of Posts and Telecommunication, Nanjing 210003 (China); Key Lab of Broadband Wireless Communication and Sensor Network Technology, Ministry of Education (China)

    2012-09-01

    We investigate the quantum critical behavior in the XX spin chain with a XZY-YZX type multiple interaction by means of quantum correlation (Concurrence C, quantum discord D{sub Q} and geometric discord D{sub G}). Around the critical point, the values of these quantum correlations and corresponding derivatives are investigated numerically and analytically. The results show that the non-analyticity property of the concurrence cannot signal well the quantum phase transition, but both the quantum discord and geometric discord can characterize the critical behavior in such model exactly.

  17. Single-copy entanglement in critical quantum spin chains

    International Nuclear Information System (INIS)

    Eisert, J.; Cramer, M.

    2005-01-01

    We consider the single-copy entanglement as a quantity to assess quantum correlations in the ground state in quantum many-body systems. We show for a large class of models that already on the level of single specimens of spin chains, criticality is accompanied with the possibility of distilling a maximally entangled state of arbitrary dimension from a sufficiently large block deterministically, with local operations and classical communication. These analytical results--which refine previous results on the divergence of block entropy as the rate at which maximally entangled pairs can be distilled from many identically prepared chains--are made quantitative for general isotropic translationally invariant spin chains that can be mapped onto a quasifree fermionic system, and for the anisotropic XY model. For the XX model, we provide the asymptotic scaling of ∼(1/6)log 2 (L), and contrast it with the block entropy

  18. Quantum Chemical: New name and focus for National Distillers

    Energy Technology Data Exchange (ETDEWEB)

    Reisch, M.S.

    1988-03-14

    This article explains why the National Distillers and Chemical Corporation has narrowed its focus on petrochemicals and energy. At one time the company had diversified into wine and spirits, insurance, metals, chemicals and energy. However, the company decided to reexamine where its commitments should be. It decided to stick with chemicals and energy because it could be a leader in these fields and not in its other interests. The article explains how the new company, Quantum Chemical, is doing and where it is headed in the future.

  19. Engineering Surface Critical Behavior of (2 +1 )-Dimensional O(3) Quantum Critical Points

    Science.gov (United States)

    Ding, Chengxiang; Zhang, Long; Guo, Wenan

    2018-06-01

    Surface critical behavior (SCB) refers to the singularities of physical quantities on the surface at the bulk phase transition. It is closely related to and even richer than the bulk critical behavior. In this work, we show that three types of SCB universality are realized in the dimerized Heisenberg models at the (2 +1 )-dimensional O(3) quantum critical points by engineering the surface configurations. The ordinary transition happens if the surface is gapped in the bulk disordered phase, while the gapless surface state generally leads to the multicritical special transition, even though the latter is precluded in classical phase transitions because the surface is in the lower critical dimension. An extraordinary transition is induced by the ferrimagnetic order on the surface of the staggered Heisenberg model, in which the surface critical exponents violate the results of the scaling theory and thus seriously challenge our current understanding of extraordinary transitions.

  20. Quantum chemical approach to estimating the thermodynamics of metabolic reactions.

    Science.gov (United States)

    Jinich, Adrian; Rappoport, Dmitrij; Dunn, Ian; Sanchez-Lengeling, Benjamin; Olivares-Amaya, Roberto; Noor, Elad; Even, Arren Bar; Aspuru-Guzik, Alán

    2014-11-12

    Thermodynamics plays an increasingly important role in modeling and engineering metabolism. We present the first nonempirical computational method for estimating standard Gibbs reaction energies of metabolic reactions based on quantum chemistry, which can help fill in the gaps in the existing thermodynamic data. When applied to a test set of reactions from core metabolism, the quantum chemical approach is comparable in accuracy to group contribution methods for isomerization and group transfer reactions and for reactions not including multiply charged anions. The errors in standard Gibbs reaction energy estimates are correlated with the charges of the participating molecules. The quantum chemical approach is amenable to systematic improvements and holds potential for providing thermodynamic data for all of metabolism.

  1. Nonequilibrium dynamic critical scaling of the quantum Ising chain.

    Science.gov (United States)

    Kolodrubetz, Michael; Clark, Bryan K; Huse, David A

    2012-07-06

    We solve for the time-dependent finite-size scaling functions of the one-dimensional transverse-field Ising chain during a linear-in-time ramp of the field through the quantum critical point. We then simulate Mott-insulating bosons in a tilted potential, an experimentally studied system in the same equilibrium universality class, and demonstrate that universality holds for the dynamics as well. We find qualitatively athermal features of the scaling functions, such as negative spin correlations, and we show that they should be robustly observable within present cold atom experiments.

  2. Quantum chemical investigation of mechanisms of silane oxidation

    DEFF Research Database (Denmark)

    Mader, Mary M.; Norrby, Per-Ola

    2001-01-01

    Several mechanisms for the peroxide oxidation of organosilanes to alcohols are compared by quantum chemical calculations, including solvation with the PCM method. Without doubt, the reaction proceeds via anionic, pentacoordinate silicate species, but a profound difference is found between in vacuo...

  3. Experimental and quantum chemical studies on corrosion inhibition ...

    Indian Academy of Sciences (India)

    Abstract. The corrosion inhibition effect of fluconazole (FLU) was investigated on steel in 1 M hydrochloric acid solution. Weight loss measurements and atomic force microscope analysis were utilized to investigate the corrosion inhibition properties and film formation behaviour of FLU. Quantum chemical approach was also ...

  4. Quantum Dots Embedded in Graphene Nanoribbons by Chemical Substitution

    DEFF Research Database (Denmark)

    Carbonell-Sanroma, Eduard; Brandimarte, Pedro; Balog, Richard

    2017-01-01

    Bottom-up chemical reactions of selected molecular precursors on a gold surface can produce high quality graphene nanoribbons (GNRs). Here, we report on the formation of quantum dots embedded in an armchair GNR by substitutional inclusion of pairs of boron atoms into the GNR backbone. The boron...

  5. Experimental and quantum chemical studies on corrosion inhibition

    Indian Academy of Sciences (India)

    The corrosion inhibition effect of fluconazole (FLU) was investigated on steel in 1 M hydrochloric acid solution. Weight loss measurements and atomic force microscope analysis were utilized to investigate the corrosion inhibition properties and film formation behaviour of FLU. Quantum chemical approach was also used to ...

  6. Quantum critical behaviour of the plateau-insulator transition in the quantum Hall regime

    International Nuclear Information System (INIS)

    Visser, A de; Ponomarenko, L A; Galistu, G; Lang, D T N de; Pruisken, A M M; Zeitler, U; Maude, D

    2006-01-01

    High-field magnetotransport experiments provide an excellent tool to investigate the plateau-insulator phase transition in the integral quantum Hall effect. Here we review recent low-temperature high-field magnetotransport studies carried out on several InGaAs/InP heterostructures and an InGaAs/GaAs quantum well. We find that the longitudinal resistivity ρ xx near the critical filling factor ν c ∼ 0.5 follows the universal scaling law ρ xx (ν, T) ∝ exp(-Δν/(T/T 0 ) κ ), where Δν = ν-ν c . The critical exponent κ equals 0.56 ± 0.02, which indicates that the plateau-insulator transition falls in a non-Fermi liquid universality class

  7. Quantum Critical Point revisited by the Dynamical Mean Field Theory

    Science.gov (United States)

    Xu, Wenhu; Kotliar, Gabriel; Tsvelik, Alexei

    Dynamical mean field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. The QCP is characterized by a universal scaling form of the self energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low energy kink and the high energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high energy antiferromagnetic paramagnons. We use the frequency dependent four-point correlation function of spin operators to calculate the momentum dependent correction to the electron self energy. Our results reveal a substantial difference with the calculations based on the Spin-Fermion model which indicates that the frequency dependence of the the quasiparitcle-paramagnon vertices is an important factor. The authors are supported by Center for Computational Design of Functional Strongly Correlated Materials and Theoretical Spectroscopy under DOE Grant DE-FOA-0001276.

  8. Quantum critical point revisited by dynamical mean-field theory

    Science.gov (United States)

    Xu, Wenhu; Kotliar, Gabriel; Tsvelik, Alexei M.

    2017-03-01

    Dynamical mean-field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. The QCP is characterized by a universal scaling form of the self-energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low-energy kink and the high-energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high-energy antiferromagnetic paramagnons. We use the frequency-dependent four-point correlation function of spin operators to calculate the momentum-dependent correction to the electron self-energy. By comparing with the calculations based on the spin-fermion model, our results indicate the frequency dependence of the quasiparticle-paramagnon vertices is an important factor to capture the momentum dependence in quasiparticle scattering.

  9. Quantum critical point revisited by dynamical mean-field theory

    International Nuclear Information System (INIS)

    Xu, Wenhu; Kotliar, Gabriel; Rutgers University, Piscataway, NJ; Tsvelik, Alexei M.

    2017-01-01

    Dynamical mean-field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. We characterize the QCP by a universal scaling form of the self-energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low-energy kink and the high-energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high-energy antiferromagnetic paramagnons. Here, we use the frequency-dependent four-point correlation function of spin operators to calculate the momentum-dependent correction to the electron self-energy. Furthermore, by comparing with the calculations based on the spin-fermion model, our results indicate the frequency dependence of the quasiparticle-paramagnon vertices is an important factor to capture the momentum dependence in quasiparticle scattering.

  10. Critical exponents for the Reggeon quantum spin model

    International Nuclear Information System (INIS)

    Brower, R.C.; Furman, M.A.

    1978-01-01

    The Reggeon quantum spin (RQS) model on the transverse lattice in D dimensional impact parameter space has been conjectured to have the same critical behaviour as the Reggeon field theory (RFT). Thus from a high 'temperature' series of ten (D=2) and twenty (D=1) terms for the RQS model the authors extrapolate to the critical temperature T=Tsub(c) by Pade approximants to obtain the exponents eta=0.238 +- 0.008, z=1.16 +- 0.01, γ=1.271 +- 0.007 for D=2 and eta=0.317 +- 0.002, z=1.272 +- 0.007, γ=1.736 +- 0.001, lambda=0.57 +- 0.03 for D=1. These exponents naturally interpolate between the D=0 and D=4-epsilon results for RFT as expected on the basis of the universality conjecture. (Auth.)

  11. Quantum critical scaling for field-induced quantum phase transition in a periodic Anderson-like model polymer chain

    Energy Technology Data Exchange (ETDEWEB)

    Ding, L.J., E-mail: dinglinjie82@126.com; Zhong, Y.

    2017-07-15

    Highlights: • The quantum critical scaling is investigated by Green’s function theory. • The obtained power-law critical exponents (β, δ and α) obey the critical scaling relation α + β(1 + δ) = 2. • The scaling hypothesis equations are proposed to verify the scaling analysis. - Abstract: The quantum phase transition and thermodynamics of a periodic Anderson-like polymer chain in a magnetic field are investigated by Green’s function theory. The T-h phase diagram is explored, wherein a crossover temperature T{sup ∗} denoting the gapless phase crossover into quantum critical regimes, smoothly connects near the critical fields to the universal linear line T{sup ∗} ∼ (h − h{sub c,s}), and ends at h{sub c,s}, providing a new route to capture quantum critical point (QCP). The quantum critical scaling around QCPs is demonstrated by analyzing magnetization, specific heat and Grüneisen parameter Γ{sub h}, which provide direct access to distill the power-law critical exponents (β, δ and α) obeying the critical scaling relation α + β(1 + δ) = 2, analogous to the quantum spin system. Furthermore, scaling hypothesis equations are proposed to check the scaling analysis, for which all the data collapse onto a single curve or two independent branches for the plot against an appropriate scaling variable, indicating the self-consistency and reliability of the obtained critical exponents.

  12. Use of ab initio quantum chemical methods in battery technology

    Energy Technology Data Exchange (ETDEWEB)

    Deiss, E [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1997-06-01

    Ab initio quantum chemistry can nowadays predict physical and chemical properties of molecules and solids. An attempt should be made to use this tool more widely for predicting technologically favourable materials. To demonstrate the use of ab initio quantum chemistry in battery technology, the theoretical energy density (energy per volume of active electrode material) and specific energy (energy per mass of active electrode material) of a rechargeable lithium-ion battery consisting of a graphite electrode and a nickel oxide electrode has been calculated with this method. (author) 1 fig., 1 tab., 7 refs.

  13. Two-loop disorder effects on the nematic quantum criticality in d-wave superconductors

    International Nuclear Information System (INIS)

    Wang, Jing

    2015-01-01

    The gapless nodal fermions exhibit non-Fermi liquid behaviors at the nematic quantum critical point that is supposed to exist in some d-wave cuprate superconductors. This non-Fermi liquid state may be turned into a disorder-dominated diffusive metal if the fermions also couple to a disordered potential that generates a relevant perturbation in the sense of renormalization group theory. It is therefore necessary to examine whether a specific disorder is relevant or not. We study the interplay between critical nematic fluctuation and random chemical potential by performing renormalization group analysis. The parameter that characterizes the strength of random chemical potential is marginal at the one-loop level, but becomes marginally relevant after including the two-loop corrections. Thus even weak random chemical potential leads to diffusive motion of nodal fermions and the significantly critical behaviors of physical implications, since the strength flows eventually to large values at low energies. - Highlights: • The gapless nodal fermions exhibit non-Fermi liquid behaviors at the nematic QCP. • The strength of random chemical potential is marginal at the one-loop level. • The strength becomes marginally relevant after including the two-loop corrections. • The diffusive metallic state is induced by the marginally relevant disorder. • The behaviors of some physical observables are presented at the nematic QCP

  14. Chemical dynamics in the gas phase: Time-dependent quantum mechanics of chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Gray, S.K. [Argonne National Laboratory, IL (United States)

    1993-12-01

    A major goal of this research is to obtain an understanding of the molecular reaction dynamics of three and four atom chemical reactions using numerically accurate quantum dynamics. This work involves: (i) the development and/or improvement of accurate quantum mechanical methods for the calculation and analysis of the properties of chemical reactions (e.g., rate constants and product distributions), and (ii) the determination of accurate dynamical results for selected chemical systems, which allow one to compare directly with experiment, determine the reliability of the underlying potential energy surfaces, and test the validity of approximate theories. This research emphasizes the use of recently developed time-dependent quantum mechanical methods, i.e. wave packet methods.

  15. Improve photocurrent quantum efficiency of carbon nanotube by chemical treatment

    International Nuclear Information System (INIS)

    Wang Hongguang; Wei Jinquan; Jia Yi; Li Zhen; Zhu Hongwei; Wang Kunlin; Wu Dehai

    2012-01-01

    Highlights: ► The QE of photocurrent for the H 2 O 2 -treated CNTs reaches to 5.28% at U bias = 0.1 V. ► Moderate chemical treatment can enhance the QE of photocurrent of CNTs. ► Excessive chemical treatment decreases the photocurrent quantum efficiency of CNTs. - Abstract: High photocurrent quantum efficiency (QE) of carbon nanotubes (CNTs) is important to their photovoltaic applications. The ability of photocurrent generation of CNTs depends on their band structure and surface state. For given CNTs, it is possible to improve the QE of photocurrent by chemical modification. Here, we study the effects of simple chemical treatment on the QE of CNTs by measuring the photocurrent of macroscopic CNT bundles. The QE of the H 2 O 2 -treated CNT bundle reaches 5.28% at 0.1 V bias voltage at a laser (λ = 473 nm) illumination, which is 85% higher than that of the pristine sample. But the QE of the CNTs treated in concentrated HNO 3 is lower than that of the pristine sample. It shows that moderate chemical treatment can enhance the photocurrent QE and excessive chemical treatment will decrease the QE because of introducing lots of structural defects.

  16. Critical properties of effective gauge theories for novel quantum fluids

    Energy Technology Data Exchange (ETDEWEB)

    Smoergrav, Eivind

    2005-07-01

    Critical properties of U(1) symmetric gauge theories are studied in 2+1 dimensions, analytically through duality transformations and numerically through Monte Carlo simulations. Physical applications range from quantum phase transitions in two dimensional insulating materials to superfluid and superconducting properties of light atoms such as hydrogen under extreme pressure. A novel finite size scaling method, utilizing the third moment M{sub 3} of the action, is developed. Finite size scaling analysis of M{sub 3} yields the ratio (1 + alpha)/ny and 1/ny separately, so that critical exponents alpha and ny can be obtained independently without invoking hyperscaling. This thesis contains eight research papers and an introductory part covering some basic concepts and techniques. Paper 1: The novel M{sub 3} method is introduced and employed together with Monte Carlo simulations to study the compact Abelian Higgs model in the adjoint representation with q = 2. Paper 2: We study phase transitions in the compact Abelian Higgs model for fundamental charge q = 2; 3; 4; 5. Various other models are studied to benchmark the M{sub 3} method. Paper 3: This is a proceeding paper based on a talk given by F. S. Nogueira at the Aachen EPS HEP 2003 conference. A review of the results from Paper 1 and Paper 2 on the compact Abelian Higgs model together with some results on q = 1 obtained by F. S. Nogueira, H. Kleinert, and A. Sudboe is given. Paper 4: The effect of a Chern-Simons (CS) term in the phase structure of two Abelian gauge theories is studied. Paper 5: We study the critical properties of the N-component Ginzburg-Landau theory. Paper 6: We consider the vortices in the 2-component Ginzburg-Landau model in a finite but low magnetic field. The ground state is a lattice of co centered vortices in both order parameters. We find two novel phase transitions. i) A 'vortex sub-lattice melting' transition where vortices in the field with lowest phase stiffness (&apos

  17. Recent Trends in Quantum Chemical Modeling of Enzymatic Reactions.

    Science.gov (United States)

    Himo, Fahmi

    2017-05-24

    The quantum chemical cluster approach is a powerful method for investigating enzymatic reactions. Over the past two decades, a large number of highly diverse systems have been studied and a great wealth of mechanistic insight has been developed using this technique. This Perspective reviews the current status of the methodology. The latest technical developments are highlighted, and challenges are discussed. Some recent applications are presented to illustrate the capabilities and progress of this approach, and likely future directions are outlined.

  18. Lighting up micromotors with quantum dots for smart chemical sensing.

    Science.gov (United States)

    Jurado-Sánchez, B; Escarpa, A; Wang, J

    2015-09-25

    A new "on-the-fly" chemical optical detection strategy based on the incorporation of fluorescence CdTe quantum dots (QDs) on the surface of self-propelled tubular micromotors is presented. The motion-accelerated binding of trace Hg to the QDs selectively quenches the fluorescence emission and leads to an effective discrimination between different mercury species and other co-existing ions.

  19. Mechanical and chemical spinodal instabilities in finite quantum systems

    International Nuclear Information System (INIS)

    Colonna, M.; Chomaz, Ph.; Ayik, S.

    2001-01-01

    Self consistent quantum approaches are used to study the instabilities of finite nuclear systems. The frequencies of multipole density fluctuations are determined as a function of dilution and temperature, for several isotopes. The spinodal region of the phase diagrams is determined and it appears reduced by finite size effects. The role of surface and volume instabilities is discussed. Important chemical effects are associated with mechanical disruption and may lead to isospin fractionation. (authors)

  20. Quantum chemical studies on the some inorganic corrosion inhibitors

    International Nuclear Information System (INIS)

    Sayin, Koray; Karakaş, Duran

    2013-01-01

    Highlights: •Some quantum chemical parameters are important to determine inhibition efficiency. •Quantum chemical calculations were performed on six inorganic inhibitors. •Five experimental reports were used to explain the theoretical results. •Atomic charges and %contributions were used to determine the atom at protonation process. •For inorganic inhibitors, the best method and basis set were investigated. -- Abstract: Some quantum chemical parameters were calculated by using Hartree–Fock (HF) approximation, Density Functional Theory (DFT/B3LYP) and Møller Plesset perturbation theory (MP3) methods at LANL2DZ, LANL2MB and SDD levels in gas phase and water for dichromate (Cr 2 O 7 2- ), chromate (CrO 4 2- ), tungstate (WO 4 2- ), molybdate (MoO 4 2- ), nitrite (NO 2 - ) and nitrate (NO 3 - ) which are used as inorganic corrosion inhibitors. All theoretical results and experimental inhibition efficiencies of inhibitors were subjected to correlation analyses. In a summary, MP3/SDD level in water was found as the best level. In this level, the inhibition efficiency ranking was found as CrO 4 2- >WO 4 2- >MoO 4 2- >Cr 2 O 7 2- >NO 2 - ≈NO 3 -

  1. Quantum-critical scaling of fidelity in 2D pairing models

    Energy Technology Data Exchange (ETDEWEB)

    Adamski, Mariusz, E-mail: mariusz.adamski@ift.uni.wroc.pl [Institute of Theoretical Physics, University of Wrocław, pl. Maksa Borna 9, 50–204, Wrocław (Poland); Jȩdrzejewski, Janusz [Institute of Theoretical Physics, University of Wrocław, pl. Maksa Borna 9, 50–204, Wrocław (Poland); Krokhmalskii, Taras [Institute for Condensed Matter Physics, 1 Svientsitski Street, 79011, Lviv (Ukraine)

    2017-01-15

    The laws of quantum-critical scaling theory of quantum fidelity, dependent on the underlying system dimensionality D, have so far been verified in exactly solvable 1D models, belonging to or equivalent to interacting, quadratic (quasifree), spinless or spinfull, lattice-fermion models. The obtained results are so appealing that in quest for correlation lengths and associated universal critical indices ν, which characterize the divergence of correlation lengths on approaching critical points, one might be inclined to substitute the hard task of determining an asymptotic behavior at large distances of a two-point correlation function by an easier one, of determining the quantum-critical scaling of the quantum fidelity. However, the role of system's dimensionality has been left as an open problem. Our aim in this paper is to fill up this gap, at least partially, by verifying the laws of quantum-critical scaling theory of quantum fidelity in a 2D case. To this end, we study correlation functions and quantum fidelity of 2D exactly solvable models, which are interacting, quasifree, spinfull, lattice-fermion models. The considered 2D models exhibit new, as compared with 1D ones, features: at a given quantum-critical point there exists a multitude of correlation lengths and multiple universal critical indices ν, since these quantities depend on spatial directions, moreover, the indices ν may assume larger values. These facts follow from the obtained by us analytical asymptotic formulae for two-point correlation functions. In such new circumstances we discuss the behavior of quantum fidelity from the perspective of quantum-critical scaling theory. In particular, we are interested in finding out to what extent the quantum fidelity approach may be an alternative to the correlation-function approach in studies of quantum-critical points beyond 1D.

  2. Critical quasiparticle theory applied to heavy fermion metals near an antiferromagnetic quantum phase transition

    Science.gov (United States)

    Abrahams, Elihu; Wölfle, Peter

    2012-01-01

    We use the recently developed critical quasiparticle theory to derive the scaling behavior associated with a quantum critical point in a correlated metal. This is applied to the magnetic-field induced quantum critical point observed in YbRh2Si2, for which we also derive the critical behavior of the specific heat, resistivity, thermopower, magnetization and susceptibility, the Grüneisen coefficient, and the thermal expansion coefficient. The theory accounts very well for the available experimental results. PMID:22331893

  3. Quantum mechanical cluster calculations of critical scintillation processes

    International Nuclear Information System (INIS)

    Derenzo, Stephen E.; Klintenberg, Mattias K.; Weber, Marvin J.

    2000-01-01

    This paper describes the use of commercial quantum chemistry codes to simulate several critical scintillation processes. The crystal is modeled as a cluster of typically 50 atoms embedded in an array of typically 5,000 point charges designed to reproduce the electrostatic field of the infinite crystal. The Schrodinger equation is solved for the ground, ionized, and excited states of the system to determine the energy and electron wave function. Computational methods for the following critical processes are described: (1) the formation and diffusion of relaxed holes, (2) the formation of excitons, (3) the trapping of electrons and holes by activator atoms, (4) the excitation of activator atoms, and (5) thermal quenching. Examples include hole diffusion in CsI, the exciton in CsI, the excited state of CsI:Tl, the energy barrier for the diffusion of relaxed holes in CaF2 and PbF2, and prompt hole trapping by activator atoms in CaF2:Eu and CdS:Te leading to an ultra-fast (<50ps) scintillation rise time.

  4. Universal conductance and conductivity at critical points in integer quantum Hall systems.

    Science.gov (United States)

    Schweitzer, L; Markos, P

    2005-12-16

    The sample averaged longitudinal two-terminal conductance and the respective Kubo conductivity are calculated at quantum critical points in the integer quantum Hall regime. In the limit of large system size, both transport quantities are found to be the same within numerical uncertainty in the lowest Landau band, and , respectively. In the second-lowest Landau band, a critical conductance is obtained which indeed supports the notion of universality. However, these numbers are significantly at variance with the hitherto commonly believed value . We argue that this difference is due to the multifractal structure of critical wave functions, a property that should generically show up in the conductance at quantum critical points.

  5. Theory of finite-entanglement scaling at one-dimensional quantum critical points.

    Science.gov (United States)

    Pollmann, Frank; Mukerjee, Subroto; Turner, Ari M; Moore, Joel E

    2009-06-26

    Studies of entanglement in many-particle systems suggest that most quantum critical ground states have infinitely more entanglement than noncritical states. Standard algorithms for one-dimensional systems construct model states with limited entanglement, which are a worse approximation to quantum critical states than to others. We give a quantitative theory of previously observed scaling behavior resulting from finite entanglement at quantum criticality. Finite-entanglement scaling in one-dimensional systems is governed not by the scaling dimension of an operator but by the "central charge" of the critical point. An important ingredient is the universal distribution of density-matrix eigenvalues at a critical point [P. Calabrese and A. Lefevre, Phys. Rev. A 78, 032329 (2008)10.1103/PhysRevA.78.032329]. The parameter-free theory is checked against numerical scaling at several quantum critical points.

  6. Fluctuation induced critical behavior at nonzero temperature and chemical potential

    International Nuclear Information System (INIS)

    Splittorff, K.; Lenaghan, J.T.; Wirstam, J.

    2003-01-01

    We discuss phase transitions in relativistic systems as a function of both the chemical potential and temperature. The presence of a chemical potential explicitly breaks Lorentz invariance and may additionally break other internal symmetries. This introduces new subtleties in the determination of the critical properties. We discuss separately three characteristic effects of a nonzero chemical potential. First, we consider only the explicit breaking of Lorentz invariance using a scalar field theory with a global U(1) symmetry. Second, we study the explicit breaking of an internal symmetry in addition to Lorentz invariance using two-color QCD at nonzero baryonic chemical potential. Finally, we consider the spontaneous breaking of a symmetry using three-color QCD at nonzero baryonic and isospin chemical potential. For each case, we derive the appropriate three-dimensional effective theory at criticality and study the effect of the chemical potential on the fixed point structure of the β functions. We find that the order of the phase transition is not affected by the explicit breaking of Lorentz invariance but is sensitive to the breaking of additional symmetries by the chemical potential

  7. Phase transition with trivial quantum criticality in an anisotropic Weyl semimetal

    Science.gov (United States)

    Li, Xin; Wang, Jing-Rong; Liu, Guo-Zhu

    2018-05-01

    When a metal undergoes continuous quantum phase transition, the correlation length diverges at the critical point and the quantum fluctuation of order parameter behaves as a gapless bosonic mode. Generically, the coupling of this boson to fermions induces a variety of unusual quantum critical phenomena, such as non-Fermi liquid behavior and various emergent symmetries. Here, we perform a renormalization group analysis of the semimetal-superconductor quantum criticality in a three-dimensional anisotropic Weyl semimetal. Surprisingly, distinct from previously studied quantum critical systems, the anomalous dimension of anisotropic Weyl fermions flows to zero very quickly with decreasing energy, and the quasiparticle residue takes a nonzero value. These results indicate that the quantum fluctuation of superconducting order parameter is irrelevant at low energies, and a simple mean-field calculation suffices to capture the essential physics of the superconducting transition. We thus obtain a phase transition that exhibits trivial quantum criticality, which is unique comparing to other invariably nontrivial quantum critical systems. Our theoretical prediction can be experimentally verified by measuring the fermion spectral function and specific heat.

  8. Fermionic quantum critical point of spinless fermions on a honeycomb lattice

    International Nuclear Information System (INIS)

    Wang, Lei; Corboz, Philippe; Troyer, Matthias

    2014-01-01

    Spinless fermions on a honeycomb lattice provide a minimal realization of lattice Dirac fermions. Repulsive interactions between nearest neighbors drive a quantum phase transition from a Dirac semimetal to a charge-density-wave state through a fermionic quantum critical point, where the coupling of the Ising order parameter to the Dirac fermions at low energy drastically affects the quantum critical behavior. Encouraged by a recent discovery (Huffman and Chandrasekharan 2014 Phys. Rev. B 89 111101) of the absence of the fermion sign problem in this model, we study the fermionic quantum critical point using the continuous-time quantum Monte Carlo method with a worm-sampling technique. We estimate the transition point V/t=1.356(1) with the critical exponents ν=0.80(3) and η=0.302(7). Compatible results for the transition point are also obtained with infinite projected entangled-pair states. (paper)

  9. Energy scales and magnetoresistance at a quantum critical point

    Energy Technology Data Exchange (ETDEWEB)

    Shaginyan, V.R. [Petersburg Nuclear Physics Institute, RAS, Gatchina, 188300 (Russian Federation); Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); CTSPS, Clark Atlanta University, Atlanta, GA 30314 (United States)], E-mail: vrshag@thd.pnpi.spb.ru; Amusia, M.Ya. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Msezane, A.Z. [CTSPS, Clark Atlanta University, Atlanta, GA 30314 (United States); Popov, K.G. [Komi Science Center, Ural Division, RAS, 3a Chernova street, Syktyvkar, 167982 (Russian Federation); Stephanovich, V.A. [Opole University, Institute of Mathematics and Informatics, Opole, 45-052 (Poland)

    2009-03-02

    The magnetoresistance (MR) of CeCoIn{sub 5} is notably different from that in many conventional metals. We show that a pronounced crossover from negative to positive MR at elevated temperatures and fixed magnetic fields is determined by the scaling behavior of quasiparticle effective mass. At a quantum critical point (QCP) this dependence generates kinks (crossover points from fast to slow growth) in thermodynamic characteristics (like specific heat, magnetization, etc.) at some temperatures when a strongly correlated electron system transits from the magnetic field induced Landau-Fermi liquid (LFL) regime to the non-Fermi liquid (NFL) one taking place at rising temperatures. We show that the above kink-like peculiarity separates two distinct energy scales in QCP vicinity - low temperature LFL scale and high temperature one related to NFL regime. Our comprehensive theoretical analysis of experimental data permits to reveal for the first time new MR and kinks scaling behavior as well as to identify the physical reasons for above energy scales.

  10. CePdAl. A frustrated Kondo lattice at a quantum critical point

    Energy Technology Data Exchange (ETDEWEB)

    Fritsch, Veronika [EP 6, Electronic Correlations and Magnetism, University of Augsburg (Germany); Karlsruhe Institute of Technology (Germany); Sakai, Akito; Gegenwart, Philipp [EP 6, Electronic Correlations and Magnetism, University of Augsburg (Germany); Huesges, Zita; Lucas, Stefan; Stockert, Oliver [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Kittler, Wolfram; Taubenheim, Christian; Grube, Kai; Loehneysen, Hilbert von [Karlsruhe Institute of Technology (Germany); Huang, Chien-Lung [Karlsruhe Institute of Technology (Germany); Max Planck Institute for Chemical Physics of Solids, Dresden (Germany)

    2016-07-01

    CePdAl is one of the rare frustrated Kondo lattice systems that can be tuned across a quantum critical point (QCP) by means of chemical pressure, i. e., the substitution of Pd by Ni. Magnetic frustration and Kondo effect are antithetic phenomena: The Kondo effect with the incipient delocalization of the magnetic moments, is not beneficial for the formation of a frustrated state. On the other hand, magnetic frustrated exchange interactions between the local moments can result in a breakdown of Kondo screening. Furthermore, the fate of frustration is unclear when approaching the QCP, since there is no simple observable to quantify the degree of frustration. We present thermodynamic and neutron scattering experiments on CePd{sub 1-x}Ni{sub x}Al close to the critical concentration x ∼0.14. Our experiments indicate that even at the QCP magnetic frustration is still present, opening the perspective to find new universality classes at such a quantum phase transition.

  11. Surface emitting ring quantum cascade lasers for chemical sensing

    Science.gov (United States)

    Szedlak, Rolf; Hayden, Jakob; Martín-Mateos, Pedro; Holzbauer, Martin; Harrer, Andreas; Schwarz, Benedikt; Hinkov, Borislav; MacFarland, Donald; Zederbauer, Tobias; Detz, Hermann; Andrews, Aaron Maxwell; Schrenk, Werner; Acedo, Pablo; Lendl, Bernhard; Strasser, Gottfried

    2018-01-01

    We review recent advances in chemical sensing applications based on surface emitting ring quantum cascade lasers (QCLs). Such lasers can be implemented in monolithically integrated on-chip laser/detector devices forming compact gas sensors, which are based on direct absorption spectroscopy according to the Beer-Lambert law. Furthermore, we present experimental results on radio frequency modulation up to 150 MHz of surface emitting ring QCLs. This technique provides detailed insight into the modulation characteristics of such lasers. The gained knowledge facilitates the utilization of ring QCLs in combination with spectroscopic techniques, such as heterodyne phase-sensitive dispersion spectroscopy for gas detection and analysis.

  12. Zero-field quantum critical point in CeCoIn5.

    Science.gov (United States)

    Tokiwa, Y; Bauer, E D; Gegenwart, P

    2013-09-06

    Quantum criticality in the normal and superconducting states of the heavy-fermion metal CeCoIn5 is studied by measurements of the magnetic Grüneisen ratio ΓH and specific heat in different field orientations and temperatures down to 50 mK. A universal temperature over magnetic field scaling of ΓH in the normal state indicates a hidden quantum critical point at zero field. Within the superconducting state, the quasiparticle entropy at constant temperature increases upon reducing the field towards zero, providing additional evidence for zero-field quantum criticality.

  13. From quantum chemical formation free energies to evaporation rates

    Directory of Open Access Journals (Sweden)

    I. K. Ortega

    2012-01-01

    Full Text Available Atmospheric new particle formation is an important source of atmospheric aerosols. Large efforts have been made during the past few years to identify which molecules are behind this phenomenon, but the actual birth mechanism of the particles is not yet well known. Quantum chemical calculations have proven to be a powerful tool to gain new insights into the very first steps of particle formation. In the present study we use formation free energies calculated by quantum chemical methods to estimate the evaporation rates of species from sulfuric acid clusters containing ammonia or dimethylamine. We have found that dimethylamine forms much more stable clusters with sulphuric acid than ammonia does. On the other hand, the existence of a very deep local minimum for clusters with two sulfuric acid molecules and two dimethylamine molecules hinders their growth to larger clusters. These results indicate that other compounds may be needed to make clusters grow to larger sizes (containing more than three sulfuric acid molecules.

  14. Development and new applications of quantum chemical simulation methodology

    International Nuclear Information System (INIS)

    Weiss, A. K. H.

    2012-01-01

    The Division of Theoretical Chemistry at the University of Innsbruck is focused on the study of chemical compounds in aqueous solution, in terms of mainly hybrid quantum mechanical / molecular mechanical molecular dynamics simulations (QM/MM MD). Besides the standard means of data analysis employed for such simulations, this study presents several advanced and capable algorithms for the description of structural and dynamic properties of the simulated species and its hydration. The first part of this thesis further presents selected exemplary simulations, in particular a comparative study of Formamide and N-methylformamide, Guanidinium, and Urea. An included review article further summarizes the major advances of these studies. The computer programs developed in the course of this thesis are by now well established in the research field. The second part of this study presents the theory and a development guide for a quantum chemical program, QuMuLuS, that is by now used as a QM program for recent QM/MM simulations at the division. In its course, this part presents newly developed algorithms for electron integral evaluation and point charge embedding. This program is validated in terms of benchmark computations. The associated theory is presented on a detailed level, to serve as a source for contemporary and future studies in the division. In the third and final part, further investigations of related topics are addressed. This covers additional schemes of molecular simulation analysis, new software, as well as a mathematical investigation of a non-standard two-electron integral. (author)

  15. Holographic aspects of black holes, matrix models and quantum criticality

    NARCIS (Netherlands)

    Papadoulaki, O.

    2017-01-01

    In one word the core subject of this thesis is holography. What we mean by holography broadly is the mapping of a gravitational theory in D dimensions to a quantum mechanics system or quantum field theory in one less dimension In chapter 1, we give a basic and self-contained introduction of the

  16. A critical analysis of the quantum theory of measurement

    International Nuclear Information System (INIS)

    Fer, F.

    1984-01-01

    Keeping strictly in the positivist and probabilistic, hence hilbertian frame of Quantum Mechanics, the author tries to ascertain whether or not Quantum Mechanics, starting from its axioms, reaches the aim of any physical theory, that is, comparison with experiment. The answer is: no, as long as it keeps close to the existing axiomatics, and also to accurate mathematics. (Auth.)

  17. Quantum wavepacket ab initio molecular dynamics: an approach for computing dynamically averaged vibrational spectra including critical nuclear quantum effects.

    Science.gov (United States)

    Sumner, Isaiah; Iyengar, Srinivasan S

    2007-10-18

    We have introduced a computational methodology to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach is based on the recently developed quantum wavepacket ab initio molecular dynamics method that combines quantum wavepacket dynamics with ab initio molecular dynamics. The computational efficiency of the dynamical procedure is drastically improved (by several orders of magnitude) through the utilization of wavelet-based techniques combined with the previously introduced time-dependent deterministic sampling procedure measure to achieve stable, picosecond length, quantum-classical dynamics of electrons and nuclei in clusters. The dynamical information is employed to construct a novel cumulative flux/velocity correlation function, where the wavepacket flux from the quantized particle is combined with classical nuclear velocities to obtain the vibrational density of states. The approach is demonstrated by computing the vibrational density of states of [Cl-H-Cl]-, inclusive of critical quantum nuclear effects, and our results are in good agreement with experiment. A general hierarchical procedure is also provided, based on electronic structure harmonic frequencies, classical ab initio molecular dynamics, computation of nuclear quantum-mechanical eigenstates, and employing quantum wavepacket ab initio dynamics to understand vibrational spectroscopy in hydrogen-bonded clusters that display large degrees of anharmonicities.

  18. Quantum criticality in electron-doped BaFe2-xNixAs2.

    Science.gov (United States)

    Zhou, R; Li, Z; Yang, J; Sun, D L; Lin, C T; Zheng, Guo-qing

    2013-01-01

    A quantum critical point is a point in a system's phase diagram at which an order is completely suppressed at absolute zero temperature (T). The presence of a quantum critical point manifests itself in the finite-T physical properties, and often gives rise to new states of matter. Superconductivity in the cuprates and in heavy fermion materials is believed by many to be mediated by fluctuations associated with a quantum critical point. In the recently discovered iron-pnictide superconductors, we report transport and NMR measurements on BaFe(2-x)Ni(x)As₂ (0≤x≤0.17). We find two critical points at x(c1)=0.10 and x(c2)=0.14. The electrical resistivity follows ρ=ρ₀+AT(n), with n=1 around x(c1) and another minimal n=1.1 at x(c2). By NMR measurements, we identity x(c1) to be a magnetic quantum critical point and suggest that x(c2) is a new type of quantum critical point associated with a nematic structural phase transition. Our results suggest that the superconductivity in carrier-doped pnictides is closely linked to the quantum criticality.

  19. A non-critical string approach to black holes, time and quantum dynamics

    CERN Document Server

    Ellis, John R.; Nanopoulos, Dimitri V.

    1994-01-01

    We review our approach to time and quantum dynamics based on non-critical string theory, developing its relationship to previous work on non-equilibrium quantum statistical mechanics and the microscopic arrow of time. We exhibit specific non-factorizing contributions to the {\

  20. Improved performance of nanowire–quantum-dot–polymer solar cells by chemical treatment of the quantum dot with ligand and solvent materials

    International Nuclear Information System (INIS)

    Nadarajah, A; Smith, T; Könenkamp, R

    2012-01-01

    We report a nanowire–quantum-dot–polymer solar cell consisting of a chemically treated CdSe quantum dot film deposited on n-type ZnO nanowires. The electron and hole collecting contacts are a fluorine-doped tin-oxide/zinc oxide layer and a P3HT/Au layer. This device architecture allows for enhanced light absorption and an efficient collection of photogenerated carriers. A detailed analysis of the chemical treatment of the quantum dots, their deposition, and the necessary annealing processes are discussed. We find that the surface treatment of CdSe quantum dots with pyridine, and the use of 1,2-ethanedithiol (EDT) ligands, critically improves the device performance. Annealing at 380 °C for 2 h is found to cause a structural conversion of the CdSe from its initial isolated quantum dot arrangement into a polycrystalline film with excellent surface conformality, thereby resulting in a further enhancement of device performance. Moreover, long-term annealing of 24 h leads to additional increases in device efficiency. Our best conversion efficiency reached for this type of cell is 3.4% under 85 mW cm −2 illumination. (paper)

  1. Precise Determination of Quantum Critical Points by the Violation of the Entropic Area Law

    OpenAIRE

    Xavier, J. C.; Alcaraz, F. C.

    2011-01-01

    Finite-size scaling analysis turns out to be a powerful tool to calculate the phase diagram as well as the critical properties of two dimensional classical statistical mechanics models and quantum Hamiltonians in one dimension. The most used method to locate quantum critical points is the so called crossing method, where the estimates are obtained by comparing the mass gaps of two distinct lattice sizes. The success of this method is due to its simplicity and the ability to provide accurate r...

  2. Model for a Ferromagnetic Quantum Critical Point in a 1D Kondo Lattice

    Science.gov (United States)

    Komijani, Yashar; Coleman, Piers

    2018-04-01

    Motivated by recent experiments, we study a quasi-one-dimensional model of a Kondo lattice with ferromagnetic coupling between the spins. Using bosonization and dynamical large-N techniques, we establish the presence of a Fermi liquid and a magnetic phase separated by a local quantum critical point, governed by the Kondo breakdown picture. Thermodynamic properties are studied and a gapless charged mode at the quantum critical point is highlighted.

  3. Critical components for diamond-based quantum coherent devices

    International Nuclear Information System (INIS)

    Greentree, Andrew D; Olivero, Paolo; Draganski, Martin; Trajkov, Elizabeth; Rabeau, James R; Reichart, Patrick; Gibson, Brant C; Rubanov, Sergey; Huntington, Shane T; Jamieson, David N; Prawer, Steven

    2006-01-01

    The necessary elements for practical devices exploiting quantum coherence in diamond materials are summarized, and progress towards their realization documented. A brief review of future prospects for diamond-based devices is also provided

  4. A critical note on the greatest days of quantum theory

    International Nuclear Information System (INIS)

    Popper, K.

    1984-01-01

    The paper traces the scientific ideas of Louis de Broglie, concerning quantum theory. Uncertainty and scatter; Copenhagen or realism; the argument of Einstein, Podolski and Rosen; and realistic consequences of aspect's experiment; are all discussed. (U.K.)

  5. Quantum critical scaling at the edge of Fermi liquid stability in a cuprate superconductor.

    Science.gov (United States)

    Butch, Nicholas P; Jin, Kui; Kirshenbaum, Kevin; Greene, Richard L; Paglione, Johnpierre

    2012-05-29

    In the high-temperature cuprate superconductors, the pervasiveness of anomalous electronic transport properties suggests that violation of conventional Fermi liquid behavior is closely tied to superconductivity. In other classes of unconventional superconductors, atypical transport is well correlated with proximity to a quantum critical point, but the relative importance of quantum criticality in the cuprates remains uncertain. Here, we identify quantum critical scaling in the electron-doped cuprate material La(2-x)Ce(x)CuO(4) with a line of quantum critical points that surrounds the superconducting phase as a function of magnetic field and charge doping. This zero-temperature phase boundary, which delineates a metallic Fermi liquid regime from an extended non-Fermi liquid ground state, closely follows the upper critical field of the overdoped superconducting phase and gives rise to an expanse of distinct non-Fermi liquid behavior at finite temperatures. Together with signatures of two distinct flavors of quantum fluctuations, these facts suggest that quantum criticality plays a significant role in shaping the anomalous properties of the cuprate phase diagram.

  6. Quantum-chemical consideration of extermal valent forms of actinides

    International Nuclear Information System (INIS)

    Ionova, G.V.; Pershina, V.G.; Spitsyn, V.I.

    1982-01-01

    Stability of valent forms of actinides that has not yet studied experimentally, is considered within the framework of quantum-chemical considerations. Oxidizing potentials E 0 for actinide elements are determined theoretically. A dependence of the definite valent state stability on relativistic effect is shown. A conclusion is made that oxidizing potential E 0 (4-5) for americium should be higher than E 0 (4-5) for plutonium. A relatively small oxidizing potential E 0 (4-5) for curium speaks about principle possibility of production of five-valent curium in solution, though it is less stable than the six-valent one. Oxidizing potential corresponding to transition of three-valent californium into the four-valent state should be less than the value adopted in literature. A relatively small oxidizing potential of californium E 0 (4-5) speaks about possible existence of five-valent californium in solution

  7. Quantum Chemical Modeling of Enzymatic Reactions: The Case of Decarboxylation.

    Science.gov (United States)

    Liao, Rong-Zhen; Yu, Jian-Guo; Himo, Fahmi

    2011-05-10

    We present a systematic study of the decarboxylation step of the enzyme aspartate decarboxylase with the purpose of assessing the quantum chemical cluster approach for modeling this important class of decarboxylase enzymes. Active site models ranging in size from 27 to 220 atoms are designed, and the barrier and reaction energy of this step are evaluated. To model the enzyme surrounding, homogeneous polarizable medium techniques are used with several dielectric constants. The main conclusion is that when the active site model reaches a certain size, the solvation effects from the surroundings saturate. Similar results have previously been obtained from systematic studies of other classes of enzymes, suggesting that they are of a quite general nature.

  8. Quantum chemical prediction of antennae structures in lanthanide complexes

    International Nuclear Information System (INIS)

    Ottonelli, M.; Musso, G.F.; Rizzo, F.; Dellepiane, G.; Porzio, W.; Destri, S.

    2008-01-01

    In this paper the quantum chemical semiempirical procedure recently proposed by us to predict ground- and excited-state geometries of lanthanide complexes, the pseudo coordination centre method (PCC), is preliminarily compared with the semiempirical sparkle model for the calculation of lanthanide complexes (SMLC). Contrary to the SMLC method, where the rare-earth ion is replaced by a reparameterized sparkle atom, in our approach we replace it with a metal ion which is already present in the chosen semiempirical parameterization. This implies that in the optimization of the geometry of the complexes a different weight is implicitly given to the complex region including the rare-earth ion and its neighbour atoms with respect to the region of the ligands aggregate. As a consequence our approach is expected to reproduce better than the SMLC one the geometry of the ligands aggregate embedded in the complex, while the contrary happens for the coordination distances

  9. One-norm geometric quantum discord and critical point estimation in the XY spin chain

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Chang-Cheng; Wang, Yao; Guo, Jin-Liang, E-mail: guojinliang80@163.com

    2016-11-15

    In contrast with entanglement and quantum discord (QD), we investigate the thermal quantum correlation in terms of Schatten one-norm geometric quantum discord (GQD) in the XY spin chain, and analyze their capabilities in detecting the critical point of quantum phase transition. We show that the one-norm GQD can reveal more properties about quantum correlation between two spins, especially for the long-range quantum correlation at finite temperature. Under the influences of site distance, anisotropy and temperature, one-norm GQD and its first derivative make it possible to detect the critical point efficiently for a general XY spin chain. - Highlights: • Comparing with entanglement and QD, one-norm GQD is more robust versus the temperature. • One-norm GQD is more efficient in characterization of long-range quantum correlation between two distant qubits. • One-norm GQD performs well in highlighting the critical point of QPT at zero or low finite temperature. • One-norm GQD has a number of advantages over QD in detecting the critical point of the spin chain.

  10. Quantum criticality around metal-insulator transitions of strongly correlated electron systems

    Science.gov (United States)

    Misawa, Takahiro; Imada, Masatoshi

    2007-03-01

    Quantum criticality of metal-insulator transitions in correlated electron systems is shown to belong to an unconventional universality class with violation of the Ginzburg-Landau-Wilson (GLW) scheme formulated for symmetry breaking transitions. This unconventionality arises from an emergent character of the quantum critical point, which appears at the marginal point between the Ising-type symmetry breaking at nonzero temperatures and the topological transition of the Fermi surface at zero temperature. We show that Hartree-Fock approximations of an extended Hubbard model on square lattices are capable of such metal-insulator transitions with unusual criticality under a preexisting symmetry breaking. The obtained universality is consistent with the scaling theory formulated for Mott transitions and with a number of numerical results beyond the mean-field level, implying that preexisting symmetry breaking is not necessarily required for the emergence of this unconventional universality. Examinations of fluctuation effects indicate that the obtained critical exponents remain essentially exact beyond the mean-field level. It further clarifies the whole structure of singularities by a unified treatment of the bandwidth-control and filling-control transitions. Detailed analyses of the criticality, containing diverging carrier density fluctuations around the marginal quantum critical point, are presented from microscopic calculations and reveal the nature as quantum critical “opalescence.” The mechanism of emerging marginal quantum critical point is ascribed to a positive feedback and interplay between the preexisting gap formation present even in metals and kinetic energy gain (loss) of the metallic carrier. Analyses of crossovers between GLW type at nonzero temperature and topological type at zero temperature show that the critical exponents observed in (V,Cr)2O3 and κ-ET -type organic conductors provide us with evidence for the existence of the present marginal

  11. Non-linear quantum critical dynamics and fluctuation-dissipation ratios far from equilibrium

    Energy Technology Data Exchange (ETDEWEB)

    Zamani, Farzaneh [Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, 01187 Dresden (Germany); Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); Ribeiro, Pedro [CeFEMA, Instituto Superior Tcnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Russian Quantum Center, Novaya Street 100 A, Skolkovo, Moscow Area, 143025 (Russian Federation); Kirchner, Stefan, E-mail: stefan.kirchner@correlated-matter.com [Center for Correlated Matter, Zhejiang University, Hangzhou, Zhejiang 310058 (China)

    2016-02-15

    Non-thermal correlations of strongly correlated electron systems and the far-from-equilibrium properties of phases of condensed matter have become a topical research area. Here, an overview of the non-linear dynamics found near continuous zero-temperature phase transitions within the context of effective temperatures is presented. In particular, we focus on models of critical Kondo destruction. Such a quantum critical state, where Kondo screening is destroyed in a critical fashion, is realized in a number of rare earth intermetallics. This raises the possibility of experimentally testing for the existence of fluctuation-dissipation relations far from equilibrium in terms of effective temperatures. Finally, we present an analysis of a non-interacting, critical reference system, the pseudogap resonant level model, in terms of effective temperatures and contrast these results with those obtained near interacting quantum critical points. - Highlights: • Critical Kondo destruction explains the unusual properties of quantum critical heavy fermion compounds. • We review the concept of effective temperatures in models of critical Kondo destruction. • We compare effective temperatures found near non-interacting and fully interacting fixed points. • A comparison with non-interacting quantum impurity models is presented.

  12. Criticality of the anisotropic quantum Heisenberg model on a simple cubic lattice

    International Nuclear Information System (INIS)

    Mariz, A.M.; Santos, R.M.Z. dos; Tsallis, C.; Santos, R.R. dos.

    1984-01-01

    Within a Real Space Renormalization group framework, the criticality (phase diagram, and critical thermal and crossover exponents) of the spin 1/2 - anisotropic quantum Heisenberg ferromagnet on a simple cubic lattice is studied. The results obtained are in satisfactory agreement with known results whenever available. (Author) [pt

  13. Criticality of the anisotropic quantum Heisenberg model on a simple cubic lattice

    International Nuclear Information System (INIS)

    Mariz, A.M.; Tsallis, C.; Santos, R.M.Z. dos; Santos, Raimundo R. dos.

    1984-11-01

    Within a Real Space Renormalization Group Framework, the criticality (phase diagram, and critical thermal and crossover exponents) of the spin 1/2 - anisotropic quantum Heisenberg ferromagnet on a simple cubic lattice is studied. The results obtained are in antisfactory agreement with known results whenever available. (Author) [pt

  14. Environment-assisted Quantum Critical Effect for Excitation Energy Transfer in a LH2-type Trimer

    Science.gov (United States)

    Xu, Lan; Xu, Bo

    2015-10-01

    In this article, we are investigating excitation energy transfer (EET) in a basic unit cell of light-harvesting complex II (LH2), named a LH2-type trimer. Calculation of energy transfer efficiency (ETE) in the framework of non-Markovian environment is also implemented. With these achievements, we theoretically predict the environment-assisted quantum critical effect, where ETE exhibits a sudden change at the critical point of quantum phase transition (QPT) for the LH2-type trimer. It is found that highly efficient EET with nearly unit efficiency may occur in the vicinity of the critical point of QPT.

  15. Cation solvation with quantum chemical effects modeled by a size-consistent multi-partitioning quantum mechanics/molecular mechanics method.

    Science.gov (United States)

    Watanabe, Hiroshi C; Kubillus, Maximilian; Kubař, Tomáš; Stach, Robert; Mizaikoff, Boris; Ishikita, Hiroshi

    2017-07-21

    In the condensed phase, quantum chemical properties such as many-body effects and intermolecular charge fluctuations are critical determinants of the solvation structure and dynamics. Thus, a quantum mechanical (QM) molecular description is required for both solute and solvent to incorporate these properties. However, it is challenging to conduct molecular dynamics (MD) simulations for condensed systems of sufficient scale when adapting QM potentials. To overcome this problem, we recently developed the size-consistent multi-partitioning (SCMP) quantum mechanics/molecular mechanics (QM/MM) method and realized stable and accurate MD simulations, using the QM potential to a benchmark system. In the present study, as the first application of the SCMP method, we have investigated the structures and dynamics of Na + , K + , and Ca 2+ solutions based on nanosecond-scale sampling, a sampling 100-times longer than that of conventional QM-based samplings. Furthermore, we have evaluated two dynamic properties, the diffusion coefficient and difference spectra, with high statistical certainty. Furthermore the calculation of these properties has not previously been possible within the conventional QM/MM framework. Based on our analysis, we have quantitatively evaluated the quantum chemical solvation effects, which show distinct differences between the cations.

  16. The quantum dynamics of electronically nonadiabatic chemical reactions

    Science.gov (United States)

    Truhlar, Donald G.

    1993-01-01

    Considerable progress was achieved on the quantum mechanical treatment of electronically nonadiabatic collisions involving energy transfer and chemical reaction in the collision of an electronically excited atom with a molecule. In the first step, a new diabatic representation for the coupled potential energy surfaces was created. A two-state diabatic representation was developed which was designed to realistically reproduce the two lowest adiabatic states of the valence bond model and also to have the following three desirable features: (1) it is more economical to evaluate; (2) it is more portable; and (3) all spline fits are replaced by analytic functions. The new representation consists of a set of two coupled diabatic potential energy surfaces plus a coupling surface. It is suitable for dynamics calculations on both the electronic quenching and reaction processes in collisions of Na(3p2p) with H2. The new two-state representation was obtained by a three-step process from a modified eight-state diatomics-in-molecules (DIM) representation of Blais. The second step required the development of new dynamical methods. A formalism was developed for treating reactions with very general basis functions including electronically excited states. Our formalism is based on the generalized Newton, scattered wave, and outgoing wave variational principles that were used previously for reactive collisions on a single potential energy surface, and it incorporates three new features: (1) the basis functions include electronic degrees of freedom, as required to treat reactions involving electronic excitation and two or more coupled potential energy surfaces; (2) the primitive electronic basis is assumed to be diabatic, and it is not assumed that it diagonalizes the electronic Hamiltonian even asymptotically; and (3) contracted basis functions for vibrational-rotational-orbital degrees of freedom are included in a very general way, similar to previous prescriptions for locally

  17. Exploring the role of quantum chemical descriptors in modeling acute toxicity of diverse chemicals to Daphnia magna.

    Science.gov (United States)

    Reenu; Vikas

    2015-09-01

    Various quantum-mechanically computed molecular and thermodynamic descriptors along with physico-chemical, electrostatic and topological descriptors are compared while developing quantitative structure-activity relationships (QSARs) for the acute toxicity of 252 diverse organic chemicals towards Daphnia magna. QSAR models based on the quantum-chemical descriptors, computed with routinely employed advanced semi-empirical and ab-initio methods, along with the electron-correlation contribution (CORR) of the descriptors, are analyzed for the external predictivity of the acute toxicity. The models with reliable internal stability and external predictivity are found to be based on the HOMO energy along with the physico-chemical, electrostatic and topological descriptors. Besides this, the total energy and electron-correlation energy are also observed as highly reliable descriptors, suggesting that the intra-molecular interactions between the electrons play an important role in the origin of the acute toxicity, which is in fact an unexplored phenomenon. The models based on quantum-chemical descriptors such as chemical hardness, absolute electronegativity, standard Gibbs free energy and enthalpy are also observed to be reliable. A comparison of the robust models based on the quantum-chemical descriptors computed with various quantum-mechanical methods suggests that the advanced semi-empirical methods such as PM7 can be more reliable than the ab-initio methods which are computationally more expensive. Copyright © 2015 Elsevier Inc. All rights reserved.

  18. Quantum chemical approaches: semiempirical molecular orbital and hybrid quantum mechanical/molecular mechanical techniques.

    Science.gov (United States)

    Bryce, Richard A; Hillier, Ian H

    2014-01-01

    The use of computational quantum chemical methods to aid drug discovery is surveyed. An overview of the various computational models spanning ab initio, density function theory, semiempirical molecular orbital (MO), and hybrid quantum mechanical (QM)/molecular mechanical (MM) methods is given and their strengths and weaknesses are highlighted, focussing on the challenge of obtaining the accuracy essential for them to make a meaningful contribution to drug discovery. Particular attention is given to hybrid QM/MM and semiempirical MO methods which have the potential to yield the necessary accurate predictions of macromolecular structure and reactivity. These methods are shown to have advanced the study of many aspects of substrate-ligand interactions relevant to drug discovery. Thus, the successful parametrization of semiempirical MO methods and QM/MM methods can be used to model noncovalent substrate-protein interactions, and to lead to improved scoring functions. QM/MM methods can be used in crystal structure refinement and are particularly valuable for modelling covalent protein-ligand interactions and can thus aid the design of transition state analogues. An extensive collection of examples from the areas of metalloenzyme structure, enzyme inhibition, and ligand binding affinities and scoring functions are used to illustrate the power of these techniques.

  19. Tunable quantum criticality and super-ballistic transport in a "charge" Kondo circuit.

    Science.gov (United States)

    Iftikhar, Z; Anthore, A; Mitchell, A K; Parmentier, F D; Gennser, U; Ouerghi, A; Cavanna, A; Mora, C; Simon, P; Pierre, F

    2018-05-03

    Quantum phase transitions (QPTs) are ubiquitous in strongly-correlated materials. However the microscopic complexity of these systems impedes the quantitative understanding of QPTs. Here, we observe and thoroughly analyze the rich strongly-correlated physics in two profoundly dissimilar regimes of quantum criticality. With a circuit implementing a quantum simulator for the three-channel Kondo model, we reveal the universal scalings toward different low-temperature fixed points and along the multiple crossovers from quantum criticality. Notably, an unanticipated violation of the maximum conductance for ballistic free electrons is uncovered. The present charge pseudospin implementation of a Kondo impurity opens access to a broad variety of strongly-correlated phenomena. Copyright © 2018, American Association for the Advancement of Science.

  20. Critical behaviour of SU(n) quantum chains and topological non-linear σ-models

    International Nuclear Information System (INIS)

    Affleck, I.; British Columbia Univ., Vancouver

    1988-01-01

    The critical behaviour of SU(n) quantum ''spin'' chains, Wess-Zumino-Witten σ-models and grassmanian σ-models at topological angle θ = π (of possible relevance to the quantum Hall effect) is reexamined. It is argued that an additional Z n symmetry is generally necessary to stabilize the massless phase. This symmetry is not present for the σ-models for n>2 and is only present for certain representations of ''spin'' chains. (orig.)

  1. Characterization of the Quantized Hall Insulator Phase in the Quantum Critical Regime

    OpenAIRE

    Song, Juntao; Prodan, Emil

    2013-01-01

    The conductivity $\\sigma$ and resistivity $\\rho$ tensors of the disordered Hofstadter model are mapped as functions of Fermi energy $E_F$ and temperature $T$ in the quantum critical regime of the plateau-insulator transition (PIT). The finite-size errors are eliminated by using the non-commutative Kubo-formula. The results reproduce all the key experimental characteristics of this transition in Integer Quantum Hall (IQHE) systems. In particular, the Quantized Hall Insulator (QHI) phase is det...

  2. Sudden transitions and scaling behavior of geometric quantum correlation for two qubits in quantum critical environments at finite temperature

    International Nuclear Information System (INIS)

    Luo, Da-Wei; Xu, Jing-Bo

    2014-01-01

    We investigate the phenomenon of sudden transitions in geometric quantum correlation of two qubits in spin chain environments at finite temperature. It is shown that when only one qubit is coupled to the spin environment, the geometric discord exhibits a double sudden transition behavior, which is closely related to the quantum criticality of the spin chain environment. When two qubits are uniformly coupled to a common spin chain environment, the geometric discord is found to display a sudden transition behavior whereby the system transits from pure classical decoherence to pure quantum decoherence. Moreover, an interesting scaling behavior is revealed for the frozen time, and we also present a scheme to prolong the time during which the discord remains constant by applying bang–bang pulses. (paper)

  3. Protein Structure Validation and Refinement Using Chemical Shifts Derived from Quantum Mechanics

    DEFF Research Database (Denmark)

    Bratholm, Lars Andersen

    to within 3 A. Furthermore, a fast quantum mechanics based chemical shift predictor was developed together with methodology for using chemical shifts in structure simulations. The developed predictor was used for renement of several protein structures and for reducing the computational cost of quantum...... mechanics / molecular mechanics (QM/MM) computations of chemical shieldings. Several improvements to the predictor is ongoing, where among other things, kernel based machine learning techniques have successfully been used to improve the quantum mechanical level of theory used in the predictions....

  4. Bound on quantum computation time: Quantum error correction in a critical environment

    International Nuclear Information System (INIS)

    Novais, E.; Mucciolo, Eduardo R.; Baranger, Harold U.

    2010-01-01

    We obtain an upper bound on the time available for quantum computation for a given quantum computer and decohering environment with quantum error correction implemented. First, we derive an explicit quantum evolution operator for the logical qubits and show that it has the same form as that for the physical qubits but with a reduced coupling strength to the environment. Using this evolution operator, we find the trace distance between the real and ideal states of the logical qubits in two cases. For a super-Ohmic bath, the trace distance saturates, while for Ohmic or sub-Ohmic baths, there is a finite time before the trace distance exceeds a value set by the user.

  5. Protein structure refinement using a quantum mechanics-based chemical shielding predictor

    DEFF Research Database (Denmark)

    Bratholm, Lars Andersen; Jensen, Jan Halborg

    2017-01-01

    The accurate prediction of protein chemical shifts using a quantum mechanics (QM)-based method has been the subject of intense research for more than 20 years but so far empirical methods for chemical shift prediction have proven more accurate. In this paper we show that a QM-based predictor...... of a protein backbone and CB chemical shifts (ProCS15, PeerJ, 2016, 3, e1344) is of comparable accuracy to empirical chemical shift predictors after chemical shift-based structural refinement that removes small structural errors. We present a method by which quantum chemistry based predictions of isotropic...

  6. Tuning the Emission Energy of Chemically Doped Graphene Quantum Dots

    Directory of Open Access Journals (Sweden)

    Noor-Ul-Ain

    2016-11-01

    Full Text Available Tuning the emission energy of graphene quantum dots (GQDs and understanding the reason of tunability is essential for the GOD function in optoelectronic devices. Besides material-based challenges, the way to realize chemical doping and band gap tuning also pose a serious challenge. In this study, we tuned the emission energy of GQDs by substitutional doping using chlorine, nitrogen, boron, sodium, and potassium dopants in solution form. Photoluminescence data obtained from (Cl- and N-doped GQDs and (B-, Na-, and K-doped GQDs, respectively exhibited red- and blue-shift with respect to the photoluminescence of the undoped GQDs. X-ray photoemission spectroscopy (XPS revealed that oxygen functional groups were attached to GQDs. We qualitatively correlate red-shift of the photoluminescence with the oxygen functional groups using literature references which demonstrates that more oxygen containing groups leads to the formation of more defect states and is the reason of observed red-shift of luminescence in GQDs. Further on, time resolved photoluminescence measurements of Cl- and N-GQDs demonstrated that Cl substitution in GQDs has effective role in radiative transition whereas in N-GQDs leads to photoluminescence (PL quenching with non-radiative transition to ground state. Presumably oxidation or reduction processes cause a change of effective size and the bandgap.

  7. Critical current anomaly at the topological quantum phase transition in a Majorana Josephson junction

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Hong [School of Physics, Sun Yat-sen University, Guangzhou 510275 (China); Liang, Qi-Feng [Department of Physics, Shaoxing University, Shaoxing 312000 (China); Yao, Dao-Xin, E-mail: yaodaox@mail.sysu.edu.cn [School of Physics, Sun Yat-sen University, Guangzhou 510275 (China); Wang, Zhi, E-mail: physicswangzhi@gmail.com [School of Physics, Sun Yat-sen University, Guangzhou 510275 (China)

    2017-06-28

    Majorana bound states in topological Josephson junctions induce a 4π period current-phase relation. Direct detection of the 4π periodicity is complicated by the quasiparticle poisoning. We reveal that Majorana bound states are also signaled by the anomalous enhancement on the critical current of the junction. We show the landscape of the critical current for a nanowire Josephson junction under a varying Zeeman field, and reveal a sharp step feature at the topological quantum phase transition point, which comes from the anomalous enhancement of the critical current at the topological regime. In multi-band wires, the anomalous enhancement disappears for an even number of bands, where the Majorana bound states fuse into Andreev bound states. This anomalous critical current enhancement directly signals the existence of the Majorana bound states, and also provides a valid signature for the topological quantum phase transition. - Highlights: • We introduce the critical current step as a signal for the topological quantum phase transition. • We study the quantum phase transition in the topological nanowire under a rotating Zeeman field. • We show that the critical current anomaly gradually disappears for systems with more sub-bands.

  8. Quantum critical point in high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Shaginyan, V.R. [Petersburg Nuclear Physics Institute, RAS, Gatchina 188300 (Russian Federation); Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)], E-mail: vrshag@thd.pnpi.spb.ru; Amusia, M.Ya. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Popov, K.G. [Komi Science Center, Ural Division, RAS, Syktyvkar 167982 (Russian Federation); Stephanovich, V.A. [Opole University, Institute of Mathematics and Informatics, Opole 45-052 (Poland)], E-mail: stef@math.uni.opole.pl

    2009-02-02

    Recently, in high-T{sub c} superconductors (HTSC), exciting measurements have been performed revealing their physics in superconducting and pseudogap states and in normal one induced by the application of magnetic field, when the transition from non-Fermi liquid to Landau-Fermi liquid behavior occurs. We employ a theory, based on fermion condensation quantum phase transition which is able to explain facts obtained in the measurements. We also show, that in spite of very different microscopic nature of HTSC, heavy-fermion metals and 2D {sup 3}He, the physical properties of these three classes of substances are similar to each other.

  9. The critical point of quantum chromodynamics through lattice and ...

    Indian Academy of Sciences (India)

    The Padé approximants are the rational functions. PL. M (z) = .... Deviations from a smooth behaviour near the critical point are visible in these extrap- ... see that there is evidence, albeit statistically not very significant, that the kurtosis changes.

  10. Quantum-chemical study of hydride transfer in catalytic transformation of paraffins on zeolites

    NARCIS (Netherlands)

    Kazansky, V.B.; Frash, M.V.; Santen, van R.A.; Chon, H.; Ihm, S.-K.; Uh, Y.S.

    1997-01-01

    Ab initio quantum-chemical cluster calculations demonstrate that the activated complexes of hydride transfer reaction in catalytic transformation of paraffins on zeolites very much resembles adsorbed nonclassical carbonium ions. The calculated activation energies for reactions involving propane and

  11. Green wet chemical route to synthesize capped CdSe quantum dots

    Indian Academy of Sciences (India)

    In the present work, we report green synthesis of tartaric acid (TA) and triethanolamine (TEA) capped ... CdSe quantum dots; chemical bath deposition; capping; green chemistry; nanomaterials. 1. .... at high concentration of nanoparticles.

  12. Origin of chaos near critical points of quantum flow.

    Science.gov (United States)

    Efthymiopoulos, C; Kalapotharakos, C; Contopoulos, G

    2009-03-01

    The general theory of motion in the vicinity of a moving quantum nodal point (vortex) is studied in the framework of the de Broglie-Bohm trajectory method of quantum mechanics. Using an adiabatic approximation, we find that near any nodal point of an arbitrary wave function psi there is an unstable point (called the X point) in a frame of reference moving with the nodal point. The local phase portrait forms always a characteristic pattern called the "nodal-point- X -point complex." We find general formulas for this complex as well as necessary and sufficient conditions of validity of the adiabatic approximation. We demonstrate that chaos emerges from the consecutive scattering events of the orbits with nodal-point- X -point complexes. The scattering events are of two types (called type I and type II). A theoretical model is constructed yielding the local value of the Lyapunov characteristic numbers in scattering events of both types. The local Lyapunov characteristic number scales as an inverse power of the speed of the nodal point in the rest frame, implying that it scales proportionally to the size of the nodal-point- X -point complex. It is also an inverse power of the distance of a trajectory from the X point's stable manifold far from the complex. This distance plays the role of an effective "impact parameter." The results of detailed numerical experiments with different wave functions, possessing one, two, or three moving nodal points, are reported. Examples are given of regular and chaotic trajectories, and the statistics of the Lyapunov characteristic numbers of the orbits are found and compared to the number of encounter events of each orbit with the nodal-point- X -point complexes. The numerical results are in agreement with the theory, and various phenomena appearing at first as counterintuitive find a straightforward explanation.

  13. Duality between the Deconfined Quantum-Critical Point and the Bosonic Topological Transition

    Directory of Open Access Journals (Sweden)

    Yan Qi Qin

    2017-09-01

    Full Text Available Recently, significant progress has been made in (2+1-dimensional conformal field theories without supersymmetry. In particular, it was realized that different Lagrangians may be related by hidden dualities; i.e., seemingly different field theories may actually be identical in the infrared limit. Among all the proposed dualities, one has attracted particular interest in the field of strongly correlated quantum-matter systems: the one relating the easy-plane noncompact CP^{1} model (NCCP^{1} and noncompact quantum electrodynamics (QED with two flavors (N=2 of massless two-component Dirac fermions. The easy-plane NCCP^{1} model is the field theory of the putative deconfined quantum-critical point separating a planar (XY antiferromagnet and a dimerized (valence-bond solid ground state, while N=2 noncompact QED is the theory for the transition between a bosonic symmetry-protected topological phase and a trivial Mott insulator. In this work, we present strong numerical support for the proposed duality. We realize the N=2 noncompact QED at a critical point of an interacting fermion model on the bilayer honeycomb lattice and study it using determinant quantum Monte Carlo (QMC simulations. Using stochastic series expansion QMC simulations, we study a planar version of the S=1/2 J-Q spin Hamiltonian (a quantum XY model with additional multispin couplings and show that it hosts a continuous transition between the XY magnet and the valence-bond solid. The duality between the two systems, following from a mapping of their phase diagrams extending from their respective critical points, is supported by the good agreement between the critical exponents according to the proposed duality relationships. In the J-Q model, we find both continuous and first-order transitions, depending on the degree of planar anisotropy, with deconfined quantum criticality surviving only up to moderate strengths of the anisotropy. This explains previous claims of no deconfined

  14. Rounding by disorder of first-order quantum phase transitions: emergence of quantum critical points.

    Science.gov (United States)

    Goswami, Pallab; Schwab, David; Chakravarty, Sudip

    2008-01-11

    We give a heuristic argument for disorder rounding of a first-order quantum phase transition into a continuous phase transition. From both weak and strong disorder analysis of the N-color quantum Ashkin-Teller model in one spatial dimension, we find that, for N > or =3, the first-order transition is rounded to a continuous transition and the physical picture is the same as the random transverse field Ising model for a limited parameter regime. The results are strikingly different from the corresponding classical problem in two dimensions where the fate of the renormalization group flows is a fixed point corresponding to N-decoupled pure Ising models.

  15. Universality and Quantum Criticality of the One-Dimensional Spinor Bose Gas

    Science.gov (United States)

    PâÅ£u, Ovidiu I.; Klümper, Andreas; Foerster, Angela

    2018-06-01

    We investigate the universal thermodynamics of the two-component one-dimensional Bose gas with contact interactions in the vicinity of the quantum critical point separating the vacuum and the ferromagnetic liquid regime. We find that the quantum critical region belongs to the universality class of the spin-degenerate impenetrable particle gas which, surprisingly, is very different from the single-component case and identify its boundaries with the peaks of the specific heat. In addition, we show that the compressibility Wilson ratio, which quantifies the relative strength of thermal and quantum fluctuations, serves as a good discriminator of the quantum regimes near the quantum critical point. Remarkably, in the Tonks-Girardeau regime, the universal contact develops a pronounced minimum, reflected in a counterintuitive narrowing of the momentum distribution as we increase the temperature. This momentum reconstruction, also present at low and intermediate momenta, signals the transition from the ferromagnetic to the spin-incoherent Luttinger liquid phase and can be detected in current experiments with ultracold atomic gases in optical lattices.

  16. Quantum chemical calculations in the structural analysis of phloretin

    Science.gov (United States)

    Gómez-Zavaglia, Andrea

    2009-07-01

    In this work, a conformational search on the molecule of phloretin [2',4',6'-Trihydroxy-3-(4-hydroxyphenyl)-propiophenone] has been performed. The molecule of phloretin has eight dihedral angles, four of them taking part in the carbon backbone and the other four, related with the orientation of the hydroxyl groups. A systematic search involving a random variation of the dihedral angles has been used to generate input structures for the quantum chemical calculations. Calculations at the DFT(B3LYP)/6-311++G(d,p) level of theory permitted the identification of 58 local minima belonging to the C 1 symmetry point group. The molecular structures of the conformers have been analyzed using hierarchical cluster analysis. This method allowed us to group conformers according to their similarities, and thus, to correlate the conformers' stability with structural parameters. The dendrogram obtained from the hierarchical cluster analysis depicted two main clusters. Cluster I included all the conformers with relative energies lower than 25 kJ mol -1 and cluster II, the remaining conformers. The possibility of forming intramolecular hydrogen bonds resulted the main factor contributing for the stability. Accordingly, all conformers depicting intramolecular H-bonds belong to cluster I. These conformations are clearly favored when the carbon backbone is as planar as possible. The values of the νC dbnd O and νOH vibrational modes were compared among all the conformers of phloretin. The redshifts associated with intramolecular H-bonds were correlated with the H-bonds distances and energies.

  17. Critical excitation spectrum of a quantum chain with a local three-spin coupling.

    Science.gov (United States)

    McCabe, John F; Wydro, Tomasz

    2011-09-01

    Using the phenomenological renormalization group (PRG), we evaluate the low-energy excitation spectrum along the critical line of a quantum spin chain having a local interaction between three Ising spins and longitudinal and transverse magnetic fields, i.e., a Turban model. The low-energy excitation spectrum found with the PRG agrees with the spectrum predicted for the (D(4),A(4)) conformal minimal model under a nontrivial correspondence between translations at the critical line and discrete lattice translations. Under this correspondence, the measurements confirm a prediction that the critical line of this quantum spin chain and the critical point of the two-dimensional three-state Potts model are in the same universality class.

  18. Critical excitation spectrum of a quantum chain with a local three-spin coupling

    International Nuclear Information System (INIS)

    McCabe, John F.; Wydro, Tomasz

    2011-01-01

    Using the phenomenological renormalization group (PRG), we evaluate the low-energy excitation spectrum along the critical line of a quantum spin chain having a local interaction between three Ising spins and longitudinal and transverse magnetic fields, i.e., a Turban model. The low-energy excitation spectrum found with the PRG agrees with the spectrum predicted for the (D 4 ,A 4 ) conformal minimal model under a nontrivial correspondence between translations at the critical line and discrete lattice translations. Under this correspondence, the measurements confirm a prediction that the critical line of this quantum spin chain and the critical point of the two-dimensional three-state Potts model are in the same universality class.

  19. Quantum critical phase and Lifshitz transition in an extended periodic Anderson model

    International Nuclear Information System (INIS)

    Laad, M S; Koley, S; Taraphder, A

    2012-01-01

    We study the quantum phase transition in f-electron systems as a quantum Lifshitz transition driven by selective-Mott localization in a realistic extended Anderson lattice model. Using dynamical mean-field theory (DMFT), we find that a quantum critical phase with anomalous ω/T scaling separates a heavy Landau-Fermi liquid from ordered phase(s). This non-Fermi liquid state arises from a lattice orthogonality catastrophe originating from orbital-selective Mott localization. Fermi surface reconstruction occurs via the interplay between and penetration of the Green function zeros to the poles, leading to violation of Luttinger’s theorem in the strange metal. We show how this naturally leads to scale-invariant responses in transport. Thus, our work represents a specific DMFT realization of the hidden-FL and FL* theories, and holds promise for the study of ‘strange’ metal phases in quantum matter. (fast track communication)

  20. Quantum criticality of geometric phase in coupled optical cavity arrays under linear quench

    OpenAIRE

    Sarkar, Sujit

    2013-01-01

    The atoms trapped in microcavities and interacting through the exchange of virtual photons can be modeled as an anisotropic Heisenberg spin-1/2 lattice. We study the dynamics of the geometric phase of this system under the linear quenching process of laser field detuning which shows the XX criticality of the geometric phase in presence of single Rabi frequency oscillation. We also study the quantum criticality for different quenching rate in the presence of single or two Rabi frequencies osci...

  1. Topology and Edge Modes in Quantum Critical Chains

    Science.gov (United States)

    Verresen, Ruben; Jones, Nick G.; Pollmann, Frank

    2018-02-01

    We show that topology can protect exponentially localized, zero energy edge modes at critical points between one-dimensional symmetry-protected topological phases. This is possible even without gapped degrees of freedom in the bulk—in contrast to recent work on edge modes in gapless chains. We present an intuitive picture for the existence of these edge modes in the case of noninteracting spinless fermions with time-reversal symmetry (BDI class of the tenfold way). The stability of this phenomenon relies on a topological invariant defined in terms of a complex function, counting its zeros and poles inside the unit circle. This invariant can prevent two models described by the same conformal field theory (CFT) from being smoothly connected. A full classification of critical phases in the noninteracting BDI class is obtained: Each phase is labeled by the central charge of the CFT, c ∈1/2 N , and the topological invariant, ω ∈Z . Moreover, c is determined by the difference in the number of edge modes between the phases neighboring the transition. Numerical simulations show that the topological edge modes of critical chains can be stable in the presence of interactions and disorder.

  2. Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain

    DEFF Research Database (Denmark)

    Stone, M.B.; Reich, D.H.; Broholm, C.

    2003-01-01

    Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/Jless than or equal to0.025 for H=0 and H=8.7 T, where...

  3. Matter fields near quantum critical point in (2+1)-dimensional U(1) gauge theory

    International Nuclear Information System (INIS)

    Liu Guozhu; Li Wei; Cheng Geng

    2010-01-01

    We study chiral phase transition and confinement of matter fields in (2+1)-dimensional U(1) gauge theory of massless Dirac fermions and scalar bosons. The vanishing scalar boson mass, r=0, defines a quantum critical point between the Higgs phase and the Coulomb phase. We consider only the critical point r=0 and the Coulomb phase with r>0. The Dirac fermion acquires a dynamical mass when its flavor is less than certain critical value N f c , which depends quantitatively on the flavor N b and the scalar boson mass r. When N f f c , the matter fields carrying internal gauge charge are all confined if r≠0 but are deconfined at the quantum critical point r=0. The system has distinct low-energy elementary excitations at the critical point r=0 and in the Coulomb phase with r≠0. We calculate the specific heat and susceptibility of the system at r=0 and r≠0, which can help to detect the quantum critical point and to judge whether dynamical fermion mass generation takes place.

  4. Quantum chemical modeling of zeolite-catalyzed methylation reactions: toward chemical accuracy for barriers.

    Science.gov (United States)

    Svelle, Stian; Tuma, Christian; Rozanska, Xavier; Kerber, Torsten; Sauer, Joachim

    2009-01-21

    The methylation of ethene, propene, and t-2-butene by methanol over the acidic microporous H-ZSM-5 catalyst has been investigated by a range of computational methods. Density functional theory (DFT) with periodic boundary conditions (PBE functional) fails to describe the experimentally determined decrease of apparent energy barriers with the alkene size due to inadequate description of dispersion forces. Adding a damped dispersion term expressed as a parametrized sum over atom pair C(6) contributions leads to uniformly underestimated barriers due to self-interaction errors. A hybrid MP2:DFT scheme is presented that combines MP2 energy calculations on a series of cluster models of increasing size with periodic DFT calculations, which allows extrapolation to the periodic MP2 limit. Additionally, errors caused by the use of finite basis sets, contributions of higher order correlation effects, zero-point vibrational energy, and thermal contributions to the enthalpy were evaluated and added to the "periodic" MP2 estimate. This multistep approach leads to enthalpy barriers at 623 K of 104, 77, and 48 kJ/mol for ethene, propene, and t-2-butene, respectively, which deviate from the experimentally measured values by 0, +13, and +8 kJ/mol. Hence, enthalpy barriers can be calculated with near chemical accuracy, which constitutes significant progress in the quantum chemical modeling of reactions in heterogeneous catalysis in general and microporous zeolites in particular.

  5. Acute enhancement of the upper critical field for superconductivity approaching a quantum critical point in URhGe

    Energy Technology Data Exchange (ETDEWEB)

    Levy, F; Huxley, A [CEA, SPSMS, DRFMC, F-38054 Grenoble, (France); Levy, F; Sheikin, I [CNRS, GHMFL, F-38042 Grenoble, (France); Huxley, A [Univ Edinburgh, Scottish Univ Phys Alliance, Sch Phys, Edinburgh EH9 3JZ, Midlothian, (United Kingdom)

    2007-07-01

    When a pure material is tuned to the point where a continuous phase-transition line is crossed at zero temperature, known as a quantum critical point (QCP), completely new correlated quantum ordered states can form. These phases include exotic forms of superconductivity. However, as superconductivity is generally suppressed by a magnetic field, the formation of superconductivity ought not to be possible at extremely high field. Here, we report that as we tune the ferromagnet, URhGe, towards a QCP by applying a component of magnetic field in the material's easy magnetic plane, superconductivity survives in progressively higher fields applied simultaneously along the material's magnetic hard axis. Thus, although superconductivity never occurs above a temperature of 0.5 K, we find that it can survive in extremely high magnetic fields, exceeding 28 T. (authors)

  6. A quantum criticality perspective on the charging of narrow quantum-dot levels

    OpenAIRE

    Kashcheyevs, V.; Karrasch, C.; Hecht, T.; Weichselbaum, A.; Meden, V.; Schiller, A.

    2008-01-01

    Understanding the charging of exceptionally narrow levels in quantum dots in the presence of interactions remains a challenge within mesoscopic physics. We address this fundamental question in the generic model of a narrow level capacitively coupled to a broad one. Using bosonization we show that for arbitrary capacitive coupling charging can be described by an analogy to the magnetization in the anisotropic Kondo model, featuring a low-energy crossover scale that depends in a power-law fashi...

  7. Vertex functions at finite momentum: Application to antiferromagnetic quantum criticality

    Science.gov (United States)

    Wölfle, Peter; Abrahams, Elihu

    2016-02-01

    We analyze the three-point vertex function that describes the coupling of fermionic particle-hole pairs in a metal to spin or charge fluctuations at nonzero momentum. We consider Ward identities, which connect two-particle vertex functions to the self-energy, in the framework of a Hubbard model. These are derived using conservation laws following from local symmetries. The generators considered are the spin density and particle density. It is shown that at certain antiferromagnetic critical points, where the quasiparticle effective mass is diverging, the vertex function describing the coupling of particle-hole pairs to the spin density Fourier component at the antiferromagnetic wave vector is also divergent. Then we give an explicit calculation of the irreducible vertex function for the case of three-dimensional antiferromagnetic fluctuations, and show that it is proportional to the diverging quasiparticle effective mass.

  8. Field-induced quantum criticality of a spin-1/2 planar ferromagnet

    International Nuclear Information System (INIS)

    Mercaldo, M T; Rabuffo, I; Cesare, L De; D'Auria, A Caramico

    2009-01-01

    The low-temperature critical properties and crossovers of a spin- 1/2 planar ferromagnet in a longitudinal magnetic field are explored in terms of an anisotropic bosonic action, suitable to describe the spin model in the low-temperature regime. This is performed adopting a procedure which combines an averaging over dynamic degrees of freedom and the classical Wilson renormalization group transformation. Within this framework we get the phase boundary, ending in a quantum critical point, and general expressions for the correlation length and susceptibility as functions of the temperature and the applied magnetic field within the disordered phase. In particular, two crossovers occur decreasing the temperature with the magnetic field fixed at its quantum critical point value, which might be actually observable in complex magnetic compounds, as suggested by recent experiments.

  9. Quantum influence in the criticality of the spin- {1}/{2} anisotropic Heisenberg model

    Science.gov (United States)

    Ricardo de Sousa, J.; Araújo, Ijanílio G.

    1999-07-01

    We study the spin- {1}/{2} anisotropic Heisenberg antiferromagnetic model using the effective field renormalization group (EFRG) approach. The EFRG method is illustrated by employing approximations in which clusters with one ( N'=1) and two ( N=2) spins are used. The dependence of the critical temperature Tc (ferromagnetic-F case) and TN (antiferromagnetic-AF case) and thermal critical exponent, Yt, are obtained as a function of anisotropy parameter ( Δ) on a simple cubic lattice. We find that, in our results, TN is higher than Tc for the quantum anisotropic Heisenberg limit and TN= Tc for the Ising and quantum XY limits. We have also shown that the thermal critical exponent Yt for the isotropic Heisenberg model shows a small dependence on the type of interaction (F or AF) due to finite size effects.

  10. Critical behavior of the quantum spin- {1}/{2} anisotropic Heisenberg model

    Science.gov (United States)

    Sousa, J. Ricardo de

    A two-step renormalization group approach - a decimation followed by an effective field renormalization group (EFRG) - is proposed in this work to study the critical behavior of the quantum spin- {1}/{2} anisotropic Heisenberg model. The new method is illustrated by employing approximations in which clusters with one, two and three spins are used. The values of the critical parameter and critical exponent, in two- and three-dimensional lattices, for the Ising and isotropic Heisenberg limits are calculated and compared with other renormalization group approaches and exact (or series) results.

  11. Identification of the low-energy excitations in a quantum critical system

    Directory of Open Access Journals (Sweden)

    Tom Heitmann

    2017-05-01

    Full Text Available We have identified low-energy magnetic excitations in a doped quantum critical system by means of polarized neutron scattering experiments. The presence of these excitations could explain why Ce(Fe0.76Ru0.242Ge2 displays dynamical scaling in the absence of local critical behavior or long-range spin-density wave criticality. The low-energy excitations are associated with the reorientations of the superspins of fully ordered, isolated magnetic clusters that form spontaneously upon lowering the temperature. The system houses both frozen clusters and dynamic clusters, as predicted by Hoyos and Vojta [Phys. Rev. B 74, 140401(R (2006].

  12. Coherent inflationary dynamics for Bose-Einstein condensates crossing a quantum critical point

    Science.gov (United States)

    Feng, Lei; Clark, Logan W.; Gaj, Anita; Chin, Cheng

    2018-03-01

    Quantum phase transitions, transitions between many-body ground states, are of extensive interest in research ranging from condensed-matter physics to cosmology1-4. Key features of the phase transitions include a stage with rapidly growing new order, called inflation in cosmology5, followed by the formation of topological defects6-8. How inflation is initiated and evolves into topological defects remains a hot topic of debate. Ultracold atomic gas offers a pristine and tunable platform to investigate quantum critical dynamics9-21. We report the observation of coherent inflationary dynamics across a quantum critical point in driven Bose-Einstein condensates. The inflation manifests in the exponential growth of density waves and populations in well-resolved momentum states. After the inflation stage, extended coherent dynamics is evident in both real and momentum space. We present an intuitive description of the quantum critical dynamics in our system and demonstrate the essential role of phase fluctuations in the formation of topological defects.

  13. On the possibility of complete revivals after quantum quenches to a critical point

    Science.gov (United States)

    Najafi, K.; Rajabpour, M. A.

    2017-07-01

    In a recent letter [J. Cardy, Phys. Rev. Lett. 112, 220401 (2014), 10.1103/PhysRevLett.112.220401], the author made a very interesting observation that complete revivals of quantum states after quantum quench can happen in a period that is a fraction of the system size. This is possible for critical systems that can be described by minimal conformal field theories with central charge c detect a regime in the phase diagram of the XY chain in which one can not determine the period of the partial revivals using the quasiparticle picture.

  14. Some critical considerations on the present epistemological and scientific debate on quantum mechanics

    International Nuclear Information System (INIS)

    Ghirardi, G.C.

    1985-09-01

    Some general methodological considerations aimed to guarantee the necessary logical rigor to the present debate on quantum mechanics are presented. In particular some misunderstandings about the implications of the critical analysis put forward by Einstein, Podolsky and Rosen (EPR) which can be found in the literature, are discussed. These misunderstandings are shown to arise from possible underestimates, overestimates and misinterpretations of the EPR argument. It is argued that the difficulties pointed out by EPR are, in a sense that will be defined precisely, unavoidable. A model which tries to solve the difficulties arising from quantum non separability effects when macroscopic systems are involved, is briefly sketched. (author)

  15. Quantum chemical aided prediction of the thermal decomposition mechanisms and temperatures of ionic liquids

    International Nuclear Information System (INIS)

    Kroon, Maaike C.; Buijs, Wim; Peters, Cor J.; Witkamp, Geert-Jan

    2007-01-01

    The long-term thermal stability of ionic liquids is of utmost importance for their industrial application. Although the thermal decomposition temperatures of various ionic liquids have been measured previously, experimental data on the thermal decomposition mechanisms and kinetics are scarce. It is desirable to develop quantitative chemical tools that can predict thermal decomposition mechanisms and temperatures (kinetics) of ionic liquids. In this work ab initio quantum chemical calculations (DFT-B3LYP) have been used to predict thermal decomposition mechanisms, temperatures and the activation energies of the thermal breakdown reactions. These quantum chemical calculations proved to be an excellent method to predict the thermal stability of various ionic liquids

  16. Modeling the role of microplastics in Bioaccumulation of organic chemicals to marine aquatic organisms. Critical Review

    NARCIS (Netherlands)

    Koelmans, A.A.

    2015-01-01

    It has been shown that ingestion of microplastics may increase bioaccumulation of organic chemicals by aquatic organisms. This paper critically reviews the literature on the effects of plastic ingestion on the bioaccumulation of organic chemicals, emphasizing quantitative approaches and mechanistic

  17. Increasing the critical thickness of InGaAs quantum wells using strain-relief technologies

    Science.gov (United States)

    Jones, Andrew Marquis

    The advantages of optical communication through silica fiber have made long-distance electrical communication through copper wire obsolete. The two windows of operation for long-haul optical communication are centered around the wavelengths of 1.3 mum and 1.55 mum, which have minimal amounts of signal attenuation and dispersion. Benefits of optical communications within these windows include low system costs, high bandwidth, and high system reliability which have encouraged the development of emitters and receivers at these relatively long wavelengths. Long-wavelength semiconductor lasers are typically fabricated on InP substrates, but their performance suffers greatly with increases in operating temperature. Laser diodes on GaAs substrates are not as sensitive to operating temperature due to quantum-well active regions with relative deep potential barriers, but critical thickness limits the wavelength ceiling to 1.1 mum. Strain-relief technologies are currently being investigated to enable long-wavelength lasers with deeper potential wells leading to a corresponding increase in characteristic temperatures. Having a larger lattice constant than GaAs enables ternary InGaAs substrates to increase the 1.1-mum wavelength ceiling. Extending this ceiling to one of the optical communication windows could enable high-characteristic-temperature, long-wavelength lasers. Broad-area and buried-heterostructure lasers have demonstrated the potential of ternary substrates to increase characteristic temperatures and emission wavelengths. Wavelengths as long as 1.15 mum and characteristic temperatures as high as 145 K have been achieved. Reduced-area metalorganic chemical vapor deposition involves the deposition of strained materials on isolated islands. Due to the discontinuous nature of reduced-area epitaxy, strained materials are allowed to expand near the mesa edges, decreasing the overall strain in the structure. Laser diodes using this technology have been successfully

  18. The Amplification of the Critical Temperature by Quantum Size Effects In a Superlattice of Quantum Wires

    International Nuclear Information System (INIS)

    Bianconi, A.; Missori, M.; Saini, N.L.; Oyanagi, H.; Yamaguchi, H.; Nishihara, Y.; Ha, D.H.; Della Longa, S.

    1995-01-01

    Here we report experimental evidence that the high Tc superconductivity in a cuprate perovskite occurs in a superlattice of quantum wires. The structure of the high Tc superconducting CuO 2 plane in Bi 2 Sr 2 CaCu 2 O 8+y (Bi2212) at the mesoscopic level (10-100 A) has been determined. It is decorated by a plurality of parallel superconducting stripes of width L=14± 1 A defined by the domain walls formed by stripes of width W=11+1 A characterized by a 0.17 A shorter Cu-O (apical) distance and a large tilting angle θ =12±4degree of the distorted square pyramids. We show that this particular heterostructure provides the physical mechanism raising Tc from the low temperature range Tc 2 plane by a factor ∼10 is realized by 1) tuning the Fermi level near the bottom of the second ubband of the stripes, with k y =2π/L, formed by the quantum size effect and 2) by forming a superlattice of wires with domain walls of width W of the order of the superconducting coherence length ξ 0 . (author)

  19. Quantum critical behavior in three-dimensional one-band Hubbard model at half-filling

    International Nuclear Information System (INIS)

    Karchev, Naoum

    2013-01-01

    A one-band Hubbard model with hopping parameter t and Coulomb repulsion U is considered at half-filling. By means of the Schwinger bosons and slave fermions representation of the electron operators and integrating out the spin–singlet Fermi fields an effective Heisenberg model with antiferromagnetic exchange constant is obtained for vectors which identifies the local orientation of the spin of the itinerant electrons. The amplitude of the spin vectors is an effective spin of the itinerant electrons accounting for the fact that some sites, in the ground state, are doubly occupied or empty. Accounting adequately for the magnon–magnon interaction the Néel temperature is calculated. When the ratio t/U is small enough (t/U ≤0.09) the effective model describes a system of localized electrons. Increasing the ratio increases the density of doubly occupied states which in turn decreases the effective spin and Néel temperature. The phase diagram in the plane of temperature (T N )/U and parameter t/U is presented. The quantum critical point (T N =0) is reached at t/U =0.9. The magnons in the paramagnetic phase are studied and the contribution of the magnons’ fluctuations to the heat capacity is calculated. At the Néel temperature the heat capacity has a peak which is suppressed when the system approaches a quantum critical point. It is important to stress that, at half-filling, the ground state, determined by fermions, is antiferromagnetic. The magnon fluctuations drive the system to quantum criticality and when the effective spin is critically small these fluctuations suppress the magnetic order. -- Highlights: •Technique of calculation is introduced which permits us to study the magnons’ fluctuations. •Quantum critical point is obtained in the one-band 3D Hubbard model at half-filling. •The present analytical results supplement the numerical ones (see Fig. 7)

  20. Nonlinear quenches of power-law confining traps in quantum critical systems

    International Nuclear Information System (INIS)

    Collura, Mario; Karevski, Dragi

    2011-01-01

    We describe the coherent quantum evolution of a quantum many-body system with a time-dependent power-law confining potential. The amplitude of the inhomogeneous potential is driven in time along a nonlinear ramp which crosses a critical point. Using Kibble-Zurek-like scaling arguments we derive general scaling laws for the density of excitations and energy excess generated during the nonlinear sweep of the confining potential. It is shown that, with respect to the sweeping rate, the densities follow algebraic laws with exponents that depend on the space-time properties of the potential and on the scaling dimensions of the densities. We support our scaling predictions with both analytical and numerical results on the Ising quantum chain with an inhomogeneous transverse field varying in time.

  1. Universal Scaling and Critical Exponents of the Anisotropic Quantum Rabi Model

    Science.gov (United States)

    Liu, Maoxin; Chesi, Stefano; Ying, Zu-Jian; Chen, Xiaosong; Luo, Hong-Gang; Lin, Hai-Qing

    2017-12-01

    We investigate the quantum phase transition of the anisotropic quantum Rabi model, in which the rotating and counterrotating terms are allowed to have different coupling strengths. The model interpolates between two known limits with distinct universal properties. Through a combination of analytic and numerical approaches, we extract the phase diagram, scaling functions, and critical exponents, which determine the universality class at finite anisotropy (identical to the isotropic limit). We also reveal other interesting features, including a superradiance-induced freezing of the effective mass and discontinuous scaling functions in the Jaynes-Cummings limit. Our findings are extended to the few-body quantum phase transitions with N >1 spins, where we expose the same effective parameters, scaling properties, and phase diagram. Thus, a stronger form of universality is established, valid from N =1 up to the thermodynamic limit.

  2. Quantum chemical analysis of potential anti-Parkinson agents

    Indian Academy of Sciences (India)

    Intermolecular binding energy components could not be analyzed by docking and due to this limitation, quantum mechanical (QM) calculations including functional B3LYP in association with split valence basis set (Def2-SVP) were applied to estimate the ligand-residue binding energies in the MAO-B active site. Moreover ...

  3. Superconductivity mediated by quantum critical antiferromagnetic fluctuations: The rise and fall of hot spots

    Science.gov (United States)

    Wang, Xiaoyu; Schattner, Yoni; Berg, Erez; Fernandes, Rafael M.

    2017-05-01

    In several unconventional superconductors, the highest superconducting transition temperature Tc is found in a region of the phase diagram where the antiferromagnetic transition temperature extrapolates to zero, signaling a putative quantum critical point. The elucidation of the interplay between these two phenomena—high-Tc superconductivity and magnetic quantum criticality—remains an important piece of the complex puzzle of unconventional superconductivity. In this paper, we combine sign-problem-free quantum Monte Carlo simulations and field-theoretical analytical calculations to unveil the microscopic mechanism responsible for the superconducting instability of a general low-energy model, called the spin-fermion model. In this approach, low-energy electronic states interact with each other via the exchange of quantum critical magnetic fluctuations. We find that even in the regime of moderately strong interactions, both the superconducting transition temperature and the pairing susceptibility are governed not by the properties of the entire Fermi surface, but instead by the properties of small portions of the Fermi surface called hot spots. Moreover, Tc increases with increasing interaction strength, until it starts to saturate at the crossover from hot-spots-dominated to Fermi-surface-dominated pairing. Our work provides not only invaluable insights into the system parameters that most strongly affect Tc, but also important benchmarks to assess the origin of superconductivity in both microscopic models and actual materials.

  4. Performance test of multicomponent quantum mechanical calculation with polarizable continuum model for proton chemical shift.

    Science.gov (United States)

    Kanematsu, Yusuke; Tachikawa, Masanori

    2015-05-21

    Multicomponent quantum mechanical (MC_QM) calculations with polarizable continuum model (PCM) have been tested against liquid (1)H NMR chemical shifts for a test set of 80 molecules. Improvement from conventional quantum mechanical calculations was achieved for MC_QM calculations. The advantage of the multicomponent scheme could be attributed to the geometrical change from the equilibrium geometry by the incorporation of the hydrogen nuclear quantum effect, while that of PCM can be attributed to the change of the electronic structure according to the polarization by solvent effects.

  5. Tuning electronic properties in graphene quantum dots by chemical functionalization: Density functional theory calculations

    Science.gov (United States)

    Abdelsalam, Hazem; Elhaes, Hanan; Ibrahim, Medhat A.

    2018-03-01

    The energy gap and dipole moment of chemically functionalized graphene quantum dots are investigated by density functional theory. The energy gap can be tuned through edge passivation by different elements or groups. Edge passivation by oxygen considerably decreases the energy gap in hexagonal nanodots. Edge states in triangular quantum dots can also be manipulated by passivation with fluorine. The dipole moment depends on: (a) shape and edge termination of the quantum dot, (b) attached group, and (c) position to which the groups are attached. Depending on the position of attached groups, the total dipole can be increased, decreased, or eliminated.

  6. Decofinement, dimensional crossover and quantum criticality in coupled correlated chains with frustration

    International Nuclear Information System (INIS)

    Lal, Siddhartha; Laad, Mukul S.

    2007-08-01

    The dynamics of the charge sector of a one-dimensional quarter-filled electronic system with extended Hubbard interactions were recently mapped onto that of an effective pseudospin transverse-field Ising model (TFIM) in the strong coupling limit. Motivated by studying the effects of inter-chain couplings, we investigate the phase diagram for the case of a system of many coupled effective (TFIM) chains. A random phase approximation analysis reveals a phase diagram with an ordered phase existing at finite temperatures. The phase boundary ends at a zero temperature quantum critical point. Critical quantum fluctuations are found to drive a zero temperature deconfinement transition, as well as enhance the dispersion of excitations in the transverse directions, leading to a dimensional crossover at finite temperatures. Our work is potentially relevant for a unified description of a class of strongly correlated, quarter-filled chain and ladder systems. (author)

  7. Ferromagnetic quantum criticality: New aspects from the phase diagram of LaCrGe3

    Science.gov (United States)

    Taufour, Valentin; Kaluarachchi, Udhara S.; Bud'ko, Sergey L.; Canfield, Paul C.

    2018-05-01

    Recent theoretical and experimental studies have shown that ferromagnetic quantum criticality is always avoided in clean systems. Two possibilities have been identified. In the first scenario, the ferromagnetic transition becomes of the first order at a tricritical point before being suppressed. A wing structure phase diagram is observed indicating the possibility of a new type of quantum critical point under magnetic field. In a second scenario, a transition to a modulated magnetic phase occurs. Our recent studies on the compound LaCrGe3 illustrate a third scenario where not only a new magnetic phase occurs, but also a change of order of the transition at a tricritical point leading to a wing-structure phase diagram. Careful experimental study of the phase diagram near the tricritical point also illustrates new rules near this type of point.

  8. Critical fluctuations and the rates of interstate switching near the excitation threshold of a quantum parametric oscillator.

    Science.gov (United States)

    Lin, Z R; Nakamura, Y; Dykman, M I

    2015-08-01

    We study the dynamics of a nonlinear oscillator near the critical point where period-two vibrations are first excited with the increasing amplitude of parametric driving. Above the threshold, quantum fluctuations induce transitions between the period-two states over the quasienergy barrier. We find the effective quantum activation energies for such transitions and their scaling with the difference of the driving amplitude from its critical value. We also find the scaling of the fluctuation correlation time with the quantum noise parameters in the critical region near the threshold. The results are extended to oscillators with nonlinear friction.

  9. Quantum chemical evaluation for the stability of liquid sodium containing titanium nanoparticles

    International Nuclear Information System (INIS)

    Suzuki, Ai; Inaba, Kenji; Ishizawa, Yukie; Miura, Ryuji; Hatakeyama, Nozomu; Miyamoto, Akira; Saito, Jun-ichi; Ara, Kuniaki

    2015-01-01

    Recently, liquid sodium containing titanium nanoparticles (LSnanop) have attracted considerable attention. In this study, suspension state of Ti nanoparticle in liquid sodium was quantum chemically evaluated. The atomic interaction between Ti nanoparticles and sodium atoms in the liquid sodium medium was investigated. There were some literatures which gained quantum chemical insight into a nanoparticle with the surrounding sodium atom. However, liquid sodium medium itself together with a Ti nanoparticle under the realistic temperature has not yet been investigated theoretically. To overcome the problem of conventional theoretical method, we applied computationally low-load Tight Binding Quantum Chemical Molecular Dynamics (TB-QCMD) calculation method to investigate the suspension state of the Ti nanoparticle in liquid sodium metal. (author)

  10. Quantum chemical investigation of levofloxacin-boron complexes: A computational approach

    Science.gov (United States)

    Sayin, Koray; Karakaş, Duran

    2018-04-01

    Quantum chemical calculations are performed over some boron complexes with levofloxacin. Boron complex with fluorine atoms are optimized at three different methods (HF, B3LYP and M062X) with 6-31 + G(d) basis set. The best level is determined as M062X/6-31 + G(d) by comparison of experimental and calculated results of complex (1). The other complexes are optimized by using the best level. Structural properties, IR and NMR spectrum are examined in detail. Biological activities of mentioned complexes are investigated by some quantum chemical descriptors and molecular docking analyses. As a result, biological activities of complex (2) and (4) are close to each other and higher than those of other complexes. Additionally, NLO properties of mentioned complexes are investigated by some quantum chemical parameters. It is found that complex (3) is the best candidate for NLO applications.

  11. Electron-beam generated porous dextran gels: experimental and quantum chemical studies.

    Science.gov (United States)

    Naumov, Sergej; Knolle, Wolfgang; Becher, Jana; Schnabelrauch, Matthias; Reichelt, Senta

    2014-06-01

    The aim of this work was to investigate the reaction mechanism of electron-beam generated macroporous dextran cryogels by quantum chemical calculation and electron paramagnetic resonance measurements. Electron-beam radiation was used to initiate the cross-linking reaction of methacrylated dextran in semifrozen aqueous solutions. The pore morphology of the resulting cryogels was visualized by scanning electron microscopy. Quantum chemical calculations and electron paramagnetic resonance studies provided information on the most probable reaction pathway and the chain growth radicals. The most probable reaction pathway was a ring opening reaction and the addition of a C-atom to the double-bond of the methacrylated dextran molecule. First detailed quantum chemical calculation on the reaction mechanism of electron-beam initiated cross-linking reaction of methacrylated dextran are presented.

  12. Relative criterion for validity of a semiclassical approach to the dynamics near quantum critical points.

    Science.gov (United States)

    Wang, Qian; Qin, Pinquan; Wang, Wen-ge

    2015-10-01

    Based on an analysis of Feynman's path integral formulation of the propagator, a relative criterion is proposed for validity of a semiclassical approach to the dynamics near critical points in a class of systems undergoing quantum phase transitions. It is given by an effective Planck constant, in the relative sense that a smaller effective Planck constant implies better performance of the semiclassical approach. Numerical tests of this relative criterion are given in the XY model and in the Dicke model.

  13. Rare-Region-Induced Avoided Quantum Criticality in Disordered Three-Dimensional Dirac and Weyl Semimetals

    Directory of Open Access Journals (Sweden)

    J. H. Pixley

    2016-06-01

    Full Text Available We numerically study the effect of short-ranged potential disorder on massless noninteracting three-dimensional Dirac and Weyl fermions, with a focus on the question of the proposed (and extensively theoretically studied quantum critical point separating semimetal and diffusive-metal phases. We determine the properties of the eigenstates of the disordered Dirac Hamiltonian (H and exactly calculate the density of states (DOS near zero energy, using a combination of Lanczos on H^{2} and the kernel polynomial method on H. We establish the existence of two distinct types of low-energy eigenstates contributing to the disordered density of states in the weak-disorder semimetal regime. These are (i typical eigenstates that are well described by linearly dispersing perturbatively dressed Dirac states and (ii nonperturbative rare eigenstates that are weakly dispersive and quasilocalized in the real-space regions with the largest (and rarest local random potential. Using twisted boundary conditions, we are able to systematically find and study these two (essentially independent types of eigenstates. We find that the Dirac states contribute low-energy peaks in the finite-size DOS that arise from the clean eigenstates which shift and broaden in the presence of disorder. On the other hand, we establish that the rare quasilocalized eigenstates contribute a nonzero background DOS which is only weakly energy dependent near zero energy and is exponentially small at weak disorder. We also find that the expected semimetal to diffusive-metal quantum critical point is converted to an avoided quantum criticality that is “rounded out” by nonperturbative effects, with no signs of any singular behavior in the DOS at the energy of the clean Dirac point. However, the crossover effects of the avoided (or hidden criticality manifest themselves in a so-called quantum critical fan region away from the Dirac energy. We discuss the implications of our results for

  14. Non-critical string theory formulation of microtubule dynamics and quantum aspects of brain function

    CERN Document Server

    Mavromatos, Nikolaos E

    1995-01-01

    Microtubule (MT) networks, subneural paracrystalline cytosceletal structures, seem to play a fundamental role in the neurons. We cast here the complicated MT dynamics in the form of a 1+1-dimensional non-critical string theory, thus enabling us to provide a consistent quantum treatment of MTs, including enviromental {\\em friction} effects. We suggest, thus, that the MTs are the microsites, in the brain, for the emergence of stable, macroscopic quantum coherent states, identifiable with the {\\em preconscious states}. Quantum space-time effects, as described by non-critical string theory, trigger then an {\\em organized collapse} of the coherent states down to a specific or {\\em conscious state}. The whole process we estimate to take {\\cal O}(1\\,{\\rm sec}), in excellent agreement with a plethora of experimental/observational findings. The {\\em microscopic arrow of time}, endemic in non-critical string theory, and apparent here in the self-collapse process, provides a satisfactory and simple resolution to the age...

  15. Quantum criticality and emergence of the T/B scaling in strongly correlated metals

    International Nuclear Information System (INIS)

    Watanabe, Shinji; Miyake, Kazumasa

    2016-01-01

    A new type of scaling observed in heavy-electron metal β-YbAlB_4, where the magnetic susceptibility is expressed as a single scaling function of the ratio of temperature T and magnetic field B over four decades, is examined theoretically. We develop the mode-coupling theory for critical Yb-valence fluctuations under a magnetic field, verifying that the T/B scaling behavior appears near the QCP of the valence transition. Emergence of the T/B scaling indicates the presence of the small characteristic temperature of the critical Yb-valence fluctuation due to the strong local correlation effect. It is discussed that the T/B scaling as well as the unconventional criticality is explained from the viewpoint of the quantum valence criticality in a unified way.

  16. Quantum criticality and first-order transitions in the extended periodic Anderson model

    Science.gov (United States)

    Hagymási, I.; Itai, K.; Sólyom, J.

    2013-03-01

    We investigate the behavior of the periodic Anderson model in the presence of d-f Coulomb interaction (Udf) using mean-field theory, variational calculation, and exact diagonalization of finite chains. The variational approach based on the Gutzwiller trial wave function gives a critical value of Udf and two quantum critical points (QCPs), where the valence susceptibility diverges. We derive the critical exponent for the valence susceptibility and investigate how the position of the QCP depends on the other parameters of the Hamiltonian. For larger values of Udf, the Kondo regime is bounded by two first-order transitions. These first-order transitions merge into a triple point at a certain value of Udf. For even larger Udf valence skipping occurs. Although the other methods do not give a critical point, they support this scenario.

  17. Singularity of the London penetration depth at quantum critical points in superconductors.

    Science.gov (United States)

    Chowdhury, Debanjan; Swingle, Brian; Berg, Erez; Sachdev, Subir

    2013-10-11

    We present a general theory of the singularity in the London penetration depth at symmetry-breaking and topological quantum critical points within a superconducting phase. While the critical exponents and ratios of amplitudes on the two sides of the transition are universal, an overall sign depends upon the interplay between the critical theory and the underlying Fermi surface. We determine these features for critical points to spin density wave and nematic ordering, and for a topological transition between a superconductor with Z2 fractionalization and a conventional superconductor. We note implications for recent measurements of the London penetration depth in BaFe2(As(1-x)P(x))2 [K. Hashimoto et al., Science 336, 1554 (2012)].

  18. Conductivity of Weakly Disordered Metals Close to a "Ferromagnetic" Quantum Critical Point

    Science.gov (United States)

    Kastrinakis, George

    2018-05-01

    We calculate analytically the conductivity of weakly disordered metals close to a "ferromagnetic" quantum critical point in the low-temperature regime. Ferromagnetic in the sense that the effective carrier potential V(q,ω ), due to critical fluctuations, is peaked at zero momentum q=0. Vertex corrections, due to both critical fluctuations and impurity scattering, are explicitly considered. We find that only the vertex corrections due to impurity scattering, combined with the self-energy, generate appreciable effects as a function of the temperature T and the control parameter a, which measures the proximity to the critical point. Our results are consistent with resistivity experiments in several materials displaying typical Fermi liquid behaviour, but with a diverging prefactor of the T^2 term for small a.

  19. Quantum criticality and emergence of the T/B scaling in strongly correlated metals

    Energy Technology Data Exchange (ETDEWEB)

    Watanabe, Shinji [Department of Basic Sciences, Kyushu Institute of Technology, Kitakyushu (Japan); Miyake, Kazumasa [Toyota Physical and Chemical Research Institute, Nagakute (Japan)

    2016-02-15

    A new type of scaling observed in heavy-electron metal β-YbAlB{sub 4}, where the magnetic susceptibility is expressed as a single scaling function of the ratio of temperature T and magnetic field B over four decades, is examined theoretically. We develop the mode-coupling theory for critical Yb-valence fluctuations under a magnetic field, verifying that the T/B scaling behavior appears near the QCP of the valence transition. Emergence of the T/B scaling indicates the presence of the small characteristic temperature of the critical Yb-valence fluctuation due to the strong local correlation effect. It is discussed that the T/B scaling as well as the unconventional criticality is explained from the viewpoint of the quantum valence criticality in a unified way.

  20. Evaluation of quantum-chemical methods of radiolysis stability for macromolecular structures

    International Nuclear Information System (INIS)

    Postolache, Cristian; Matei, Lidia

    2005-01-01

    The behavior of macromolecular structures in ionising fields was analyzed by quantum-chemical methods. In this study the primary radiolytic effect was analyzed using a two-step radiolytic mechanism: a) ionisation of molecule and spatial redistribution of atoms in order to reach a minimum value of energy, characteristic to the quantum state; b) neutralisation of the molecule by electron capture and its rapid dissociation into free radicals. Chemical bonds suspected to break are located in the distribution region of LUMO orbital and have minimal homolytic dissociation energies. Representative polymer structures (polyethylene, polypropylene, polystyrene, poly α and β polystyrene, polyisobutylene, polytetrafluoroethylene, poly methylsiloxanes) were analyzed. (authors)

  1. Differential multiple quantum relaxation caused by chemical exchange outside the fast exchange limit

    International Nuclear Information System (INIS)

    Wang Chunyu; Palmer, Arthur G.

    2002-01-01

    Differential relaxation of multiple quantum coherences is a signature for chemical exchange processes in proteins. Previous analyses of experimental data have used theoretical descriptions applicable only in the limit of fast exchange. Theoretical expressions for differential relaxation rate constants that are accurate outside fast exchange are presented for two-spin-system subject to two-site chemical exchange. The theoretical expressions are validated using experimental results for 15 N- 1 H relaxation in basic pancreatic trypsin inhibitor. The new theoretical expression is valuable for identification and characterization of exchange processes in proteins using differential relaxation of multiple quantum coherences

  2. Non-Fermi Liquid Behavior Close to a Quantum Critical Point in a Ferromagnetic State without Local Moments

    Directory of Open Access Journals (Sweden)

    E. Svanidze

    2015-03-01

    Full Text Available A quantum critical point (QCP occurs upon chemical doping of the weak itinerant ferromagnet Sc_{3.1}In. Remarkable for a system with no local moments, the QCP is accompanied by non-Fermi liquid behavior, manifested in the logarithmic divergence of the specific heat both in the ferro-and the paramagnetic states, as well as linear temperature dependence of the low-temperature resistivity. With doping, critical scaling is observed close to the QCP, as the critical exponents δ, γ, and β have weak composition dependence, with δ nearly twice and β almost half of their respective mean-field values. The unusually large paramagnetic moment μ_{PM}∼1.3μ_{B}/F.U. is nearly composition independent. Evidence for strong spin fluctuations, accompanying the QCP at x_{c}=0.035±0.005, may be ascribed to the reduced dimensionality of Sc_{3.1}In, associated with the nearly one-dimensional Sc-In chains.

  3. Ising critical behaviour in the one-dimensional frustrated quantum XY model

    International Nuclear Information System (INIS)

    Granato, E.

    1993-06-01

    A generalization of the one-dimensional frustrated quantum XY model is considered in which the inter and intra-chain coupling constants of the two infinite XY (planar rotor) chains have different strengths. The model can describe the superconductor-insulator transition due to charging effects in a ladder of Josephson junctions in a magnetic field with half a flux quantum per plaquette. From a fluctuation-effective action, this transition is expected to be in the universality class of the two-dimensional classical XY-Ising model. The critical behaviour is studied using a Monte Carlo transfer matrix applied to the path-integral representation of the model and a finite-size-scaling analysis of data on small system sizes. It is found that, unlike the previous studied case of equal inter and intra-chain coupling constants, the XY and Ising-like excitations of the quantum model decouple for large interchain coupling, giving rise to pure Ising model critical behaviour for the chirality order parameter in good agreement with the results for the XY-Ising model. (author). 18 refs, 4 figs

  4. Universal Quantum Criticality in the Metal-Insulator Transition of Two-Dimensional Interacting Dirac Electrons

    Directory of Open Access Journals (Sweden)

    Yuichi Otsuka

    2016-03-01

    Full Text Available The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.

  5. Physico-chemical mechanism for the vapors sensitivity of photoluminescent InP quantum dots

    Science.gov (United States)

    Prosposito, P.; De Angelis, R.; De Matteis, F.; Hatami, F.; Masselink, W. T.; Zhang, H.; Casalboni, M.

    2016-03-01

    InP/InGaP surface quantum dots are interesting materials for optical chemical sensors since they present an intense emission at room temperature, whose intensity changes rapidly and reversibly depending on the composition of the environmental atmosphere. We present here their emission properties by time resolved photoluminescence spectroscopy investigation and we discuss the physico-chemical mechanism behind their sensitivity to the surrounding atmosphere. Photoluminescence transients in inert atmosphere (N2) and in solvent vapours of methanol, clorophorm, acetone and water were measured. The presence of vapors of clorophorm, acetone and water showed a very weak effect on the transient times, while an increase of up to 15% of the decay time was observed for methanol vapour exposure. On the basis of the vapor molecule nature (polarity, proticity, steric hindrance, etc.) and of the interaction of the vapor molecules with the quantum dots surface a sensing mechanism involving quantum dots non-radiative surface states is proposed.

  6. Physico-chemical mechanism for the vapors sensitivity of photoluminescent InP quantum dots

    International Nuclear Information System (INIS)

    Prosposito, P.; De Angelis, R.; De Matteis, F.; Casalboni, M.; Hatami, F.; Masselink, W.T.; Zhang, H.

    2016-01-01

    InP/InGaP surface quantum dots are interesting materials for optical chemical sensors since they present an intense emission at room temperature, whose intensity changes rapidly and reversibly depending on the composition of the environmental atmosphere. We present here their emission properties by time resolved photoluminescence spectroscopy investigation and we discuss the physico-chemical mechanism behind their sensitivity to the surrounding atmosphere. Photoluminescence transients in inert atmosphere (N 2 ) and in solvent vapours of methanol, chloroform, acetone and water were measured. The presence of vapors of chloroform, acetone and water showed a very weak effect on the transient times, while an increase of up to 15% of the decay time was observed for methanol vapour exposure. On the basis of the vapor molecule nature (polarity, proticity, steric hindrance, etc.) and of the interaction of the vapor molecules with the quantum dots surface a sensing mechanism involving quantum dots non-radiative surface states is proposed. (paper)

  7. Predicting allergic contact dermatitis: a hierarchical structure activity relationship (SAR) approach to chemical classification using topological and quantum chemical descriptors

    Science.gov (United States)

    Basak, Subhash C.; Mills, Denise; Hawkins, Douglas M.

    2008-06-01

    A hierarchical classification study was carried out based on a set of 70 chemicals—35 which produce allergic contact dermatitis (ACD) and 35 which do not. This approach was implemented using a regular ridge regression computer code, followed by conversion of regression output to binary data values. The hierarchical descriptor classes used in the modeling include topostructural (TS), topochemical (TC), and quantum chemical (QC), all of which are based solely on chemical structure. The concordance, sensitivity, and specificity are reported. The model based on the TC descriptors was found to be the best, while the TS model was extremely poor.

  8. dc Resistivity of Quantum Critical, Charge Density Wave States from Gauge-Gravity Duality

    Science.gov (United States)

    Amoretti, Andrea; Areán, Daniel; Goutéraux, Blaise; Musso, Daniele

    2018-04-01

    In contrast to metals with weak disorder, the resistivity of weakly pinned charge density waves (CDWs) is not controlled by irrelevant processes relaxing momentum. Instead, the leading contribution is governed by incoherent, diffusive processes which do not drag momentum and can be evaluated in the clean limit. We compute analytically the dc resistivity for a family of holographic charge density wave quantum critical phases and discuss its temperature scaling. Depending on the critical exponents, the ground state can be conducting or insulating. We connect our results to dc electrical transport in underdoped cuprate high Tc superconductors. We conclude by speculating on the possible relevance of unstable, semilocally critical CDW states to the strange metallic region.

  9. dc Resistivity of Quantum Critical, Charge Density Wave States from Gauge-Gravity Duality.

    Science.gov (United States)

    Amoretti, Andrea; Areán, Daniel; Goutéraux, Blaise; Musso, Daniele

    2018-04-27

    In contrast to metals with weak disorder, the resistivity of weakly pinned charge density waves (CDWs) is not controlled by irrelevant processes relaxing momentum. Instead, the leading contribution is governed by incoherent, diffusive processes which do not drag momentum and can be evaluated in the clean limit. We compute analytically the dc resistivity for a family of holographic charge density wave quantum critical phases and discuss its temperature scaling. Depending on the critical exponents, the ground state can be conducting or insulating. We connect our results to dc electrical transport in underdoped cuprate high T_{c} superconductors. We conclude by speculating on the possible relevance of unstable, semilocally critical CDW states to the strange metallic region.

  10. Magnetic-field control of quantum critical points of valence transition.

    Science.gov (United States)

    Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques

    2008-06-13

    We study the mechanism of how critical end points of first-order valence transitions are controlled by a magnetic field. We show that the critical temperature is suppressed to be a quantum critical point (QCP) by a magnetic field, and unexpectedly, the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to the emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be cooperative phenomena of the Zeeman and Kondo effects, which create a distinct energy scale from the Kondo temperature. This mechanism explains the peculiar magnetic response in CeIrIn(5) and the metamagnetic transition in YbXCu(4) for X=In as well as the sharp contrast between X=Ag and Cd.

  11. Protein structure validation and refinement using amide proton chemical shifts derived from quantum mechanics

    DEFF Research Database (Denmark)

    Christensen, Anders Steen; Linnet, Troels Emtekær; Borg, Mikael

    2013-01-01

    We present the ProCS method for the rapid and accurate prediction of protein backbone amide proton chemical shifts - sensitive probes of the geometry of key hydrogen bonds that determine protein structure. ProCS is parameterized against quantum mechanical (QM) calculations and reproduces high level...

  12. The use of quantum chemically derived descriptors for QSAR modelling of reductive dehalogenation of aromatic compounds

    NARCIS (Netherlands)

    Rorije E; Richter J; Peijnenburg WJGM; ECO; IHE Delft

    1994-01-01

    In this study, quantum-chemically derived parameters are developed for a limited number of halogenated aromatic compounds to model the anaerobic reductive dehalogenation reaction rate constants of these compounds. It is shown that due to the heterogeneity of the set of compounds used, no single

  13. Complementing high-throughput X-ray powder diffraction data with quantum-chemical calculations

    DEFF Research Database (Denmark)

    Naelapaa, Kaisa; van de Streek, Jacco; Rantanen, Jukka

    2012-01-01

    of piroxicam form III. These combined experimental/quantum-chemical methods can provide access to reliable structural information in the course of an intensive experimentally based solid-form screening activity or in other circumstances wherein single crystals might never be viable, for example, for polymorphs...

  14. Electrochemical and Quantum Chemical Study of Reactivity of Orthophthalaldehyde with Aliphatic Primary Amines

    Czech Academy of Sciences Publication Activity Database

    Donkeng Dazie, Joel; Liška, Alan; Ludvík, Jiří

    2016-01-01

    Roč. 163, č. 9 (2016), G127-G132 ISSN 0013-4651 R&D Projects: GA ČR GA13-21704S Institutional support: RVO:61388955 Keywords : electrochemistry * quantum chemical study * amines Subject RIV: CG - Electrochemistry Impact factor: 3.259, year: 2016

  15. Avoided Quantum Criticality and Magnetoelastic Coupling in BaFe2-xNixAs2

    DEFF Research Database (Denmark)

    Lu, Xingye; Gretarsson, H.; Zhang, Rui

    2013-01-01

    suppressed and separated, resulting in sNT>T with increasing x, as was previously observed. However, the temperature separation between sT and NT decreases with increasing x for x≥0.065, tending toward a quantum bicritical point near optimal superconductivity at x≈0.1. The zero-temperature transition...... is preempted by the formation of a secondary incommensurate magnetic phase in the region 0.088≲x≲0.104, resulting in a finite value of NT≈cT+10 K above the superconducting dome around x≈0.1. Our results imply an avoided quantum critical point, which is expected to strongly influence the properties of both...

  16. Inhomogeneous quasi-adiabatic driving of quantum critical dynamics in weakly disordered spin chains

    International Nuclear Information System (INIS)

    Rams, Marek M; Mohseni, Masoud; Campo, Adolfo del

    2016-01-01

    We introduce an inhomogeneous protocol to drive a weakly disordered quantum spin chain quasi-adiabatically across a quantum phase transition and minimize the residual energy of the final state. The number of spins that simultaneously reach the critical point is controlled by the length scale in which the magnetic field is modulated, introducing an effective size that favors adiabatic dynamics. The dependence of the residual energy on this length scale and the velocity at which the magnetic field sweeps out the chain is shown to be nonmonotonic. We determine the conditions for an optimal suppression of the residual energy of the final state and show that inhomogeneous driving can outperform conventional adiabatic schemes based on homogeneous control fields by several orders of magnitude. (paper)

  17. Dipolar Antiferromagnetism and Quantum Criticality in LiErF4

    International Nuclear Information System (INIS)

    Kraemer, Conradin; Nikseresht, Neda; Piatek, Julian; Tsyrulin, Nikolay; Piazza, Bastien; Kiefer, Klaus; Klemke, Bastian; Rosenbaum, Thomas; Aeppli, Gabriel; Gannarelli, Che; Prokes, Karel; Straessle, Thierry; Keller, Lukas; Zaharko, Oksana; Kraemer, Karl; Ronnow, Henrik

    2012-01-01

    Magnetism has been predicted to occur in systems in which dipolar interactions dominate exchange. We present neutron scattering, specific heat, and magnetic susceptibility data for LiErF 4 , establishing it as a model dipolar-coupled antiferromagnet with planar spin-anisotropy and a quantum phase transition in applied field H c# parallel# = 4.0 ± 0.1 kilo-oersteds. We discovered non-mean-field critical scaling for the classical phase transition at the antiferromagnetic transition temperature that is consistent with the two-dimensional XY/h 4 universality class; in accord with this, the quantum phase transition at H c exhibits three-dimensional classical behavior. The effective dimensional reduction may be a consequence of the intrinsic frustrated nature of the dipolar interaction, which strengthens the role of fluctuations.

  18. Photosensitization and phototherapy with furocoumarins: A quantum-chemical study

    International Nuclear Information System (INIS)

    Serrano-Perez, Juan Jose; Serrano-Andres, Luis; Merchan, Manuela

    2008-01-01

    The effect of electromagnetic radiation on biological objects extends from heating to complex photochemistry, and includes DNA alteration, that properly modified in damaged cells may entail beneficial effects. In this regard, psoralen + UV-A (PUVA) therapy, in which furocoumarins, psoralen-like chromophores, are used as photosensitizers and photoreactants with DNA bases, is one of the most promising strategies against a plethora of diseases. Understanding the underlying photochemical mechanisms is crucial to design effective drugs without undesired side effects. We have undertaken a quantum-mechanical study on the photophysics and photochemistry of furocoumarins, analyzing firstly the most efficient way in which the lowest excited triplet state, as protagonist of the photosensitizing action, is populated from the initially promoted singlet states, and secondly the basics of the formation of furocoumarin-DNA photoadducts

  19. Experimental and quantum chemical studies on corrosion inhibition ...

    Indian Academy of Sciences (India)

    the metal surface and form barrier film. .... with time may be attributed to the formation of a barrier film, which prevents the ..... high chemical activity and low kinetic stability and is termed ... Physical adsorption of the organic inhibitor on the metal.

  20. Anomalous properties and coexistence of antiferromagnetism and superconductivity near a quantum critical point in rare-earth intermetallides

    International Nuclear Information System (INIS)

    Val’kov, V. V.; Zlotnikov, A. O.

    2013-01-01

    Mechanisms of the appearance of anomalous properties experimentally observed at the transition through the quantum critical point in rare-earth intermetallides have been studied. Quantum phase transitions are induced by the external pressure and are manifested as the destruction of the long-range antiferromagnetic order at zero temperature. The suppression of the long-range order is accompanied by an increase in the area of the Fermi surface, and the effective electron mass is strongly renormalized near the quantum critical point. It has been shown that such a renormalization is due to the reconstruction of the quasiparticle band, which is responsible for the formation of heavy fermions. It has been established that these features hold when the coexistence phase of antiferromagnetism and superconductivity is implemented near the quantum critical point.

  1. Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn_{5}.

    Science.gov (United States)

    Paglione, Johnpierre; Tanatar, M A; Reid, J-Ph; Shakeripour, H; Petrovic, C; Taillefer, Louis

    2016-07-01

    The thermal conductivity κ of the heavy-fermion metal CeCoIn_{5} was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field H_{c2}, κ/T is found to increase as T→0, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ/T with field reveals that the electron-electron scattering (or transport mass m^{⋆}) of those unpaired electrons diverges as H→H_{c2} from below, in the same way that it does in the normal state as H→H_{c2} from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn_{5} at H^{⋆}=H_{c2} even from inside the superconducting state. The fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k-space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.

  2. Origin of quantum criticality in Yb-Al-Au approximant crystal and quasicrystal

    International Nuclear Information System (INIS)

    Watanabe, Shinji; Miyake, Kazumasa

    2016-01-01

    To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb 15 Al 34 Au 51 , the approximant crystal Yb 14 Al 35 Au 51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits χ ∼ T -0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size. (author)

  3. High spin cycles: topping the spin record for a single molecule verging on quantum criticality

    Science.gov (United States)

    Baniodeh, Amer; Magnani, Nicola; Lan, Yanhua; Buth, Gernot; Anson, Christopher E.; Richter, Johannes; Affronte, Marco; Schnack, Jürgen; Powell, Annie K.

    2018-03-01

    The cyclisation of a short chain into a ring provides fascinating scenarios in terms of transforming a finite array of spins into a quasi-infinite structure. If frustration is present, theory predicts interesting quantum critical points, where the ground state and thus low-temperature properties of a material change drastically upon even a small variation of appropriate external parameters. This can be visualised as achieving a very high and pointed summit where the way down has an infinity of possibilities, which by any parameter change will be rapidly chosen, in order to reach the final ground state. Here we report a mixed 3d/4f cyclic coordination cluster that turns out to be very near or even at such a quantum critical point. It has a ground state spin of S = 60, the largest ever observed for a molecule (120 times that of a single electron). [Fe10Gd10(Me-tea)10(Me-teaH)10(NO3)10].20MeCN forms a nano-torus with alternating gadolinium and iron ions with a nearest neighbour Fe-Gd coupling and a frustrating next-nearest neighbour Fe-Fe coupling. Such a spin arrangement corresponds to a cyclic delta or saw-tooth chain, which can exhibit unusual frustration effects. In the present case, the quantum critical point bears a `flatland' of tens of thousands of energetically degenerate states between which transitions are possible at no energy costs with profound caloric consequences. Entropy-wise the energy flatland translates into the pointed summit overlooking the entropy landscape. Going downhill several target states can be reached depending on the applied physical procedure which offers new prospects for addressability.

  4. Stokes phenomena and quantum integrability in non-critical string/M theory

    International Nuclear Information System (INIS)

    Chan, Chuan-Tsung; Irie, Hirotaka; Yeh, Chi-Hsien

    2012-01-01

    We study Stokes phenomena of the k×k isomonodromy systems with an arbitrary Poincaré index r, especially which correspond to the fractional-superstring (or parafermionic-string) multi-critical points (p-hat,q-hat)=(1,r-1) in the k-cut two-matrix models. Investigation of this system is important for the purpose of figuring out the non-critical version of M theory which was proposed to be the strong-coupling dual of fractional superstring theory as a two-matrix model with an infinite number of cuts. Surprisingly the multi-cut boundary-condition recursion equations have a universal form among the various multi-cut critical points, and this enables us to show explicit solutions of Stokes multipliers in quite wide classes of (k,r). Although these critical points almost break the intrinsic Z k symmetry of the multi-cut two-matrix models, this feature makes manifest a connection between the multi-cut boundary-condition recursion equations and the structures of quantum integrable systems. In particular, it is uncovered that the Stokes multipliers satisfy multiple Hirota equations (i.e. multiple T-systems). Therefore our result provides a large extension of the ODE/IM correspondence to the general isomonodromy ODE systems endowed with the multi-cut boundary conditions. We also comment about a possibility that N=2 QFT of Cecotti-Vafa would be “topological series” in non-critical M theory equipped with a single quantum integrability.

  5. Theory of critical phenomena in finite-size systems scaling and quantum effects

    CERN Document Server

    Brankov, Jordan G; Tonchev, Nicholai S

    2000-01-01

    The aim of this book is to familiarise the reader with the rich collection of ideas, methods and results available in the theory of critical phenomena in systems with confined geometry. The existence of universal features of the finite-size effects arising due to highly correlated classical or quantum fluctuations is explained by the finite-size scaling theory. This theory (1) offers an interpretation of experimental results on finite-size effects in real systems; (2) gives the most reliable tool for extrapolation to the thermodynamic limit of data obtained by computer simulations; (3) reveals

  6. Finite-dimensional effects and critical indices of one-dimensional quantum models

    International Nuclear Information System (INIS)

    Bogolyubov, N.M.; Izergin, A.G.; Reshetikhin, N.Yu.

    1986-01-01

    Critical indices, depending on continuous parameters in Bose-gas quantum models and Heisenberg 1/2 spin antiferromagnetic in two-dimensional space-time at zero temperature, have been calculated by means of finite-dimensional effects. In this case the long-wave asymptotics of the correlation functions is of a power character. Derivation of man asymptotics terms is reduced to the determination of a central charge in the appropriate Virassoro algebra representation and the anomalous dimension-operator spectrum in this representation. The finite-dimensional effects allow to find these values

  7. Machine learning of parameters for accurate semiempirical quantum chemical calculations

    International Nuclear Information System (INIS)

    Dral, Pavlo O.; Lilienfeld, O. Anatole von; Thiel, Walter

    2015-01-01

    We investigate possible improvements in the accuracy of semiempirical quantum chemistry (SQC) methods through the use of machine learning (ML) models for the parameters. For a given class of compounds, ML techniques require sufficiently large training sets to develop ML models that can be used for adapting SQC parameters to reflect changes in molecular composition and geometry. The ML-SQC approach allows the automatic tuning of SQC parameters for individual molecules, thereby improving the accuracy without deteriorating transferability to molecules with molecular descriptors very different from those in the training set. The performance of this approach is demonstrated for the semiempirical OM2 method using a set of 6095 constitutional isomers C 7 H 10 O 2 , for which accurate ab initio atomization enthalpies are available. The ML-OM2 results show improved average accuracy and a much reduced error range compared with those of standard OM2 results, with mean absolute errors in atomization enthalpies dropping from 6.3 to 1.7 kcal/mol. They are also found to be superior to the results from specific OM2 reparameterizations (rOM2) for the same set of isomers. The ML-SQC approach thus holds promise for fast and reasonably accurate high-throughput screening of materials and molecules

  8. Extraction of conformal data in critical quantum spin chains using the Koo-Saleur formula

    Science.gov (United States)

    Milsted, Ashley; Vidal, Guifre

    2017-12-01

    We study the emergence of two-dimensional conformal symmetry in critical quantum spin chains on the finite circle. Our goal is to characterize the conformal field theory (CFT) describing the universality class of the corresponding quantum phase transition. As a means to this end, we propose and demonstrate automated procedures which, using only the lattice Hamiltonian H =∑jhj as an input, systematically identify the low-energy eigenstates corresponding to Virasoro primary and quasiprimary operators, and assign the remaining low-energy eigenstates to conformal towers. The energies and momenta of the primary operator states are needed to determine the primary operator scaling dimensions and conformal spins, an essential part of the conformal data that specifies the CFT. Our techniques use the action, on the low-energy eigenstates of H , of the Fourier modes Hn of the Hamiltonian density hj. The Hn were introduced as lattice representations of the Virasoro generators by Koo and Saleur [Nucl. Phys. B 426, 459 (1994), 10.1016/0550-3213(94)90018-3]. In this paper, we demonstrate that these operators can be used to extract conformal data in a nonintegrable quantum spin chain.

  9. Quantum entanglement and criticality of the antiferromagnetic Heisenberg model in an external field

    International Nuclear Information System (INIS)

    Liu Guanghua; Li Ruoyan; Tian Guangshan

    2012-01-01

    By Lanczos exact diagonalization and the infinite time-evolving block decimation (iTEBD) technique, the two-site entanglement as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization in the antiferromagnetic Heisenberg (AFH) model under an external field are investigated. With increasing external field, the small size system shows some distinct upward magnetization stairsteps, accompanied synchronously with some downward two-site entanglement stairsteps. In the thermodynamic limit, the two-site entanglement, as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization are calculated, and the critical magnetic field h c = 2.0 is determined exactly. Our numerical results show that the quantum entanglement is sensitive to the subtle changing of the ground state, and can be used to describe the magnetization and quantum phase transition. Based on the discontinuous behavior of the first-order derivative of the entanglement entropy and fidelity per site, we think that the quantum phase transition in this model should belong to the second-order category. Furthermore, in the magnon existence region (h < 2.0), a logarithmically divergent behavior of block entanglement which can be described by a free bosonic field theory is observed, and the central charge c is determined to be 1. (paper)

  10. Quantum confinement of lead titanate nanocrystals by wet chemical method

    Energy Technology Data Exchange (ETDEWEB)

    Kaviyarasu, K., E-mail: kaviyarasuloyolacollege@gmail.com [UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology Laboratories, College of Graduate Studies, University of South Africa (UNISA), Muckleneuk Ridge, P O Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), Materials Research Department (MSD), iThemba LABS-National Research Foundation - NRF, 1 Old Faure Road, 7129, P O Box 722, Somerset West, Western Cape Province (South Africa); Manikandan, E., E-mail: maniphysics@gmail.com [Nanosciences African Network (NANOAFNET), Materials Research Department (MSD), iThemba LABS-National Research Foundation - NRF, 1 Old Faure Road, 7129, P O Box 722, Somerset West, Western Cape Province (South Africa); Central Research Laboratory, Sree Balaji Medical College & Hospital, Bharath University, Chrompet, Chennai, Tamil Nadu (India); Nuru, Z.Y. [UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology Laboratories, College of Graduate Studies, University of South Africa (UNISA), Muckleneuk Ridge, P O Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), Materials Research Department (MSD), iThemba LABS-National Research Foundation - NRF, 1 Old Faure Road, 7129, P O Box 722, Somerset West, Western Cape Province (South Africa); Maaza, M., E-mail: likmaaz@gmail.com [UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology Laboratories, College of Graduate Studies, University of South Africa (UNISA), Muckleneuk Ridge, P O Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), Materials Research Department (MSD), iThemba LABS-National Research Foundation - NRF, 1 Old Faure Road, 7129, P O Box 722, Somerset West, Western Cape Province (South Africa)

    2015-11-15

    Lead Titanate (PbTiO{sub 3)} is a category of the practical semiconductor metal oxides, which is widely applied in various scientific and industrial fields because of its catalytic, optical, and electrical properties. PbTiO{sub 3} nanocrystalline materials have attracted a wide attention due to their unique properties. PbTiO{sub 3} nanocrystals were investigated by X-ray diffraction (XRD) to identify the PbTiO{sub 3} nanocrystals were composed a tetragonal structure. The diameter of a single sphere was around 20 nm and the diameter reached up to 3 μm. The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy (XPS) in detail. - Highlights: • Single crystalline NSs of PbTiO{sub 3} fabricated by wet chemical method. • PbTiO{sub 3} NSs were uniform and continuous along the long axis. • Tetragonal perovskite structure with the diameter 20 nm and length 3 μm. • XPS spectrum was fitted with Lorentzian function respectively. • The size of the images is also 10 μm × 10 μm.

  11. Chemicals regulation and the Porter Hypothesis:a critical review of the new European chemicals regulation

    OpenAIRE

    Frohwein, T. (Torsten); Hansjürgens, B. (Bernd)

    2005-01-01

    In this contribution, discussions about the Porter Hypothesis and the pros and cons of the new European chemicals regulation system REACH are tied together. The contribution seeks to apply the Porter Hypothesis to the field of European chemicals regulation. Porter’s claim of positive effects of regulation on innovations seems especially important for the chemicals sector pursuing differentiation. But, understanding Porter’s concept of strategic management indicates that certain segments of th...

  12. Vibrational spectroscopic studies of Isoleucine by quantum chemical calculations.

    Science.gov (United States)

    Moorthi, P P; Gunasekaran, S; Ramkumaar, G R

    2014-04-24

    In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of Isoleucine (2-Amino-3-methylpentanoic acid). The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments, thermodynamics properties, NBO analyses, NMR chemical shifts and ultraviolet-visible spectral interpretation of Isoleucine have been studied by performing MP2 and DFT/cc-pVDZ level of theory. The FTIR, FT-Raman spectra were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. The UV-visible absorption spectra of the compound were recorded in the range of 200-800 nm. Computational calculations at MP2 and B3LYP level with basis set of cc-pVDZ is employed in complete assignments of Isoleucine molecule on the basis of the potential energy distribution (PED) of the vibrational modes, calculated using VEDA-4 program. The calculated wavenumbers are compared with the experimental values. The difference between the observed and calculated wavenumber values of most of the fundamentals is very small. (13)C and (1)H nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method and compared with experimental results. The formation of hydrogen bond was investigated in terms of the charge density by the NBO calculations. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands were carried out. Besides, molecular electrostatic potential (MEP) were investigated using theoretical calculations. Copyright © 2014 Elsevier B.V. All rights reserved.

  13. Quantum criticality in He3 bi-layers and heavy fermion compounds

    International Nuclear Information System (INIS)

    Benlagra, A.

    2009-11-01

    Despite intense experimental as well as theoretical efforts the understanding of physical phenomena peculiar to heavy fermion compounds remains one of the major problems in condensed matter physics; this research thesis considers the recently proposed theoretical approaches to describe the critical regime properties. This approach is based on the following idea: critical modes which are responsible for this regime are non-magnetic and are associated to the destruction of the Kondo effect between localized magnetic impurities and travelling conduction electrons at the quantum critical point. The author derives an analytic expression for the free energy within this model by using the Luttinger-Ward functional approach within the frame of the Eliashberg theory. The obtained expressions are transparently including the effect of critical fluctuations, integrated in a self-coherent way. The behaviour of different thermodynamic quantities is then deduced from these expressions. The result is compared with recent experiments on heavy fermion compounds as well as on a Helium-3 bilayer system adsorbed on graphite substrate in order to test the validity of such a model. Strengths and drawbacks of the model are outlined

  14. In Vivo Anti-Leukemia, Quantum Chemical Calculations and ADMET Investigations of Some Quaternary and Isothiouronium Surfactants

    Directory of Open Access Journals (Sweden)

    Ahmed A. El-Henawy

    2013-04-01

    Full Text Available Anti-leukemia screening of previously prepared isothiouronium and quaternary salts was performed, and some salts exhibited promising activity as anticancer agents. Quantum chemical calculations were utilized to explore the electronic structure and stability of these compounds. Computational studies have been carried out at the PM3 semiempirical molecular orbitals level, to establish the HOMO-LUMO, IP and ESP mapping of these compounds. The ADMET properties were also studied to gain a clear view of the potential oral bioavailability of these compounds. The surface properties calculated included critical micelle concentration (CMC, maximum surface excess (Γmax, minimum surface area (Amin, free energy of micellization (ΔGomic and adsorption (ΔGoads.

  15. Application of quantum dots as analytical tools in automated chemical analysis: A review

    International Nuclear Information System (INIS)

    Frigerio, Christian; Ribeiro, David S.M.; Rodrigues, S. Sofia M.; Abreu, Vera L.R.G.; Barbosa, João A.C.; Prior, João A.V.; Marques, Karine L.; Santos, João L.M.

    2012-01-01

    Highlights: ► Review on quantum dots application in automated chemical analysis. ► Automation by using flow-based techniques. ► Quantum dots in liquid chromatography and capillary electrophoresis. ► Detection by fluorescence and chemiluminescence. ► Electrochemiluminescence and radical generation. - Abstract: Colloidal semiconductor nanocrystals or quantum dots (QDs) are one of the most relevant developments in the fast-growing world of nanotechnology. Initially proposed as luminescent biological labels, they are finding new important fields of application in analytical chemistry, where their photoluminescent properties have been exploited in environmental monitoring, pharmaceutical and clinical analysis and food quality control. Despite the enormous variety of applications that have been developed, the automation of QDs-based analytical methodologies by resorting to automation tools such as continuous flow analysis and related techniques, which would allow to take advantage of particular features of the nanocrystals such as the versatile surface chemistry and ligand binding ability, the aptitude to generate reactive species, the possibility of encapsulation in different materials while retaining native luminescence providing the means for the implementation of renewable chemosensors or even the utilisation of more drastic and even stability impairing reaction conditions, is hitherto very limited. In this review, we provide insights into the analytical potential of quantum dots focusing on prospects of their utilisation in automated flow-based and flow-related approaches and the future outlook of QDs applications in chemical analysis.

  16. Quantum chemical studies on the corrosion inhibition of some sulphonamides on mild steel in acidic medium

    International Nuclear Information System (INIS)

    Arslan, Taner; Kandemirli, Fatma; Ebenso, Eno E.; Love, Ian; Alemu, Hailemichael

    2009-01-01

    Quantum chemical calculations using the density functional theory (DFT) and some semi-empirical methods were performed on four sulphonamides (sulfaguanidine, sulfamethazine, sulfamethoxazole and sulfadiazine) used as corrosion inhibitors for mild steel in acidic medium to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental %IE were subjected to correlation analysis and indicate that their inhibition effect are closely related to E HOMO , E LUMO , hardness, polarizability, dipole moment and charges. The %IE increased with increase in the E HOMO and decrease in E HOMO - E LUMO . The negative sign of the E HOMO values and other kinetic and thermodynamic parameters indicates that the data obtained support physical adsorption mechanism

  17. Quantum chemical modeling of enzymatic reactions: the case of 4-oxalocrotonate tautomerase.

    Science.gov (United States)

    Sevastik, Robin; Himo, Fahmi

    2007-12-01

    The reaction mechanism of 4-oxalocrotonate tautomerase (4-OT) is studied using the density functional theory method B3LYP. This enzyme catalyzes the isomerisation of unconjugated alpha-keto acids to their conjugated isomers. Two different quantum chemical models of the active site are devised and the potential energy curves for the reaction are computed. The calculations support the proposed reaction mechanism in which Pro-1 acts as a base to shuttle a proton from the C3 to the C5 position of the substrate. The first step (proton transfer from C3 to proline) is shown to be the rate-limiting step. The energy of the charge-separated intermediate (protonated proline-deprotonated substrate) is calculated to be quite low, in accordance with measured pKa values. The results of the two models are used to evaluate the methodology employed in modeling enzyme active sites using quantum chemical cluster models.

  18. Combined Docking with Classical Force Field and Quantum Chemical Semiempirical Method PM7

    Directory of Open Access Journals (Sweden)

    A. V. Sulimov

    2017-01-01

    Full Text Available Results of the combined use of the classical force field and the recent quantum chemical PM7 method for docking are presented. Initially the gridless docking of a flexible low molecular weight ligand into the rigid target protein is performed with the energy function calculated in the MMFF94 force field with implicit water solvent in the PCM model. Among several hundred thousand local minima, which are found in the docking procedure, about eight thousand lowest energy minima are chosen and then energies of these minima are recalculated with the recent quantum chemical semiempirical PM7 method. This procedure is applied to 16 test complexes with different proteins and ligands. For almost all test complexes such energy recalculation results in the global energy minimum configuration corresponding to the ligand pose near the native ligand position in the crystalized protein-ligand complex. A significant improvement of the ligand positioning accuracy comparing with MMFF94 energy calculations is demonstrated.

  19. Combined Docking with Classical Force Field and Quantum Chemical Semiempirical Method PM7.

    Science.gov (United States)

    Sulimov, A V; Kutov, D C; Katkova, E V; Sulimov, V B

    2017-01-01

    Results of the combined use of the classical force field and the recent quantum chemical PM7 method for docking are presented. Initially the gridless docking of a flexible low molecular weight ligand into the rigid target protein is performed with the energy function calculated in the MMFF94 force field with implicit water solvent in the PCM model. Among several hundred thousand local minima, which are found in the docking procedure, about eight thousand lowest energy minima are chosen and then energies of these minima are recalculated with the recent quantum chemical semiempirical PM7 method. This procedure is applied to 16 test complexes with different proteins and ligands. For almost all test complexes such energy recalculation results in the global energy minimum configuration corresponding to the ligand pose near the native ligand position in the crystalized protein-ligand complex. A significant improvement of the ligand positioning accuracy comparing with MMFF94 energy calculations is demonstrated.

  20. Oxygen-vacancy defects on BaTiO3 (001) surface: a quantum chemical study

    International Nuclear Information System (INIS)

    Duque, Carlos; Stashans, Arvids

    2003-01-01

    A quantum-chemical study of technologically important BaTiO 3 crystal and oxygen-vacancy defects on its (001) surface is reported in the present work. The computations are made using a quantum-chemical method developed for periodic systems (crystals), which is based on the Hartree-Fock theory. The atomic rearrangement due to the surface creation is obtained for a pure BaTiO 3 by means of the periodic large unit cell (LUC) model and using an automated geometry optimisation procedure. The same technique is employed to study the electronic and structural properties of the material due to the presence of an O vacancy and F centre (two electrons trapped in an oxygen vacancy). The computations are carried out for both cubic and tetragonal lattices

  1. Quantum chemical modeling of antioxidant activity of glutathione interacting with hydroxyl- and superoxide anion radicals

    Directory of Open Access Journals (Sweden)

    N. V. Solovyova

    2015-04-01

    Full Text Available Following the analysis of the results of quantum chemical simulation of interaction between a GSH molecule and oxygen radicals •ОН and •ООˉ, it was found that it takes place through the acid-base mechanism, where GSH acts as a base towards •ОН, and as an acid towards •ООˉ. The results of quantum chemical calculations (electron density redistribution, energy characteristics were correlated at the time of interaction of a GSH molecule with •ОН and •ООˉ with a change of macroscopic parameters of the process of free oxygen radical electroreduction in the presence of GSH (potential and maximum current of reduction waves, which is a direct experimental macroscale evidence of results of the conducted nanoscale theoretical simulation.

  2. Mechanisms of gas phase decomposition of C-nitro compounds from quantum chemical data

    International Nuclear Information System (INIS)

    Khrapkovskii, Grigorii M; Shamov, Alexander G; Nikolaeva, E V; Chachkov, D V

    2009-01-01

    Data on the mechanisms of gas-phase monomolecular decomposition of nitroalkanes, nitroalkenes and nitroarenes obtained using modern quantum chemical methods are described systematically. The attention is focused on the discussion of multistage decomposition of nitro compounds to elementary experimentally observed products. Characteristic features of competition of different mechanisms and the effect of molecular structure on the change in the Arrhenius parameters of the primary reaction step are considered.

  3. Mechanisms of gas phase decomposition of C-nitro compounds from quantum chemical data

    Energy Technology Data Exchange (ETDEWEB)

    Khrapkovskii, Grigorii M; Shamov, Alexander G; Nikolaeva, E V; Chachkov, D V [Kazan State Technological University, Kazan (Russian Federation)

    2009-10-31

    Data on the mechanisms of gas-phase monomolecular decomposition of nitroalkanes, nitroalkenes and nitroarenes obtained using modern quantum chemical methods are described systematically. The attention is focused on the discussion of multistage decomposition of nitro compounds to elementary experimentally observed products. Characteristic features of competition of different mechanisms and the effect of molecular structure on the change in the Arrhenius parameters of the primary reaction step are considered.

  4. Molecular interactions of nucleic acid bases. A review of quantum-chemical studies

    Czech Academy of Sciences Publication Activity Database

    Šponer, Jiří; Hobza, Pavel

    2003-01-01

    Roč. 68, č. 12 (2003), s. 2231-2282 ISSN 0010-0765 R&D Projects: GA MŠk LN00A032; GA AV ČR IAA4040904 Grant - others:Wellcome Trust(GB) GR067507MF Institutional research plan: CEZ:AV0Z5004920; CEZ:AV0Z4040901 Keywords : DNA base pairs * initio quantum -chemical calculations * electron correlation Subject RIV: BO - Biophysics Impact factor: 1.041, year: 2003

  5. Protein structure refinement using a quantum mechanics-based chemical shielding predictor.

    Science.gov (United States)

    Bratholm, Lars A; Jensen, Jan H

    2017-03-01

    The accurate prediction of protein chemical shifts using a quantum mechanics (QM)-based method has been the subject of intense research for more than 20 years but so far empirical methods for chemical shift prediction have proven more accurate. In this paper we show that a QM-based predictor of a protein backbone and CB chemical shifts (ProCS15, PeerJ , 2016, 3, e1344) is of comparable accuracy to empirical chemical shift predictors after chemical shift-based structural refinement that removes small structural errors. We present a method by which quantum chemistry based predictions of isotropic chemical shielding values (ProCS15) can be used to refine protein structures using Markov Chain Monte Carlo (MCMC) simulations, relating the chemical shielding values to the experimental chemical shifts probabilistically. Two kinds of MCMC structural refinement simulations were performed using force field geometry optimized X-ray structures as starting points: simulated annealing of the starting structure and constant temperature MCMC simulation followed by simulated annealing of a representative ensemble structure. Annealing of the CHARMM structure changes the CA-RMSD by an average of 0.4 Å but lowers the chemical shift RMSD by 1.0 and 0.7 ppm for CA and N. Conformational averaging has a relatively small effect (0.1-0.2 ppm) on the overall agreement with carbon chemical shifts but lowers the error for nitrogen chemical shifts by 0.4 ppm. If an amino acid specific offset is included the ProCS15 predicted chemical shifts have RMSD values relative to experiments that are comparable to popular empirical chemical shift predictors. The annealed representative ensemble structures differ in CA-RMSD relative to the initial structures by an average of 2.0 Å, with >2.0 Å difference for six proteins. In four of the cases, the largest structural differences arise in structurally flexible regions of the protein as determined by NMR, and in the remaining two cases, the large structural

  6. Quantum chemical and spectroscopic analysis of calcium hydroxyapatite and related materials

    International Nuclear Information System (INIS)

    Khavryuchenko, V.D.; Khavryuchenko, O.V.; Lisnyak, V.V.

    2007-01-01

    Amorphous calcium hydroxyapatite was examined by vibrational spectroscopy (Raman and infra-red (IR)) and quantum chemical simulation techniques. The structures and vibrational (IR, Raman and inelastic neutron scattering) spectra of PO 4 3- ion, Ca 3 (PO 4 ) 2 , [Ca 3 (PO 4 ) 2 ] 3 , Ca 5 (PO 4 ) 3 OH, CaHPO 4 , [CaHPO 4 ] 2 , Ca 3 (PO 4 ) 2 .H 2 O, Ca 3 (PO 4 ) 2 .2H 2 O and Ca 3 (PO 4 ) 2 .3H 2 O clusters were quantum chemically simulated at ab initio and semiempirical levels of approximation. A complete coordinate analysis of the vibrational spectra was performed. The comparison of the theoretically simulated spectra with the experimental ones allows to identify correctly the phase composition of the amorphous calcium hydroxyapatite and related materials. The shape of the bands in the IR spectra of the hydroxoapatite can be used in order to characterize the structural properties of the material, e.g., the PO 4 3- ion status, the degree of hydrolysis of the material and the presence of hydrolysis products. - Graphical abstract: The structure of the quantum chemically optimized Ca 5 (PO 4 ) 3 (OH) cluster, which was used for vibrations spectra simulation

  7. Metal compounds in zeolites as active components of chemisorption and catalysis. Quantum chemical approach

    International Nuclear Information System (INIS)

    Zhidomirov, G.M.

    1996-01-01

    A short review of possible catalitic active sites associated with various types of metal species in zoolite is presented. The structural and electronic peculiarity of aluminum ions in zeolite lattice and their distribution in the lattice are discussed on the basis of quantum chemical calculations in connection with the formation of Broensted activity of zeolites. Various molecular models of Lewis Acid Sites associated the extra-lattice oxide-hydroxide aluminum species have been investigated by means of density functional model cluster calculations using CO molecule as a probe. Probable ways of formation of the selective oxidation center in FeZSM-5 by decomposition of dinitrogen monoxide have been studied by ab-initio quantum chemical calculations. The immediate oxidizing site is reasonably represented by the binuclear iron-hydroxide cluster with peroxo-like fragment located between iron atoms. Various probable intermediates of the selective oxidation center formation resulted from interaction of a hydroperoxide molecule with a lattice titanium ion in titanium silicalite have been investigated by quantum chemical calculations. It was concluded that this reaction requires essential structural reconstruction in the vicinity of the titanium ion. Probability of this structural reconstruction is discussed. Possible reasons of an electron-deficient and electron-enriched state of metal particles entrapped in zoolite cavities are discussed. Also, various probable molecular models of such modified metal particles in zeolite are considered

  8. Sub-nanometrically resolved chemical mappings of quantum-cascade laser active regions

    International Nuclear Information System (INIS)

    Pantzas, Konstantinos; Beaudoin, Grégoire; Patriarche, Gilles; Largeau, Ludovic; Mauguin, Olivia; Sagnes, Isabelle; Pegolotti, Giulia; Vasanelli, Angela; Calvar, Ariane; Amanti, Maria; Sirtori, Carlo

    2016-01-01

    A procedure that produces sub-nanometrically resolved chemical mappings of MOCVD-grown InGaAs/InAlAs/InP quantum cascade lasers is presented. The chemical mappings reveal that, although the structure is lattice-matched to InP, the InAlAs barriers do not attain the nominal aluminum content—48%—and are, in fact, InGaAlAs quaternaries. This information is used to adjust the aluminum precursor flow and fine-tune the composition of the barriers, resulting in a significant improvement of the fabricated lasers. (paper)

  9. Quantum-Chemical Electron Densities of Proteins and of Selected Protein Sites from Subsystem Density Functional Theory

    NARCIS (Netherlands)

    Kiewisch, K.; Jacob, C.R.; Visscher, L.

    2013-01-01

    The ability to calculate accurate electron densities of full proteins or of selected sites in proteins is a prerequisite for a fully quantum-mechanical calculation of protein-protein and protein-ligand interaction energies. Quantum-chemical subsystem methods capable of treating proteins and other

  10. A quantum-chemical perspective into low optical-gap polymers for highly-efficient organic solar cells

    KAUST Repository

    Risko, Chad; McGehee, Michael D.; Bré das, Jean-Luc

    2011-01-01

    in photocurrent generation. In this Perspective, we first present an overview of the application of quantum-chemical techniques to study the intrinsic material properties and molecular- and nano-scale processes involved in device operation. In the second part

  11. Entropy excess in strongly correlated Fermi systems near a quantum critical point

    Energy Technology Data Exchange (ETDEWEB)

    Clark, J.W., E-mail: jwc@wuphys.wustl.edu [McDonnell Center for the Space Sciences and Department of Physics, Washington University, St. Louis, MO 63130 (United States); Zverev, M.V. [Russian Research Centre Kurchatov Institute, Moscow, 123182 (Russian Federation); Moscow Institute of Physics and Technology, Moscow, 123098 (Russian Federation); Khodel, V.A. [Russian Research Centre Kurchatov Institute, Moscow, 123182 (Russian Federation); McDonnell Center for the Space Sciences and Department of Physics, Washington University, St. Louis, MO 63130 (United States)

    2012-12-15

    A system of interacting, identical fermions described by standard Landau Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if the correlations grow sufficiently strong, as occurs at a quantum critical point where the effective mass diverges. As yet, this phenomenon defies full understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior observed beyond the quantum critical point are still accessible within the general framework of the Landau quasiparticle picture. Self-consistent solutions of the coupled Landau equations for the quasiparticle momentum distribution n(p) and quasiparticle energy spectrum {epsilon}(p) are shown to exist in two distinct classes, depending on coupling strength and on whether the quasiparticle interaction is regular or singular at zero momentum transfer. One class of solutions maintains the idempotency condition n{sup 2}(p)=n(p) of standard FL theory at zero temperature T while adding pockets to the Fermi surface. The other solutions are characterized by a swelling of the Fermi surface and a flattening of the spectrum {epsilon}(p) over a range of momenta in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The latter, non-idempotent solution is revealed by analysis of a Poincare mapping associated with the fundamental Landau equation connecting n(p) and {epsilon}(p) and validated by solution of a variational condition that yields the symmetry-preserving ground state. Significantly, this extraordinary solution carries the burden of a large temperature-dependent excess entropy down to very low temperatures, threatening violation of the Nernst Theorem. It is argued that certain low-temperature phase transitions, notably those involving Cooper-pair formation, offer effective mechanisms for shedding the entropy excess. Available measurements in heavy-fermion compounds provide concrete support for such a scenario. - Highlights: Black-Right-Pointing-Pointer Extension of Landau

  12. Proton chemical shift tensors determined by 3D ultrafast MAS double-quantum NMR spectroscopy

    International Nuclear Information System (INIS)

    Zhang, Rongchun; Mroue, Kamal H.; Ramamoorthy, Ayyalusamy

    2015-01-01

    Proton NMR spectroscopy in the solid state has recently attracted much attention owing to the significant enhancement in spectral resolution afforded by the remarkable advances in ultrafast magic angle spinning (MAS) capabilities. In particular, proton chemical shift anisotropy (CSA) has become an important tool for obtaining specific insights into inter/intra-molecular hydrogen bonding. However, even at the highest currently feasible spinning frequencies (110–120 kHz), 1 H MAS NMR spectra of rigid solids still suffer from poor resolution and severe peak overlap caused by the strong 1 H– 1 H homonuclear dipolar couplings and narrow 1 H chemical shift (CS) ranges, which render it difficult to determine the CSA of specific proton sites in the standard CSA/single-quantum (SQ) chemical shift correlation experiment. Herein, we propose a three-dimensional (3D) 1 H double-quantum (DQ) chemical shift/CSA/SQ chemical shift correlation experiment to extract the CS tensors of proton sites whose signals are not well resolved along the single-quantum chemical shift dimension. As extracted from the 3D spectrum, the F1/F3 (DQ/SQ) projection provides valuable information about 1 H– 1 H proximities, which might also reveal the hydrogen-bonding connectivities. In addition, the F2/F3 (CSA/SQ) correlation spectrum, which is similar to the regular 2D CSA/SQ correlation experiment, yields chemical shift anisotropic line shapes at different isotropic chemical shifts. More importantly, since the F2/F1 (CSA/DQ) spectrum correlates the CSA with the DQ signal induced by two neighboring proton sites, the CSA spectrum sliced at a specific DQ chemical shift position contains the CSA information of two neighboring spins indicated by the DQ chemical shift. If these two spins have different CS tensors, both tensors can be extracted by numerical fitting. We believe that this robust and elegant single-channel proton-based 3D experiment provides useful atomistic-level structural and dynamical

  13. Quantum critical fluctuations due to nested Fermi surface: The case of spinless fermions

    International Nuclear Information System (INIS)

    Schlottmann, P.

    2007-01-01

    A quantum critical point (QCP) can be obtained by tuning the critical temperature of a second-order phase transition to zero. A simple model of spinless fermions with nested Fermi surface leading to a charge density wave is considered. The QCP is obtained by tuning the nesting mismatch of the Fermi surface, which has the following consequences: (i) For the tuned QCP, the specific heat over T and the effective mass increase with the logarithm of the temperature as T is lowered. (ii) For the tuned QCP the linewidth of the quasi-particles is sublinear in T and ω. (iii) The specific heat and the linewidth display a crossover from non-Fermi liquid (∼T) to Fermi liquid (∼T 2 ) behavior with increasing nesting mismatch and decreasing temperature. (iv) For the tuned QCP, the dynamical charge susceptibility has a quasi-elastic peak with a linewidth proportional to T. (v) For non-critical Fermi vector mismatch the peak is inelastic. (vi) While the specific heat and the quasi-particle linewidth are only weakly dependent on the geometry of the nested Fermi surfaces, the momentum-dependent dynamical susceptibility is expected to be affected by the shape of the Fermi surface

  14. Weakly interacting topological insulators: Quantum criticality and the renormalization group approach

    Science.gov (United States)

    Chen, Wei

    2018-03-01

    For D -dimensional weakly interacting topological insulators in certain symmetry classes, the topological invariant can be calculated from a D - or (D +1 ) -dimensional integration over a certain curvature function that is expressed in terms of single-particle Green's functions. Based on the divergence of curvature function at the topological phase transition, we demonstrate how a renormalization group approach circumvents these integrations and reduces the necessary calculation to that for the Green's function alone, rendering a numerically efficient tool to identify topological phase transitions in a large parameter space. The method further unveils a number of statistical aspects related to the quantum criticality in weakly interacting topological insulators, including correlation function, critical exponents, and scaling laws, that can be used to characterize the topological phase transitions driven by either interacting or noninteracting parameters. We use 1D class BDI and 2D class A Dirac models with electron-electron and electron-phonon interactions to demonstrate these principles and find that interactions may change the critical exponents of the topological insulators.

  15. Landau-Ginzburg Limit of Black Hole's Quantum Portrait: Self Similarity and Critical Exponent

    CERN Document Server

    Dvali, Gia

    2012-01-01

    Recently we have suggested that the microscopic quantum description of a black hole is an overpacked self-sustained Bose-condensate of N weakly-interacting soft gravitons, which obeys the rules of 't Hooft's large-N physics. In this note we derive an effective Landau-Ginzburg Lagrangian for the condensate and show that it becomes an exact description in a semi-classical limit that serves as the black hole analog of 't Hooft's planar limit. The role of a weakly-coupled Landau-Ginzburg order parameter is played by N. This description consistently reproduces the known properties of black holes in semi-classical limit. Hawking radiation, as the quantum depletion of the condensate, is described by the slow-roll of the field N. In the semiclassical limit, where black holes of arbitrarily small size are allowed, the equation of depletion is self similar leading to a scaling law for the black hole size with critical exponent 1/3.

  16. Transport anomalies and quantum criticality in electron-doped cuprate superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xu; Yu, Heshan; He, Ge; Hu, Wei; Yuan, Jie; Zhu, Beiyi [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Jin, Kui, E-mail: kuijin@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Collaborative Innovation Center of Quantum Matter, Beijing 100190 (China)

    2016-06-15

    Highlights: • Electrical transport and its complementary thermal transport on electron-doped cuprates are reviewed. • The common features of electron-doped cuprates are sorted out and shown in the last figure. • The complex superconducting fluctuations and quantum fluctuations are distinguished. - Abstract: Superconductivity research is like running a marathon. Three decades after the discovery of high-T{sub c} cuprates, there have been mass data generated from transport measurements, which bring fruitful information. In this review, we give a brief summary of the intriguing phenomena reported in electron-doped cuprates from the aspect of electrical transport as well as the complementary thermal transport. We attempt to sort out common features of the electron-doped family, e.g. the strange metal, negative magnetoresistance, multiple sign reversals of Hall in mixed state, abnormal Nernst signal, complex quantum criticality. Most of them have been challenging the existing theories, nevertheless, a unified diagram certainly helps to approach the nature of electron-doped cuprates.

  17. Electron spin resonance and quantum critical phenomena in VOx multiwall nanotubes

    International Nuclear Information System (INIS)

    Demishev, S.V.; Chernobrovkin, A.L.; Glushkov, V.V.; Samarin, N.A.; Sluchanko, N.E.; Semeno, A.V.; Goodilin, E.A.; Grigorieva, A.V.; Tretyakov, Yu.D.

    2008-01-01

    Basing on the high frequency (60 GHz) electron spin resonance study of the VO x multiwall nanotubes (VO x -NTs) carried out in the temperature range 4.2-200 K we report: (i) the first direct experimental evidence of the presence of the antiferromagnetic dimers in VO x -NTs and (ii) the observation of an anomalous low temperature growth of the magnetic susceptibility for quasi-free spins, which obey the power law χ(T)∝1/T α with the exponent α∼0.6 in a wide temperature range 4.2-50 K. We argue that the observed departures from the Curie-Weiss behaviour manifest the onset of the quantum critical regime and formation of the Griffiths phase as a magnetic ground state of these spin species. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Finite-temperature spin dynamics in a perturbed quantum critical Ising chain with an E₈ symmetry.

    Science.gov (United States)

    Wu, Jianda; Kormos, Márton; Si, Qimiao

    2014-12-12

    A spectrum exhibiting E₈ symmetry is expected to arise when a small longitudinal field is introduced in the transverse-field Ising chain at its quantum critical point. Evidence for this spectrum has recently come from neutron scattering measurements in cobalt niobate, a quasi-one-dimensional Ising ferromagnet. Unlike its zero-temperature counterpart, the finite-temperature dynamics of the model has not yet been determined. We study the dynamical spin structure factor of the model at low frequencies and nonzero temperatures, using the form factor method. Its frequency dependence is singular, but differs from the diffusion form. The temperature dependence of the nuclear magnetic resonance (NMR) relaxation rate has an activated form, whose prefactor we also determine. We propose NMR experiments as a means to further test the applicability of the E₈ description for CoNb₂O₆.

  19. Quantum criticality and duality in the Sachdev-Ye-Kitaev/AdS2 chain

    Science.gov (United States)

    Jian, Shao-Kai; Xian, Zhuo-Yu; Yao, Hong

    2018-05-01

    We show that the quantum critical point (QCP) between a diffusive metal and ferromagnetic (or antiferromagnetic) phases in the SYK chain has a gravitational description corresponding to the double-trace deformation in an AdS2 chain. Specifically, by studying a double-trace deformation of a Z2 scalar in an AdS2 chain where the Z2 scalar is dual to the order parameter in the SYK chain, we find that the susceptibility and renormalization group equation describing the QCP in the SYK chain can be exactly reproduced in the holographic model. Our results suggest that the infrared geometry in the gravity theory dual to the diffusive metal of the SYK chain is also an AdS2 chain. We further show that the transition in SYK model captures universal information about double-trace deformation in generic black holes with near horizon AdS2 space-time.

  20. LaCu6-xAgx : A promising host of an elastic quantum critical point

    Science.gov (United States)

    Poudel, L.; Cruz, C. de la; Koehler, M. R.; McGuire, M. A.; Keppens, V.; Mandrus, D.; Christianson, A. D.

    2018-05-01

    Structural properties of LaCu6-xAgx have been investigated using neutron and x-ray diffraction, and resonant ultrasound spectroscopy (RUS) measurements. Diffraction measurements indicate a continuous structural transition from orthorhombic (Pnma) to monoclinic (P21 / c) structure. RUS measurements show softening of natural frequencies at the structural transition, consistent with the elastic nature of the structural ground state. The structural transition temperatures in LaCu6-xAgx decrease with Ag composition until the monoclinic phase is completely suppressed at xc = 0.225 . All of the evidence is consistent with the presence of an elastic quantum critical point in LaCu6-xAgx .

  1. Critical strain region evaluation of self-assembled semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Sales, D L [Departamento de Ciencia de los Materiales e I. M. y Q. I., Universidad de Cadiz, Puerto Real, Cadiz (Spain); Pizarro, J [Departamento de Lenguajes y Sistemas Informaticos, Universidad de Cadiz, Puerto Real, Cadiz (Spain); Galindo, P L [Departamento de Lenguajes y Sistemas Informaticos, Universidad de Cadiz, Puerto Real, Cadiz (Spain); Garcia, R [Departamento de Ciencia de los Materiales e I. M. y Q. I., Universidad de Cadiz, Puerto Real, Cadiz (Spain); Trevisi, G [CNR-IMEM Institute, Parco delle Scienze 37a, 43100, Parma (Italy); Frigeri, P [CNR-IMEM Institute, Parco delle Scienze 37a, 43100, Parma (Italy); Nasi, L [CNR-IMEM Institute, Parco delle Scienze 37a, 43100, Parma (Italy); Franchi, S [CNR-IMEM Institute, Parco delle Scienze 37a, 43100, Parma (Italy); Molina, S I [Departamento de Ciencia de los Materiales e I. M. y Q. I., Universidad de Cadiz, Puerto Real, Cadiz (Spain)

    2007-11-28

    A novel peak finding method to map the strain from high resolution transmission electron micrographs, known as the Peak Pairs method, has been applied to In(Ga)As/AlGaAs quantum dot (QD) samples, which present stacking faults emerging from the QD edges. Moreover, strain distribution has been simulated by the finite element method applying the elastic theory on a 3D QD model. The agreement existing between determined and simulated strain values reveals that these techniques are consistent enough to qualitatively characterize the strain distribution of nanostructured materials. The correct application of both methods allows the localization of critical strain zones in semiconductor QDs, predicting the nucleation of defects, and being a very useful tool for the design of semiconductor devices.

  2. At the Limits of Criticality-Based Quantum Metrology: Apparent Super-Heisenberg Scaling Revisited

    Science.gov (United States)

    Rams, Marek M.; Sierant, Piotr; Dutta, Omyoti; Horodecki, Paweł; Zakrzewski, Jakub

    2018-04-01

    We address the question of whether the super-Heisenberg scaling for quantum estimation is indeed realizable. We unify the results of two approaches. In the first one, the original system is compared with its copy rotated by the parameter-dependent dynamics. If the parameter is coupled to the one-body part of the Hamiltonian, the precision of its estimation is known to scale at most as N-1 (Heisenberg scaling) in terms of the number of elementary subsystems used N . The second approach compares the overlap between the ground states of the parameter-dependent Hamiltonian in critical systems, often leading to an apparent super-Heisenberg scaling. However, we point out that if one takes into account the scaling of time needed to perform the necessary operations, i.e., ensuring adiabaticity of the evolution, the Heisenberg limit given by the rotation scenario is recovered. We illustrate the general theory on a ferromagnetic Heisenberg spin chain example and show that it exhibits such super-Heisenberg scaling of ground-state fidelity around the critical value of the parameter (magnetic field) governing the one-body part of the Hamiltonian. Even an elementary estimator represented by a single-site magnetization already outperforms the Heisenberg behavior providing the N-1.5 scaling. In this case, Fisher information sets the ultimate scaling as N-1.75, which can be saturated by measuring magnetization on all sites simultaneously. We discuss universal scaling predictions of the estimation precision offered by such observables, both at zero and finite temperatures, and support them with numerical simulations in the model. We provide an experimental proposal of realization of the considered model via mapping the system to ultracold bosons in a periodically shaken optical lattice. We explicitly derive that the Heisenberg limit is recovered when the time needed for preparation of quantum states involved is taken into account.

  3. Automated chemical kinetic modeling via hybrid reactive molecular dynamics and quantum chemistry simulations.

    Science.gov (United States)

    Döntgen, Malte; Schmalz, Felix; Kopp, Wassja A; Kröger, Leif C; Leonhard, Kai

    2018-06-13

    An automated scheme for obtaining chemical kinetic models from scratch using reactive molecular dynamics and quantum chemistry simulations is presented. This methodology combines the phase space sampling of reactive molecular dynamics with the thermochemistry and kinetics prediction capabilities of quantum mechanics. This scheme provides the NASA polynomial and modified Arrhenius equation parameters for all species and reactions that are observed during the simulation and supplies them in the ChemKin format. The ab initio level of theory for predictions is easily exchangeable and the presently used G3MP2 level of theory is found to reliably reproduce hydrogen and methane oxidation thermochemistry and kinetics data. Chemical kinetic models obtained with this approach are ready-to-use for, e.g., ignition delay time simulations, as shown for hydrogen combustion. The presented extension of the ChemTraYzer approach can be used as a basis for methodologically advancing chemical kinetic modeling schemes and as a black-box approach to generate chemical kinetic models.

  4. Degradation of di(2-ethyl hexyl) phthalate by Fusarium culmorum: Kinetics, enzymatic activities and biodegradation pathway based on quantum chemical modelingpathway based on quantum chemical modeling

    International Nuclear Information System (INIS)

    Ahuactzin-Pérez, Miriam; Tlecuitl-Beristain, Saúl; García-Dávila, Jorge; González-Pérez, Manuel; Gutiérrez-Ruíz, María Concepción; Sánchez, Carmen

    2016-01-01

    Di(2-ethylhexyl) phthalate (DEHP) is a plasticizer widely used in the manufacture of plastics, and it is an environmental contaminant. The specific growth rate (μ), maximum biomass (X_m_a_x), biodegradation constant of DEHP (k), half-life (t_1_/_2) of DEHP biodegradation and removal efficiency of DEHP, esterase and laccase specific activities, and enzymatic yield parameters were evaluated for Fusarium culmorum grown on media containing glucose and different concentrations of DEHP (0, 500 and 1000 mg/L). The greatest μ and the largest X_m_a_x occurred in media supplemented with 1000 mg of DEHP/L. F. culmorum degraded 95% of the highest amount of DEHP tested (1000 mg/L) within 60 h of growth. The k and t_1_/_2 were 0.024 h"−"1 and 28 h, respectively, for both DEHP concentrations. The removal efficiency of DEHP was 99.8% and 99.9% for 1000 and 500 mg/L, respectively. Much higher specific esterase activity than specific laccase activity was observed in all media tested. The compounds of biodegradation of DEHP were identified by GC–MS. A DEHP biodegradation pathway by F. culmorum was proposed on the basis of the intermolecular flow of electrons of the identified intermediate compounds using quantum chemical modeling. DEHP was fully metabolized by F. culmorum with butanediol as the final product. This fungus offers great potential in bioremediation of environments polluted with DEHP. - Highlights: • F. culmorum degraded 95% of DEHP (1000 mg/L) within 60 h. • Removal efficiency of DEHP was 99.8% and 99.9% for 1000 and 500 mg/L, respectively. • DEHP was fully metabolized by F. culmorum, with butanediol as the final product. • A DEHP biodegradation pathway was proposed using on quantum chemical modeling.

  5. Degradation of di(2-ethyl hexyl) phthalate by Fusarium culmorum: Kinetics, enzymatic activities and biodegradation pathway based on quantum chemical modelingpathway based on quantum chemical modeling

    Energy Technology Data Exchange (ETDEWEB)

    Ahuactzin-Pérez, Miriam [Doctorado en Biología Experimental, Universidad Autónoma Metropolitana-Iztapalapa (UAM-I) (Mexico); Facultad de Agrobiología, Universidad Autónoma de Tlaxcala, Ixtacuixtla, Tlaxcala (Mexico); Tlecuitl-Beristain, Saúl; García-Dávila, Jorge [Universidad Politécnica de Tlaxcala, San Pedro Xalcatzinco, Tepeyanco, Tlaxcala CP 90180 (Mexico); González-Pérez, Manuel [Universidad Popular Autónoma del Estado de Puebla, Puebla CP 72410 (Mexico); Gutiérrez-Ruíz, María Concepción [Departamento de Ciencias de la Salud, Universidad Autónoma Metropolitana-Iztapalapa, D.F (Mexico); Sánchez, Carmen, E-mail: sanher6@hotmail.com [Laboratory of Biotechnology, Research Centre for Biological Sciences, Universidad Autónoma de Tlaxcala, Ixtacuixtla, Tlaxcala CP. 90062 (Mexico)

    2016-10-01

    Di(2-ethylhexyl) phthalate (DEHP) is a plasticizer widely used in the manufacture of plastics, and it is an environmental contaminant. The specific growth rate (μ), maximum biomass (X{sub max}), biodegradation constant of DEHP (k), half-life (t{sub 1/2}) of DEHP biodegradation and removal efficiency of DEHP, esterase and laccase specific activities, and enzymatic yield parameters were evaluated for Fusarium culmorum grown on media containing glucose and different concentrations of DEHP (0, 500 and 1000 mg/L). The greatest μ and the largest X{sub max} occurred in media supplemented with 1000 mg of DEHP/L. F. culmorum degraded 95% of the highest amount of DEHP tested (1000 mg/L) within 60 h of growth. The k and t{sub 1/2} were 0.024 h{sup −1} and 28 h, respectively, for both DEHP concentrations. The removal efficiency of DEHP was 99.8% and 99.9% for 1000 and 500 mg/L, respectively. Much higher specific esterase activity than specific laccase activity was observed in all media tested. The compounds of biodegradation of DEHP were identified by GC–MS. A DEHP biodegradation pathway by F. culmorum was proposed on the basis of the intermolecular flow of electrons of the identified intermediate compounds using quantum chemical modeling. DEHP was fully metabolized by F. culmorum with butanediol as the final product. This fungus offers great potential in bioremediation of environments polluted with DEHP. - Highlights: • F. culmorum degraded 95% of DEHP (1000 mg/L) within 60 h. • Removal efficiency of DEHP was 99.8% and 99.9% for 1000 and 500 mg/L, respectively. • DEHP was fully metabolized by F. culmorum, with butanediol as the final product. • A DEHP biodegradation pathway was proposed using on quantum chemical modeling.

  6. The Radical Pair Mechanism and the Avian Chemical Compass: Quantum Coherence and Entanglement

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yiteng [Purdue Univ., West Lafayette, IN (United States); Kais, Sabre [Purdue Univ., West Lafayette, IN (United States); Berman, Gennady Petrovich [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-02-02

    We review the spin radical pair mechanism which is a promising explanation of avian navigation. This mechanism is based on the dependence of product yields on 1) the hyperfine interaction involving electron spins and neighboring nuclear spins and 2) the intensity and orientation of the geomagnetic field. One surprising result is that even at ambient conditions quantum entanglement of electron spins can play an important role in avian magnetoreception. This review describes the general scheme of chemical reactions involving radical pairs generated from singlet and triplet precursors; the spin dynamics of the radical pairs; and the magnetic field dependence of product yields caused by the radical pair mechanism. The main part of the review includes a description of the chemical compass in birds. We review: the general properties of the avian compass; the basic scheme of the radical pair mechanism; the reaction kinetics in cryptochrome; quantum coherence and entanglement in the avian compass; and the effects of noise. We believe that the quantum avian compass can play an important role in avian navigation and can also provide the foundation for a new generation of sensitive and selective magnetic-sensing nano-devices.

  7. Soft Coulomb gap and asymmetric scaling towards metal-insulator quantum criticality in multilayer MoS2.

    Science.gov (United States)

    Moon, Byoung Hee; Bae, Jung Jun; Joo, Min-Kyu; Choi, Homin; Han, Gang Hee; Lim, Hanjo; Lee, Young Hee

    2018-05-24

    Quantum localization-delocalization of carriers are well described by either carrier-carrier interaction or disorder. When both effects come into play, however, a comprehensive understanding is not well established mainly due to complexity and sparse experimental data. Recently developed two-dimensional layered materials are ideal in describing such mesoscopic critical phenomena as they have both strong interactions and disorder. The transport in the insulating phase is well described by the soft Coulomb gap picture, which demonstrates the contribution of both interactions and disorder. Using this picture, we demonstrate the critical power law behavior of the localization length, supporting quantum criticality. We observe asymmetric critical exponents around the metal-insulator transition through temperature scaling analysis, which originates from poor screening in insulating regime and conversely strong screening in metallic regime due to free carriers. The effect of asymmetric scaling behavior is weakened in monolayer MoS 2 due to a dominating disorder.

  8. Quantum Chemical Studies of Actinides and Lanthanides: From Small Molecules to Nanoclusters

    Science.gov (United States)

    Vlaisavljevich, Bess

    Research into actinides is of high interest because of their potential applications as an energy source and for the environmental implications therein. Global concern has arisen since the development of the actinide concept in the 1940s led to the industrial scale use of the commercial nuclear energy cycle and nuclear weapons production. Large quantities of waste have been generated from these processes inspiring efforts to address fundamental questions in actinide science. In this regard, the objective of this work is to use theory to provide insight and predictions into actinide chemistry, where experimental work is extremely challenging because of the intrinsic difficulties of the experiments themselves and the safety issues associated with this type of chemistry. This thesis is a collection of theoretical studies of actinide chemistry falling into three categories: quantum chemical and matrix isolation studies of small molecules, the electronic structure of organoactinide systems, and uranyl peroxide nanoclusters and other solid state actinide compounds. The work herein not only spans a wide range of systems size but also investigates a range of chemical problems. Various quantum chemical approaches have been employed. Wave function-based methods have been used to study the electronic structure of actinide containing molecules of small to middle-size. Among these methods, the complete active space self consistent field (CASSCF) approach with corrections from second-order perturbation theory (CASPT2), the generalized active space SCF (GASSCF) approach, and Moller-Plesset second-order perturbation theory (MP2) have been employed. Likewise, density functional theory (DFT) has been used along with analysis tools like bond energy decomposition, bond orders, and Bader's Atoms in Molecules. From these quantum chemical results, comparison with experimentally obtained structures and spectra are made.

  9. Applications of Canonical transformations and nontrivial vacuum solutions to flavor mixing and critical phenomena in quantum field theory

    International Nuclear Information System (INIS)

    Mishchenko, Yuriy

    2004-01-01

    MISHCHENKO, YURIY. Applications of Canonical Transformations and Nontrivial Vacuum Solutions to flavor mixing and critical phenomena in Quantum Field Theory. (Under the direction of Chueng-Ryong Ji.) In this dissertation we consider two recent applications of Bogoliubov Transformation to the phenomenology of quantum mixing and the theory of critical phenomena. In recent years quantum mixing got in the focus of the searches for New Physics due to its unparalleled sensitivity to SM parameters and indications of neutrino mixing. It was recently suggested that Bogoliubov Transformation may be important in proper definition of the flavor states that otherwise results in problems in perturbative treatment. As first part of this dissertation we investigate this conjecture and develop a complete formulation of such a mixing field theory involving introduction of general formalism, analysis of space-time conversion and phenomenological implications. As second part of this dissertati

  10. Applications of Canonical transformations and nontrivial vacuum solutions to flavor mixing and critical phenomena in quantum field theory

    Energy Technology Data Exchange (ETDEWEB)

    Mishchenko, Yuriy [North Carolina State Univ., Raleigh, NC (United States)

    2004-12-01

    MISHCHENKO, YURIY. Applications of Canonical Transformations and Nontrivial Vacuum Solutions to flavor mixing and critical phenomena in Quantum Field Theory. (Under the direction of Chueng-Ryong Ji.) In this dissertation we consider two recent applications of Bogoliubov Transformation to the phenomenology of quantum mixing and the theory of critical phenomena. In recent years quantum mixing got in the focus of the searches for New Physics due to its unparalleled sensitivity to SM parameters and indications of neutrino mixing. It was recently suggested that Bogoliubov Transformation may be important in proper definition of the flavor states that otherwise results in problems in perturbative treatment. As first part of this dissertation we investigate this conjecture and develop a complete formulation of such a mixing field theory involving introduction of general formalism, analysis of space-time conversion and phenomenological implications. As second part of this dissertati

  11. Contradiction between the results of observations of resistance and critical current quantum oscillations in asymmetric superconducting rings

    International Nuclear Information System (INIS)

    Gurtovoi, V. L.; Dubonos, S. V.; Karpii, S. V.; Nikulov, A. V.; Tulin, V. A.

    2007-01-01

    Magnetic field dependences of critical current, resistance, and rectified voltage of asymmetric (half circles of different widths) and symmetrical (half circles of equal widths) aluminum rings close to the super-conducting transition were measured. All these dependences are periodic magnetic field functions with periods corresponding to the flux quantum in the ring. The periodic dependences of critical current measured in opposite directions were found to be close to each other for symmetrical rings and shifted with respect to each other by half the flux quantum in asymmetric rings with ratios between half circle widths of from 1.25 to 2. This shift of the dependences by a quarter of the flux quantum as the ring becomes asymmetric makes critical current anisotropic, which explains the effect of alternating current rectification observed for asymmetric rings. Shifts of the extrema of the periodic dependences of critical current by a quarter of the flux quantum directly contradict the results obtained by measuring asymmetric ring resistance oscillations, whose extrema are, as for symmetrical rings, observed at magnetic fluxes equal to an integer and a half of flux quanta

  12. Spectral analysis and quantum chemical studies of chair and twist-boat conformers of cycloheximide in gas and solution phases

    Science.gov (United States)

    Tokatli, A.; Ucun, F.; Sütçü, K.; Osmanoğlu, Y. E.; Osmanoğlu, Ş.

    2018-02-01

    In this study the conformational behavior of cycloheximide in the gas and solution (CHCl3) phases has theoretically been investigated by spectroscopic and quantum chemical properties using density functional theory (wB97X-D) method with 6-31++G(d,p) basis set, for the first time. The calculated IR results reveal that in the ground state the molecule exits as a mixture of the chair and twist-boat conformers in the gas phase, while the calculated NMR results reveal that it only exits as the chair conformer in the solution phase. In order to obtain the contributions coming from intramolecular interactions to the stability of the conformers in the gas and solution phases, the quantum theory of atoms in molecules (QTAIM), noncovalent interactions (NCI) method, and natural bond orbital analysis (NBO) have been employed. The QTAIM and NCI methods indicated that by intramolecular interactions with bond critical point (BCP) the twist-boat conformer is more stabilized than the chair conformer, while by steric interactions it is more destabilized. Considering that these interactions balance each other, the stabilities of the conformers are understood to be dictated by the van der Waals interactions. The NBO analyses show that the hyperconjugative and steric effects play an important role in the stabilization in the gas and solution phases. Furthermore, to get a better understanding of the chemical behavior of this important antibiotic drug we have evaluated and, commented the global and local reactivity descriptors of the both conformers. Finally, the EPR analysis of γ-irradiated cycloheximide has been done. The comparison of the experimental and calculated data have showed the inducement of a radical structure of (CH2)2ĊCH2 in the molecule. The experimental EPR spectrum has also confirmed that the molecule simultaneously exists in the chair and twist-boat conformers in the solid phase.

  13. Include dispersion in quantum chemical modeling of enzymatic reactions: the case of isoaspartyl dipeptidase.

    Science.gov (United States)

    Zhang, Hai-Mei; Chen, Shi-Lu

    2015-06-09

    The lack of dispersion in the B3LYP functional has been proposed to be the main origin of big errors in quantum chemical modeling of a few enzymes and transition metal complexes. In this work, the essential dispersion effects that affect quantum chemical modeling are investigated. With binuclear zinc isoaspartyl dipeptidase (IAD) as an example, dispersion is included in the modeling of enzymatic reactions by two different procedures, i.e., (i) geometry optimizations followed by single-point calculations of dispersion (approach I) and (ii) the inclusion of dispersion throughout geometry optimization and energy evaluation (approach II). Based on a 169-atom chemical model, the calculations show a qualitative consistency between approaches I and II in energetics and most key geometries, demonstrating that both approaches are available with the latter preferential since both geometry and energy are dispersion-corrected in approach II. When a smaller model without Arg233 (147 atoms) was used, an inconsistency was observed, indicating that the missing dispersion interactions are essentially responsible for determining equilibrium geometries. Other technical issues and mechanistic characteristics of IAD are also discussed, in particular with respect to the effects of Arg233.

  14. Reassigning the Structures of Natural Products Using NMR Chemical Shifts Computed with Quantum Mechanics: A Laboratory Exercise

    Science.gov (United States)

    Palazzo, Teresa A.; Truong, Tiana T.; Wong, Shirley M. T.; Mack, Emma T.; Lodewyk, Michael W.; Harrison, Jason G.; Gamage, R. Alan; Siegel, Justin B.; Kurth, Mark J.; Tantillo, Dean J.

    2015-01-01

    An applied computational chemistry laboratory exercise is described in which students use modern quantum chemical calculations of chemical shifts to assign the structure of a recently isolated natural product. A pre/post assessment was used to measure student learning gains and verify that students demonstrated proficiency of key learning…

  15. Controlling organic chemical hazards in food manufacturing: a hazard analysis critical control points (HACCP) approach.

    Science.gov (United States)

    Ropkins, K; Beck, A J

    2002-08-01

    Hazard analysis by critical control points (HACCP) is a systematic approach to the identification, assessment and control of hazards. Effective HACCP requires the consideration of all hazards, i.e., chemical, microbiological and physical. However, to-date most 'in-place' HACCP procedures have tended to focus on the control of microbiological and physical food hazards. In general, the chemical component of HACCP procedures is either ignored or limited to applied chemicals, e.g., food additives and pesticides. In this paper we discuss the application of HACCP to a broader range of chemical hazards, using organic chemical contaminants as examples, and the problems that are likely to arise in the food manufacturing sector. Chemical HACCP procedures are likely to result in many of the advantages previously identified for microbiological HACCP procedures: more effective, efficient and economical than conventional end-point-testing methods. However, the high costs of analytical monitoring of chemical contaminants and a limited understanding of formulation and process optimisation as means of controlling chemical contamination of foods are likely to prevent chemical HACCP becoming as effective as microbiological HACCP.

  16. Some approaches to the quantum-chemical theory of heterogeneous catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Zhidomirov, G M

    1977-09-01

    A discussion of mathematical methods, models, and parameters used in various quantum-chemical descriptions of chemisorption and reaction at silica and aluminosilicate surfaces covers the continuous-surface model, the cluster model of the surface, the variation of pseudo-atom parameters to reduce the magnitude of boundary effects in the cluster model, the calculation of individual bond strengths in chemisorbed molecules, dissociative adsorption, applications to adsorption on silica and aluminosilicates, the mechanisms of hydrogen-deuterium exchange, etc. Diagrams, graphs, and 42 references.

  17. Compensation effects in molecular interactions and the quantum chemical le Chatelier principle.

    Science.gov (United States)

    Mezey, Paul G

    2015-05-28

    Components of molecular interactions and various changes in the components of total energy changes during molecular processes typically exhibit some degrees of compensation. This may be as prominent as the over 90% compensation of the electronic energy and nuclear repulsion energy components of the total energy in some conformational changes. Some of these compensations are enhanced by solvent effects. For various arrangements of ions in a solvent, however, not only compensation but also a formal, mutual enhancement between the electronic energy and nuclear repulsion energy components of the total energy may also occur, when the tools of nuclear charge variation are applied to establish quantum chemically rigorous energy inequalities.

  18. On the origin of the gauche effect. A quantum chemical study of 1,2-difluoroethane

    Science.gov (United States)

    Engkvist, O.; Karlström, G.; Widmark, P.-O.

    1997-01-01

    The conformational equilibrium of 1,2-difluoroethane has been investigated using ab initio quantum chemical calculations at the SCF, MP2 and CCSD(T) levels, with ANO basis sets. The relative stability of the gauche-conformation of 1,2-difluoroethane is found to be a consequence of the nodal structure of the singly occupied orbital in the CFH 2 radical. It is also shown that the nodal structure of the singly occupied orbitals in the CFH biradical can explain the stability of the cis conformation of 1,2-difluoroethene.

  19. Ab initio quantum chemical calculation as a tool of evaluating diamagnetic susceptibility of magnetically levitating substances

    Energy Technology Data Exchange (ETDEWEB)

    Fujiwara, Y [Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Tanimoto, Y [Faculty of Pharmacy, Osaka Ohtani University, Nishikiorikita, Tondabayashi 584-8540 (Japan)], E-mail: fuji0710@sci.hiroshima-u.ac.jp

    2009-03-01

    On magnetic force evaluation necessary for magnetically levitated diamagnetic substances, isotropic diamagnetic susceptibility estimation by the ab initio quantum chemical calculation using Gaussian03W was verified for more than 300 molecules in a viewpoint of the accuracy in the absolute value and the calculation level affording good cost performance. From comparison, the method of B3PW91 / 6-311+G(d,p) was found to give the adequate absolute value by the relation of (observed) = (1.03 {+-} 0.005) x (calculated) - (1.22 {+-} 0.60) x 10{sup -6} in a unit of cm{sup 3} mol{sup -1} and good cost performance.

  20. Ab initio quantum chemical calculation as a tool of evaluating diamagnetic susceptibility of magnetically levitating substances

    International Nuclear Information System (INIS)

    Fujiwara, Y; Tanimoto, Y

    2009-01-01

    On magnetic force evaluation necessary for magnetically levitated diamagnetic substances, isotropic diamagnetic susceptibility estimation by the ab initio quantum chemical calculation using Gaussian03W was verified for more than 300 molecules in a viewpoint of the accuracy in the absolute value and the calculation level affording good cost performance. From comparison, the method of B3PW91 / 6-311+G(d,p) was found to give the adequate absolute value by the relation of (observed) = (1.03 ± 0.005) x (calculated) - (1.22 ± 0.60) x 10 -6 in a unit of cm 3 mol -1 and good cost performance.

  1. ELECTROREDUCTION MECHANISM OF Ni(DMG)-2 COMPLEX STUDIED WITH QUANTUM CHEMICAL METHOD

    Institute of Scientific and Technical Information of China (English)

    倪亚明; 任镜清; 黎健; 王德民; 梁伟根; 朱芝仙; 高小霞

    1990-01-01

    The electronic structures of the species Ni(DMG)2, (Ni(DMG)2)- and (Ni(DMG)2)2- have been studied by INDO quantum chemical method. The results have clearly shown that in the first stage of the electroreduction of Ni(DMG)2, one electron interacts with the d orbitals on the nickel atom, while in the further stage the second electron interacts with the p orbitals on the nitrogen atoms. It conforms with our electrochemical experimental studies which showed that not only Ni(Ⅱ) is reduced but also DMG is catalytically reduced during the reduction of Ni(DMG)2.

  2. Quantum Chemical Prediction of Equilibrium Acidities of Ureas, Deltamides, Squaramides, and Croconamides.

    Science.gov (United States)

    Ho, Junming; Zwicker, Vincent E; Yuen, Karen K Y; Jolliffe, Katrina A

    2017-10-06

    Robust quantum chemical methods are employed to predict the pK a 's of several families of dual hydrogen-bonding organocatalysts/anion receptors, including deltamides and croconamides as well as their thio derivatives. The average accuracy of these predictions is ∼1 pK a unit and allows for a comparison of the acidity between classes of receptors and for quantitative studies of substituent effects. These computational insights further explain the relationship between pK a and chloride anion affinity of these receptors that will be important for designing future anion receptors and organocatalysts.

  3. Dynamical Quantum Phase Transitions in Spin Chains with Long-Range Interactions: Merging Different Concepts of Nonequilibrium Criticality

    Science.gov (United States)

    Žunkovič, Bojan; Heyl, Markus; Knap, Michael; Silva, Alessandro

    2018-03-01

    We theoretically study the dynamics of a transverse-field Ising chain with power-law decaying interactions characterized by an exponent α , which can be experimentally realized in ion traps. We focus on two classes of emergent dynamical critical phenomena following a quantum quench from a ferromagnetic initial state: The first one manifests in the time-averaged order parameter, which vanishes at a critical transverse field. We argue that such a transition occurs only for long-range interactions α ≤2 . The second class corresponds to the emergence of time-periodic singularities in the return probability to the ground-state manifold which is obtained for all values of α and agrees with the order parameter transition for α ≤2 . We characterize how the two classes of nonequilibrium criticality correspond to each other and give a physical interpretation based on the symmetry of the time-evolved quantum states.

  4. On the Higher Moments of Particle Multiplicity, Chemical Freeze-Out, and QCD Critical Endpoint

    Directory of Open Access Journals (Sweden)

    A. Tawfik

    2013-01-01

    Full Text Available We calculate the first six nonnormalized moments of particle multiplicity within the framework of the hadron resonance gas model. In terms of the lower order moments and corresponding correlation functions, general expressions of higher order moments are derived. Thermal evolution of the first four normalized moments and their products (ratios are studied at different chemical potentials, so that it is possible to evaluate them at chemical freeze-out curve. It is found that a nonmonotonic behaviour reflecting the dynamical fluctuation and strong correlation of particles starts to appear from the normalized third order moment. We introduce novel conditions for describing the chemical freeze-out curve. Although the hadron resonance gas model does not contain any information on the criticality related to the chiral dynamics and singularity in the physical observables, we are able to find out the location of the QCD critical endpoint at μ ~ 350  MeV and temperature T ~ 162  MeV.

  5. Deconfined quantum criticality of the O(3) nonlinear σ model in two spatial dimensions: A renormalization-group study

    International Nuclear Information System (INIS)

    Kim, Ki-Seok

    2005-01-01

    We investigate the quantum phase transition of the O(3) nonlinear σ model without Berry phase in two spatial dimensions. Utilizing the CP 1 representation of the nonlinear σ model, we obtain an effective action in terms of bosonic spinons interacting via compact U(1) gauge fields. Based on the effective field theory, we find that the bosonic spinons are deconfined to emerge at the quantum critical point of the nonlinear σ model. It is emphasized that the deconfinement of spinons is realized in the absence of Berry phase. This is in contrast to the previous study of Senthil et al. [Science 303, 1490 (2004)], where the Berry phase plays a crucial role, resulting in the deconfinement of spinons. It is the reason why the deconfinement is obtained even in the absence of the Berry phase effect that the quantum critical point is described by the XY ('neutral') fixed point, not the IXY ('charged') fixed point. The IXY fixed point is shown to be unstable against instanton excitations and the instanton excitations are proliferated. At the IXY fixed point it is the Berry phase effect that suppresses the instanton excitations, causing the deconfinement of spinons. On the other hand, the XY fixed point is found to be stable against instanton excitations because an effective internal charge is zero at the neutral XY fixed point. As a result the deconfinement of spinons occurs at the quantum critical point of the O(3) nonlinear σ model in two dimensions

  6. Benchmarking quantum mechanical calculations with experimental NMR chemical shifts of 2-HADNT

    Science.gov (United States)

    Liu, Yuemin; Junk, Thomas; Liu, Yucheng; Tzeng, Nianfeng; Perkins, Richard

    2015-04-01

    In this study, both GIAO-DFT and GIAO-MP2 calculations of nuclear magnetic resonance (NMR) spectra were benchmarked with experimental chemical shifts. The experimental chemical shifts were determined experimentally for carbon-13 (C-13) of seven carbon atoms for the TNT degradation product 2-hydroxylamino-4,6-dinitrotoluene (2-HADNT). Quantum mechanics GIAO calculations were implemented using Becke-3-Lee-Yang-Parr (B3LYP) and other six hybrid DFT methods (Becke-1-Lee-Yang-Parr (B1LYP), Becke-half-and-half-Lee-Yang-Parr (BH and HLYP), Cohen-Handy-3-Lee-Yang-Parr (O3LYP), Coulomb-attenuating-B3LYP (CAM-B3LYP), modified-Perdew-Wang-91-Lee-Yang-Parr (mPW1LYP), and Xu-3-Lee-Yang-Parr (X3LYP)) which use the same correlation functional LYP. Calculation results showed that the GIAO-MP2 method gives the most accurate chemical shift values, and O3LYP method provides the best prediction of chemical shifts among the B3LYP and other five DFT methods. Three types of atomic partial charges, Mulliken (MK), electrostatic potential (ESP), and natural bond orbital (NBO), were also calculated using MP2/aug-cc-pVDZ method. A reasonable correlation was discovered between NBO partial charges and experimental chemical shifts of carbon-13 (C-13).

  7. The Alexandria library, a quantum-chemical database of molecular properties for force field development.

    Science.gov (United States)

    Ghahremanpour, Mohammad M; van Maaren, Paul J; van der Spoel, David

    2018-04-10

    Data quality as well as library size are crucial issues for force field development. In order to predict molecular properties in a large chemical space, the foundation to build force fields on needs to encompass a large variety of chemical compounds. The tabulated molecular physicochemical properties also need to be accurate. Due to the limited transparency in data used for development of existing force fields it is hard to establish data quality and reusability is low. This paper presents the Alexandria library as an open and freely accessible database of optimized molecular geometries, frequencies, electrostatic moments up to the hexadecupole, electrostatic potential, polarizabilities, and thermochemistry, obtained from quantum chemistry calculations for 2704 compounds. Values are tabulated and where available compared to experimental data. This library can assist systematic development and training of empirical force fields for a broad range of molecules.

  8. Influence of wet chemical cleaning on quantum efficiency of GaN photocathode

    International Nuclear Information System (INIS)

    Wang Xiao-Hui; Gao Pin; Wang Hong-Gang; Li Biao; Chang Ben-Kang

    2013-01-01

    GaN samples 1–3 are cleaned by a 2:2:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%) to de-ionized water; hydrochloric acid (37%); or a 4:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%). The samples are activated by Cs/O after the same annealing process. X-ray photoelectron spectroscopy after the different ways of wet chemical cleaning shows: sample 1 has the largest proportion of Ga, N, and O among the three samples, while its C content is the lowest. After activation the quantum efficiency curves show sample 1 has the best photocathode performance. We think the wet chemical cleaning method is a process which will mainly remove C contamination. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  9. Vibrational, electronic and quantum chemical studies of 1,2,4-benzenetricarboxylic-1,2-anhydride.

    Science.gov (United States)

    Arjunan, V; Raj, Arushma; Subramanian, S; Mohan, S

    2013-06-01

    The FTIR and FT-Raman spectra of 1,2,4-benzenetricarboxylic-1,2-anhydride (BTCA) have been recorded in the range 4000-400 and 4000-100 cm(-1), respectively. The complete vibrational assignments and analysis of BTCA have been performed. More support on the experimental findings was added from the quantum chemical studies performed with DFT (B3LYP, MP2, B3PW91) method using 6-311++G(**), 6-31G(**) and cc-pVTZ basis sets. The structural parameters, energies, thermodynamic parameters, vibrational frequencies and the NBO charges of BTCA were determined by the DFT method. The (1)H and (13)C isotropic chemical shifts (δ ppm) of BTCA with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. The delocalization energies of different types of interactions were determined. Copyright © 2013 Elsevier B.V. All rights reserved.

  10. The Alexandria library, a quantum-chemical database of molecular properties for force field development

    Science.gov (United States)

    Ghahremanpour, Mohammad M.; van Maaren, Paul J.; van der Spoel, David

    2018-04-01

    Data quality as well as library size are crucial issues for force field development. In order to predict molecular properties in a large chemical space, the foundation to build force fields on needs to encompass a large variety of chemical compounds. The tabulated molecular physicochemical properties also need to be accurate. Due to the limited transparency in data used for development of existing force fields it is hard to establish data quality and reusability is low. This paper presents the Alexandria library as an open and freely accessible database of optimized molecular geometries, frequencies, electrostatic moments up to the hexadecupole, electrostatic potential, polarizabilities, and thermochemistry, obtained from quantum chemistry calculations for 2704 compounds. Values are tabulated and where available compared to experimental data. This library can assist systematic development and training of empirical force fields for a broad range of molecules.

  11. Recovery from chemical, biological, and radiological incidents. Critical infrastructure and economic impact considerations

    Energy Technology Data Exchange (ETDEWEB)

    Franco, David Oliver [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Yang, Lynn I. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Hammer, Ann E. [Sandia National Lab. (SNL-CA), Livermore, CA (United States)

    2012-06-01

    To restore regional lifeline services and economic activity as quickly as possible after a chemical, biological or radiological incident, emergency planners and managers will need to prioritize critical infrastructure across many sectors for restoration. In parallel, state and local governments will need to identify and implement measures to promote reoccupation and economy recovery in the region. This document provides guidance on predisaster planning for two of the National Disaster Recovery Framework Recovery Support Functions: Infrastructure Systems and Economic Recovery. It identifies key considerations for infrastructure restoration, outlines a process for prioritizing critical infrastructure for restoration, and identifies critical considerations for promoting regional economic recovery following a widearea disaster. Its goal is to equip members of the emergency preparedness community to systematically prioritize critical infrastructure for restoration, and to develop effective economic recovery plans in preparation for a widearea CBR disaster.

  12. Quantum chemical molecular dynamical investigation of alkyl nitrite photo-dissociated on copper surfaces

    International Nuclear Information System (INIS)

    Wang Xiaojing; Wang Wei; Han Peilin; Kubo, Momoji; Miyamoto, Akira

    2008-01-01

    An accelerated quantum chemical molecular dynamical code 'Colors-Excite' was used to investigate the photolysis of alkyl nitrites series, RONO (R=CH 3 and C(CH 3 ) 3 ) on copper surfaces. Our calculations showed that the photo-dissociated processes are associated with the alkyl substituents of RONO when adsorbed on copper surfaces. For R=CH 3 , a two-step photolysis reaction occurred, yielding diverse intermediate products including RO radical, NO, and HNO, consistent with those reported in gas phase. While for R=C(CH 3 ) 3 , only one-step photolysis reaction occurred and gave intermediate products of RO radical and NO. Consequently, pure RO species were achieved to adsorb on metal surfaces by removing the NO species in photolysis reaction. The detailed photo-dissociated behaviors of RONO on copper surfaces with different alkyl substituents which are uncovered by the present simulation can be extended to explain the diverse dissociative mechanism experimentally observed. The quantum chemical molecular dynamical code 'Colors-Excite' is proved to be highly applicable to the photo-dissociations on metal surfaces

  13. TG-FTIR, DSC and quantum chemical studies of the thermal decomposition of quaternary methylammonium halides

    International Nuclear Information System (INIS)

    Sawicka, Marlena; Storoniak, Piotr; Skurski, Piotr; Blazejowski, Jerzy; Rak, Janusz

    2006-01-01

    The thermal decomposition of quaternary methylammonium halides was studied using thermogravimetry coupled to FTIR (TG-FTIR) and differential scanning calorimetry (DSC) as well as the DFT, MP2 and G2 quantum chemical methods. There is almost perfect agreement between the experimental IR spectra and those predicted at the B3LYP/6-311G(d,p) level: this has demonstrated for the first time that an equimolar mixture of trimethylamine and a methyl halide is produced as a result of decomposition. The experimental enthalpies of dissociation are 153.4, 171.2, and 186.7 kJ/mol for chloride, bromide and iodide, respectively, values that correlate well with the calculated enthalpies of dissociation based on crystal lattice energies and quantum chemical thermodynamic barriers. The experimental activation barriers estimated from the least-squares fit of the F1 kinetic model (first-order process) to thermogravimetric traces - 283, 244 and 204 kJ/mol for chloride, bromide and iodide, respectively - agree very well with theoretically calculated values. The theoretical approach assumed in this work has been shown capable of predicting the relevant characteristics of the thermal decomposition of solids with experimental accuracy

  14. Nematic quantum critical point without magnetism in FeSe1-xSx superconductors.

    Science.gov (United States)

    Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

    2016-07-19

    In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near [Formula: see text], the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.

  15. Quench dynamics near a quantum critical point: Application to the sine-Gordon model

    International Nuclear Information System (INIS)

    De Grandi, C.; Polkovnikov, A.; Gritsev, V.

    2010-01-01

    We discuss the quench dynamics near a quantum critical point focusing on the sine-Gordon model as a primary example. We suggest a unified approach to sudden and slow quenches, where the tuning parameter λ(t) changes in time as λ(t)∼υt r , based on the adiabatic expansion of the excitation probability in powers of υ. We show that the universal scaling of the excitation probability can be understood through the singularity of the generalized adiabatic susceptibility χ 2r+2 (λ), which for sudden quenches (r=0) reduces to the fidelity susceptibility. In turn this class of susceptibilities is expressed through the moments of the connected correlation function of the quench operator. We analyze the excitations created after a sudden quench of the cosine potential using a combined approach of form-factors expansion and conformal perturbation theory for the low-energy and high-energy sector, respectively. We find the general scaling laws for the probability of exciting the system, the density of excited quasiparticles, the entropy and the heat generated after the quench. In the two limits where the sine-Gordon model maps to hard-core bosons and free massive fermions we provide the exact solutions for the quench dynamics and discuss the finite temperature generalizations.

  16. Development of a quantum chemical molecular dynamics tribochemical simulator and its application to tribochemical reaction dynamics of lubricant additives

    International Nuclear Information System (INIS)

    Onodera, T; Tsuboi, H; Hatakeyama, N; Endou, A; Miyamoto, A; Miura, R; Takaba, H; Suzuki, A; Kubo, M

    2010-01-01

    Tribology at the atomistic and molecular levels has been theoretically studied by a classical molecular dynamics (MD) method. However, this method inherently cannot simulate the tribochemical reaction dynamics because it does not consider the electrons in nature. Although the first-principles based MD method has recently been used for understanding the chemical reaction dynamics of several molecules in the tribology field, the method cannot simulate the tribochemical reaction dynamics of a large complex system including solid surfaces and interfaces due to its huge computation costs. On the other hand, we have developed a quantum chemical MD tribochemical simulator on the basis of a hybrid tight-binding quantum chemical/classical MD method. In the simulator, the central part of the chemical reaction dynamics is calculated by the tight-binding quantum chemical MD method, and the remaining part is calculated by the classical MD method. Therefore, the developed tribochemical simulator realizes the study on tribochemical reaction dynamics of a large complex system, which cannot be treated by using the conventional classical MD or the first-principles MD methods. In this paper, we review our developed quantum chemical MD tribochemical simulator and its application to the tribochemical reaction dynamics of a few lubricant additives

  17. Chemical Distances for Percolation of Planar Gaussian Free Fields and Critical Random Walk Loop Soups

    Science.gov (United States)

    Ding, Jian; Li, Li

    2018-06-01

    We initiate the study on chemical distances of percolation clusters for level sets of two-dimensional discrete Gaussian free fields as well as loop clusters generated by two-dimensional random walk loop soups. One of our results states that the chemical distance between two macroscopic annuli away from the boundary for the random walk loop soup at the critical intensity is of dimension 1 with positive probability. Our proof method is based on an interesting combination of a theorem of Makarov, isomorphism theory, and an entropic repulsion estimate for Gaussian free fields in the presence of a hard wall.

  18. Hybrid quantum and classical methods for computing kinetic isotope effects of chemical reactions in solutions and in enzymes.

    Science.gov (United States)

    Gao, Jiali; Major, Dan T; Fan, Yao; Lin, Yen-Lin; Ma, Shuhua; Wong, Kin-Yiu

    2008-01-01

    A method for incorporating quantum mechanics into enzyme kinetics modeling is presented. Three aspects are emphasized: 1) combined quantum mechanical and molecular mechanical methods are used to represent the potential energy surface for modeling bond forming and breaking processes, 2) instantaneous normal mode analyses are used to incorporate quantum vibrational free energies to the classical potential of mean force, and 3) multidimensional tunneling methods are used to estimate quantum effects on the reaction coordinate motion. Centroid path integral simulations are described to make quantum corrections to the classical potential of mean force. In this method, the nuclear quantum vibrational and tunneling contributions are not separable. An integrated centroid path integral-free energy perturbation and umbrella sampling (PI-FEP/UM) method along with a bisection sampling procedure was summarized, which provides an accurate, easily convergent method for computing kinetic isotope effects for chemical reactions in solution and in enzymes. In the ensemble-averaged variational transition state theory with multidimensional tunneling (EA-VTST/MT), these three aspects of quantum mechanical effects can be individually treated, providing useful insights into the mechanism of enzymatic reactions. These methods are illustrated by applications to a model process in the gas phase, the decarboxylation reaction of N-methyl picolinate in water, and the proton abstraction and reprotonation process catalyzed by alanine racemase. These examples show that the incorporation of quantum mechanical effects is essential for enzyme kinetics simulations.

  19. Quantum

    CERN Document Server

    Al-Khalili, Jim

    2003-01-01

    In this lively look at quantum science, a physicist takes you on an entertaining and enlightening journey through the basics of subatomic physics. Along the way, he examines the paradox of quantum mechanics--beautifully mathematical in theory but confoundingly unpredictable in the real world. Marvel at the Dual Slit experiment as a tiny atom passes through two separate openings at the same time. Ponder the peculiar communication of quantum particles, which can remain in touch no matter how far apart. Join the genius jewel thief as he carries out a quantum measurement on a diamond without ever touching the object in question. Baffle yourself with the bizzareness of quantum tunneling, the equivalent of traveling partway up a hill, only to disappear then reappear traveling down the opposite side. With its clean, colorful layout and conversational tone, this text will hook you into the conundrum that is quantum mechanics.

  20. Theory of First Order Chemical Kinetics at the Critical Point of Solution.

    Science.gov (United States)

    Baird, James K; Lang, Joshua R

    2017-10-26

    Liquid mixtures, which have a phase diagram exhibiting a miscibility gap ending in a critical point of solution, have been used as solvents for chemical reactions. The reaction rate in the forward direction has often been observed to slow down as a function of temperature in the critical region. Theories based upon the Gibbs free energy of reaction as the driving force for chemical change have been invoked to explain this behavior. With the assumption that the reaction is proceeding under relaxation conditions, these theories expand the free energy in a Taylor series about the position of equilibrium. Since the free energy is zero at equilibrium, the leading term in the Taylor series is proportional to the first derivative of the free energy with respect to the extent of reaction. To analyze the critical behavior of this derivative, the theories exploit the principle of critical point isomorphism, which is thought to govern all critical phenomena. They find that the derivative goes to zero in the critical region, which accounts for the slowing down observed in the reaction rate. As has been pointed out, however, most experimental rate investigations have been carried out under irreversible conditions as opposed to relaxation conditions [Shen et al. J. Phys. Chem. A 2015, 119, 8784-8791]. Below, we consider a reaction governed by first order kinetics and invoke transition state theory to take into account the irreversible conditions. We express the apparent activation energy in terms of thermodynamic derivatives evaluated under standard conditions as well as the pseudoequilibrium conditions associated with the reactant and the activated complex. We show that these derivatives approach infinity in the critical region. The apparent activation energy follows this behavior, and its divergence accounts for the slowing down of the reaction rate.

  1. Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5

    Energy Technology Data Exchange (ETDEWEB)

    Helm, T. [MPI-CPFS (Germany); Bachmann, M. [MPI-CPFS (Germany); Moll, P.J.W. [MPI-CPFS (Germany); Balicas, L. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab); Chan, Mun Keat [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Ramshaw, Brad [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Mcdonald, Ross David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Balakirev, Fedor Fedorovich [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Bauer, Eric Dietzgen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Ronning, Filip [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-03-23

    Electronic nematicity appears in proximity to unconventional high-temperature superconductivity in the cuprates and iron-arsenides, yet whether they cooperate or compete is widely discussed. While many parallels are drawn between high-Tc and heavy fermion superconductors, electronic nematicity was not believed to be an important aspect in their superconductivity. We have found evidence for a field-induced strong electronic in-plane symmetry breaking in the tetragonal heavy fermion superconductor CeRhIn5. At ambient pressure and zero field, it hosts an anti-ferromagnetic order (AFM) of nominally localized 4f electrons at TN=3.8K(1). Moderate pressure of 17kBar suppresses the AFM order and a dome of superconductivity appears around the quantum critical point. Similarly, a density-wave-like correlated phase appears centered around the field-induced AFM quantum critical point. In this phase, we have now observed electronic nematic behavior.

  2. Theory of Correlated Pairs of Electrons Oscillating in Resonant Quantum States to Reach the Critical Temperature in a Metal

    OpenAIRE

    Aroche, Raúl Riera; Rosas-Cabrera, Rodrigo Arturo; Burgos, Rodrigo Arturo Rosas; Betancourt-Riera, René; Betancourt-Riera, Ricardo

    2017-01-01

    The formation of Correlated Electron Pairs Oscillating around the Fermi level in Resonant Quantum States (CEPO-RQS), when a metal is cooled to its critical temperature T=Tc, is studied. The necessary conditions for the existence of CEPO-RQS are analyzed. The participation of electron-electron interaction screened by an electron dielectric constant of the form proposed by Thomas Fermi is considered and a physical meaning for the electron-phonon-electron interaction in the formation of the CEPO...

  3. Accurate Determination of the Quasiparticle and Scaling Properties Surrounding the Quantum Critical Point of Disordered Three-Dimensional Dirac Semimetals.

    Science.gov (United States)

    Fu, Bo; Zhu, Wei; Shi, Qinwei; Li, Qunxiang; Yang, Jinlong; Zhang, Zhenyu

    2017-04-07

    Exploiting the enabling power of the Lanczos method in momentum space, we determine accurately the quasiparticle and scaling properties of disordered three-dimensional Dirac semimetals surrounding the quantum critical point separating the semimetal and diffusive metal regimes. We unveil that the imaginary part of the quasiparticle self-energy obeys a common power law before, at, and after the quantum phase transition, but the power law is nonuniversal, whose exponent is dependent on the disorder strength. More intriguingly, whereas a common power law is also found for the real part of the self-energy before and after the phase transition, a distinctly different behavior is identified at the critical point, characterized by the existence of a nonanalytic logarithmic singularity. This nonanalytical correction serves as the very basis for the unusual power-law behaviors of the quasiparticles and many other physical properties surrounding the quantum critical point. Our approach also allows the ready and reliable determination of the scaling properties of the correlation length and dynamical exponents. We further show that the central findings are valid for both uncorrelated and correlated disorder distributions and should be directly comparable with future experimental observations.

  4. Off-criticality behaviour of the Blume-Capel quantum chain as a check of Zamolodchikov's conjecture

    International Nuclear Information System (INIS)

    Gehlen, G. v.

    1989-07-01

    Using finite-size numerical calculations, we study the off-criticality behaviour of the Blume-Capel quantum chain in the neighbourhood of the c=7/10 tricritical Ising point. Moving from the tricritical point in the (1/10, 1/10)- and (3/5, 3/5)-directions into the disordered region, we find masses and thresholds in agreement with the structure proposed by Zamolodchikov from conformal field theory. Moving in the opposite directions, the spectrum is degenerate between the Z 2 -even and Z 2 -odd sectors, suggesting an underlying supersymmetry. The free-particle energy momentum relation and the scaling properties off criticality are checked. (orig.)

  5. Atomic spin-chain realization of a model for quantum criticality

    NARCIS (Netherlands)

    Toskovic, R.; van den Berg, R.; Spinelli, A.; Eliens, I.S.; van den Toorn, B.; Bryant, B.; Caux, J.-S.; Otte, A.F.

    The ability to manipulate single atoms has opened up the door to constructing interesting and useful quantum structures from the ground up. On the one hand, nanoscale arrangements of magnetic atoms are at the heart of future quantum computing and spintronic devices; on the other hand, they can be

  6. Chemical effects of alkali atoms on critical temperature in superconducting alkali-doped fullerides

    Science.gov (United States)

    Hetfleisch, F.; Gunnarsson, O.; Srama, R.; Han, J. E.; Stepper, M.; Roeser, H.-P.; Bohr, A.; Lopez, J. S.; Mashmool, M.; Roth, S.

    2018-03-01

    Alkali metal doped fullerides (A3C60) are superconductors with critical temperatures, Tc, extending up to 38 K. Tc is known to depend strongly on the lattice parameter a, which can be adjusted by physical or chemical pressure. In the latter case an alkali atom is replaced by a different sized one, which changes a. We have collected an extensive data base of experimental data for Tc from very early up to recent measurements. We disentangle alkali atom chemical effects on Tc, beyond the well-known consequences of changing a. It is found that Tc, for a fixed a, is typically increased as smaller alkali atoms are replaced by larger ones, except for very large a. Possible reasons for these results are discussed. Although smaller in size than the lattice parameter contribution, the chemical effect is not negligible and should be considered in future physical model developments.

  7. DTADH and quantum critical phenomena caused by anisotropy and external magnetic field for spin-1/2 Heisenberg diamond chains

    International Nuclear Information System (INIS)

    Li Yanchao

    2010-01-01

    Using the transfer matrix renormalization group (TMRG) method, we study the connection between the first derivative of the thermal average of driving-term Hamiltonian (DTADH) and the trace of quantum critical behaviors at finite temperatures. Connecting with the exact diagonalization method, we give the phase diagrams and analyze the properties of each phase for both the ferromagnetic and anti-ferromagnetic frustrated J 3 anisotropy diamond chain models. The finite-temperature scaling behaviors near the critical regions are also investigated. Further, we show the critical behaviors driven by external magnetic field, analyze the formation of the 1/3 magnetic plateau and the influence of different interactions on those critical points for both the ferrimagnetic and anti-ferromagnetic distorted diamond chains.

  8. Comparison of sugar molecule decomposition through glucose and fructose: a high-level quantum chemical study.

    Energy Technology Data Exchange (ETDEWEB)

    Assary, R. S.; Curtiss, L. A. (Center for Nanoscale Materials); ( MSD); (Northwestern Univ.)

    2012-02-01

    Efficient chemical conversion of biomass is essential to produce sustainable energy and industrial chemicals. Industrial level conversion of glucose to useful chemicals, such as furfural, hydroxymethylfurfural, and levulinic acid, is a major step in the biomass conversion but is difficult because of the formation of undesired products and side reactions. To understand the molecular level reaction mechanisms involved in the decomposition of glucose and fructose, we have carried out high-level quantum chemical calculations [Gaussian-4 (G4) theory]. Selective 1,2-dehydration, keto-enol tautomerization, isomerization, retro-aldol condensation, and hydride shifts of glucose and fructose molecules were investigated. Detailed kinetic and thermodynamic analyses indicate that, for acyclic glucose and fructose molecules, the dehydration and isomerization require larger activation barriers compared to the retro-aldol reaction at 298 K in neutral medium. The retro-aldol reaction results in the formation of C2 and C4 species from glucose and C3 species from fructose. The formation of the most stable C3 species, dihydroxyacetone from fructose, is thermodynamically downhill. The 1,3-hydride shift leads to the cleavage of the C-C bond in the acyclic species; however, the enthalpy of activation is significantly higher (50-55 kcal/mol) than that of the retro-aldol reaction (38 kcal/mol) mainly because of the sterically hindered distorted four-membered transition state compared to the hexa-membered transition state in the retro-aldol reaction. Both tautomerization and dehydration are catalyzed by a water molecule in aqueous medium; however, water has little effect on the retro-aldol reaction. Isomerization of glucose to fructose and glyceraldehyde to dihydroxyacetone proceeds through hydride shifts that require an activation enthalpy of about 40 kcal/mol at 298 K in water medium. This investigation maps out accurate energetics of the decomposition of glucose and fructose molecules

  9. Standoff detection of turbulent chemical mixture plumes using a swept external cavity quantum cascade laser

    Energy Technology Data Exchange (ETDEWEB)

    Phillips, Mark C. [Pacific Northwest National Laboratory, Richland, Washington; Brumfield, Brian E. [Pacific Northwest National Laboratory, Richland, Washington

    2017-08-21

    We demonstrate standoff detection of turbulent mixed-chemical plumes using a broadly-tunable external cavity quantum cascade laser (ECQCL). The ECQCL was directed through plumes of mixed methanol/ethanol vapor to a partially-reflective surface located 10 m away. The reflected power was measured as the ECQCL was swept over its tuning range of 930-1065 cm-1 (9.4-10.8 µm) at rates up to 200 Hz. Analysis of the transmission spectra though the plume was performed to determine chemical concentrations with time resolution of 0.005 s. Comparison of multiple spectral sweep rates of 2 Hz, 20 Hz, and 200 Hz shows that higher sweep rates reduce effects of atmospheric and source turbulence, resulting in lower detection noise and more accurate measurement of the rapidly-changing chemical concentrations. Detection sensitivities of 0.13 ppm*m for MeOH and 1.2 ppm*m for EtOH are demonstrated for a 200 Hz spectral sweep rate, normalized to 1 s detection time.

  10. Structure activity studies of an analgesic drug tapentadol hydrochloride by spectroscopic and quantum chemical methods

    Science.gov (United States)

    Arjunan, V.; Santhanam, R.; Marchewka, M. K.; Mohan, S.; Yang, Haifeng

    2015-11-01

    Tapentadol is a novel opioid pain reliever drug with a dual mechanism of action, having potency between morphine and tramadol. Quantum chemical calculations have been carried out for tapentadol hydrochloride (TAP.Cl) to determine the properties. The geometry is optimised and the structural properties of the compound were determined from the optimised geometry by B3LYP method using 6-311++G(d,p), 6-31G(d,p) and cc-pVDZ basis sets. FT-IR and FT-Raman spectra are recorded in the solid phase in the region of 4000-400 and 4000-100 cm-1, respectively. Frontier molecular orbital energies, LUMO-HOMO energy gap, ionisation potential, electron affinity, electronegativity, hardness and chemical potential are also calculated. The stability of the molecule arising from hyperconjugative interactions and charge delocalisation has been analysed using NBO analysis. The 1H and 13C nuclear magnetic resonance chemical shifts of the molecule are analysed.

  11. Recent developments of the quantum chemical cluster approach for modeling enzyme reactions.

    Science.gov (United States)

    Siegbahn, Per E M; Himo, Fahmi

    2009-06-01

    The quantum chemical cluster approach for modeling enzyme reactions is reviewed. Recent applications have used cluster models much larger than before which have given new modeling insights. One important and rather surprising feature is the fast convergence with cluster size of the energetics of the reactions. Even for reactions with significant charge separation it has in some cases been possible to obtain full convergence in the sense that dielectric cavity effects from outside the cluster do not contribute to any significant extent. Direct comparisons between quantum mechanics (QM)-only and QM/molecular mechanics (MM) calculations for quite large clusters in a case where the results differ significantly have shown that care has to be taken when using the QM/MM approach where there is strong charge polarization. Insights from the methods used, generally hybrid density functional methods, have also led to possibilities to give reasonable error limits for the results. Examples are finally given from the most extensive study using the cluster model, the one of oxygen formation at the oxygen-evolving complex in photosystem II.

  12. Quantum-Chemical Insights into the Self-Assembly of Carbon-Based Supramolecular Complexes

    Directory of Open Access Journals (Sweden)

    Joaquín Calbo

    2018-01-01

    Full Text Available Understanding how molecular systems self-assemble to form well-organized superstructures governed by noncovalent interactions is essential in the field of supramolecular chemistry. In the nanoscience context, the self-assembly of different carbon-based nanoforms (fullerenes, carbon nanotubes and graphene with, in general, electron-donor molecular systems, has received increasing attention as a means of generating potential candidates for technological applications. In these carbon-based systems, a deep characterization of the supramolecular organization is crucial to establish an intimate relation between supramolecular structure and functionality. Detailed structural information on the self-assembly of these carbon-based nanoforms is however not always accessible from experimental techniques. In this regard, quantum chemistry has demonstrated to be key to gain a deep insight into the supramolecular organization of molecular systems of high interest. In this review, we intend to highlight the fundamental role that quantum-chemical calculations can play to understand the supramolecular self-assembly of carbon-based nanoforms through a limited selection of supramolecular assemblies involving fullerene, fullerene fragments, nanotubes and graphene with several electron-rich π-conjugated systems.

  13. Degradation of Perfluorinated Ether Lubricants on Pure Aluminum Surfaces: Semiempirical Quantum Chemical Modeling

    Science.gov (United States)

    Slaby, Scott M.; Ewing, David W.; Zehe, Michael J.

    1997-01-01

    The AM1 semiempirical quantum chemical method was used to model the interaction of perfluoroethers with aluminum surfaces. Perfluorodimethoxymethane and perfluorodimethyl ether were studied interacting with aluminum surfaces, which were modeled by a five-atom cluster and a nine-atom cluster. Interactions were studied for edge (high index) sites and top (low index) sites of the clusters. Both dissociative binding and nondissociative binding were found, with dissociative binding being stronger. The two different ethers bound and dissociated on the clusters in different ways: perfluorodimethoxymethane through its oxygen atoms, but perfluorodimethyl ether through its fluorine atoms. The acetal linkage of perfluorodimeth-oxymethane was the key structural feature of this molecule in its binding and dissociation on the aluminum surface models. The high-index sites of the clusters caused the dissociation of both ethers. These results are consistent with the experimental observation that perfluorinated ethers decompose in contact with sputtered aluminum surfaces.

  14. QSAR analysis of salicylamide isosteres with the use of quantum chemical molecular descriptors.

    Science.gov (United States)

    Dolezal, R; Van Damme, S; Bultinck, P; Waisser, K

    2009-02-01

    Quantitative relationships between the molecular structure and the biological activity of 49 isosteric salicylamide derivatives as potential antituberculotics with a new mechanism of action against three Mycobacterial strains were investigated. The molecular structures were represented by quantum chemical B3LYP/6-31G( *) based molecular descriptors. A resulting set of 220 molecular descriptors, including especially electronic properties, was statistically analyzed using multiple linear regression, resulting in acceptable and robust QSAR models. The best QSAR model was found for Mycobacterium tuberculosis (r(2)=0.92; q(2)=0.89), and somewhat less good QSAR models were found for Mycobacterium avium (r(2)=0.84; q(2)=0.78) and Mycobacterium kansasii (r(2)=0.80; q(2)=0.56). All QSAR models were cross-validated using the leave-10-out procedure.

  15. Quantum chemical simulation of hydrogen like states in silicon and diamond

    International Nuclear Information System (INIS)

    Gel'fand, R.B.; Gordeev, V.A.; Gorelkinskij, Yu.V.

    1989-01-01

    The quantum-chemical methods of the complete neglect of differential overlap (CNDO) and intermediate neglect of differential overlap (INDO) are used to calculate the electronic structure of atomic hydrogen (muonium) located at different interstital sites of the silicon and diamond crystal lattices. The electronic g- and hyperfine interaction tensors of the impure atom are determined.The results obtained are compared with the experimental data on the 'normal' (Mu') and 'anomalous' (Mu * ) muonium centers as well as on the hydrogen-bearing Si-AA9 EPR center which is a hydrogen-bearing analogue of (Mu * ). The most likely localization sites for hydrogen (muonium) atoms in silicon and diamond crystals are established. 22 refs

  16. Random Forest Approach to QSPR Study of Fluorescence Properties Combining Quantum Chemical Descriptors and Solvent Conditions.

    Science.gov (United States)

    Chen, Chia-Hsiu; Tanaka, Kenichi; Funatsu, Kimito

    2018-04-22

    The Quantitative Structure - Property Relationship (QSPR) approach was performed to study the fluorescence absorption wavelengths and emission wavelengths of 413 fluorescent dyes in different solvent conditions. The dyes included the chromophore derivatives of cyanine, xanthene, coumarin, pyrene, naphthalene, anthracene and etc., with the wavelength ranging from 250 nm to 800 nm. An ensemble method, random forest (RF), was employed to construct nonlinear prediction models compared with the results of linear partial least squares and nonlinear support vector machine regression models. Quantum chemical descriptors derived from density functional theory method and solvent information were also used by constructing models. The best prediction results were obtained from RF model, with the squared correlation coefficients [Formula: see text] of 0.940 and 0.905 for λ abs and λ em , respectively. The descriptors used in the models were discussed in detail in this report by comparing the feature importance of RF.

  17. Chemically functionalized ZnS quantum dots as new optical nanosensor of herbicides

    Science.gov (United States)

    Masteri-Farahani, M.; Mahdavi, S.; Khanmohammadi, H.

    2018-03-01

    Surface chemical functionalization of ZnS quantum dots (ZnS-QDs) with cysteamine hydrochloride resulted in the preparation of an optical nanosensor for detection of herbicides. Characterization of the functionalized ZnS-QDs was performed with physicochemical methods such as x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, energy dispersive x-ray (EDX) analysis, ultraviolet-visible (UV–vis) and photoluminescence (PL) spectroscopies. The optical band gap of the functionalized ZnS-QDs was determined by using Tauc plot as 4.1 eV. Addition of various herbicides resulted in the linearly fluorescence quenching of the functionalized ZnS-QDs according to the Stern-Volmer equation. The functionalized ZnS-QDs can be used as simple, rapid, and inexpensive nanosensor for practical detection and measurement of various herbicides.

  18. Quantum chemical modeling of the inhibition mechanism of monoamine oxidase by oxazolidinone and analogous heterocyclic compounds.

    Science.gov (United States)

    Erdem, Safiye Sağ; Özpınar, Gül Altınbaş; Boz, Ümüt

    2014-02-01

    Monoamine oxidase (MAO, EC 1.4.3.4) is responsible from the oxidation of a variety of amine neurotransmitters. MAO inhibitors are used for the treatment of depression or Parkinson's disease. They also inhibit the catabolism of dietary amines. According to one hypothesis, inactivation results from the formation of a covalent adduct to a cysteine residue in the enzyme. If the adduct is stable enough, the enzyme is inhibited for a long time. After a while, enzyme can turn to its active form as a result of adduct breakdown by β-elimination. In this study, the proposed inactivation mechanism was modeled and tested by quantum chemical calculations. Eight heterocyclic methylthioamine derivatives were selected to represent the proposed covalent adducts. Activation energies related to their β-elimination reactions were calculated using ab initio and density functional theory methods. Calculated activation energies were in good agreement with the relative stabilities of the hypothetical adducts predicted in the literature by enzyme inactivation measurements.

  19. Molecular interactions in ethyl acetate-chlorobenzene binary solution: Dielectric, spectroscopic studies and quantum chemical calculations

    Science.gov (United States)

    Karthick, N. K.; Kumbharkhane, A. C.; Joshi, Y. S.; Mahendraprabu, A.; Shanmugam, R.; Elangovan, A.; Arivazhagan, G.

    2017-05-01

    Dielectric studies using Time Domain Reflectometry method has been carried out on the binary solution of Ethyl acetate (EA) with Chlorobenzene (CBZ) over the entire composition range. Spectroscopic (FTIR and 13C NMR) signatures of neat EA, CBZ and their equimolar binary solution have also been recorded. The results of the spectroscopic studies favour the presence of (CBZ) Csbnd H ⋯ Odbnd C (EA), (EA) methylene Csbnd H ⋯ π electrons (CBZ) and (EA) methyl Csbnd H ⋯ Cl (CBZ) contacts which have been validated using quantum chemical calculations. Dimerization of CBZ has been identified. Presence of β-clusters has been identified in all the solutions. Although EA and CBZ molecules have nearly equal molar volumes, CBZ molecules experience larger hindrance for the rotation than EA molecules. Very small excess dielectric constant (εE) values may be correlated with weak heteromolecular forces and/or closed heteromolecular association.

  20. Semiempirical Quantum Chemical Calculations Accelerated on a Hybrid Multicore CPU-GPU Computing Platform.

    Science.gov (United States)

    Wu, Xin; Koslowski, Axel; Thiel, Walter

    2012-07-10

    In this work, we demonstrate that semiempirical quantum chemical calculations can be accelerated significantly by leveraging the graphics processing unit (GPU) as a coprocessor on a hybrid multicore CPU-GPU computing platform. Semiempirical calculations using the MNDO, AM1, PM3, OM1, OM2, and OM3 model Hamiltonians were systematically profiled for three types of test systems (fullerenes, water clusters, and solvated crambin) to identify the most time-consuming sections of the code. The corresponding routines were ported to the GPU and optimized employing both existing library functions and a GPU kernel that carries out a sequence of noniterative Jacobi transformations during pseudodiagonalization. The overall computation times for single-point energy calculations and geometry optimizations of large molecules were reduced by one order of magnitude for all methods, as compared to runs on a single CPU core.

  1. Low Temperature Synthesis of CdSe Quantum Dots with Amine Derivative and Their Chemical Kinetics

    Science.gov (United States)

    Seongmi Hwang,; Youngmin Choi,; Sunho Jeong,; Hakyun Jung,; Chang Gyoun Kim,; Teak-Mo Chung,; Beyong-Hwan Ryu,

    2010-05-01

    The chemical kinetics of growing CdSe nanocrystals was studied in order to investigate the effects of amine capping agents on the size of resulting quantum dots (QDs). CdSe QDs were prepared in phenyl ether, and the amine ligand dependence of QD size was determined. The results show that the size of CdSe nanocrystals can be regulated by controlling reaction rate, with smaller QDs being formed in slower processes. The results of photoluminescence (PL) studies show that the emission wavelengths of the QDs well correlate with particle size. This simple process for forming different-sized QDs, which uses a cheap solvent and various capping agents, has the potential for preparing CdSe nanocrystals more economically.

  2. A theoretical quantum chemical study of alanine formation in interstellar medium

    Science.gov (United States)

    Shivani; Pandey, Parmanad; Misra, Alka; Tandon, Poonam

    2017-08-01

    The interstellar medium, the vast space between the stars, is a rich reservoir of molecular material ranging from simple diatomic molecules to more complex, astrobiologically important molecules such as amino acids, nucleobases, and other organic species. Radical-radical and radical-neutral interaction schemes are very important for the formation of comparatively complex molecules in low temperature chemistry. An attempt has been made to explore the possibility of formation of complex organic molecules in interstellar medium, through detected interstellar molecules like CH3CN and HCOOH. The gas phase reactions are theoretically studied using quantum chemical techniques. We used the density functional theory (DFT) at the B3LYP/6-311G( d, p) level. The reaction energies, potential barrier and optimized structures of all the geometries, involved in the reaction path, has been discussed. We report the potential energy surfaces for the reactions considered in this work.

  3. Prediction of monomer reactivity in radical copolymerizations from transition state quantum chemical descriptors

    Directory of Open Access Journals (Sweden)

    Zhengde Tan

    2013-01-01

    Full Text Available In comparison with the Q-e scheme, the Revised Patterns Scheme: the U, V Version (the U-V scheme has greatly improved both its accessibility and its accuracy in interpreting and predicting the reactivity of a monomer in free-radical copolymerizations. Quantitative structure-activity relationship (QSAR models were developed to predict the reactivity parameters u and v of the U-V scheme, by applying genetic algorithm (GA and support vector machine (SVM techniques. Quantum chemical descriptors used for QSAR models were calculated from transition state species with structures C¹H3 - C²HR³• or •C¹H2 - C²H2R³ (formed from vinyl monomers C¹H²=C²HR³ + H•, using density functional theory (DFT, at the UB3LYP level of theory with 6-31G(d basis set. The optimum support vector regression (SVR model of the reactivity parameter u based on Gaussian radial basis function (RBF kernel (C = 10, ε = 10- 5 and γ = 1.0 produced root-mean-square (rms errors for the training, validation and prediction sets being 0.220, 0.326 and 0.345, respectively. The optimal SVR model for v with the RBF kernel (C = 20, ε = 10- 4 and γ = 1.2 produced rms errors for the training set of 0.123, the validation set of 0.206 and the prediction set of 0.238. The feasibility of applying the transition state quantum chemical descriptors to develop SVM models for reactivity parameters u and v in the U-V scheme has been demonstrated.

  4. Proton exchange between oxymethyl radical and acids and bases: semiempirical quantum-chemical study

    Directory of Open Access Journals (Sweden)

    Irina Pustolaikina

    2016-12-01

    Full Text Available The reactions with proton participation are widely represented in the analytical, technological and biological chemistry. Quantum-chemical study of the exchange processes in hydrogen bonding complexes will allow us to achieve progress in the understanding of the elementary act mechanism of proton transfer in hydrogen bonding chain as well as the essence of the acid-base interactions. Oxymethyl radical •CH2ОН is small in size and comfortable as a model particle that well transmits protolytic properties of paramagnetic acids having more complex structure. Quantum-chemical modeling of proton exchange reaction oxymethyl radical ∙CH2OH and its diamagnetic analog CH3OH with amines, carboxylic acids and water was carried out using UAM1 method with the help of Gaussian-2009 program. QST2 method was used for the search of transition state, IRC procedure was applied for the calculation of descents along the reaction coordinate. The difference in the structure of transition states of ∙CH2OH/ CH3OH with bases and acids has been shown. It has been confirmed that in the case of bases, consecutive proton exchange mechanism was fixed, and in the case of complexes with carboxylic acids parallel proton exchange mechanism was fixed. The similarity in the reaction behavior of paramagnetic and diamagnetic systems in the proton exchange has been found. It was suggested that the mechanism of proton exchange reaction is determined by the structure of the hydrogen bonding cyclic complex, which is, in turn, depends from the nature of the acid-base interactions partners.

  5. Application of hazard analysis critical control points (HACCP) to organic chemical contaminants in food.

    Science.gov (United States)

    Ropkins, K; Beck, A J

    2002-03-01

    Hazard Analysis Critical Control Points (HACCP) is a systematic approach to the identification, assessment, and control of hazards that was developed as an effective alternative to conventional end-point analysis to control food safety. It has been described as the most effective means of controlling foodborne diseases, and its application to the control of microbiological hazards has been accepted internationally. By contrast, relatively little has been reported relating to the potential use of HACCP, or HACCP-like procedures, to control chemical contaminants of food. This article presents an overview of the implementation of HACCP and discusses its application to the control of organic chemical contaminants in the food chain. Although this is likely to result in many of the advantages previously identified for microbiological HACCP, that is, more effective, efficient, and economical hazard management, a number of areas are identified that require further research and development. These include: (1) a need to refine the methods of chemical contaminant identification and risk assessment employed, (2) develop more cost-effective monitoring and control methods for routine chemical contaminant surveillance of food, and (3) improve the effectiveness of process optimization for the control of chemical contaminants in food.

  6. Chemical Potential for the Interacting Classical Gas and the Ideal Quantum Gas Obeying a Generalized Exclusion Principle

    Science.gov (United States)

    Sevilla, F. J.; Olivares-Quiroz, L.

    2012-01-01

    In this work, we address the concept of the chemical potential [mu] in classical and quantum gases towards the calculation of the equation of state [mu] = [mu](n, T) where n is the particle density and "T" the absolute temperature using the methods of equilibrium statistical mechanics. Two cases seldom discussed in elementary textbooks are…

  7. Quantum-chemical calculations and electron diffraction study of the equilibrium molecular structure of vitamin K3

    Science.gov (United States)

    Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.

    2014-05-01

    The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.

  8. Investigation of some critical parameters of buffer conditions for the development of quantum dots-based optical sensors

    International Nuclear Information System (INIS)

    Yuan Jipei; Guo Weiwei; Wang Erkang

    2008-01-01

    The unique surface-sensitive properties make quantum dots (QDs) great potential in the development of sensors for various analytes. However, quantum dots are not only sensitive to a certain analyte, but also to the surrounding conditions. The controlled response to analyte may be the first step in the designing of functional quantum dots sensors. In this study, taking the quenching effect of benzoquinone (BQ) on CdTe QDs as model, several critical parameters of buffer solution conditions with potential effect on the sensors were investigated. The pH value and the concentration of sodium citrate in the buffer solution critically influenced the quenching effects of BQ. Dozens folds elevation of the quenching extents were observed with the increase of concentrations of H + and sodium citrate, and the quenching mechanisms were also fundamentally different with the changes of the surrounding buffer solutions. The quenching models were proposed and analyzed at different buffer conditions. Taking pH values for example, QDs quenching obeyed the sphere of effective quenching model with the sphere radii of 8.29 nm at pH 8.0, the linear Stern-Volmer equation with Stern-Volmer constant of 2.0 x 10 3 mol -1 L at pH 7.0, and the two binding site static quenching model at basic conditions. The elucidation of parameters for assay performance was important in the development of QDs-based optical sensors

  9. Evaluation of the catalytic mechanism of AICAR transformylase by pH-dependent kinetics, mutagenesis, and quantum chemical calculations.

    Science.gov (United States)

    Shim, J H; Wall, M; Benkovic, S J; Díaz, N; Suárez, D; Merz, K M

    2001-05-23

    The catalytic mechanism of 5-aminoimidazole-4-carboxamide ribonucleotide transformylase (AICAR Tfase) is evaluated with pH dependent kinetics, site-directed mutagenesis, and quantum chemical calculations. The chemistry step, represented by the burst rates, was not pH-dependent, which is consistent with our proposed mechanism that the 4-carboxamide of AICAR assists proton shuttling. Quantum chemical calculations on a model system of 5-amino-4-carboxamide imidazole (AICA) and formamide using the B3LYP/6-31G level of theory confirmed that the 4-carboxamide participated in the proton-shuttling mechanism. The result also indicated that the amide-assisted mechanism is concerted such that the proton transfers from the 5-amino group to the formamide are simultaneous with nucleophilic attack by the 5-amino group. Because the process does not lead to a kinetically stable intermediate, the intramolecular proton transfer from the 5-amino group through the 4-carboxamide to the formamide proceeds in the same transition state. Interestingly, the calculations predicted that protonation of the N3 of the imidazole of AICA would reduce the energy barrier significantly. However, the pK(a) of the imidazole of AICAR was determined to be 3.23 +/- 0.01 by NMR titration, and AICAR is likely to bind to the enzyme with its imidazole in the free base form. An alternative pathway was suggested by modeling Lys266 to have a hydrogen-bonding interaction with the N3 of the imidazole of AICAR. Lys266 has been implicated in catalysis based on mutagenesis studies and the recent X-ray structure of AICAR Tfase. The quantum chemical calculations on a model system that contains AICA complexed with CH3NH3+ as a mimic of the Lys residue confirmed that such an interaction lowered the activation energy of the reaction and likewise implicated the 4-carboxamide. To experimentally verify this hypothesis, we prepared the K266R mutant and found that its kcat is reduced by 150-fold from that of the wild type

  10. Critical regions with central charge c=1/2,7/10,4/5 in the spin-1 quantum chain

    International Nuclear Information System (INIS)

    Mueller, E.

    1991-01-01

    The phase diagramm of the Blume-Emery-Griffiths spin-1-quantum chain is calculated by finite-size scaling with respect to all four parameters. We locate the three-dimensional critical manifold and determine a two-dimensional tricritical surface where the spectra exhibit conformal invariance corresponding to the central charges c=7/10 and 4/5. Choosing one parameter to be zero, we can treat the model analytically and from this the spectrum on a large part of the Ising-like critical region can be understood: there the spectrum consists of conformal c=1/2-levels on which a massive spectrum is superimposed. Calculating three-point functions we study which perturbations by primary fields lead from c=4/5 or c=7/10-critical points to Ising-type regions. (orig.) [de

  11. Chemically modulated graphene quantum dot for tuning the photoluminescence as novel sensory probe

    Science.gov (United States)

    Hwang, Eunhee; Hwang, Hee Min; Shin, Yonghun; Yoon, Yeoheung; Lee, Hanleem; Yang, Junghee; Bak, Sora; Lee, Hyoyoung

    2016-12-01

    A band gap tuning of environmental-friendly graphene quantum dot (GQD) becomes a keen interest for novel applications such as photoluminescence (PL) sensor. Here, for tuning the band gap of GQD, a hexafluorohydroxypropanyl benzene (HFHPB) group acted as a receptor of a chemical warfare agent was chemically attached on the GQD via the diazonium coupling reaction of HFHPB diazonium salt, providing new HFHPB-GQD material. With a help of the electron withdrawing HFHPB group, the energy band gap of the HFHPB-GQD was widened and its PL decay life time decreased. As designed, after addition of dimethyl methyl phosphonate (DMMP), the PL intensity of HFHPB-GQD sensor sharply increased up to approximately 200% through a hydrogen bond with DMMP. The fast response and short recovery time was proven by quartz crystal microbalance (QCM) analysis. This HFHPB-GQD sensor shows highly sensitive to DMMP in comparison with GQD sensor without HFHPB and graphene. In addition, the HFHPB-GQD sensor showed high selectivity only to the phosphonate functional group among many other analytes and also stable enough for real device applications. Thus, the tuning of the band gap of the photoluminescent GQDs may open up new promising strategies for the molecular detection of target substrates.

  12. Molecular structure, vibrational analysis (IR and Raman) and quantum chemical investigations of 1-aminoisoquinoline

    Science.gov (United States)

    Sivaprakash, S.; Prakash, S.; Mohan, S.; Jose, Sujin P.

    2017-12-01

    Quantum chemical calculations of energy and geometrical parameters of 1-aminoisoquinoline [1-AIQ] were carried out by using DFT/B3LYP method using 6-311G (d,p), 6-311G++(d,p) and cc-pVTZ basis sets. The vibrational wavenumbers were computed for the energetically most stable, optimized geometry. The vibrational assignments were performed on the basis of potential energy distribution (PED) using VEDA program. The NBO analysis was done to investigate the intra molecular charge transfer of the molecule. The frontier molecular orbital (FMO) analysis was carried out and the chemical reactivity descriptors of the molecule were studied. The Mulliken charge analysis, molecular electrostatic potential (MEP), HOMO-LUMO energy gap and the related properties were also investigated at B3LYP level. The absorption spectrum of the molecule was studied from UV-Visible analysis by using time-dependent density functional theory (TD-DFT). Fourier Transform Infrared spectrum (FT-IR) and Raman spectrum of 1-AIQ compound were analyzed and recorded in the range 4000-400 cm-1 and 3500-100 cm-1 respectively. The experimentally determined wavenumbers were compared with those calculated theoretically and they complement each other.

  13. Spectroscopic studies and quantum chemical investigations of (3,4-dimethoxybenzylidene) propanedinitrile.

    Science.gov (United States)

    Gupta, Ujval; Kumar, Vinay; Singh, Vivek K; Kant, Rajni; Khajuria, Yugal

    2015-04-05

    The Fourier Transform Infrared (FTIR), Ultra-Violet Visible (UV-Vis) spectroscopy and Thermogravimetric (TG) analysis of (3,4-dimethoxybenzylidene) propanedinitrile have been carried out and investigated using quantum chemical calculations. The molecular geometry, harmonic vibrational frequencies, Mulliken charges, natural atomic charges and thermodynamic properties in the ground state have been investigated by using Hartree Fock Theory (HF) and Density Functional Theory (DFT) using B3LYP functional with 6-311G(d,p) basis set. Both HF and DFT methods yield good agreement with the experimental data. Vibrational modes are assigned with the help of Vibrational Energy Distribution Analysis (VEDA) program. UV-Visible spectrum was recorded in the spectral range of 190-800nm and the results are compared with the calculated values using TD-DFT approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results obtained from the studies of Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) are used to calculate molecular parameters like ionization potential, electron affinity, global hardness, electron chemical potential and global electrophilicity. Copyright © 2014 Elsevier B.V. All rights reserved.

  14. FragIt: a tool to prepare input files for fragment based quantum chemical calculations.

    Directory of Open Access Journals (Sweden)

    Casper Steinmann

    Full Text Available Near linear scaling fragment based quantum chemical calculations are becoming increasingly popular for treating large systems with high accuracy and is an active field of research. However, it remains difficult to set up these calculations without expert knowledge. To facilitate the use of such methods, software tools need to be available to support these methods and help to set up reasonable input files which will lower the barrier of entry for usage by non-experts. Previous tools relies on specific annotations in structure files for automatic and successful fragmentation such as residues in PDB files. We present a general fragmentation methodology and accompanying tools called FragIt to help setup these calculations. FragIt uses the SMARTS language to locate chemically appropriate fragments in large structures and is applicable to fragmentation of any molecular system given suitable SMARTS patterns. We present SMARTS patterns of fragmentation for proteins, DNA and polysaccharides, specifically for D-galactopyranose for use in cyclodextrins. FragIt is used to prepare input files for the Fragment Molecular Orbital method in the GAMESS program package, but can be extended to other computational methods easily.

  15. A general intermolecular force field based on tight-binding quantum chemical calculations

    Science.gov (United States)

    Grimme, Stefan; Bannwarth, Christoph; Caldeweyher, Eike; Pisarek, Jana; Hansen, Andreas

    2017-10-01

    A black-box type procedure is presented for the generation of a molecule-specific, intermolecular potential energy function. The method uses quantum chemical (QC) information from our recently published extended tight-binding semi-empirical scheme (GFN-xTB) and can treat non-covalently bound complexes and aggregates with almost arbitrary chemical structure. The necessary QC information consists of the equilibrium structure, Mulliken atomic charges, charge centers of localized molecular orbitals, and also of frontier orbitals and orbital energies. The molecular pair potential includes model density dependent Pauli repulsion, penetration, as well as point charge electrostatics, the newly developed D4 dispersion energy model, Drude oscillators for polarization, and a charge-transfer term. Only one element-specific and about 20 global empirical parameters are needed to cover systems with nuclear charges up to radon (Z = 86). The method is tested for standard small molecule interaction energy benchmark sets where it provides accurate intermolecular energies and equilibrium distances. Examples for structures with a few hundred atoms including charged systems demonstrate the versatility of the approach. The method is implemented in a stand-alone computer code which enables rigid-body, global minimum energy searches for molecular aggregation or alignment.

  16. Synthesis, vibrational and quantum chemical investigations of hydrogen bonded complex betaine dihydrogen selenite

    Science.gov (United States)

    Arjunan, V.; Marchewka, Mariusz K.; Kalaivani, M.

    2012-10-01

    The molecular complex of betaine with selenious acid namely, betaine dihydrogen selenite (C5H13NO5Se, BDHSe) was synthesised by the reaction of betaine and SeO2 in a 1:1:1 solution of isopropanol, methanol and water. Crystals were grown from this solution by cooling to 253 K for few days. The complex was formed without accompanying proton transfer from selenious acid molecule to betaine. The complete vibrational assignments and analysis of BDHSe have been performed by FTIR, FT-Raman and far-infrared spectral studies. More support on the experimental findings was added from the quantum chemical studies performed with DFT (B3LYP) method using 6-311++G∗∗, 6-31G∗∗, cc-pVDZ and 3-21G basis sets. The structural parameters, energies, thermodynamic parameters and the NBO charges of BDHSe were determined by the DFT method. The 1H and 13C isotropic chemical shifts (δ ppm) of BDHSe with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. SHG experiment was carried out using Kurtz-Perry powder technique. The efficiency of second harmonic generation for BDHSe was estimated relatively to KDP: deff = 0.97 deff (KDP).

  17. Logarithmic terms in entanglement entropies of 2D quantum critical points and Shannon entropies of spin chains.

    Science.gov (United States)

    Zaletel, Michael P; Bardarson, Jens H; Moore, Joel E

    2011-07-08

    Universal logarithmic terms in the entanglement entropy appear at quantum critical points (QCPs) in one dimension (1D) and have been predicted in 2D at QCPs described by 2D conformal field theories. The entanglement entropy in a strip geometry at such QCPs can be obtained via the "Shannon entropy" of a 1D spin chain with open boundary conditions. The Shannon entropy of the XXZ chain is found to have a logarithmic term that implies, for the QCP of the square-lattice quantum dimer model, a logarithm with universal coefficient ±0.25. However, the logarithm in the Shannon entropy of the transverse-field Ising model, which corresponds to entanglement in the 2D Ising conformal QCP, is found to have a singular dependence on the replica or Rényi index resulting from flows to different boundary conditions at the entanglement cut.

  18. Finite temperature and chemical potential in lattice QCD and its critical point

    International Nuclear Information System (INIS)

    Fodor, Z.

    2002-01-01

    We propose a method to study lattice QCD at finite temperature (T) and chemical potential (μ). We compare the method with direct results and with the Glasgow method by using n f =4 QCD at Im(μ)≠0. We locate the critical endpoint (E) of QCD on the Re(μ)-T plane. We use n f =2+1 dynamical staggered quarks with semi-realistic masses on L t =4 lattices. Our results are based on O(10 3 - 10 4 ) configurations. (orig.)

  19. Critical phenomena and chemical potential of a charged AdS black hole

    Science.gov (United States)

    Wei, Shao-Wen; Liang, Bin; Liu, Yu-Xiao

    2017-12-01

    Inspired by the interpretation of the cosmological constant from the boundary gauge theory, we here treat it as the number of colors N and its conjugate quantity as the associated chemical potential μ in the black hole side. Then the thermodynamics and the chemical potential for a five-dimensional charged AdS black hole are studied. It is found that there exists a small-large black hole phase transition of van der Waals type. The critical phenomena are investigated in the N2-μ chart. The result implies that the phase transition can occur for large number of colors N , while is forbidden for small number. This to some extent implies that the interaction of the system increases with the number. In particular, in the reduced parameter space, all the thermodynamic quantities can be rescaled with the black hole charge such that these reduced quantities are charge-independent. Then we obtain the coexistence curve and the phase diagram. The latent heat is also numerically calculated. Moreover, the heat capacity and the thermodynamic scalar are studied. The result indicates that the information of the first-order black hole phase transition is encoded in the heat capacity and scalar. However, the phase transition point cannot be directly calculated with them. Nevertheless, the critical point linked to a second-order phase transition can be determined by either the heat capacity or the scalar. In addition, we calculate the critical exponents of the heat capacity and the scalar for the saturated small and large black holes near the critical point.

  20. Atomistic-level non-equilibrium model for chemically reactive systems based on steepest-entropy-ascent quantum thermodynamics

    International Nuclear Information System (INIS)

    Li, Guanchen; Al-Abbasi, Omar; Von Spakovsky, Michael R

    2014-01-01

    This paper outlines an atomistic-level framework for modeling the non-equilibrium behavior of chemically reactive systems. The framework called steepest- entropy-ascent quantum thermodynamics (SEA-QT) is based on the paradigm of intrinsic quantum thermodynamic (IQT), which is a theory that unifies quantum mechanics and thermodynamics into a single discipline with wide applications to the study of non-equilibrium phenomena at the atomistic level. SEA-QT is a novel approach for describing the state of chemically reactive systems as well as the kinetic and dynamic features of the reaction process without any assumptions of near-equilibrium states or weak-interactions with a reservoir or bath. Entropy generation is the basis of the dissipation which takes place internal to the system and is, thus, the driving force of the chemical reaction(s). The SEA-QT non-equilibrium model is able to provide detailed information during the reaction process, providing a picture of the changes occurring in key thermodynamic properties (e.g., the instantaneous species concentrations, entropy and entropy generation, reaction coordinate, chemical affinities, reaction rate, etc). As an illustration, the SEA-QT framework is applied to an atomistic-level chemically reactive system governed by the reaction mechanism F + H 2 ↔ FH + H

  1. Ferromagnetic quantum criticality in the uranium-based ternary compounds URhSi, URhAl, and UCoAl

    International Nuclear Information System (INIS)

    Combier, Tristan

    2014-01-01

    In this thesis we explore the ferromagnetic quantum criticality in three uranium-based ternary compounds, by means of thermodynamical and transport measurements on single crystal samples, at low temperature and high pressure. URhSi and URhAl are itinerant ferromagnets, while UCoAl is a paramagnet being close to a ferromagnetic instability. All of them have Ising-type magnetic ordering. In the orthorhombic compound URhSi, we show that the Curie temperature decreases upon applying a magnetic field perpendicular to the easy magnetization axis, and a quantum phase transition is expected around 40 T. In the hexagonal system URhAl, we establish the pressure-temperature phase diagram for the first time, indicating a quantum phase transition around 5 GPa. In the isostructural compound UCoAl, we investigate the metamagnetic transition with measurements of magnetization, Hall effect, resistivity and X-ray magnetic circular dichroism. Some intriguing magnetic relaxation phenomena are observed, with step-like features. Hall effect and resistivity have been measured at dilution temperatures, under hydrostatic pressure up to 2.2 GPa and magnetic field up to 16 T. The metamagnetic transition terminates under pressure and magnetic field at a quantum critical endpoint. In this region, a strong effective mass enhancement occurs, and an intriguing difference between up and down field sweeps appears in transverse resistivity. This may be the signature of a new phase, supposedly linked to the relaxation phenomena observed in magnetic measurements, arising from frustration on the quasi-Kagome lattice of uranium atoms in this crystal structure. (author) [fr

  2. DFT simulation, quantum chemical electronic structure, spectroscopic and structure-activity investigations of 2-benzothiazole acetonitrile.

    Science.gov (United States)

    Arjunan, V; Thillai Govindaraja, S; Jose, Sujin P; Mohan, S

    2014-07-15

    The Fourier transform infrared and FT-Raman spectra of 2-benzothiazole acetonitrile (BTAN) have been recorded in the range 4000-450 and 4000-100 cm(-1) respectively. The conformational analysis of the compound has been carried out to obtain the stable geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compound are carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The experimental vibrational frequencies are compared with the wavenumbers derived theoretically by B3LYP gradient calculations employing the standard 6-31G(**), high level 6-311++G(**) and cc-pVTZ basis sets. The structural parameters, thermodynamic properties and vibrational frequencies of the normal modes obtained from the B3LYP methods are in good agreement with the experimental data. The (1)H (400 MHz; CDCl3) and (13)C (100 MHz;CDCl3) nuclear magnetic resonance (NMR) spectra are also recorded. The electronic properties, the energies of the highest occupied and lowest unoccupied molecular orbitals are measured by DFT approach. The kinetic stability of the molecule has been determined from the frontier molecular orbital energy gap. The charges of the atoms and the structure-chemical reactivity relations of the compound are determined by its chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods. The non-linear optical properties of the compound have been discussed by measuring the polarisability and hyperpolarisability tensors. Copyright © 2014 Elsevier B.V. All rights reserved.

  3. A quantum-chemical perspective into low optical-gap polymers for highly-efficient organic solar cells

    KAUST Repository

    Risko, Chad

    2011-03-15

    The recent and rapid enhancement in power conversion efficiencies of organic-based, bulk heterojunction solar cells has been a consequence of both improved materials design and better understanding of the underlying physical processes involved in photocurrent generation. In this Perspective, we first present an overview of the application of quantum-chemical techniques to study the intrinsic material properties and molecular- and nano-scale processes involved in device operation. In the second part, these quantum-chemical tools are applied to an oligomer-based study on a collection of donor-acceptor copolymers that have been used in the highest-efficiency solar cell devices reported to date. The quantum-chemical results are found to be in good agreement with the empirical data related to the electronic and optical properties. In particular, they provide insight into the natures of the electronic excitations responsible for the near-infrared/visible absorption profiles, as well as into the energetics of the low-lying singlet and triplet states. These results lead to a better understanding of the inherent differences among the materials, and highlight the usefulness of quantum chemistry as an instrument for material design. Importantly, the results also point to the need to continue the development of integrated, multi scale modeling approaches to provide a thorough understanding of the materials properties. © The Royal Society of Chemistry 2011.

  4. Critical investigation of Jauch's approach to the quantum theory of measurement

    International Nuclear Information System (INIS)

    Herbut, Fedor

    1986-01-01

    To make Jauch's approach more realistic, his assumptions are modified in two ways: (1) On the quantum system plus the measuring apparatus (S + MA) after the measuring interaction has ceased, one can actually measure only operators of the form given. (2) Measurement is defined in the most general way (including, besides first-kind, also second-kind and third-kind or indirect measurements). It is shown that Jauch's basic result that the microstates (statistical operators) of S + MA before and after the collapse correspond to the same macrostate (belong to the same equivalence class of microstates) remains valid under the above modifications, and that the significance of this result goes beyond measurement theory. On the other hand, it is argued that taking the orthodox (i.e. uncompromisingly quantum) view of quantum mechanics, it is not the collapse, but the Jauch-type macrostates that are spurious in a Jauch-type theory. (author)

  5. A criticism to the fundamental principles of physics: The problem of the quantum measurement (I)

    International Nuclear Information System (INIS)

    Mormontoy Cardenas, Oscar; Marquez Jacome, Mateo

    2008-01-01

    The wave packet model collapse debt to extremely fast fluctuations of quantum field leads to interpreting the phase speed of the harmonic waves that compose the packet, as the speed of time flux. If it consider that harmonics waves keep different phases, the waves packet scattered almost instantly and, as consequence of that, allows the possibility of the quantum system energy it is measure with exactitude absolute in given time. These results induce to think that the time would being a superforce which would determine finally the events of universe and being responsible of the intrinsic pulsations observable in the physics systems. (author)

  6. A QCD chiral critical point at small chemical potential: is it there or not?

    CERN Document Server

    de Forcrand, Philippe; Philipsen, Owe

    2007-01-01

    For a QCD chiral critical point to exist, the parameter region of small quark masses for which the finite temperature transition is first-order must expand when the chemical potential is turned on. This can be tested by a Taylor expansion of the critical surface (m_{u,d},m_s)_c(mu). We present a new method to perform this Taylor expansion numerically, which we first test on an effective model of QCD with static, dense quarks. We then present the results for QCD with 3 degenerate flavors. For a lattice with N_t=4 time-slices, the first-order region shrinks as the chemical potential is turned on. This implies that, for physical quark masses, the analytic crossover which occurs at mu=0 between the hadronic and the plasma regimes remains crossover in the mu-region where a Taylor expansion is reliable, i.e. mu less than or similar to T. We present preliminary results from finer lattices indicating that this situation persists, as does the discrepancy between the curvature of T_c(mu) and the experimentally observed...

  7. Novel quantum criticality in CeRu2Si2 near absolute zero observed by thermal expansion and magnetostriction.

    Science.gov (United States)

    Yoshida, J; Abe, S; Takahashi, D; Segawa, Y; Komai, Y; Tsujii, H; Matsumoto, K; Suzuki, H; Onuki, Y

    2008-12-19

    We report linear thermal expansion and magnetostriction measurements for CeRu2Si2 in magnetic fields up to 52.6 mT and at temperatures down to 1 mK. At high temperatures, this compound showed Landau-Fermi-liquid behavior: The linear thermal expansion coefficient and the magnetostriction coefficient were proportional to the temperature and magnetic field, respectively. In contrast, a pronounced non-Fermi-liquid effect was found below 50 mK. The negative contribution of thermal expansion and magnetostriction suggests the existence of an additional quantum critical point.

  8. Quantum criticality and the formation of a putative electronic liquid crystal in Sr3Ru2O7

    International Nuclear Information System (INIS)

    Mackenzie, A.P.; Bruin, J.A.N.; Borzi, R.A.; Rost, A.W.; Grigera, S.A.

    2012-01-01

    We present a brief review of the physical properties of Sr 3 Ru 2 O 7 , in which the approach to a magnetic-field-tuned quantum critical point is cut off by the formation of a novel phase with transport characteristics consistent with those of a nematic electronic liquid crystal. Our goal is to summarise the physics that led to that conclusion being drawn, describing the key experiments and discussing the theoretical approaches that have been adopted. Throughout the review we also attempt to highlight observations that are not yet understood, and to discuss the future challenges that will need to be addressed by both experiment and theory.

  9. Adaptive Neuro-Fuzzy Inference System Applied QSAR with Quantum Chemical Descriptors for Predicting Radical Scavenging Activities of Carotenoids.

    Science.gov (United States)

    Jhin, Changho; Hwang, Keum Taek

    2015-01-01

    One of the physiological characteristics of carotenoids is their radical scavenging activity. In this study, the relationship between radical scavenging activities and quantum chemical descriptors of carotenoids was determined. Adaptive neuro-fuzzy inference system (ANFIS) applied quantitative structure-activity relationship models (QSAR) were also developed for predicting and comparing radical scavenging activities of carotenoids. Semi-empirical PM6 and PM7 quantum chemical calculations were done by MOPAC. Ionisation energies of neutral and monovalent cationic carotenoids and the product of chemical potentials of neutral and monovalent cationic carotenoids were significantly correlated with the radical scavenging activities, and consequently these descriptors were used as independent variables for the QSAR study. The ANFIS applied QSAR models were developed with two triangular-shaped input membership functions made for each of the independent variables and optimised by a backpropagation method. High prediction efficiencies were achieved by the ANFIS applied QSAR. The R-square values of the developed QSAR models with the variables calculated by PM6 and PM7 methods were 0.921 and 0.902, respectively. The results of this study demonstrated reliabilities of the selected quantum chemical descriptors and the significance of QSAR models.

  10. Adaptive Neuro-Fuzzy Inference System Applied QSAR with Quantum Chemical Descriptors for Predicting Radical Scavenging Activities of Carotenoids.

    Directory of Open Access Journals (Sweden)

    Changho Jhin

    Full Text Available One of the physiological characteristics of carotenoids is their radical scavenging activity. In this study, the relationship between radical scavenging activities and quantum chemical descriptors of carotenoids was determined. Adaptive neuro-fuzzy inference system (ANFIS applied quantitative structure-activity relationship models (QSAR were also developed for predicting and comparing radical scavenging activities of carotenoids. Semi-empirical PM6 and PM7 quantum chemical calculations were done by MOPAC. Ionisation energies of neutral and monovalent cationic carotenoids and the product of chemical potentials of neutral and monovalent cationic carotenoids were significantly correlated with the radical scavenging activities, and consequently these descriptors were used as independent variables for the QSAR study. The ANFIS applied QSAR models were developed with two triangular-shaped input membership functions made for each of the independent variables and optimised by a backpropagation method. High prediction efficiencies were achieved by the ANFIS applied QSAR. The R-square values of the developed QSAR models with the variables calculated by PM6 and PM7 methods were 0.921 and 0.902, respectively. The results of this study demonstrated reliabilities of the selected quantum chemical descriptors and the significance of QSAR models.

  11. Theoretical study of the electronic structure of f-element complexes by quantum chemical methods

    International Nuclear Information System (INIS)

    Vetere, V.

    2002-09-01

    This thesis is related to comparative studies of the chemical properties of molecular complexes containing lanthanide or actinide trivalent cations, in the context of the nuclear waste disposal. More precisely, our aim was a quantum chemical analysis of the metal-ligand bonding in such species. Various theoretical approaches were compared, for the inclusion of correlation (density functional theory, multiconfigurational methods) and of relativistic effects (relativistic scalar and 2-component Hamiltonians, relativistic pseudopotentials). The performance of these methods were checked by comparing computed structural properties to published experimental data, on small model systems: lanthanide and actinide tri-halides and on X 3 M-L species (X=F, Cl; M=La, Nd, U; L = NH 3 , acetonitrile, CO). We have thus shown the good performance of density functionals combined with a quasi-relativistic method, as well as of gradient-corrected functionals associated with relativistic pseudopotentials. In contrast, functionals including some part of exact exchange are less reliable to reproduce experimental trends, and we have given a possible explanation for this result . Then, a detailed analysis of the bonding has allowed us to interpret the discrepancies observed in the structural properties of uranium and lanthanides complexes, based on a covalent contribution to the bonding, in the case of uranium(III), which does not exist in the lanthanide(III) homologues. Finally, we have examined more sizeable systems, closer to experimental species, to analyse the influence of the coordination number, of the counter-ions and of the oxidation state of uranium, on the metal-ligand bonding. (author)

  12. Magneto-acoustic study near the quantum critical point of the frustrated quantum antiferromagnet Cs{sub 2}CuCl{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Cong, P. T., E-mail: t.pham@hzdr.de [Dresden High Magnetic Field Laboratory, Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden (Germany); Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Postulka, L.; Wolf, B.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M., E-mail: michael.lang@physik.uni-frankfurt.de [Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Well, N. van [Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen (Switzerland)

    2016-10-14

    Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs{sub 2}CuCl{sub 4} were performed for the longitudinal modes c{sub 11} and c{sub 33} in magnetic fields along the a-axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at T{sub N}. Isothermal measurements at T < T{sub N} of the sound attenuation α reveal two closely spaced features of different characters on approaching the material's quantum-critical point (QCP) at B{sub s} ≈ 8.5 T for B || a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature T{sub N}(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material's spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/k{sub B} ≈ 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.

  13. Quantum Monte Carlo for large chemical systems: implementing efficient strategies for peta scale platforms and beyond

    International Nuclear Information System (INIS)

    Scemama, Anthony; Caffarel, Michel; Oseret, Emmanuel; Jalby, William

    2013-01-01

    Various strategies to implement efficiently quantum Monte Carlo (QMC) simulations for large chemical systems are presented. These include: (i) the introduction of an efficient algorithm to calculate the computationally expensive Slater matrices. This novel scheme is based on the use of the highly localized character of atomic Gaussian basis functions (not the molecular orbitals as usually done), (ii) the possibility of keeping the memory footprint minimal, (iii) the important enhancement of single-core performance when efficient optimization tools are used, and (iv) the definition of a universal, dynamic, fault-tolerant, and load-balanced framework adapted to all kinds of computational platforms (massively parallel machines, clusters, or distributed grids). These strategies have been implemented in the QMC-Chem code developed at Toulouse and illustrated with numerical applications on small peptides of increasing sizes (158, 434, 1056, and 1731 electrons). Using 10-80 k computing cores of the Curie machine (GENCI-TGCC-CEA, France), QMC-Chem has been shown to be capable of running at the peta scale level, thus demonstrating that for this machine a large part of the peak performance can be achieved. Implementation of large-scale QMC simulations for future exa scale platforms with a comparable level of efficiency is expected to be feasible. (authors)

  14. Predicting Hydride Donor Strength via Quantum Chemical Calculations of Hydride Transfer Activation Free Energy.

    Science.gov (United States)

    Alherz, Abdulaziz; Lim, Chern-Hooi; Hynes, James T; Musgrave, Charles B

    2018-01-25

    We propose a method to approximate the kinetic properties of hydride donor species by relating the nucleophilicity (N) of a hydride to the activation free energy ΔG ⧧ of its corresponding hydride transfer reaction. N is a kinetic parameter related to the hydride transfer rate constant that quantifies a nucleophilic hydridic species' tendency to donate. Our method estimates N using quantum chemical calculations to compute ΔG ⧧ for hydride transfers from hydride donors to CO 2 in solution. A linear correlation for each class of hydrides is then established between experimentally determined N values and the computationally predicted ΔG ⧧ ; this relationship can then be used to predict nucleophilicity for different hydride donors within each class. This approach is employed to determine N for four different classes of hydride donors: two organic (carbon-based and benzimidazole-based) and two inorganic (boron and silicon) hydride classes. We argue that silicon and boron hydrides are driven by the formation of the more stable Si-O or B-O bond. In contrast, the carbon-based hydrides considered herein are driven by the stability acquired upon rearomatization, a feature making these species of particular interest, because they both exhibit catalytic behavior and can be recycled.

  15. Molecular Structure of Phenytoin: NMR, UV-Vis and Quantum Chemical Calculations

    Directory of Open Access Journals (Sweden)

    Raluca Luchian

    2015-12-01

    Full Text Available Due to the presence of the carbonyl and imide groups in the structure of 5,5-diphenylhydantoin (DPH, the possibility for this compound to be involved in hydrogen bonding intermolecular interactions is obvious. Even though such interactions are presumably responsible for the mechanism of action of this drug, however, to the best of our knowledge, the self-hydrogen bonding interactions between the DPH monomers have not been addressed till now. Furthermore, studies reporting on the spectroscopic characteristics of this molecule are scarcely reported in the literature. Here we report on the possible dimers of DPH, investigated by quantum chemical calculations at B3LYP/6-31+G(2d,2p level of theory. Twelve unique DPH dimers were structurally optimized in gas-phase, as well as in ethanol and DMSO and then were used to compute the population-averaged UV-Vis and NMR spectra using Boltzmann statistics. UV-Vis and NMR techniques were employed to assess experimentally the spectroscopical response of this compound. DFT calculations are also used to investigate the structural transformations between the solid and liquid phase, as well as for describing the electronic transitions and for the assignment of NMR spectra of DPH.

  16. How to compute isomerization energies of organic molecules with quantum chemical methods.

    Science.gov (United States)

    Grimme, Stefan; Steinmetz, Marc; Korth, Martin

    2007-03-16

    The reaction energies for 34 typical organic isomerizations including oxygen and nitrogen heteroatoms are investigated with modern quantum chemical methods that have the perspective of also being applicable to large systems. The experimental reaction enthalpies are corrected for vibrational and thermal effects, and the thus derived "experimental" reaction energies are compared to corresponding theoretical data. A series of standard AO basis sets in combination with second-order perturbation theory (MP2, SCS-MP2), conventional density functionals (e.g., PBE, TPSS, B3-LYP, MPW1K, BMK), and new perturbative functionals (B2-PLYP, mPW2-PLYP) are tested. In three cases, obvious errors of the experimental values could be detected, and accurate coupled-cluster [CCSD(T)] reference values have been used instead. It is found that only triple-zeta quality AO basis sets provide results close enough to the basis set limit and that sets like the popular 6-31G(d) should be avoided in accurate work. Augmentation of small basis sets with diffuse functions has a notable effect in B3-LYP calculations that is attributed to intramolecular basis set superposition error and covers basic deficiencies of the functional. The new methods based on perturbation theory (SCS-MP2, X2-PLYP) are found to be clearly superior to many other approaches; that is, they provide mean absolute deviations of less than 1.2 kcal mol-1 and only a few (computational thermochemistry methods.

  17. Quantum chemical modeling of enzymatic reactions: the case of histone lysine methyltransferase.

    Science.gov (United States)

    Georgieva, Polina; Himo, Fahmi

    2010-06-01

    Quantum chemical cluster models of enzyme active sites are today an important and powerful tool in the study of various aspects of enzymatic reactivity. This methodology has been applied to a wide spectrum of reactions and many important mechanistic problems have been solved. Herein, we report a systematic study of the reaction mechanism of the histone lysine methyltransferase (HKMT) SET7/9 enzyme, which catalyzes the methylation of the N-terminal histone tail of the chromatin structure. In this study, HKMT SET7/9 serves as a representative case to examine the modeling approach for the important class of methyl transfer enzymes. Active site models of different sizes are used to evaluate the methodology. In particular, the dependence of the calculated energies on the model size, the influence of the dielectric medium, and the particular choice of the dielectric constant are discussed. In addition, we examine the validity of some technical aspects, such as geometry optimization in solvent or with a large basis set, and the use of different density functional methods. Copyright 2010 Wiley Periodicals, Inc.

  18. Energetics and stability of azulene: From experimental thermochemistry to high-level quantum chemical calculations

    International Nuclear Information System (INIS)

    Sousa, Clara C.S.; Matos, M. Agostinha R.; Morais, Victor M.F.

    2014-01-01

    Highlights: • Experimental standard molar enthalpy of formation, sublimation azulene. • Mini-bomb combustion calorimetry, sublimation Calvet microcalorimetry. • High level composite ab initio calculations. • Computational estimate of the enthalpy of formation of azulene. • Discussion of stability and aromaticity of azulene. - Abstract: The standard (p 0 = 0.1 MPa) molar enthalpy of formation for crystalline azulene was derived from the standard molar enthalpy of combustion, in oxygen, at T = 298.15 K, measured in a mini-bomb combustion calorimeter (aneroid isoperibol calorimeter) and the standard molar enthalpy of sublimation, at T = 298.15 K, measured by Calvet microcalorimetry. From these experiments, the standard molar enthalpy of formation of azulene in the gaseous phase at T = 298.15 K was calculated. In addition, very accurate quantum chemical calculations at the G3 and G4 composite levels of calculation were conducted in order to corroborate our experimental findings and further clarify and establish the definitive standard enthalpy of formation of this interesting non-benzenoid hydrocarbon

  19. Synthesis, structural characterization and quantum chemical studies of silicon-containing benzoic acid derivatives

    Science.gov (United States)

    Zaltariov, Mirela-Fernanda; Cojocaru, Corneliu; Shova, Sergiu; Sacarescu, Liviu; Cazacu, Maria

    2016-09-01

    The present paper is concerned with the synthesis and molecular structure investigation of two new benzoic acid derivatives having trimethylsilyl tails, 4-((trimethylsilyl)methoxy) and 4-(3-(trimethylsilyl)propoxy)benzoic acids. The structures of the novel compounds have been confirmed by X-ray crystallography, Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H and 13C NMR). The theoretical studies of molecules were conducted by using the quantum chemical methods, such as Density Functional Theory (DFT B3LYP/6-31 + G**), Hartree-Fock (HF/6-31 + G**) and semiempirical computations (PM3, PM6 and PM7). The optimized molecular geometries have been found to be in good agreement with experimental structures resulted from the X-ray diffraction. The maximum electronic absorption bands observed at 272-287 nm (UV-vis spectra) have been assigned to π → π* transitions, which were in reasonable agreement with the time dependent density functional theory (TD-DFT) calculations. The computed vibrational frequencies by DFT method were assigned and compared with the experimental FTIR spectra. The mapped electrostatic potentials revealed the reactive sites, which corroborated the observation of the dimer supramolecular structures formed in the crystals by hydrogen-bonding. The energies of frontier molecular orbitals (HOMO and LUMO), energy gap, dipole moment and molecular descriptors for the new compounds were calculated and discussed.

  20. Thiobenzamide: Structure of a free molecule as studied by gas electron diffraction and quantum chemical calculations

    Science.gov (United States)

    Kolesnikova, Inna N.; Putkov, Andrei E.; Rykov, Anatolii N.; Shishkov, Igor F.

    2018-06-01

    The equilibrium (re) molecular structure of thiobenzamide along with rh1 structure has been determined in gas phase using gas electron-diffraction (GED) at about 127 °C and quantum-chemical calculations (QC). Rovibrational distance corrections to the thermal averaged GED structure have been computed with anharmonic force constants obtained at the MP2/cc-pVTZ level of theory. According to the results of GED and QC thiobenzamide exists as mixture of two non-planar enantiomers of C1 symmetry. The selected equilibrium geometrical parameters of thiobenzamide (re, Å and ∠e, deg) are the following: (Cdbnd S) = 1.641(4), (Csbnd N) = 1.352(2), (Csbnd C) = 1.478(9), (Cdbnd C)av = 1.395(2), CCN = 114.7(5), CCS = 123.4(5), C2C1C7S = 31(4), C6C1C7N = 29(4). The structure of thiobenzamide in the gas phase is markedly different to that in the literature for the single crystal. The differences between the gas and the solid structures are ascribed to the presence of intermolecular hydrogen bonding in the solid phase.

  1. Quantum chemical spectral characterization of CH2NH2+ for remote sensing of Titan's atmosphere

    Science.gov (United States)

    Thackston, Russell; Fortenberry, Ryan C.

    2018-01-01

    Cassini has shown that CH2NH2+ is likely present in relatively high abundance in Titan's upper atmosphere. Relatively little is known about this molecule even though it contains the same number of electrons as ethylene, a molecule of significance to Titan's chemistry. Any studies on CH2NH2+ with application to Titan or its atmospheric chemistry will have to be done remotely at this point with the end of the fruitful Cassini mission. Consequently, trusted quantum chemical techniques are utilized here to produce the rotational, vibrational, and rovibrational spectroscopic constants for CH2NH2+ for the first time. The methodology produces a tightly fit potential energy surface here that is well-behaved indicating a strong credence in the accuracy for the produced values. Most notably, the 884.1 cm-1 NH2 out-of-plane bend is the brightest of the vibrational frequencies reported here for CH2NH2+ , and an observed and unattributed feature in this spectral region has been documented but never assigned to a molecular carrier. Follow-up IR or radio observations making use of the 540 GHz to 660 GHz range with the 0.45 D molecular dipole moment will have to be undertaken in order to confirm this or any attribution, but the data provided in this work will greatly assist in any such studies related to CH2NH2+.

  2. Detailed solvent, structural, quantum chemical study and antimicrobial activity of isatin Schiff base

    Science.gov (United States)

    Brkić, Dominik R.; Božić, Aleksandra R.; Marinković, Aleksandar D.; Milčić, Miloš K.; Prlainović, Nevena Ž.; Assaleh, Fathi H.; Cvijetić, Ilija N.; Nikolić, Jasmina B.; Drmanić, Saša Ž.

    2018-05-01

    The ratios of E/Z isomers of sixteen synthesized 1,3-dihydro-3-(substituted phenylimino)-2H-indol-2-one were studied using experimental and theoretical methodology. Linear solvation energy relationships (LSER) rationalized solvent influence of the solvent-solute interactions on the UV-Vis absorption maxima shifts (νmax) of both geometrical isomers using the Kamlet-Taft equation. Linear free energy relationships (LFER) in the form of single substituent parameter equation (SSP) was used to analyze substituent effect on pKa, NMR chemical shifts and νmax values. Electron charge density was obtained by the use of Quantum Theory of Atoms in Molecules, i.e. Bader's analysis. The substituent and solvent effect on intramolecular charge transfer (ICT) were interpreted with the aid of time-dependent density functional (TD-DFT) method. Additionally, the results of TD-DFT calculations quantified the efficiency of ICT from the calculated charge-transfer distance (DCT) and amount of transferred charge (QCT). The antimicrobial activity was evaluated using broth microdilution method. 3D QSAR modeling was used to demonstrate the influence of substituents effect as well as molecule geometry on antimicrobial activity.

  3. The Nature of the Interactions in Triethanolammonium-Based Ionic Liquids. A Quantum Chemical Study.

    Science.gov (United States)

    Fedorova, Irina V; Safonova, Lyubov P

    2018-05-10

    Structural features and interionic interactions play a crucial role in determining the overall stability of ionic liquids and their physicochemical properties. Therefore, we performed high-level quantum-chemical study of different cation-anion pairs representing the building units of protic ionic liquids based on triethanolammonium cation and anions of sulfuric, nitric, phosphoric, and phosphorus acids to provide essential insight into these phenomena at the molecular level. It was shown that every structure is stabilized through multiple H bonds between the protons in the N-H and O-H groups of the cation and different oxygen atoms of the anion acid. Using atoms in molecules topological parameters and natural bond orbital analysis, we determined the nature and strength of these interactions. Our calculations suggest that the N-H group of the cation has more proton donor-like character than the O-H group that makes the N-H···O hydrogen bonds stronger. A close relation between the binding energies of these ion pairs and experimental melting points was established: the smaller the absolute value of the binding energy between ions, the lower is the melting point.

  4. Interactions of ionic liquids and acetone: thermodynamic properties, quantum-chemical calculations, and NMR analysis.

    Science.gov (United States)

    Ruiz, Elia; Ferro, Victor R; Palomar, Jose; Ortega, Juan; Rodriguez, Juan Jose

    2013-06-20

    The interactions between ionic liquids (ILs) and acetone have been studied to obtain a further understanding of the behavior of their mixtures, which generally give place to an exothermic process, mutual miscibility, and negative deviation of Raoult's law. COSMO-RS was used as a suitable computational method to systematically analyze the excess enthalpy of IL-acetone systems (>300), in terms of the intermolecular interactions contributing to the mixture behavior. Spectroscopic and COSMO-RS results indicated that acetone, as a polar compound with strong hydrogen bond acceptor character, in most cases, establishes favorable hydrogen bonding with ILs. This interaction is strengthened by the presence of an acidic cation and an anion with dispersed charge and non-HB acceptor character in the IL. COSMO-RS predictions indicated that gas-liquid and vapor-liquid equilibrium data for IL-acetone systems can be finely tuned by the IL selection, that is, acting on the intermolecular interactions between the molecular and ionic species in the liquid phase. NMR measurements for IL-acetone mixtures at different concentrations were also carried out. Quantum-chemical calculations by using molecular clusters of acetone and IL species were finally performed. These results provided additional evidence of the main role played by hydrogen bonding in the behavior of systems containing ILs and HB acceptor compounds, such as acetone.

  5. From pirazoloquinolines to annulated azulene dyes: UV-VIS spectroscopy and quantum chemical study

    International Nuclear Information System (INIS)

    Gasiorski, P.; Danel, K.S.; Matusiewicz, M.; Uchacz, T.; Kityk, A.V.

    2010-01-01

    Paper reports UV-Vis absorption and photoluminescence spectra of 6-R derivatives (R=CH 3 , O-CH 3 , C(C 6 H 5 ) 3 , C 6 H 5 -N-C 10 H 7 ) of 4-(2-chlorophenyl)-1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline, belonging to pyrazoloquinoline (PQ) family, likewise its regioisomeric products 10-R derivatives of 6-phenyl-6H-5,6,7-triazadibenzo[f,h]naphtho[3,2,1-cd]azulene representing cyclized seven-membered annulated azulene (AA) dyes. Cyclization of PQs into AAs is accompanied by a significant red shift of the first optical absorption band. This finding agrees with the results of quantum-chemical calculations performed by means of the semiempirical method PM3. As the solvent polarity rises all the dyes exhibit a blue shift of the first absorption band and a red shift of the fluorescence band. Such opposite trends in solvatochromic behavior have been reproduced within the semiempirical calculations in combination with the Lippert-Mataga dielectric polarization model. Depending on solvent polarity AA dyes emit light in the green, green-yellow or orange range of the visible spectrum what may be of interest for potential luminescent or electroluminescent applications.

  6. ExcelAutomat: a tool for systematic processing of files as applied to quantum chemical calculations

    Science.gov (United States)

    Laloo, Jalal Z. A.; Laloo, Nassirah; Rhyman, Lydia; Ramasami, Ponnadurai

    2017-07-01

    The processing of the input and output files of quantum chemical calculations often necessitates a spreadsheet as a key component of the workflow. Spreadsheet packages with a built-in programming language editor can automate the steps involved and thus provide a direct link between processing files and the spreadsheet. This helps to reduce user-interventions as well as the need to switch between different programs to carry out each step. The ExcelAutomat tool is the implementation of this method in Microsoft Excel (MS Excel) using the default Visual Basic for Application (VBA) programming language. The code in ExcelAutomat was adapted to work with the platform-independent open-source LibreOffice Calc, which also supports VBA. ExcelAutomat provides an interface through the spreadsheet to automate repetitive tasks such as merging input files, splitting, parsing and compiling data from output files, and generation of unique filenames. Selected extracted parameters can be retrieved as variables which can be included in custom codes for a tailored approach. ExcelAutomat works with Gaussian files and is adapted for use with other computational packages including the non-commercial GAMESS. ExcelAutomat is available as a downloadable MS Excel workbook or as a LibreOffice workbook.

  7. Silicon Oxysulfide, OSiS: Rotational Spectrum, Quantum-Chemical Calculations, and Equilibrium Structure.

    Science.gov (United States)

    Thorwirth, Sven; Mück, Leonie Anna; Gauss, Jürgen; Tamassia, Filippo; Lattanzi, Valerio; McCarthy, Michael C

    2011-06-02

    Silicon oxysulfide, OSiS, and seven of its minor isotopic species have been characterized for the first time in the gas phase at high spectral resolution by means of Fourier transform microwave spectroscopy. The equilibrium structure of OSiS has been determined from the experimental data using calculated vibration-rotation interaction constants. The structural parameters (rO-Si = 1.5064 Å and rSi-S = 1.9133 Å) are in very good agreement with values from high-level quantum chemical calculations using coupled-cluster techniques together with sophisticated additivity and extrapolation schemes. The bond distances in OSiS are very short in comparison with those in SiO and SiS. This unexpected finding is explained by the partial charges calculated for OSiS via a natural population analysis. The results suggest that electrostatic effects rather than multiple bonding are the key factors in determining bonding in this triatomic molecule. The data presented provide the spectroscopic information needed for radio astronomical searches for OSiS.

  8. An FT-Raman, FT-IR, and Quantum Chemical Investigation of Stanozolol and Oxandrolone

    Directory of Open Access Journals (Sweden)

    Tibebe Lemma

    2017-12-01

    Full Text Available We have studied the Fourier Transform Infrared (FT-IR and the Fourier transform Raman (FT-Raman spectra of stanozolol and oxandrolone, and we have performed quantum chemical calculations based on the density functional theory (DFT with a B3LYP/6-31G (d, p level of theory. The FT-IR and FT-Raman spectra were collected in a solid phase. The consistency between the calculated and experimental FT-IR and FT-Raman data indicates that the B3LYP/6-31G (d, p can generate reliable geometry and related properties of the title compounds. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution. The good agreement between the experimental and theoretical spectra allowed positive assignment of the observed vibrational absorption bands. Finally, the calculation results were applied to simulate the Raman and IR spectra of the title compounds, which show agreement with the observed spectra.

  9. Structural and optical characteristics of InN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition

    International Nuclear Information System (INIS)

    Kim, Je Won; Lee, Kyu Han; Hong, Sangsu

    2007-01-01

    The structural and electrical properties of InN/GaN multiple quantum wells, which were grown by metalorganic chemical vapor deposition, were characterized by transmission electron microscopy (TEM) and electroluminescence measurements. From the TEM micrographs, it was shown that the well layer was grown like a quantum dot. The well layer is expected to be the nano-size structures in the InN multiple quantum well layers. The multi-photon confocal laser scanning microscopy was used to investigate the optical properties of the light emitting diode (LED) structures with InN active layers. It was found that the two-photon excitation was possible in InN system. The pit density was measured by using the far-field optical technique. In the varied current conditions, the blue LED with the InN multiple quantum well structures did not have the wavelength shift. With this result, we can expect that the white LEDs with the InN multiple quantum well structures do not show the color temperature changes with the variations of applied currents

  10. Growth of InAs Quantum Dots on Germanium Substrate Using Metal Organic Chemical Vapor Deposition Technique

    Directory of Open Access Journals (Sweden)

    Tyagi Renu

    2009-01-01

    Full Text Available Abstract Self-assembled InAs quantum dots (QDs were grown on germanium substrates by metal organic chemical vapor deposition technique. Effects of growth temperature and InAs coverage on the size, density, and height of quantum dots were investigated. Growth temperature was varied from 400 to 450 °C and InAs coverage was varied between 1.40 and 2.35 monolayers (MLs. The surface morphology and structural characteristics of the quantum dots analyzed by atomic force microscope revealed that the density of the InAs quantum dots first increased and then decreased with the amount of InAs coverage; whereas density decreased with increase in growth temperature. It was observed that the size and height of InAs quantum dots increased with increase in both temperature and InAs coverage. The density of QDs was effectively controlled by growth temperature and InAs coverage on GaAs buffer layer.

  11. Quantum Criticality of an Ising-like Spin-1 /2 Antiferromagnetic Chain in a Transverse Magnetic Field

    Science.gov (United States)

    Wang, Zhe; Lorenz, T.; Gorbunov, D. I.; Cong, P. T.; Kohama, Y.; Niesen, S.; Breunig, O.; Engelmayer, J.; Herman, A.; Wu, Jianda; Kindo, K.; Wosnitza, J.; Zherlitsyn, S.; Loidl, A.

    2018-05-01

    We report on magnetization, sound-velocity, and magnetocaloric-effect measurements of the Ising-like spin-1 /2 antiferromagnetic chain system BaCo2V2O8 as a function of temperature down to 1.3 K and an applied transverse magnetic field up to 60 T. While across the Néel temperature of TN˜5 K anomalies in magnetization and sound velocity confirm the antiferromagnetic ordering transition, at the lowest temperature the field-dependent measurements reveal a sharp softening of sound velocity v (B ) and a clear minimum of temperature T (B ) at B⊥c,3 D=21.4 T , indicating the suppression of the antiferromagnetic order. At higher fields, the T (B ) curve shows a broad minimum at B⊥c=40 T , accompanied by a broad minimum in the sound velocity and a saturationlike magnetization. These features signal a quantum phase transition, which is further characterized by the divergent behavior of the Grüneisen parameter ΓB∝(B -B⊥c)-1. By contrast, around the critical field, the Grüneisen parameter converges as temperature decreases, pointing to a quantum critical point of the one-dimensional transverse-field Ising model.

  12. Kinetic-quantum chemical model for catalytic cycles: the Haber-Bosch process and the effect of reagent concentration.

    Science.gov (United States)

    Kozuch, Sebastian; Shaik, Sason

    2008-07-03

    A combined kinetic-quantum chemical model is developed with the goal of estimating in a straightforward way the turnover frequency (TOF) of catalytic cycles, based on the state energies obtained by quantum chemical calculations. We describe how the apparent activation energy of the whole cycle, so-called energetic span (delta E), is influenced by the energy levels of two species: the TOF determining transition state (TDTS) and the TOF determining intermediate (TDI). Because these key species need not be adjoining states, we conclude that for catalysis there are no rate-determining steps, only rate determining states. In addition, we add here the influence of reactants concentrations. And, finally, the model is applied to the Haber-Bosch process of ammonia synthesis, for which we show how to calculate which catalyst will be the most effective under specific reagents conditions.

  13. Structural and vibrational spectral investigations of melaminium maleate monohydrate by FTIR, FT-Raman and quantum chemical calculations

    Science.gov (United States)

    Arjunan, V.; Kalaivani, M.; Marchewka, M. K.; Mohan, S.

    2013-04-01

    The structural investigations of the molecular complex of melamine with maleic acid, namely melaminium maleate monohydrate have been carried out by quantum chemical methods in addition to FTIR, FT-Raman and far-infrared spectral studies. The quantum chemical studies were performed with DFT (B3LYP) method using 6-31G**, cc-pVDZ and 6-311++G** basis sets to determine the energy, structural and thermodynamic parameters of melaminium maleate monohydrate. The hydrogen atom from maleic acid was transferred to the melamine molecule giving the singly protonated melaminium cation. The ability of ions to form spontaneous three-dimensional structure through weak Osbnd H⋯O and Nsbnd H⋯O hydrogen bonds shows notable vibrational effects.

  14. Structural and vibrational spectral investigations of melaminium maleate monohydrate by FTIR, FT-Raman and quantum chemical calculations.

    Science.gov (United States)

    Arjunan, V; Kalaivani, M; Marchewka, M K; Mohan, S

    2013-04-15

    The structural investigations of the molecular complex of melamine with maleic acid, namely melaminium maleate monohydrate have been carried out by quantum chemical methods in addition to FTIR, FT-Raman and far-infrared spectral studies. The quantum chemical studies were performed with DFT (B3LYP) method using 6-31G(**), cc-pVDZ and 6-311++G(**) basis sets to determine the energy, structural and thermodynamic parameters of melaminium maleate monohydrate. The hydrogen atom from maleic acid was transferred to the melamine molecule giving the singly protonated melaminium cation. The ability of ions to form spontaneous three-dimensional structure through weak OH···O and NH···O hydrogen bonds shows notable vibrational effects. Copyright © 2013 Elsevier B.V. All rights reserved.

  15. A method for quantitative nondestructive evaluation using high critical temperature superconducting quantum interference device

    International Nuclear Information System (INIS)

    Kojima, Fumio; Nagashima, Yoshinori; Suzuki, Daisuke; Kasai, Naoko

    1998-01-01

    This paper is concerned with a computational method for detecting and characterizing defect shapes in conducting materials using superconducting quantum interference device (SQUID). The mathematical model is described by electrical potential problems with mixed boundary condition. The model output is then represented by Biot-Savart's law. The estimation scheme is proposed for reconstructing defect shapes in sample materials with defect. Successful numerical results are reported in order to show the feasibility of the proposed algorithms. (author)

  16. A method for quantitative nondestructive evaluation using high critical temperature superconducting quantum interference device

    Energy Technology Data Exchange (ETDEWEB)

    Kojima, Fumio; Nagashima, Yoshinori [Osaka Inst. of Tech. (Japan); Suzuki, Daisuke; Kasai, Naoko

    1998-06-01

    This paper is concerned with a computational method for detecting and characterizing defect shapes in conducting materials using superconducting quantum interference device (SQUID). The mathematical model is described by electrical potential problems with mixed boundary condition. The model output is then represented by Biot-Savart`s law. The estimation scheme is proposed for reconstructing defect shapes in sample materials with defect. Successful numerical results are reported in order to show the feasibility of the proposed algorithms. (author)

  17. Dependence of the extraction capacity of neutral bidentate organophosphorus compounds on their structure: a quantum chemical study

    International Nuclear Information System (INIS)

    Sudarushkin, S.K.; Morgalyuk, V.P.; Tananaev, I.G.; Gribov, L.A.; Myasoedov, B.F.

    2006-01-01

    Correlations between the extraction capacities and molecular structures of organic phosphorus compounds (reagents for extraction of transplutonium elements from spent nuclear fuel) were studied using a quantum chemical approach. The results of calculations are in qualitative agreement with experimental data. The approach proposed can be used for analysis of the extraction properties of all classes of organic phosphorus compounds and also for prediction of the most efficient organic phosphorus extractants with preset properties [ru

  18. A quantum-chemical study of oxygen-vacancy defects in PbTiO{sub 3} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Stashans, Arvids [Laboratorio de Fisica, Escuela de Electronica y Telecomunicaciones, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador)]. E-mail: arvids@utpl.edu.ec; Serrano, Sheyla [Centro de Investigacion en Fisica de Materia Condensada, Corporacion de Fisica Fundamental y Aplicada, Apartado 17-12-637, Quito (Ecuador); Escuela de Ingenierias, Universidad Politecnica Salesiana, Campus Sur, Rumichaca s/n y Moran Valverde, Apartado 17-12-536, Quito (Ecuador); Medina, Paul [Centro de Investigacion en Fisica de Materia Condensada, Corporacion de Fisica Fundamental y Aplicada, Apartado 17-12-637, Quito (Ecuador)

    2006-05-31

    Investigation of an oxygen vacancy and F center in the cubic and tetragonal lattices of PbTiO{sub 3} crystals is done by means of quantum-chemical simulations. Displacements of defect-surrounding atoms, electronic and optical properties, lattice relaxation energies and some new effects due to the defects presence are reported and analyzed. A comparison with similar studies is made and conclusions are drawn on the basis of the obtained results.

  19. A quantum-chemical study of oxygen-vacancy defects in PbTiO3 crystals

    International Nuclear Information System (INIS)

    Stashans, Arvids; Serrano, Sheyla; Medina, Paul

    2006-01-01

    Investigation of an oxygen vacancy and F center in the cubic and tetragonal lattices of PbTiO 3 crystals is done by means of quantum-chemical simulations. Displacements of defect-surrounding atoms, electronic and optical properties, lattice relaxation energies and some new effects due to the defects presence are reported and analyzed. A comparison with similar studies is made and conclusions are drawn on the basis of the obtained results

  20. Critical Investigation of Jauch's Approach to the Quantum Theory of Measurement

    Science.gov (United States)

    Herbut, Fedor

    1986-08-01

    To make Jauch's approach more realistic, his assumptions are modified in two ways: (1) On the quantum system plus the measuring apparatus (S+MA) after the measuring interaction has ceased, one can actually measure only operators of the form A⊗∑ k b k Q k ,where A is any Hermitian operator for S, the resolution of the identity ∑kQk=1 defines MA as a classical system (following von Neumann), and the b k are real numbers (S and MA are distant). (2) Measurement is defined in the most general way (including, besides first-kind, also second-kind and third-kind or indirect measurements). It is shown that Jauch's basic result that the microstates (statistical operators) of S+MA before and after the collapse correspond to the same macrostate (belong to the same equivalence class of microstates) remains valid under the above modifications, and that the significance of this result goes beyond measurement theory. On the other hand, it is argued that taking the orthodox (i.e. uncompromisingly quantum) view of quantum mechanics, it is not the collapse, but the Jauch-type macrostates that are spurious in a Jauch-type theory.

  1. Advances in chemical physics

    CERN Document Server

    Rice, Stuart A

    2012-01-01

    The Advances in Chemical Physics series-the cutting edge of research in chemical physics The Advances in Chemical Physics series provides the chemical physics field with a forum for critical, authoritative evaluations of advances in every area of the discipline. Filled with cutting-edge research reported in a cohesive manner not found elsewhere in the literature, each volume of the Advances in Chemical Physics series serves as the perfect supplement to any advanced graduate class devoted to the study of chemical physics. This volume explores: Quantum Dynamical Resonances in Ch

  2. Singularity of classical and quantum correlations at critical points of the Lipkin-Meshkov-Glick model in bipartition and tripartition of spins

    OpenAIRE

    Xiu-Xing, Zhang; Fu-Li, Li

    2012-01-01

    We study the classical correlation (CC) and quantum discord (QD) between two spin subgroups of the Lipkin-Meshkov-Glick (LMG) model in both binary and trinary decompositions of spins. In the case of bipartition, we find that the classical correlations and all the quantum correlations including the QD, the entanglement of formation (EoF) and the logarithmic negativity (LN) are divergent in the same singular behavior at the critical point of the LMG model. In the case of tripartition, however, ...

  3. The effects of a stress field and chemical diffusion on electronic behaviour in InAs/GaAs quantum dots

    International Nuclear Information System (INIS)

    Zhang Xu; Wang Chongyu

    2006-01-01

    The effects of a stress field and chemical diffusion on electronic behaviour in self-assembled InAs/GaAs quantum dots (QD) are investigated by using first-principle calculations. We find that a potential well appears in a QD without a lattice misfit and chemical diffusion, and both stress field and Ga chemical diffusion can induce the formation of a potential barrier, which strongly affects the electronic behaviour within the QD. The stress field can localize electrons to the base of the QD. And associated with Ga diffusion, the stress field will induce an inverted electronic alignment. The electronic behaviour in the QD without a stress field does not present the confined or localized characteristics caused by a lattice misfit, atomic size and Ga diffusion. This study provides useful information for modulating electronic behaviour by introducing a stress field and chemical diffusion

  4. Complexation reactions in pyridine and 2,6-dimethylpyridine-water system: The quantum-chemical description and the path to liquid phase separation

    Science.gov (United States)

    Chernia, Zelig; Tsori, Yoav

    2018-03-01

    Phase separation in substituted pyridines in water is usually described as an interplay between temperature-driven breakage of hydrogen bonds and the associating interaction of the van der Waals force. In previous quantum-chemical studies, the strength of hydrogen bonding between one water and one pyridine molecules (the 1:1 complex) was assigned a pivotal role. It was accepted that the disassembly of the 1:1 complex at a critical temperature leads to phase separation and formation of the miscibility gap. Yet, for over two decades, notable empirical data and theoretical arguments were presented against that view, thus revealing the need in a revised quantum-mechanical description. In the present study, pyridine-water and 2,6-dimethylpyridine-water systems at different complexation stages are calculated using high level Kohn-Sham theory. The hydrophobic-hydrophilic properties are accounted for by the polarizable continuum solvation model. Inclusion of solvation in free energy of formation calculations reveals that 1:1 complexes are abundant in the organically rich solvents but higher level oligomers (i.e., 2:1 dimers with two pyridines and one water molecule) are the only feasible stable products in the more polar media. At the critical temperature, the dissolution of the external hydrogen bonds between the 2:1 dimer and the surrounding water molecules induces the demixing process. The 1:1 complex acts as a precursor in the formation of the dimers but is not directly involved in the demixing mechanism. The existence of the miscibility gap in one pyridine-water system and the lack of it in another is explained by the ability of the former to maintain stable dimerization. Free energy of formation of several reaction paths producing the 2:1 dimers is calculated and critically analyzed.

  5. Structural studies of crystals of organic and organoelement compounds using modern quantum chemical calculations within the framework of the density functional theory

    International Nuclear Information System (INIS)

    Korlyukov, Alexander A; Antipin, Mikhail Yu

    2012-01-01

    The review generalizes the results of structural studies of crystals of organic and organometallic compounds by modern quantum chemical calculations within the framework of the density functional theory reported in the last decade. Features of the software for such calculations are discussed. Examples of the use of quantum chemical calculations for the studies of the electronic structure, spectroscopic and other physicochemical properties of molecular crystals are presented. The bibliography includes 223 references.

  6. Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

    Science.gov (United States)

    Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

    2016-05-17

    Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in

  7. Incorporation of Mn2+ into CdSe quantum dots by chemical bath co-deposition method for photovoltaic enhancement of quantum dot-sensitized solar cells.

    Science.gov (United States)

    Zhang, Chenguang; Liu, Shaowen; Liu, Xingwei; Deng, Fei; Xiong, Yan; Tsai, Fang-Chang

    2018-03-01

    A photoelectric conversion efficiency (PCE) of 4.9% was obtained under 100 mW cm -2 illumination by quantum-dot-sensitized solar cells (QDSSCs) using a CdS/Mn : CdSe sensitizer. CdS quantum dots (QDs) were deposited on a TiO 2 mesoporous oxide film by successive ionic layer absorption and reaction. Mn 2+ doping into CdSe QDs is an innovative and simple method-chemical bath co-deposition, that is, mixing the Mn ion source with CdSe precursor solution for Mn : CdSe QD deposition. Compared with the CdS/CdSe sensitizer without Mn 2+ incorporation, the PCE was increased from 3.4% to 4.9%. The effects of Mn 2+ doping on the chemical, physical and photovoltaic properties of the QDSSCs were investigated by energy dispersive spectrometry, absorption spectroscopy, photocurrent density-voltage characteristics and electrochemical impedance spectroscopy. Mn-doped CdSe QDs in QDSSCs can obtain superior light absorption, faster electron transport and slower charge recombination than CdSe QDs.

  8. Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

    Science.gov (United States)

    Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

    2018-04-01

    We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three-dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb2 Pt2 Pb , a metal where itinerant electrons coexist with localized moments of Yb ions which can be described in terms of effective S =1 /2 spins with a dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasilinear temperature dependence.

  9. Radical cations in radiation chemistry of aldehydes. ESR study and quantum chemical analysis

    International Nuclear Information System (INIS)

    Belevskii, V.N.; Tyurin, D.A.; Chuvilkin, N.D.

    1998-01-01

    Quantum-chemical (MNDO-UHF) calculations of electronic, spin and energy characteristics of radical cations (RC) of ethanal, propanal, butanal, and pentanal and their distonic isomers were performed. The calculations both with 'frozen' (vertical ionization) and completely optimize geometry (adiabatic approximation) were made. It was been shown that the most positive charge and spin population are localized at O atoms and adjacent C atom as well as at aldehyde protons. The C-H bonds corresponding to those protons as well as neighboring C-O and C-C bonds are considerable weaker (longer) in radical cations as compared to their neutral precursors. That is why such reaction centers are apt to deprotonation with the formation of acyl radical as well as to α- and β-splitting (scission) which are well-known from aldehydes mass-spectra. Our calculations shown that distonic RC (products of intramolecular H-atom transfer) are more stable as compare to their classical isomers: e.g. the difference in energy ΔE = -0.95 eV, -1.2 eV, and -1.5 eV for tree distonic isomers of butanal RC as compare to classical isomer, ΔE -1.2 eV for distonic RC of ethanal. The results of calculations are effectively correlated with ESR data obtained in freonic solutions, X- and gamma-irradiated at 77 K and in liquid aldehydes, X-irradiated by using 2,4,6-tri-tert-burylnitrosobenzene (BNB) and t-BuNO (NtB) as a spin traps. (author)

  10. Photophysics of α-furil at room temperature and 77 K: Spectroscopic and quantum chemical studies

    Energy Technology Data Exchange (ETDEWEB)

    Kundu, Pronab; Chattopadhyay, Nitin, E-mail: nitin.chattopadhyay@yahoo.com [Department of Chemistry, Jadavpur University, Kolkata 700 032 (India)

    2016-06-21

    Steady state and time resolved spectroscopic measurements have been exploited to assign the emissions from different conformations of α-furil (2, 2′-furil) in solution phase at room temperature as well as cryogen (liquid nitrogen, LN{sub 2}) frozen matrices of ethanol and methylcyclohexane. Room temperature studies reveal a single fluorescence from the trans-planar conformer of the fluorophore or two fluorescence bands coming from the trans-planar and the relaxed skew forms depending on excitation at the nπ{sup ∗} or the ππ{sup ∗} absorption band, respectively. Together with the fluorescence bands, the LN{sub 2} studies in both the solvents unambiguously ascertain two phosphorescence emissions with lifetimes 5 ± 0.3 ms (trans-planar triplet) and 81 ± 3 ms (relaxed skew triplet). Quantum chemical calculations have been performed using density functional theory at CAM-B3LYP/6-311++G{sup ∗∗} level to prop up the spectroscopic surveillance. The simulated potential energy curves (PECs) illustrate that α-furil is capable of giving two emissions from each of the S{sub 1} and the T{sub 1} states—one corresponding to the trans-planar and the other to the relaxed skew conformation. Contrary to the other 1,2-dicarbonyl molecular systems like benzil and α-naphthil, α-furil does not exhibit any fluorescence from its second excited singlet (S{sub 2}) state. This is ascribed to the proximity of the minimum of the PEC of the S{sub 2} state and the hill-top of the PEC of the S{sub 1} state.

  11. Quantum Chemical Benchmarking, Validation, and Prediction of Acidity Constants for Substituted Pyridinium Ions and Pyridinyl Radicals.

    Science.gov (United States)

    Keith, John A; Carter, Emily A

    2012-09-11

    Sensibly modeling (photo)electrocatalytic reactions involving proton and electron transfer with computational quantum chemistry requires accurate descriptions of protonated, deprotonated, and radical species in solution. Procedures to do this are generally nontrivial, especially in cases that involve radical anions that are unstable in the gas phase. Recently, pyridinium and the corresponding reduced neutral radical have been postulated as key catalysts in the reduction of CO2 to methanol. To assess practical methodologies to describe the acid/base chemistry of these species, we employed density functional theory (DFT) in tandem with implicit solvation models to calculate acidity constants for 22 substituted pyridinium cations and their corresponding pyridinyl radicals in water solvent. We first benchmarked our calculations against experimental pyridinium deprotonation energies in both gas and aqueous phases. DFT with hybrid exchange-correlation functionals provide chemical accuracy for gas-phase data and allow absolute prediction of experimental pKas with unsigned errors under 1 pKa unit. The accuracy of this economical pKa calculation approach was further verified by benchmarking against highly accurate (but very expensive) CCSD(T)-F12 calculations. We compare the relative importance and sensitivity of these energies to selection of solvation model, solvation energy definitions, implicit solvation cavity definition, basis sets, electron densities, model geometries, and mixed implicit/explicit models. After determining the most accurate model to reproduce experimentally-known pKas from first principles, we apply the same approach to predict pKas for radical pyridinyl species that have been proposed relevant under electrochemical conditions. This work provides considerable insight into the pitfalls using continuum solvation models, particularly when used for radical species.

  12. Critical properties of the D=3 bond-mixed quantum Heisenberg ferromagnet

    International Nuclear Information System (INIS)

    Tsallis, C.; Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro); Stinchcombe, R.B.; Buck, B.

    1983-01-01

    Within a Migdal-Kadanoff-like real-space renormalisation group procedure critical properties of the quenched bond-mixed spin 1/2 Heisenberg ferromagnet in simple cubic lattice are treated. It is verified that it is possible, within a very simple framework, to obtain quite reliable results for the critical temperatures. In addition to that, a general method for renormalising arbitrary clusters of Heisenberg-coupled spins 1/2 is outlined. (Author) [pt

  13. Criticality of the D=2 quantum Heisenberg ferromagnet with quenched random anisotropic

    International Nuclear Information System (INIS)

    Mariz, A.M.; Tsallis, C.

    1985-01-01

    The square-lattice spin 1/2 anisotropic Heisenberg ferromagnet is considered, with interactions whose symmetry can independently (quenched model) and randomly be of two competing types, namely the isotropic Heisenberg type and the Ising one. Within a real space renormalization group framework, a quite precise numerical calculation of the critical frontier is performed, and its main asymptotic behaviour are established. The relevant universality classes are also characterized, through the analysis of the correlation length critical exponent. (Author) [pt

  14. Lake Orta chemical status 25 years after liming: problems solved and emerging critical issues

    Directory of Open Access Journals (Sweden)

    Michela Rogora

    2016-04-01

    Full Text Available Lake Orta, located in Piedmont, northwestern Italy, has been severely affected by industrial pollution since the 1930s. A successful liming intervention, performed in 1988-1990, returned pH levels in the lake to neutrality, and accelerated the reduction of aqueous trace metal concentrations. In this paper, we present an update knowledge of the chemical status of Lake Orta, focusing on the data collected from 1990 to 2014. In this period we sampled the lake at its deepest point (Qualba station, on a monthly (1990-2000 or seasonal (since 2001 basis. Samples were collected at nine depths through the water column, and analyzed for pH, conductivity, alkalinity, major ions, nutrients, and trace metals. Collectively, these data allowed us to evaluate the long-term response of the lake to the restoration treatment, with particular regard to its acid-base status; they also provided insights into emerging or potential critical issues, including eutrophication and re-suspension of trace metals that still linger in the lake. Furthermore, the evaluation of the present chemical condition of the lake is a precondition for any successive restoration measure, such as fish introduction. The recent data confirmed the lake’s water quality has recovered, i.e. returned to a pre-pollution chemical state. Lake water values of pH and concentrations of ammonium, sulphate and base cations have stabilized. Alkalinity and nitrate concentrations are also expected to reach stable level in the next few years. Levels of nitrate, reactive silica, and phosphorus compounds are now regulated by algal uptake, providing indirect evidence of a partial biological recovery. For instance, both the inter-annual average decline and the reappearance of a seasonal signal in silica confirmed the presence of a stable diatom community. The lake is presently oligotrophic, and concentrations of both N and P compounds are steady and low throughout the year. However, a monthly check of nutrient

  15. Quantum chemical analysis of binary and ternary ferromagnetic alloys; Quantenchemische Untersuchungen binaerer und ternaerer ferromagnetischer Legierungen

    Energy Technology Data Exchange (ETDEWEB)

    Jacobs, Yasemin Erika Charlotte

    2007-02-23

    In this work the electronic structures, densities of states, chemical bonding, magnetic exchange Parameters and Curie temperatures of binary and ternary ferromagnetic alloys are analyzed. The electronic structure of ferromagnetic MnAl has been calculated using density-functional techniques (TB-LMTO-ASA, FPLAPW) and quantum chemically analyzed by means of the crystal orbital Hamilton population analysis. The crystal structure of the ferromagnetic tetragonal MnAl may be understood to originate from the structure of nonmagnetic cubic MnAl with a CsCl motif through a two-step process. While the nonmagnetic cubic structure is stable against a structural deformation, antibonding Mn-Mn interactions at the Fermi level lead to spin polarization and the onset of magnetism, i.e., a symmetry reduction taking place solely in the electronic degrees of freedom, by that emptying antibonding Mn-Mn states. Residual antibonding Al--Al states can only be removed by a subsequent, energetically smaller structural deformation towards the tetragonal system. As a final result, homonuclear bonding is strengthened and heteronuclear bonding is weakened. Corresponding DFT calculations of the electronic structure as well as the calculation of the chemical bonding and the magnetic exchange interactions have been performed on the basis of LDA and GGA for a series of ferromagnetic full Heusler alloys of general formula Co2MnZ (Z=Ga,Si,Ge,Sn), Rh2MnZ (Z=Ge,Sn,Pb), Ni2MnZ (Z=Ga,In,Sn), Pd2MnZ (Z=Sn,Sb) and Cu2MnZ (Z=Al,In,Sn). The connection between the electronic spectra and the magnetic interactions have been studied. Correlations between the chemical bondings in Heusler alloys derived from COHP analysis and magnetic phenomena are obvious, and different mechanisms leading to spin polarization and ferromagnetism are derived. The band dependence of the exchange parameters, their dependence on volume and valence electron concentration have been thoroughly analyzed within the Green function technique

  16. Quasiparticle mass enhancement close to the quantum critical point in BaFe2(As(1-x)P(x))2.

    Science.gov (United States)

    Walmsley, P; Putzke, C; Malone, L; Guillamón, I; Vignolles, D; Proust, C; Badoux, S; Coldea, A I; Watson, M D; Kasahara, S; Mizukami, Y; Shibauchi, T; Matsuda, Y; Carrington, A

    2013-06-21

    We report a combined study of the specific heat and de Haas-van Alphen effect in the iron-pnictide superconductor BaFe2(As(1-x)P(x))2. Our data when combined with results for the magnetic penetration depth give compelling evidence for the existence of a quantum critical point close to x=0.30 which affects the majority of the Fermi surface by enhancing the quasiparticle mass. The results show that the sharp peak in the inverse superfluid density seen in this system results from a strong increase in the quasiparticle mass at the quantum critical point.

  17. Boundary critical phenomena and a quasiparticle-quasihole symmetric metal-insulator: transition in a constricted quantum hall circuit

    International Nuclear Information System (INIS)

    Lal, Siddhartha

    2007-09-01

    Motivated by surprises in recent experimental findings, we study transport in a model of a quantum Hall edge system with a gate-voltage controlled constriction. A finite backscattered current at finite edge-bias is explained as arising from the splitting of edge current caused by the difference in the filling fractions of the bulk (ν 1 ) and constriction (ν 2 ) quantum Hall fluid regions. We develop a hydrodynamic theory for bosonic edge modes inspired by this model. The constriction region splits the incident long-wavelength chiral edge density-wave excitations among the transmitting and reflecting edge states encircling it. The competition between two interedge tunneling processes taking place inside the constriction, related by a quasiparticle-quasihole (qp-qh) symmetry, is accounted for by computing the boundary theories of the system. This competition is found to determine the strong coupling configuration of the system. A separatrix of qp-qh symmetric gapless critical states is found to lie between the relevant RG flows to a metallic and an insulating configuration of the constriction system. This constitutes an interesting generalisation of the Kane-Fisher quantum impurity model. The features of the RG phase diagram are also confirmed by computing various correlators and chiral linear conductances of the system. In this way, our results find excellent agreement with many recent puzzling experimental results for the cases of ν 1 = 1/3, 1. We also discuss and make predictions for the case of a constriction system with ν 2 = 5/2. (author)

  18. Quantum mechanical model for the anticarcinogenic effect of extremely-low-frequency electromagnetic fields on early chemical hepatocarcinogenesis

    Science.gov (United States)

    Godina-Nava, Juan José; Torres-Vega, Gabino; López-Riquelme, Germán Octavio; López-Sandoval, Eduardo; Samana, Arturo Rodolfo; García Velasco, Fermín; Hernández-Aguilar, Claudia; Domínguez-Pacheco, Arturo

    2017-02-01

    Using the conventional Haberkorn approach, it is evaluated the recombination of the radical pair (RP) singlet spin state to study theoretically the cytoprotective effect of an extremely-low-frequency electromagnetic field (ELF-EMF) on early stages of hepatic cancer chemically induced in rats. The proposal is that ELF-EMF modulates the interconversion rate of singlet and triplet spin states of the RP populations modifying the products from the metabolization of carcinogens. Previously, we found that the daily treatment with ELF-EMF 120 Hz inhibited the number and area of preneoplastic lesions in chemical carcinogenesis. The singlet spin population is evaluated diagonalizing the spin density matrix through the Lanczos method in a radical pair mechanism (RPM). Using four values of the interchange energy, we have studied the variations over the singlet population. The low magnetic field effect as a test of the influence over the enzymatic chemical reaction is evaluated calculating the quantum yield. Through a bootstrap technique the range is found for the singlet decay rate for the process. Applying the quantum measurements concept, we addressed the impact toward hepatic cells. The result contributes to improving our understanding of the chemical carcinogenesis process affected by charged particles that damage the DNA.

  19. Crystal growth by Bridgman and Czochralski method of the ferromagnetic quantum critical material YbNi4P2

    Science.gov (United States)

    Kliemt, K.; Krellner, C.

    2016-09-01

    The tetragonal YbNi4P2 is one of the rare examples of compounds that allow the investigation of a ferromagnetic quantum critical point. We report in detail on two different methods which have been used to grow YbNi4P2 single crystals from a self-flux. The first, a modified Bridgman method, using a closed crucible system yields needle-shaped single crystals oriented along the [001]-direction. The second method, the Czochralski growth from a levitating melt, yields large single crystals which can be cut in any desired orientation. With this crucible-free method, samples without flux inclusions and a resistivity ratio at 1.8 K of RR1.8K = 17 have been grown.

  20. Mapping of parent hamiltonians from abelian and non-abelian quantum hall states to exact models of critical spin chains

    CERN Document Server

    Greiter, Martin

    2011-01-01

    This monograph introduces an exact model for a critical spin chain with arbitrary spin S, which includes the Haldane--Shastry model as the special case S=1/2.  While spinons in the Haldane-Shastry model obey abelian half-fermi statistics, the spinons in the general model introduced here obey non-abelian statistics.  This manifests itself through topological choices for the fractional momentum spacings.  The general model is derived by mapping exact models of quantized Hall states onto spin chains.  The book begins with pedagogical review of all the relevant models including the non-abelian statistics in the Pfaffian Hall state, and is understandable to every student with a graduate course in quantum mechanics.

  1. Pressure-induced unconventional superconductivity near a quantum critical point in CaFe2As2

    International Nuclear Information System (INIS)

    Kawasaki, S; Tabuchi, T; Zheng Guoqing; Wang, X F; Chen, X H

    2010-01-01

    75 As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe 2 As 2 under pressure. At P = 4.7 and 10.8 kbar, the temperature dependencies of nuclear-spin-lattice relaxation rate (1/T 1 ) measured in the tetragonal phase show no coherence peak just below T c (P) and decrease with decreasing temperature. The superconductivity is gapless at P = 4.7 kbar but evolves to that with multiple gaps at P = 10.8 kbar. We find that the superconductivity appears near a quantum critical point under pressures in the range 4.7 kbar ≤ P ≤ 10.8 kbar. Both electron correlation and superconductivity disappear in the collapsed tetragonal phase. A systematic study under pressure indicates that electron correlations play a vital role in forming Cooper pairs in this compound.

  2. Critical behavior in two-dimensional quantum gravity and equations of motion of the string

    International Nuclear Information System (INIS)

    Das, S.R.; Dhar, A.; Wadia, S.R.

    1990-01-01

    The authors show how consistent quantization determines the renormalization of couplings in a quantum field theory coupled to gravity in two dimensions. The special status of couplings corresponding to conformally invariant matter is discussed. In string theory, where the dynamical degree of freedom of the two-dimensional metric plays the role of time in target space, these renormalization group equations are themselves the classical equations of motion. Time independent solutions, like classical vacuua, correspond to the situation in which matter is conformally invariant. Time dependent solutions, like tunnelling configurations between vacuua, correspond to special trajectories in theory space. The authors discuss an example of such a trajectory in the space containing the c ≤ 1 minimal models. The authors also discuss the connection between this work and the recent attempts to construct non-pertubative string theories based on matrix models

  3. Critical issues in the formation of quantum computer test structures by ion implantation

    Energy Technology Data Exchange (ETDEWEB)

    Schenkel, T.; Lo, C. C.; Weis, C. D.; Schuh, A.; Persaud, A.; Bokor, J.

    2009-04-06

    The formation of quantum computer test structures in silicon by ion implantation enables the characterization of spin readout mechanisms with ensembles of dopant atoms and the development of single atom devices. We briefly review recent results in the characterization of spin dependent transport and single ion doping and then discuss the diffusion and segregation behaviour of phosphorus, antimony and bismuth ions from low fluence, low energy implantations as characterized through depth profiling by secondary ion mass spectrometry (SIMS). Both phosphorus and bismuth are found to segregate to the SiO2/Si interface during activation anneals, while antimony diffusion is found to be minimal. An effect of the ion charge state on the range of antimony ions, 121Sb25+, in SiO2/Si is also discussed.

  4. In situ synthesis, electrochemical and quantum chemical analysis of an amino acid-derived ionic liquid inhibitor for corrosion protection of mild steel in 1M HCl solution

    International Nuclear Information System (INIS)

    Kowsari, E.; Arman, S.Y.; Shahini, M.H.; Zandi, H.; Ehsani, A.; Naderi, R.; PourghasemiHanza, A.; Mehdipour, M.

    2016-01-01

    Highlights: • Electrochemical analysis of effectiveness of an amino acid-derived ionic liquid inhibitor. • Quantum chemical analysis of effectiveness of an amino acid-derived ionic liquid inhibitor. • Finding correlation between electrochemical analysis and quantum chemical analysis. - Abstract: In this study, an amino acid-derived ionic liquid inhibitor, namely tetra-n-butyl ammonium methioninate, was synthesized and the role this inhibitor for corrosion protection of mild steel exposed to 1.0 M HCl was investigated using electrochemical, quantum and surface analysis. By taking advantage of potentiodynamic polarization, the inhibitory action of tetra-n-butyl ammonium methioninate was found to be mainly mixed-type with dominant anodic inhibition. The effectiveness of the inhibitor was also indicated using electrochemical impedance spectroscopy (EIS). Moreover, to provide further insight into the mechanism of inhibition, electrochemical noise (EN) and quantum chemical calculations of the inhibitor were performed.

  5. Scaling behavior near the itinerant ferromagnetic quantum critical point (FQCP) of NiCoCrx for 0.8

    Science.gov (United States)

    Sales, Brian; Jin, Ke; Bei, Hongbin; Nichols, John; Chisholm, Matthew; May, Andrew; McGuire, Michael

    Low temperature magnetization, resistivity and heat capacity data are reported for the concentrated solid solution NiCoCrx as a function of temperature and magnetic field. In the quantum critical region the low field (0.001-0.01 T) magnetic susceptibility, Chi, diverges as T- 1 / 2 and the magnetization data exhibits T/B scaling from 0.001 2 Tesla, the crossover temperature from the QC to Fermi liquid regime is no longer linear in B, and is better described by B0.75. This scaling behavior is particularly accurate in describing the normalized magnetoresistance data [Rho(B,T)-Rho(0,T)]/T, which is equivalent to the ratio of relaxation rates associated with magnetic field and temperature TauT/TauB. The location of the QCP is sensitive to the composition x and the strain generated during synthesis. These medium-entropy alloys are interesting model systems to explore the role of chemical disorder at FQCP. Research supported by the DOE Office of Science, Materials Science and Engineering Division, and the Energy Dissipation to Defect Evolution EFRC.

  6. Critical tunnel currents and dissipation of Quantum-Hall bilayers in the excitonic condensate state

    International Nuclear Information System (INIS)

    Yoon, Y; Huang, X; Yarar, E; Dietsche, W; Tiemann, L; Schmult, S; Klitzing, K v

    2011-01-01

    Transport and tunneling is studied in the regime of the excitonic condensate at total filling factor one using the counterflow geometry. At small currents the coupling between the layers is large making the two layers virtually electrically inseparable. Above a critical current the tunneling becomes negligible. An onset of dissipation in the longitudinal transport is observed in the same current range.

  7. Isolation, characterization, spectroscopic properties and quantum chemical computations of an important phytoalexin resveratrol as antioxidant component from Vitis labrusca L. and their chemical compositions

    Science.gov (United States)

    Güder, Aytaç; Korkmaz, Halil; Gökce, Halil; Alpaslan, Yelda Bingöl; Alpaslan, Gökhan

    2014-12-01

    In this study, isolation and characterization of trans-resveratrol (RES) as an antioxidant compound were carried out from VLE, VLG and VLS. Furthermore, antioxidant activities were evaluated by using six different methods. Finally, total phenolic, flavonoid, ascorbic acid, anthocyanin, lycopene, β-carotene and vitamin E contents were carried out. In addition, the FT-IR, 13C and 1H NMR chemical shifts and UV-vis. spectra of trans-resveratrol were experimentally recorded. Quantum chemical computations such as the molecular geometry, vibrational frequencies, UV-vis. spectroscopic parameters, HOMOs-LUMOs energies, molecular electrostatic potential (MEP), natural bond orbitals (NBO) and nonlinear optics (NLO) properties of title molecule have been calculated by using DFT/B3PW91 method with 6-311++G(d,p) basis set in ground state for the first time. The obtained results show that the calculated spectroscopic data are in a good agreement with experimental data.

  8. Chemical elemental distribution and soil DNA fingerprints provide the critical evidence in murder case investigation.

    Directory of Open Access Journals (Sweden)

    Giuseppe Concheri

    Full Text Available BACKGROUND: The scientific contribution to the solution of crime cases, or throughout the consequent forensic trials, is a crucial aspect of the justice system. The possibility to extract meaningful information from trace amounts of samples, and to match and validate evidences with robust and unambiguous statistical tests, are the key points of such process. The present report is the authorized disclosure of an investigation, carried out by Attorney General appointment, on a murder case in northern Italy, which yielded the critical supporting evidence for the judicial trial. METHODOLOGY/PRINCIPAL FINDINGS: The proportional distribution of 54 chemical elements and the bacterial community DNA fingerprints were used as signature markers to prove the similarity of two soil samples. The first soil was collected on the crime scene, along a corn field, while the second was found in trace amounts on the carpet of a car impounded from the main suspect in a distant location. The matching similarity of the two soils was proven by crossing the results of two independent techniques: a elemental analysis via inductively coupled plasma mass spectrometry (ICP-MS and optical emission spectrometry (ICP-OES approaches, and b amplified ribosomal DNA restriction analysis by gel electrophoresis (ARDRA. CONCLUSIONS: Besides introducing the novel application of these methods to forensic disciplines, the highly accurate level of resolution observed, opens new possibilities also in the fields of soil typing and tracking, historical analyses, geochemical surveys and global land mapping.

  9. Quantum chemical analysis of Со2+ aqua complexes electrochemical reduction

    Directory of Open Access Journals (Sweden)

    Viktor F. Vargalyuk

    2017-11-01

    Full Text Available Based on the analysis of quantum chemical calculations results (GAMESS, density functional theory, B3LYP method as to [Co(H2On]z(H2O6–n clusters for z = 0, 1, 2 and n=1÷6, it has been demonstrated that electrochemical reduction of [Co(H2O6]2+ aqua complexes runs stage-wise. At the first stage, an electron injected into the [Co(H2O6]2+ complex is entirely located in the orbital of the central atom, as z(Co herewith changes from +1.714 е to +0.777 е. The weakening of Со–ОН2 bonds leads to decomposition of resulting [Co(H2O6]+ particles into two energetically related forms – [Co(H2O4]+ and [Co(H2O3]+. Further reduction of these intermediates runs differently. Electron injection into the [Co(H2O3]+ intermediate terminatesthe transition of Со2+-ions to Со0 z(Co= –0.264 е. This process is accompanied by rapid decomposition of [Co(H2O3]0 product into monohydrate atom of cobalt Со(Н2О. On the contrary, electron injection into the [Co(H2O4]+ intermediate leads to emergence of a specific structure – [Co+(H2O–(Н2О3]¹0, whereby the electron is located in the atoms of cobalt only by 28%, and by 72% in cobalt-coordinated water molecules, clearly focusing on one of the. In this molecule, z(H2O changes from +0.148 е to –0.347 е. There is an assumption that a non-equilibrium [Co+(H2O–(Н2О3]0¹ form transits to [Co(ОH(Н2О3]0 hydroxo-form, which further disproportionates turning into Co(ОH2 hydroxide. In order to reduce the impact of this unfavorable reaction pathway on the overall reaction rate Со2+ + 2ē = Со0, we suggest raising the temperature to ensure complete dissociation of [Co(H2O4]+ to [Co(H2O3]+.

  10. Quantum-chemical analysis of formation reactions of Со2+ complexes

    Directory of Open Access Journals (Sweden)

    Viktor F. Vargalyuk

    2017-11-01

    Full Text Available Based on the analysis of quantum chemical calculations results (GAMESS, density functional theory, B3LYP method as to coordination compounds of Co2+ions with H2O, NH3, OH–, F–, Cl–, Br–, I–, CN–, Ac–, Ak– generally given by [Co(H2O6–nLn]2+nx, it has been demonstrated that within the selected series of ligands, there is no correlation between the amount of energy of monosubstituted cobalt aqua complexes formation(∆Е and pK1,just like between the effective nuclear charge of the central atom (z*Со and pK1. According to the behavior of ∆Е and z*Со,we identified two groups of ligands. The first group (OH–, F–, Ac–, Ak–, CN–, NH3 demonstrates logical ∆Е decrease caused by the growth of z*Со. On the contrary, the second group (Cl–, Br–, I– demonstrates ∆Е increase caused by the growth of z*Со. This phenomenon is explained by the change in electronegativity and polarizability of donor atoms in groups and periods of the periodic table. It is established that linear correlations given by lgK = A + B·z*Со can be actualized only for complexes having ligands with similar donor atoms. Referring to the literature on stepwise complex formation of hydroxide, amine and chloride cobalt complexes in combination with z*Со calculations results, we determined A and B constants of lgK, z*Со-correlations for the atoms of oxygen (30.2, –17.7; nitrogen (125.4, –69.9 and chlorine (–6.3, 5.8. The existence of the detected correlation series enables us to lean on lgK,z*М–dependence parameters for the fixed donor atom and to determine Kn values for various complexes with complex-based ligands using calculations and z*М data. This applies to complexes having central atoms of the same nature as well as simple monodentate ligands. The mentioned approach was used to calculate the stability constants for acrylate cobalt complexes (lgK1 = 1.2 и lgК2 = 4.3, which are not covered in literature.

  11. Quantum chemical studies on electronic structure and photodynamics of ruthenium complexes

    International Nuclear Information System (INIS)

    Freitag, L.

    2015-01-01

    Ruthenium complexes have found their way into many applications in the last decades. Among those, ruthenium polypyridyl compounds have been employed as light harvesting devices and photosensitisers in artificial photosynthesis and molecular photocatalysis. Ruthenium nitrosyl complexes are rapidly emerging as NO delivery agents to biological tissues with promising applications in anticancer photodynamic therapy, thanks to their ability to photorelease nitric oxide (NO). This thesis encompasses computational studies on reactivity, electronic structure, excited states and photodynamics of several ruthenium nitrosyl and polypyridyl complexes. The first part of the thesis deals with ruthenium nitrosyls. The cis-trans isomerisation mechanism of RuHIndNO, a ruthenium nitrosyl derivate of the prominent anti-cancer drug candidate KP1019, is investigated with density functional theory calculations. Next, the electronic structure of the ground and the first excited triplet state of RuHIndNO is studied with multiconfigurational methods including the density-matrix renormalisation group (DMRG). The obtained multiconfigurational wavefunctions and DMRG-based orbital entanglement analysis provides theoretical insight into the non-innocence of the NO ligand in nitrosyl complexes by describing the electron correlation in the Ru--NO bond and assigning oxidation states to the metal and the NO ligand. Another study is performed on excited states of ruthenium nitrosyl complexes with quantum chemical calculations and surface-hopping dynamics to obtain insights into the photodissociation mechanism of NO. The second part of this thesis is devoted to the excited states and photophysics of ruthenium polypyridyl complexes. Accurate excitation energies of tris(2,2-bipyridine)ruthenium (II), the prototype ruthenium polypyridyl are obtained with multiconfigurational calculations assisted by an orbital entanglement analysis. Subsequently, the effect of the ligand substitution on the photophysics

  12. Chemical potentials and thermodynamic characteristics of ideal Bose- and Fermi-gases in the region of quantum degeneracy

    Science.gov (United States)

    Sotnikov, A. G.; Sereda, K. V.; Slyusarenko, Yu. V.

    2017-01-01

    Calculations of chemical potentials for ideal monatomic gases with Bose-Einstein and Fermi-Dirac statistics as functions of temperature, across the temperature region that is typical for the collective quantum degeneracy effect, are presented. Numerical calculations are performed without any additional approximations, and explicit dependences of the chemical potentials on temperature are constructed at a fixed density of gas particles. Approximate polynomial dependences of chemical potentials on temperature are obtained that allow for the results to be used in further studies without re-applying the involved numerical methods. The ease of using the obtained representations is demonstrated on examples of deformation of distribution for a population of energy states at low temperatures, and on the impact of quantum statistics (exchange interaction) on the equations of state for ideal gases and some of the thermodynamic properties thereof. The results of this study essentially unify two opposite limiting cases in an intermediate region that are used to describe the equilibrium states of ideal gases, which are well known from university courses on statistical physics, thus adding value from an educational point of view.

  13. Critical values of the Yang-Yang functional in the quantum sine-Gordon model

    International Nuclear Information System (INIS)

    Lukyanov, Sergei L.

    2011-01-01

    The critical values of the Yang-Yang functional corresponding to the vacuum states of the sine-Gordon QFT in the finite-volume are studied. Two major applications are discussed: (i) generalization of Fendley-Saleur-Zamolodchikov relations to arbitrary values of the sine-Gordon coupling constant, and (ii) connection problem for a certain two-parameter family of solutions of the Painleve III equation.

  14. Field induced magnetic quantum critical behavior in the Kondo necklace model

    International Nuclear Information System (INIS)

    Reyes, Daniel; Continentino, Mucio

    2008-01-01

    The Kondo necklace model augmented by a Zeeman term, serves as a useful model for heavy fermion compounds in an applied magnetic field. The phase diagram and thermodynamic behavior for arbitrary dimensions d has been investigated previously in the zero field case [D. Reyes, M. Continentino, Phys. Rev. B 76 (2007) 075114. ]. Here we extend the treatment to finite fields using a generalized bond operator representation for the localized and conduction electrons spins. A decoupling scheme on the double time Green's functions yields the dispersion relation for the excitations of the system. Two critical magnetic fields are found namely, a critical magnetic field called henceforth h c1 and a saturation field nominated h c2 . Then three important regions can be investigated: (i) Kondo spin liquid state (KSL) at low fields h c1 ; (ii) destruction of KSL state at h≥h c1 and appearance of a antiferromagnetic state; and (iii) saturated paramagnetic region above the upper critical field h c2

  15. Empirical, thermodynamic and quantum-chemical investigations of inclusion complexation between flavanones and (2-hydroxypropyl)-cyclodextrins.

    Science.gov (United States)

    Liu, Benguo; Li, Wei; Nguyen, Tien An; Zhao, Jian

    2012-09-15

    The inclusion complexation of (2-hydroxypropyl)-cyclodextrins with flavanones was investigated by phase solubility measurements, as well as thermodynamic and quantum chemical methods. Inclusion complexes were formed between (2-hydroxypropyl)-α-cyclodextrin (HP-α-CD), (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD), (2-hydroxypropyl)-γ-cyclodextrin (HP-γ-CD) and β-cyclodextrin (β-CD) and four flavanones (naringenin, naringin, hesperetin and dihydromyricetin) in aqueous solutions and their phase solubility was determined. For all the flavanones, the stability constants of their complexes formed with different CDs followed the rank order: HP-β-CD (MW 1540)>HP-β-CD (MW 1460)>HP-β-CD (MW 1380)>β-CD>HP-γ-CD>HP-α-CD. Experimental results and quantum chemical calculations showed that the ability of flavanones to form inclusion complex with (2-hydroxypropyl)-cyclodextrins was determined by both the steric effect and hydrophobicity of the flavanones. For flavanones that have similar molecular volumes, the hydrophobicity of the molecule was the main determining factor of its ability to form inclusion complexes with HP-β-CD, and the hydrophobicity parameter Log P is highly correlated with the stability constant of the complexes. Results of thermodynamic study demonstrated that hydrophobic interaction is the main driving force for the formation process of the flavanone-CD inclusion complexes. Quantum chemical analysis of the most active hydroxyl groups and HOMO (the highest occupied molecular orbital) showed that the B ring of the flavanones was most likely involved in hydrogen bonding with the side groups in the cavity of the CDs, through which the inclusion complex was stabilised. Copyright © 2012 Elsevier Ltd. All rights reserved.

  16. New generation of docking programs: Supercomputer validation of force fields and quantum-chemical methods for docking.

    Science.gov (United States)

    Sulimov, Alexey V; Kutov, Danil C; Katkova, Ekaterina V; Ilin, Ivan S; Sulimov, Vladimir B

    2017-11-01

    Discovery of new inhibitors of the protein associated with a given disease is the initial and most important stage of the whole process of the rational development of new pharmaceutical substances. New inhibitors block the active site of the target protein and the disease is cured. Computer-aided molecular modeling can considerably increase effectiveness of new inhibitors development. Reliable predictions of the target protein inhibition by a small molecule, ligand, is defined by the accuracy of docking programs. Such programs position a ligand in the target protein and estimate the protein-ligand binding energy. Positioning accuracy of modern docking programs is satisfactory. However, the accuracy of binding energy calculations is too low to predict good inhibitors. For effective application of docking programs to new inhibitors development the accuracy of binding energy calculations should be higher than 1kcal/mol. Reasons of limited accuracy of modern docking programs are discussed. One of the most important aspects limiting this accuracy is imperfection of protein-ligand energy calculations. Results of supercomputer validation of several force fields and quantum-chemical methods for docking are presented. The validation was performed by quasi-docking as follows. First, the low energy minima spectra of 16 protein-ligand complexes were found by exhaustive minima search in the MMFF94 force field. Second, energies of the lowest 8192 minima are recalculated with CHARMM force field and PM6-D3H4X and PM7 quantum-chemical methods for each complex. The analysis of minima energies reveals the docking positioning accuracies of the PM7 and PM6-D3H4X quantum-chemical methods and the CHARMM force field are close to one another and they are better than the positioning accuracy of the MMFF94 force field. Copyright © 2017 Elsevier Inc. All rights reserved.

  17. Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5.

    Science.gov (United States)

    Ronning, F; Helm, T; Shirer, K R; Bachmann, M D; Balicas, L; Chan, M K; Ramshaw, B J; McDonald, R D; Balakirev, F F; Jaime, M; Bauer, E D; Moll, P J W

    2017-08-17

    Electronic nematic materials are characterized by a lowered symmetry of the electronic system compared to the underlying lattice, in analogy to the directional alignment without translational order in nematic liquid crystals. Such nematic phases appear in the copper- and iron-based high-temperature superconductors, and their role in establishing superconductivity remains an open question. Nematicity may take an active part, cooperating or competing with superconductivity, or may appear accidentally in such systems. Here we present experimental evidence for a phase of fluctuating nematic character in a heavy-fermion superconductor, CeRhIn 5 (ref. 5). We observe a magnetic-field-induced state in the vicinity of a field-tuned antiferromagnetic quantum critical point at H c  ≈ 50 tesla. This phase appears above an out-of-plane critical field H* ≈ 28 tesla and is characterized by a substantial in-plane resistivity anisotropy in the presence of a small in-plane field component. The in-plane symmetry breaking has little apparent connection to the underlying lattice, as evidenced by the small magnitude of the magnetostriction anomaly at H*. Furthermore, no anomalies appear in the magnetic torque, suggesting the absence of metamagnetism in this field range. The appearance of nematic behaviour in a prototypical heavy-fermion superconductor highlights the interrelation of nematicity and unconventional superconductivity, suggesting nematicity to be common among correlated materials.

  18. Quantum Dot Photovoltaics in the Extreme Quantum Confinement Regime: The Surface-Chemical Origins of Exceptional Air- and Light-Stability

    KAUST Repository

    Tang, Jiang

    2010-02-23

    We report colloidal quantum dot (CQDs) photovoltaics having a ∼930 nm bandgap. The devices exhibit AM1.5G power conversion efficiencies in excess of 2%. Remarkably, the devices are stable in air under many tens of hours of solar illumination without the need for encapsulation. We explore herein the origins of this ordersof-magnitude improvement in air stability compared to larger PbS dots. We find that small and large dots form dramatically different oxidation products, with small dots forming lead sulfite primarily and large dots, lead sulfate. The lead sulfite produced on small dots results in shallow electron traps that are compatible with excellent device performance; whereas the sulfates formed on large dots lead to deep traps, midgap recombination, and consequent catastrophic loss of performance. We propose and offer evidence in support of an explanation based on the high rate of oxidation of sulfur-rich surfaces preponderant in highly faceted large-diameter PbS colloidal quantum dots. © 2010 American Chemical Society.

  19. The critical review of methodologies and approaches to assess the inherent skin sensitization potential (skin allergies) of chemicals. Part II

    DEFF Research Database (Denmark)

    Thyssen, Jacob P; Giménez-Arnau, Elena; Lepoittevin, Jean-Pierre

    2012-01-01

    To identify specific cases, classes or specific use situations of chemicals for which 'safety thresholds' or 'safety limits' were set (in regulations, standards, in scientific research/clinical work, etc.) and critically review the scientific and methodological parameters used to set those limits....

  20. Micromechanical measurement of beating patterns in the quantum oscillatory chemical potential of InGaAs quantum wells due to spin-orbit coupling

    Energy Technology Data Exchange (ETDEWEB)

    Herzog, Florian, E-mail: Florian.Herzog@ph.tum.de; Wilde, Marc A., E-mail: mwilde@ph.tum.de [Lehrstuhl für Physik funktionaler Schichtsysteme, Physik Department, Technische Universität München, James-Franck-Strasse 1, D-85748 Garching b. München (Germany); Heyn, Christian [Institut für Nanostruktur- und Festkörperphysik, Universität Hamburg, Jungiusstr. 11, D-20355 Hamburg (Germany); Hardtdegen, Hilde; Schäpers, Thomas [Peter Grünberg Institut (PGI-9) and JARA-FIT Jülich-Aachen Research Alliance, Forschungszentrum Jülich, D-52425 Jülich (Germany); Grundler, Dirk [Lehrstuhl für Physik funktionaler Schichtsysteme, Physik Department, Technische Universität München, James-Franck-Strasse 1, D-85748 Garching b. München (Germany); Laboratory of Nanoscale Magnetic Materials and Magnonics (LMGN), Institute of Materials, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland)

    2015-08-31

    The quantum oscillatory magnetization M(B) and chemical potential μ(B) of a two-dimensional (2D) electron system provide important and complementary information about its ground state energy at low temperature T. We developed a technique that provides both quantities in the same cool-down process via a decoupled static operation and resonant excitation of a micromechanical cantilever. On InGaAs/InP heterostructures, we observed beating patterns in both M(B) and μ(B) attributed to spin-orbit interaction. A significantly enhanced sensitivity in μ enabled us to extract Rashba and Dresselhaus parameters with high accuracy. The technique is powerful for detailed investigations on the electronic properties of 2D materials.

  1. Quantum chemical analysis of the electronic structure and Moessbauer spectra parameters for low spin cyanide- and pyridine-hemichromes

    International Nuclear Information System (INIS)

    Khleskov, V.I.; Kolpakov, E.V.; Smirnov, A.B.

    1992-01-01

    The work contains results of quantum-chemical calculations of electronic structure and Moessbauer spectra parameters for low spin S=1/2 hexa-coordinated ferri-porphyrin complexes with cyanide (CN) and pyridine (Py) as axial ligands. Theoretical results made it possible to explain experimentally observed regularity of anomalous quadrupole splitting decrease after substitution of Py-ligands by CN. Comparison of theoretical and experimental data indicated that 2 E g must be the ground state of investigated hemichromes. In this state unpaired electron symmetrically occupies d π -orbitals of Fe-ion. (orig.)

  2. Quantum chemical approach for condensed-phase thermochemistry (V): Development of rigid-body type harmonic solvation model

    Science.gov (United States)

    Tarumi, Moto; Nakai, Hiromi

    2018-05-01

    This letter proposes an approximate treatment of the harmonic solvation model (HSM) assuming the solute to be a rigid body (RB-HSM). The HSM method can appropriately estimate the Gibbs free energy for condensed phases even where an ideal gas model used by standard quantum chemical programs fails. The RB-HSM method eliminates calculations for intra-molecular vibrations in order to reduce the computational costs. Numerical assessments indicated that the RB-HSM method can evaluate entropies and internal energies with the same accuracy as the HSM method but with lower calculation costs.

  3. Combined friction force microscopy and quantum chemical investigation of the tribotronic response at the propylammonium nitrate-graphite interface.

    Science.gov (United States)

    Li, H; Atkin, R; Page, A J

    2015-06-28

    The energetic origins of the variation in friction with potential at the propylammonium nitrate-graphite interface are revealed using friction force microscopy (FFM) in combination with quantum chemical simulations. For boundary layer lubrication, as the FFM tip slides energy is dissipated via (1) boundary layer ions and (2) expulsion of near-surface ion layers from the space between the surface and advancing tip. Simulations reveal how changing the surface potential changes the ion composition of the boundary and near surface layer, which controls energy dissipation through both pathways, and thus the friction.

  4. Role of the chemical bonding for the time-dependent electron transport through an interacting quantum dot

    KAUST Repository

    Goker, Ali

    2011-06-01

    A combination of ab initio and many-body calculations is utilized to determine the effects of the bonding in Au electrodes on the time dependent current through a quantum dot suddenly shifted into the Kondo regime by a gate voltage. For an asymmetrically coupled system the instantaneous conductance exhibits fluctuations. The frequencies of the fluctuations turn out to be proportional to the energetic separation between the dominating peaks in the density of states and the Fermi level. The chemical bonding in the electrodes, thus, drastically alters the transient current, which can be accessed by ultrafast pump-probe techniques. © 2011 Elsevier B.V. All rights reserved.

  5. Photocatalytic oxidation dynamics of acetone on TiO2: tight-binding quantum chemical molecular dynamics study

    International Nuclear Information System (INIS)

    Lv Chen; Wang Xiaojing; Agalya, Govindasamy; Koyama, Michihisa; Kubo, Momoji; Miyamoto, Akira

    2005-01-01

    The clarification of the excited states dynamics on TiO 2 surface is important subject for the design of the highly active photocatalysts. In the present study, we applied our novel tight-binding quantum chemical molecular dynamics method to the investigation on the photocatalytic oxidation dynamics of acetone by photogenerated OH radicals on the hydrated anatase TiO 2 surface. The elucidated photocatalytic reaction mechanism strongly supports the previous experimental proposal and finally the effectiveness of our new approach for the clarification of the photocatalytic reaction dynamics employing the large simulation model was confirmed

  6. Role of the chemical bonding for the time-dependent electron transport through an interacting quantum dot

    KAUST Repository

    Goker, Ali; Zhu, Zhiyong; Manchon, Aurelien; Schwingenschlö gl, Udo

    2011-01-01

    A combination of ab initio and many-body calculations is utilized to determine the effects of the bonding in Au electrodes on the time dependent current through a quantum dot suddenly shifted into the Kondo regime by a gate voltage. For an asymmetrically coupled system the instantaneous conductance exhibits fluctuations. The frequencies of the fluctuations turn out to be proportional to the energetic separation between the dominating peaks in the density of states and the Fermi level. The chemical bonding in the electrodes, thus, drastically alters the transient current, which can be accessed by ultrafast pump-probe techniques. © 2011 Elsevier B.V. All rights reserved.

  7. The quantum phase-transitions of water

    Science.gov (United States)

    Fillaux, François

    2017-08-01

    It is shown that hexagonal ices and steam are macroscopically quantum condensates, with continuous spacetime-translation symmetry, whereas liquid water is a quantum fluid with broken time-translation symmetry. Fusion and vaporization are quantum phase-transitions. The heat capacities, the latent heats, the phase-transition temperatures, the critical temperature, the molar volume expansion of ice relative to water, as well as neutron scattering data and dielectric measurements are explained. The phase-transition mechanisms along with the key role of quantum interferences and that of Hartley-Shannon's entropy are enlightened. The notions of chemical bond and force-field are questioned.

  8. Huge residual resistivity in the quantum critical region of CeAgSb2

    International Nuclear Information System (INIS)

    Nakashima, Miho; Kirita, Shingo; Asai, Rihito; Kobayashi, Tatsuo C; Okubo, Tomoyuki; Yamada, Mineko; Thamizhavel, Arumugam; Inada, Yoshihiko; Settai, Rikio; Galatanu, Andre; Yamamoto, Etsuji; Ebihara, Takao; Onuki, Yoshichika

    2003-01-01

    We have studied the effect of pressure on the electrical resistivity of a high-quality single crystal CeAgSb 2 which has a small net ferromagnetic moment of 0.4μ B /Ce. The magnetic ordering temperature T ord = 9.7 K decreases with increasing pressure p and disappears at a critical pressure p c ≅ 3.3 GPa. The residual resistivity, which is close to zero up to 3 GPa, increases steeply above 3 GPa, reaching 55μΩ cm at p c . A huge residual resistivity is found to appear when the magnetic order disappears. (letter to the editor)

  9. Preparation of Nb3Ge films by chemical transport reaction and their critical properties

    International Nuclear Information System (INIS)

    Oya, G.; Saur, E.J.

    1979-01-01

    Niobium-germanium films have been deposited on sapphire substrates at 900 0 C by a chemical transport reaction method. The highest superconducting transition onset temperature T/sub C,on/ of 22.4K is observed for a nearly stoichiometric Nb 3 Ge film with the A15-type structure (thickness approx.93.5 μm). Lattice constants for the Nb 3 Ge phase formed in the Nb-Ge films with both T/sub C,on/ above 22 K and T/sub C,midpoint/ above 21 K are found to extend from 5.143 to 5.153 A. Deposition rates for the obtained films are in the range of 2-10 μm/min. Critical current densities for the Nb 3 Ge film with the highest T/sub C,on/ value are observed to be relatively low (approx.10 3 A/cm 2 at 19 K at self-field). This is due to the coarse grain structure of the film or the low density of effectual pinning centers in the film. Field variations of the pinning forces operating in this film in magnetic fields both parallel to the film surface and perpendicular to the film surface are found to follow closely b/sup 1/2/ (1-b) 2 , to which the pinning force for flux pinning at the surface of normal regions, such as grain boundaries, film surfaces, etc., is proportional, and where b is the reduced magnetic induction (B/B/sub C2/). A small increase in J/sub C/ at low fields is caused by the presence of a small amount of the Nb 5 Ge 3 phase in a Nb 3 Ge film, and seems attributable to additional flux pinning on Nb 5 Ge 3 -phase particles in the film

  10. Nonequilibrium chemical potential in a two-dimensional electron gas in the quantum-Hall-effect regime

    Energy Technology Data Exchange (ETDEWEB)

    Pokhabov, D. A., E-mail: pokhabov@isp.nsc.ru; Pogosov, A. G.; Budantsev, M. V.; Zhdanov, E. Yu.; Bakarov, A. K. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

    2016-08-15

    The nonequilibrium state of a two-dimensional electron gas in the quantum-Hall-effect regime is studied in Hall bars equipped with additional inner contacts situated within the bar. The magnetic-field dependence of the voltage drop between different contact pairs are studied at various temperatures. It was found that the voltage between the inner and outer contacts exhibits peaks of significant amplitude in narrow magnetic-field intervals near integer filling factors. Furthermore, the magnetic-field dependence of the voltage in these intervals exhibits a hysteresis, whereas the voltage between the outer contacts remains zero in the entire magnetic-field range. The appearance of the observed voltage peaks and their hysteretic behavior can be explained by an imbalance between the chemical potentials of edge and bulk states, resulting from nonequilibrium charge redistribution between the edge and bulk states when the magnetic field sweeps under conditions of the quantum Hall effect. The results of the study significantly complement the conventional picture of the quantum Hall effect, explicitly indicating the existence of a significant imbalance at the edge of the two-dimensional electron gas: the experimentally observed difference between the electrochemical potentials of the edge and bulk exceeds the distance between Landau levels by tens of times.

  11. Quantum chemical study of the mechanism of action of vitamin K epoxide reductase (VKOR)

    Science.gov (United States)

    Deerfield, David, II; Davis, Charles H.; Wymore, Troy; Stafford, Darrel W.; Pedersen, Lee G.

    Possible model, but simplistic, mechanisms for the action of vitamin K epoxide reductase (VKOR) are investigated with quantum mechanical methods (B3LYP/6-311G**). The geometries of proposed model intermediates in the mechanisms are energy optimized. Finally, the energetics of the proposed (pseudo-enzymatic) pathways are compared. We find that the several pathways are all energetically feasible. These results will be useful for designing quantum mechanical/molecular mechanical method (QM/MM) studies of the enzymatic pathway once three-dimensional structural data are determined and available for VKOR.

  12. Microscopic origin of the fast blue-green luminescence of chemically synthesized non-oxidized silicon quantum dots.

    Science.gov (United States)

    Dohnalová, Kateřina; Fučíková, Anna; Umesh, Chinnaswamy P; Humpolíčková, Jana; Paulusse, Jos M J; Valenta, Jan; Zuilhof, Han; Hof, Martin; Gregorkiewicz, Tom

    2012-10-22

    The microscopic origin of the bright nanosecond blue-green photoluminescence (PL), frequently reported for synthesized organically terminated Si quantum dots (Si-QDs), has not been fully resolved, hampering potential applications of this interesting material. Here a comprehensive study of the PL from alkyl-terminated Si-QDs of 2-3 nm size, prepared by wet chemical synthesis is reported. Results obtained on the ensemble and those from the single nano-object level are compared, and they provide conclusive evidence that efficient and tunable emission arises due to radiative recombination of electron-hole pairs confined in the Si-QDs. This understanding paves the way towards applications of chemical synthesis for the development of Si-QDs with tunable sizes and bandgaps. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Universal Signatures of Quantum Critical Points from Finite-Size Torus Spectra: A Window into the Operator Content of Higher-Dimensional Conformal Field Theories.

    Science.gov (United States)

    Schuler, Michael; Whitsitt, Seth; Henry, Louis-Paul; Sachdev, Subir; Läuchli, Andreas M

    2016-11-18

    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. We highlight the implications of a neighboring topological phase on the spectrum by studying the Ising* transition (i.e. the transition between a Z_{2} topological phase and a trivial paramagnet), in the example of the toric code in a longitudinal field, and advocate a phenomenological picture that provides qualitative insight into the operator content of the critical field theory.

  14. Wet chemical synthesis of quantum confined nanostructured tin oxide thin films by successive ionic layer adsorption and reaction technique

    Energy Technology Data Exchange (ETDEWEB)

    Murali, K.V., E-mail: kvmuralikv@gmail.com [School of Pure and Applied Physics, Department of Physics, Kannur University, Kerala 670327 (India); Department of Physics, Nehru Arts and Science College, Kanhangad, Kerala 671314 (India); Ragina, A.J. [School of Pure and Applied Physics, Department of Physics, Kannur University, Kerala 670327 (India); Department of Physics, Nehru Arts and Science College, Kanhangad, Kerala 671314 (India); Preetha, K.C. [School of Pure and Applied Physics, Department of Physics, Kannur University, Kerala 670327 (India); Department of Physics, Sree Narayana College, Kannur, Kerala 670007 (India); Deepa, K.; Remadevi, T.L. [School of Pure and Applied Physics, Department of Physics, Kannur University, Kerala 670327 (India); Department of Physics, Pazhassi Raja N.S.S. College, Mattannur, Kerala 670702 (India)

    2013-09-01

    Graphical abstract: - Highlights: • Quantum confined SnO{sub 2} thin films were synthesized at 80 °C by SILAR technique. • Film formation mechanism is discussed. • Films with snow like crystallite morphology offer high specific surface area. • The blue-shifted value of band gap confirmed the quantum confinement effect. • Present synthesis has advantages – low cost, low temperature and green friendly. - Abstract: Quantum confined nanostructured SnO{sub 2} thin films were synthesized at 353 K using ammonium chloride (NH{sub 4}Cl) and other chemicals by successive ionic layer adsorption and reaction technique. Film formation mechanism is discussed. Structural, morphological, optical and electrical properties were investigated and compared with the as-grown and annealed films fabricated without NH{sub 4}Cl solution. SnO{sub 2} films were polycrystalline with crystallites of tetragonal structure with grain sizes lie in the 5–8 nm range. Films with snow like crystallite morphology offer high specific surface area. The blue-shifted value of band gap of as-grown films confirmed the quantum confinement effect of grains. Refractive index of the films lies in the 2.1–2.3 range. Films prepared with NH{sub 4}Cl exhibit relatively lower resistivity of the order of 10{sup 0}–10{sup −1} Ω cm. The present synthesis has advantages such as low cost, low temperature and green friendly, which yields small particle size, large surface–volume ratio, and high crystallinity SnO{sub 2} films.

  15. A Quantum Chemical Exploration of the Horner-Wadsworth-Emmons Reaction

    DEFF Research Database (Denmark)

    Brandt, Peter; Norrby, Per-Ola; Martin, Ivar

    1998-01-01

    The mechanism of the Horner-Wadsworth-Emmons (HWE) reaction has been investigated using high level quantum mechanical calculations on a realistic model system. The solvation contribution has been evaluated using the PCM/DIR method. In the free, anionic system, the rate determining step was found ...

  16. [Mass spectrometric and quantum chemical study of dimeric associates of nucleosides].

    Science.gov (United States)

    Sukhodub, L F; Aksenov, S A; Boldeskul, A I

    1995-01-01

    Deoxyribonucleosides H-bonded pairs were investigated using fast atom bombardment mass spectrometry and MNDO/H quantum chemistry method. It was shown that "rare" (enol or imin) forms of the nitrogen bases could form pairs with energy comparable with "canonical" base pair energy. It was shown that pair stability rows, which are measured using different experimental techniques, were in conformity each with other.

  17. Chemically Triggered Formation of Two-Dimensional Epitaxial Quantum Dot Superlattices

    NARCIS (Netherlands)

    Walravens, Willem; De Roo, Jonathan; Drijvers, Emile; Ten Brinck, Stephanie; Solano, Eduardo; Dendooven, Jolien; Detavernier, Christophe; Infante, Ivan; Hens, Zeger

    2016-01-01

    Two dimensional superlattices of epitaxially connected quantum dots enable size-quantization effects to be combined with high charge carrier mobilities, an essential prerequisite for highly performing QD devices based on charge transport. Here, we demonstrate that surface active additives known to

  18. SUCCESS AND PITFALLS OF THE DIELECTRIC CONTINUUM MODEL IN QUANTUM-CHEMICAL CALCULATIONS

    NARCIS (Netherlands)

    DEVRIES, AH; VANDUIJNEN, PT; JUFFER, AH

    1993-01-01

    Recently we presented an extension of the direct reaction field (DRF) method, in which a quantum system and a set of point charges and interacting polarizabilities are embedded in a continuum that is characterized by a dielectric constant epsilon and a finite ionic strength. The reaction field of

  19. Identification of critical chemical features for Aurora kinase-B inhibitors using Hip-Hop, virtual screening and molecular docking

    Science.gov (United States)

    Sakkiah, Sugunadevi; Thangapandian, Sundarapandian; John, Shalini; Lee, Keun Woo

    2011-01-01

    This study was performed to find the selective chemical features for Aurora kinase-B inhibitors using the potent methods like Hip-Hop, virtual screening, homology modeling, molecular dynamics and docking. The best hypothesis, Hypo1 was validated toward a wide range of test set containing the selective inhibitors of Aurora kinase-B. Homology modeling and molecular dynamics studies were carried out to perform the molecular docking studies. The best hypothesis Hypo1 was used as a 3D query to screen the chemical databases. The screened molecules from the databases were sorted based on ADME and drug like properties. The selective hit compounds were docked and the hydrogen bond interactions with the critical amino acids present in Aurora kinase-B were compared with the chemical features present in the Hypo1. Finally, we suggest that the chemical features present in the Hypo1 are vital for a molecule to inhibit the Aurora kinase-B activity.

  20. Time-Resolved Quantum Cascade Laser Absorption Spectroscopy of Pulsed Plasma Assisted Chemical Vapor Deposition Processes Containing BCl3

    Science.gov (United States)

    Lang, Norbert; Hempel, Frank; Strämke, Siegfried; Röpcke, Jürgen

    2011-08-01

    In situ measurements are reported giving insight into the plasma chemical conversion of the precursor BCl3 in industrial applications of boriding plasmas. For the online monitoring of its ground state concentration, quantum cascade laser absorption spectroscopy (QCLAS) in the mid-infrared spectral range was applied in a plasma assisted chemical vapor deposition (PACVD) reactor. A compact quantum cascade laser measurement and control system (Q-MACS) was developed to allow a flexible and completely dust-sealed optical coupling to the reactor chamber of an industrial plasma surface modification system. The process under the study was a pulsed DC plasma with periodically injected BCl3 at 200 Pa. A synchronization of the Q-MACS with the process control unit enabled an insight into individual process cycles with a sensitivity of 10-6 cm-1·Hz-1/2. Different fragmentation rates of the precursor were found during an individual process cycle. The detected BCl3 concentrations were in the order of 1014 molecules·cm-3. The reported results of in situ monitoring with QCLAS demonstrate the potential for effective optimization procedures in industrial PACVD processes.

  1. Prediction of radical scavenging activities of anthocyanins applying adaptive neuro-fuzzy inference system (ANFIS) with quantum chemical descriptors.

    Science.gov (United States)

    Jhin, Changho; Hwang, Keum Taek

    2014-08-22

    Radical scavenging activity of anthocyanins is well known, but only a few studies have been conducted by quantum chemical approach. The adaptive neuro-fuzzy inference system (ANFIS) is an effective technique for solving problems with uncertainty. The purpose of this study was to construct and evaluate quantitative structure-activity relationship (QSAR) models for predicting radical scavenging activities of anthocyanins with good prediction efficiency. ANFIS-applied QSAR models were developed by using quantum chemical descriptors of anthocyanins calculated by semi-empirical PM6 and PM7 methods. Electron affinity (A) and electronegativity (χ) of flavylium cation, and ionization potential (I) of quinoidal base were significantly correlated with radical scavenging activities of anthocyanins. These descriptors were used as independent variables for QSAR models. ANFIS models with two triangular-shaped input fuzzy functions for each independent variable were constructed and optimized by 100 learning epochs. The constructed models using descriptors calculated by both PM6 and PM7 had good prediction efficiency with Q-square of 0.82 and 0.86, respectively.

  2. Prediction of Radical Scavenging Activities of Anthocyanins Applying Adaptive Neuro-Fuzzy Inference System (ANFIS with Quantum Chemical Descriptors

    Directory of Open Access Journals (Sweden)

    Changho Jhin

    2014-08-01

    Full Text Available Radical scavenging activity of anthocyanins is well known, but only a few studies have been conducted by quantum chemical approach. The adaptive neuro-fuzzy inference system (ANFIS is an effective technique for solving problems with uncertainty. The purpose of this study was to construct and evaluate quantitative structure-activity relationship (QSAR models for predicting radical scavenging activities of anthocyanins with good prediction efficiency. ANFIS-applied QSAR models were developed by using quantum chemical descriptors of anthocyanins calculated by semi-empirical PM6 and PM7 methods. Electron affinity (A and electronegativity (χ of flavylium cation, and ionization potential (I of quinoidal base were significantly correlated with radical scavenging activities of anthocyanins. These descriptors were used as independent variables for QSAR models. ANFIS models with two triangular-shaped input fuzzy functions for each independent variable were constructed and optimized by 100 learning epochs. The constructed models using descriptors calculated by both PM6 and PM7 had good prediction efficiency with Q-square of 0.82 and 0.86, respectively.

  3. Chemical potential for the interacting classical gas and the ideal quantum gas obeying a generalized exclusion principle

    International Nuclear Information System (INIS)

    Sevilla, F J; Olivares-Quiroz, L

    2012-01-01

    In this work, we address the concept of the chemical potential μ in classical and quantum gases towards the calculation of the equation of state μ = μ(n, T) where n is the particle density and T the absolute temperature using the methods of equilibrium statistical mechanics. Two cases seldom discussed in elementary textbooks are presented with detailed calculations. The first one refers to the explicit calculation of μ for the interacting classical gas exemplified by van der Waals gas. For this purpose, we used the method described by van Kampen (1961 Physica 27 783). The second one refers to the calculation of μ for ideal quantum gases that obey a generalized Pauli's exclusion principle that leads to statistics that go beyond the Bose-Einstein and Fermi-Dirac cases. The audience targeted in this work corresponds mainly to advanced undergraduates and graduate students in the physical-chemical sciences but it is not restricted to them. In regard of this, we have put a special emphasis on showing some additional details of calculations that usually do not appear explicitly in textbooks. (paper)

  4. An investigation into the effective surface passivation of quantum dots by a photo-assisted chemical method

    Directory of Open Access Journals (Sweden)

    So-Yeong Joo

    2018-01-01

    Full Text Available In this study, we have developed an effective amino passivation process for quantum dots (QDs at room temperature and have investigated a passivation mechanism using a photo-assisted chemical method. As a result of the reverse reaction of the H2O molecules, the etching kinetics of the photo-assisted chemical method increased upon increasing the 3-amino-1-propanol (APOL/H2O ratio of the etching solution. Photon-excited electron-hole pairs lead to strong bonding between the organic and surface atoms of the QDs, and results in an increase of the quantum yield (QY%. This passivation method is also applicable to CdSe/ZnSe core/shell structures of QDs, due to the passivation of mid-gap defects states at the interface. The QY% of the as-synthesized CdSe QDs is dramatically enhanced by the amino passivation from 37% to 75% and the QY% of the CdSe/ZnSe core/shell QDs is also improved by ∼28%.

  5. Conformational, structural, vibrational and quantum chemical analysis on 4-aminobenzohydrazide and 4-hydroxybenzohydrazide--a comparative study.

    Science.gov (United States)

    Arjunan, V; Jayaprakash, A; Carthigayan, K; Periandy, S; Mohan, S

    2013-05-01

    Experimental and theoretical quantum chemical studies were carried out on 4-hydroxybenzohydrazide (4HBH) and 4-aminobenzohydrazide (4ABH) using FTIR and FT-Raman spectral data. The structural characteristics and vibrational spectroscopic analysis were carried performed by quantum chemical methods with the hybrid exchange-correlation functional B3LYP using 6-31G(**), 6-311++G(**) and aug-cc-pVDZ basis sets. The most stable conformer of the title compounds have been determined from the analysis of potential energy surface. The stable molecular geometries, electronic and thermodynamic parameters, IR intensities, harmonic vibrational frequencies, depolarisation ratio and Raman intensities have been computed. Molecular electrostatic potential and frontier molecular orbitals were constructed to understand the electronic properties. The potential energy distributions (PEDs) were calculated to explain the mixing of fundamental modes. The theoretical geometrical parameters and the fundamental frequencies were compared with the experimental. The interactions of hydroxy and amino group substitutions on the characteristic vibrations of the ring and hydrazide group have been analysed. Copyright © 2013 Elsevier B.V. All rights reserved.

  6. Intra- und intermolecular hydrogen bonds. Spectroscopic, quantum chemical and molecular dynamics studies

    International Nuclear Information System (INIS)

    Simperler, A.

    1999-03-01

    Intra- and intermolecular H-bonds have been investigated with spectroscopic, quantum chemical, and molecular dynamics methods. The work is divided into the following three parts: 1. Intramolecular interactions in ortho-substituted phenols. Theoretical and experimental data that characterizes the intramolecular hydrogen bonds in 48 different o-substituted phenols are discussed. The study covers various kinds of O-H ... Y -type interactions (Y= N, O, S, F, Cl, Br, I, C=C, C=-C, and C-=N). The bond strength sequences for several series of systematically related compounds as obtained from IR spectroscopy data (i.e., v(OH) stretching frequencies) are discussed and reproduced with several theoretical methods (B3LYP/6-31G(d,p), B3LYP/6-311G(d,p), B3LYP/6-31++G(d,p), B3LYP/DZVP, MP2/6-31G(d,p), and MP2/6-31++G(d,p) levels of theory). The experimentally determined sequences are interpreted in terms of the intrinsic properties of the molecules: hydrogen bond distances, Mulliken partial charges, van der Waals radii, and electron densities of the Y-proton acceptors. 2. Competitive hydrogen bonds and conformational equilibria in 2,6-disubstituted phenols containing two different carbonyl substituents. The rotational isomers of ten unsymmetrical 2,6-disubstituted phenols as obtained by combinations of five different carbonyl substituents (COOH, COOCH 3 , CHO, COCH 3 , and CONH 2 ) have been theoretically investigated at the B3LYP/6-31G(d,p) level of theory. The relative stability of four to five conformers of each compound were determined by full geometry optimization for free molecules as well as for molecules in reaction fields with dielectric constants up to ε=37.5. A comparison with IR spectroscopic data of available compounds revealed excellent agreement with the theoretically predicted stability sequences and conformational equilibria. The stability of a conformer could be interpreted to be governed by the following two contributions: (i) an attractive hydrogen bond

  7. Interactions between superconductivity and quantum criticality in CeCoIn5, URhGe and UCoGe

    International Nuclear Information System (INIS)

    Howald, L.

    2011-01-01

    The subject of this thesis is the analyze of the superconducting upper critical field (Hc2) and the interaction between superconductivity and quantum critical points (QCP), for the compounds CeCoIn 5 , URhGe and UCoGe. In CeCoIn 5 , study by mean of resistivity of the Fermi liquid domain allows us to localize precisely the QCP at ambient pressure. This analyze rule out the previously suggested pinning of Hc2(0) at the QCP. In a second part, the evolution of Hc2 under pressure is analyzed. The superconducting dome is unconventional in this compound with two characteristic pressures: at 1.6 GPa, the superconducting transition temperature is maximum but it is at 0.4 GPa that physical properties (maximum of Hc2(0), maximum of the initial slope dHc2/dT, maximum of the specific heat jump DC/C,... ) suggest a QCP. We explain this antagonism with pair-breaking effects in the proximity of the QCP. With these two experiments, we suggest a new phase diagram for CeCoIn 5 . In a third part, measurements of thermal conductivity on URhGe and UCoGe are presented. We obtained the bulk superconducting phase transition and confirmed the unusual curvature of the slope dHc2/dT observed by resistivity. The temperatures and fields dependence of thermal conductivity allow us to identify a non-electronic contribution for heat transport down to the lowest temperature (50 mK) and probably associated with magnon or longitudinal fluctuations. We also identified two different domains in the superconducting region, These domains are compatible with a two bands model for superconductivity. Thermopower measurements on UCoGe reveal a strong anisotropy to current direction and several anomaly under field applied in the b direction. We suggest a Lifshitz transition to explain our observations in these two compounds. (author) [fr

  8. Interplay between magnetic quantum criticality, Fermi surface and unconventional superconductivity in UCoGe, URhGe and URu2Si2

    International Nuclear Information System (INIS)

    Bastien, Gael

    2017-01-01

    This thesis is concentrated on the ferromagnetic superconductors UCoGe and URhGe and on the hidden order state in URu 2 Si 2 . In the first part the pressure temperature phase diagram of UCoGe was studied up to 10.5 GPa. Ferromagnetism vanishes at the critical pressure pc≅1 GPa. Unconventional superconductivity and non Fermi liquid behavior can be observed in a broad pressure range around pc. The superconducting upper critical field properties were explained by the suppression of the magnetic fluctuations under field. In the second part the Fermi surfaces of UCoGe and URhGe were investigated by quantum oscillations. In UCoGe four Fermi surface pockets were observed. Under magnetic field successive Lifshitz transitions of the Fermi surface have been detected. The observed Fermi surface pockets in UCoGe evolve smoothly with pressure up to 2.5 GPa and do not show any Fermi surface reconstruction at the critical pressure pc. In URhGe, three heavy Fermi surface pockets were detected by quantum oscillations. In the last part the quantum oscillation study in the hidden order state of URu 2 Si 2 shows a strong g factor anisotropy for two Fermi surface pockets, which is compared to the macroscopic g factor anisotropy extracted from the upper critical field study. (author) [fr

  9. Synthesis of copper quantum dots by chemical reduction method and tailoring of its band gap

    Directory of Open Access Journals (Sweden)

    P. G. Prabhash

    2016-05-01

    Full Text Available Metallic copper nano particles are synthesized with citric acid and CTAB (cetyltrimethylammonium bromide as surfactant and chlorides as precursors. The particle size and surface morphology are analyzed by High Resolution Transmission Electron Microscopy. The average size of the nano particle is found to be 3 - 10 nm. The optical absorption characteristics are done by UV-Visible spectrophotometer. From the Tauc plots, the energy band gaps are calculated and because of their smaller size the particles have much higher band gap than the bulk material. The energy band gap is changed from 3.67 eV to 4.27 eV in citric acid coated copper quantum dots and 4.17 eV to 4.52 eV in CTAB coated copper quantum dots.

  10. Mechanism of action of anticancer titanocene derivatives: An insight from quantum chemical calculations

    Czech Academy of Sciences Publication Activity Database

    Šponer, Judit E.; Leszczynski, J.; Šponer, Jiří

    2006-01-01

    Roč. 110, č. 39 (2006), s. 19632-19636 ISSN 1520-6106 R&D Projects: GA AV ČR(CZ) 1QS500040581; GA ČR(CZ) GA203/05/0009; GA ČR(CZ) GA203/05/0388; GA MŠk(CZ) LC512 Institutional research plan: CEZ:AV0Z50040507 Keywords : titanocene * quantum chemistry * anticancer drug Subject RIV: BO - Biophysics Impact factor: 4.115, year: 2006

  11. The bell that rings light a primer in quantum mechanics and chemical bonding

    CERN Document Server

    Wallace, Dorothy

    2006-01-01

    This book is an introduction to quantum mechanics and mathematics that leads to the solution of the Schrodinger equation. It can be read and understood by undergraduates without sacrificing the mathematical details necessary for a complete solution giving the shapes of molecular orbitals seen in every chemistry text. Readers are introduced to many mathematical topics new to the undergraduate curriculum, such as basic representation theory, Schur's lemma, and the Legendre polynomials.

  12. Synthesis and characterization of CdSe quantum dots dispersed in PVA matrix by chemical route

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Zubair M. S. H.; Ganaie, Mohsin; Husain, M.; Zulfequar, M., E-mail: mzulfe@rediffmail.com [Department of Physics, Jamia Millia Islamia, New Delhi-110025 (India); Khan, Shamshad A. [Department of Physics St. Andrews College, Gorakhpur-273001,U.P,-India (India)

    2016-05-23

    CdSe quantum dots using polyvinyl alcohol as a capping agent have been synthesized via a simple heat induced thermolysis technique. The structural analysis of CdSe/PVA thin film was studied by X-ray diffraction, which confirms crystalline nature of the prepared film. The surface morphology and particle size of the prepared sample was studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The SEM studies of CdSe/PVA thin film shows the average size of particles in the form of clusters of several quantum dots in the range of 10-20 nm. The morphology of CdSe/PVA thin film was further examined by TEM. The TEM image shows the fringes of tiny dots with average sizes of 4-7 nm. The optical properties of CdSe/PVA thin film were studied by UV-VIS absorption spectroscopy. The CdSe/PVA quantum dots follow the role of direct transition and the optical band gap is found to be 4.03 eV. From dc conductivity measurement, the observed value of activation energy was found to be 0.71 eV.

  13. Conformational analysis, spectroscopic, structure-activity relations and quantum chemical simulation studies of 4-(trifluoromethyl)benzylamine

    Science.gov (United States)

    Arjunan, V.; Devi, L.; Mohan, S.

    2018-05-01

    The FT-IR and FT-Raman spectra of 4-trifluoromethylbenzylamine (TFMBA) have been recorded in the range 4000-450 and 4000-100 cm-1 respectively. The conformational analysis of the compound has been carried out to attain stable geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compound are carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The experimental vibrational frequencies are compared with the wavenumbers obtained theoretically from the B3LYP gradient calculations employing the standard high level 6-311++G** and cc-pVTZ basis sets for the optimised geometry of the compound. The structural parameters, thermodynamic properties and vibrational frequencies of the normal modes obtained from the B3LYP methods are in good agreement with the experimental data. The 1H (400 MHz; CDCl3) and 13C (100 MHz; CDCl3) nuclear magnetic resonance (NMR) spectra were also recorded. The electronic properties, highest occupied molecular orbital and lowest unoccupied molecular orbital energies are measured by DFT approach. The charges of the atoms by natural bond orbital (NBO) analysis are determined by B3LYP/cc-pVTZ method. The structure-chemical reactivity relations of the compound are determined through chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods.

  14. NMR chemical shift and J coupling parameterization and quantum mechanical reference spectrum simulation for selected nerve agent degradation products in aqueous conditions.

    Science.gov (United States)

    Koskela, Harri; Anđelković, Boban

    2017-10-01

    The spectral parameters of selected nerve agent degradation products relevant to the Chemical Weapons Convention, namely, ethyl methylphosphonate, isopropyl methylphosphonate, pinacolyl methylphosphonate and methylphosphonic acid, were studied in wide range of pH conditions and selected temperatures. The pH and temperature dependence of chemical shifts and J couplings was parameterized using Henderson-Hasselbalch-based functions. The obtained parameters allowed calculation of precise chemical shifts and J coupling constants in arbitrary pH conditions and typical measurement temperatures, thus facilitating quantum mechanical simulation of reference spectra in the chosen magnetic field strength for chemical verification. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.

  15. Actualization of physical-chemical properties and criticality data of specific fissile materials

    International Nuclear Information System (INIS)

    Strauch, V.; Deutsch, K.H.

    1991-09-01

    The purpose of this project is to update the criticality curves contained in DIN 25 403, Parts 2-8. This report contains criticality data for aqueous uranium and plutonium systems of various concentrations for spherical, cylindrical and layer geometries. The critical dimensions were calculated with the single dimensional transport code XSDRNPM-S and the 27 group-library from Scale 3.1. A 30 cm thick water reflector was taken into account. The critical masses were obtained by multiplying the volume of a critical sphere with the fissile material concentration. The moderator/fissile material relationship for each of the investigated concentration ranges were described. Checks were made using experiments with comparable fissile material systems. Due to the complex geometry of some of the chosen experiments some calculation checks were carried out using the Monte-Carlo-Codes KENO IV-S and Va. The calculation results compared very well with the experiments. Comparison of the results with the currently valid DIN curves does not show any serious differences. The new values lie however slightly below the current values and therefore represent conservative values, so that the criticality curves of DIN 25 403, Parts 2-6 and 8 should be replaced. (orig./HP) [de

  16. The molecular structure of 4-methylpyridine-N-oxide: Gas-phase electron diffraction and quantum chemical calculations

    Science.gov (United States)

    Belova, Natalya V.; Girichev, Georgiy V.; Kotova, Vitaliya E.; Korolkova, Kseniya A.; Trang, Nguyen Hoang

    2018-03-01

    The molecular structure of 4-methylpiridine-N-oxide, 4-MePyO, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both, quantum chemistry and GED analyses resulted in CS molecular symmetry with the planar pyridine ring. Obtained molecular parameters confirm the hyperconjugation in the pyridine ring and the sp2 hybridization concept of the nitrogen and carbon atoms in the ring. The experimental geometric parameters are in a good agreement with the parameters for non-substituted N-oxide and reproduced very closely by DFT calculations. The presence of the electron-donating CH3 substituent in 4-MePyO leads to a decrease of the ipso-angle and to an increase of r(N→O) in comparison with the non-substituted PyO. Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme. The nature of the semipolar N→O bond is discussed.

  17. Resonance Raman and quantum chemical studies of short polyene radical cations

    DEFF Research Database (Denmark)

    Keszthelyi, T.; Wilbrandt, R.; Bally, T.

    1997-01-01

    ,3,5-hexatriene have been studied. The radical cations were generated radiolytically in a glassy Freon matrix and investigated by optical absorption and resonance Raman spectroscopy. Ab initio and density functional molecular-orbital calculations have been carried out to predict equilibrium structures...... and to assist assignment of the resonance Raman spectra. A new and improved scaled quantum mechanical force field for the butadiene radical cation was also determined. The presence of more than one rotamer was observed in all the polyene radical cations we investigated. (C) 1997 Elsevier Science B.V....

  18. Reference quantum chemical calculations on RNA base pairs directly involving the 2'-OH group of ribose

    Czech Academy of Sciences Publication Activity Database

    Šponer, Jiří; Zgarbová, M.; Jurečka, Petr; Riley, K.E.; Šponer, Judit E.; Hobza, Pavel

    2009-01-01

    Roč. 5, č. 4 (2009), s. 1166-1179 ISSN 1549-9618 R&D Projects: GA AV ČR(CZ) IAA400040802; GA AV ČR(CZ) IAA400550701; GA MŠk(CZ) LC06030; GA MŠk(CZ) LC512 Institutional research plan: CEZ:AV0Z50040507; CEZ:AV0Z50040702; CEZ:AV0Z40550506 Keywords : RNA * ribose * quantum calculations Subject RIV: BO - Biophysics Impact factor: 4.804, year: 2009

  19. Quantum-chemical, NMR, FT IR, and ESI MS studies of complexes of colchicine with Zn(II).

    Science.gov (United States)

    Jankowski, Wojciech; Kurek, Joanna; Barczyński, Piotr; Hoffmann, Marcin

    2017-04-01

    Colchicine is a tropolone alkaloid from Colchicinum autumnale. It shows antifibrotic, antimitotic, and anti-inflammatory activities, and is used to treat gout and Mediterranean fever. In this work, complexes of colchicine with zinc(II) nitrate were synthesized and investigated using DFT, 1 H and 13 C NMR, FT IR, and ESI MS. The counterpoise-corrected and uncorrected interaction energies of these complexes were calculated. We also calculated their 1 H, 13 C NMR, and IR spectra and compared them with the corresponding experimentally obtained data. According to the ESI MS mass spectra, colchicine forms stable complexes with zinc(II) nitrate that have various stoichiometries: 2:1, 1:1:1, and 2:1:1 with respect to colchichine, Zn(II), and nitrate ion. All of the complexes were investigated using the quantum theory of atoms in molecules (QTAIM). The calculated and the measured spectra showed differences before and after the complexation process. Calculated electron densities and bond critical points indicated the presence of bonds between the ligands and the central cation in the investigated complexes that satisfied the quantum theory of atoms in molecules. Graphical Abstract DFT, NMR, FT IR, ESI MS, QTAIM and puckering studies of complexes of colchicine with Zn(II).

  20. Interwell coupling effect in Si/SiGe quantum wells grown by ultra high vacuum chemical vapor deposition

    Directory of Open Access Journals (Sweden)

    Loh Ter-Hoe

    2007-01-01

    Full Text Available AbstractSi/Si0.66Ge0.34coupled quantum well (CQW structures with different barrier thickness of 40, 4 and 2 nm were grown on Si substrates using an ultra high vacuum chemical vapor deposition (UHV-CVD system. The samples were characterized using high resolution x-ray diffraction (HRXRD, cross-sectional transmission electron microscopy (XTEM and photoluminescence (PL spectroscopy. Blue shift in PL peak energy due to interwell coupling was observed in the CQWs following increase in the Si barrier thickness. The Si/SiGe heterostructure growth process and theoretical band structure model was validated by comparing the energy of the no-phonon peak calculated by the 6 + 2-bandk·pmethod with experimental PL data. Close agreement between theoretical calculations and experimental data was obtained.

  1. Wavelength tuning of InAs quantum dots grown on InP (100) by chemical-beam epitaxy

    International Nuclear Information System (INIS)

    Gong, Q.; Noetzel, R.; Veldhoven, P.J. van; Eijkemans, T.J.; Wolter, J.H.

    2004-01-01

    We report on an effective way to continuously tune the emission wavelength of InAs quantum dots (QDs) grown on InP (100) by chemical-beam epitaxy. The InAs QD layer is embedded in a GaInAsP layer lattice matched to InP. With an ultrathin GaAs layer inserted between the InAs QD layer and the GaInAsP buffer, the peak wavelength from the InAs QDs can be continuously tuned from above 1.6 μm down to 1.5 μm at room temperature. The major role of the thin GaAs layer is to greatly suppress the As/P exchange during the deposition of InAs and subsequent growth interruption under arsenic flux, as well as to consume the segregated surface In layer floating on the GaInAsP buffer layer

  2. A quantum chemical analysis of Zn and Sb doping and co-doping in SnO2

    Directory of Open Access Journals (Sweden)

    Luis Villamagua

    2017-10-01

    Full Text Available This work presents a quantum chemical study of Zn and Sb doping and co-doping in SnO2 carried out by a DFT+U method. The analysis has been developed by introducing three different modifications in the otherwise pure SnO2 system. In the first place, an oxygen vacancy was introduced within the crystal. Following, such a system was doped (separately by Zn or Sb impurities. Finally, the best energetic positions for both Zn and Sb atoms were simultaneously introduced within the lattice. Results of the simulations show that the confined charge that appeared due to the introduction of the oxygen vacancy interacts with the dopants atoms, being this interaction mostly responsible of the observed effects, i.e., EG shrinkage, F-centers formations, and magnetic momentum rise.

  3. Combinatorial computational chemistry approach of tight-binding quantum chemical molecular dynamics method to the design of the automotive catalysts

    International Nuclear Information System (INIS)

    Ito, Yuki; Jung, Changho; Luo, Yi; Koyama, Michihisa; Endou, Akira; Kubo, Momoji; Imamura, Akira; Miyamoto, Akira

    2006-01-01

    Recently, we have developed a new tight-binding quantum chemical molecular dynamics program 'Colors' for combinatorial computational chemistry approach. This methodology is based on our original tight-binding approximation and realized over 5000 times acceleration compared to the conventional first-principles molecular dynamics method. In the present study, we applied our new program to the simulations on various realistic large-scale models of the automotive three-way catalysts, ultrafine Pt particle/CeO 2 (111) support. Significant electron transfer from the Pt particle to the CeO 2 (111) surface was observed and it was found to strongly depend on the size of the Pt particle. Furthermore, our simulation results suggest that the reduction of the Ce atom due to the electron transfer from the Pt particle to the CeO 2 surface is a main reason for the strong interaction of the Pt particle and CeO 2 (111) support

  4. Singularities of classical and quantum correlations at critical points of the Lipkin–Meshkov–Glick model in bipartitions and tripartitions of spins

    International Nuclear Information System (INIS)

    Zhang, Xiu-xing; Li, Fu-li

    2013-01-01

    By using the lowest order expansion in the number of spins, we study the classical correlation (CC) and quantum correlations (QCs) between two spin subgroups of the Lipkin–Meshkov–Glick (LMG) model in both binary and trinary decompositions of spins. In the case of bipartitions, we find that the CC and all the QCs are divergent in the same singular behavior at the critical point of the LMG model. In the case of tripartitions, however, the CC is still divergent but the QCs remain finite at the critical point. The present result shows that the CC is very robust but the QCs are much frangible to the environment disturbance.

  5. Quantitative structure-activation barrier relationship modeling for Diels-Alder ligations utilizing quantum chemical structural descriptors.

    Science.gov (United States)

    Nandi, Sisir; Monesi, Alessandro; Drgan, Viktor; Merzel, Franci; Novič, Marjana

    2013-10-30

    In the present study, we show the correlation of quantum chemical structural descriptors with the activation barriers of the Diels-Alder ligations. A set of 72 non-catalysed Diels-Alder reactions were subjected to quantitative structure-activation barrier relationship (QSABR) under the framework of theoretical quantum chemical descriptors calculated solely from the structures of diene and dienophile reactants. Experimental activation barrier data were obtained from literature. Descriptors were computed using Hartree-Fock theory using 6-31G(d) basis set as implemented in Gaussian 09 software. Variable selection and model development were carried out by stepwise multiple linear regression methodology. Predictive performance of the quantitative structure-activation barrier relationship (QSABR) model was assessed by training and test set concept and by calculating leave-one-out cross-validated Q2 and predictive R2 values. The QSABR model can explain and predict 86.5% and 80% of the variances, respectively, in the activation energy barrier training data. Alternatively, a neural network model based on back propagation of errors was developed to assess the nonlinearity of the sought correlations between theoretical descriptors and experimental reaction barriers. A reasonable predictability for the activation barrier of the test set reactions was obtained, which enabled an exploration and interpretation of the significant variables responsible for Diels-Alder interaction between dienes and dienophiles. Thus, studies in the direction of QSABR modelling that provide efficient and fast prediction of activation barriers of the Diels-Alder reactions turn out to be a meaningful alternative to transition state theory based computation.

  6. Coherent chemical kinetics as quantum walks. II. Radical-pair reactions in Arabidopsis thaliana

    Science.gov (United States)

    Chia, A.; Górecka, A.; Kurzyński, P.; Paterek, T.; Kaszlikowski, D.

    2016-03-01

    We apply the quantum-walk approach proposed in the preceding paper [A. Chia et al., preceding paper, Phys. Rev. E 93, 032407 (2016), 10.1103/PhysRevE.93.032407] to a radical-pair reaction where realistic estimates for the intermediate transition rates are available. The well-known average hitting time from quantum walks can be adopted as a measure of how quickly the reaction occurs and we calculate this for varying degrees of dephasing in the radical pair. The time for the radical pair to react to a product is found to be independent of the amount of dephasing introduced, even in the limit of no dephasing where the transient population dynamics exhibits strong coherent oscillations. This can be seen to arise from the existence of a rate-limiting step in the reaction and we argue that in such examples, a purely classical model based on rate equations can be used for estimating the time scale of the reaction but not necessarily its population dynamics.

  7. Intramolecular tautomerisation and the conformational variability of some classical mutagens – cytosine derivatives: quantum chemical study

    Directory of Open Access Journals (Sweden)

    Hovorun D. M.

    2011-04-01

    Full Text Available Aim. To determine the lifetime of the mutagenic cytosine derivatives through the investigation of the physicochemical mechanisms of their intramolecular proton transfer. Methods. Non-empirical quantum chemistry, the analysis of the electron density by means of Bader’s atoms in molecules (AIM theory and physicochemical kinetics were used. Results. It is shown that the modification of all investigated compounds, except DCyt, prevents their pairing in both mutagenic and canonical tautomeric forms with a base which is an interacting partner. This effect can inhibit their mutagenic potential. It is also established that Watson-Crick tautomeric hypothesis can be formally expanded for the investigated molecules so far as a lifetime of the mutagenic tautomers much more exceeds characteristic time for the incorporation of one nucleotides pair by DNA biosynthesis machinery. It seems that just within the frame of this hypothesis it will be possible to give an adequate explanation of the mechanisms of mutagenic action of N4-aminocytosine, N4-methoxycytosine, N4-hydroxycytosine and N4dehydrocytosine, which have much more energy advantageous imino form in comparison with amino form. Conclusions. For the first time the comprehensive conformational analysis of a number of classical mutagens, namely cytosine derivatives, has been performed using the methods of non-empirical quantum chemistry at the MP2/6-311++G (2df,pd//B3LYP/6-311++G(d,p level of theory

  8. Quantum chemical estimation of sorption/desorption of H{sub 2} and H{sub 2}O (gas) at the plasma-wall interface

    Energy Technology Data Exchange (ETDEWEB)

    Nagasaki, Shinya; Tsushima, Satoru; Tanaka, Masataka; Umemura, Yasuhiro [Tokyo Univ. (Japan). Faculty of Engineering

    1996-10-01

    By using MOPAC Code, we estimated the charge density of SiO{sub 2}-Al{sub 2}O{sub 3}-SiO{sub 2} metal oxide. We could find that the such quantum chemical calculation is a fruitful tool for understanding the plasma-wall interactions from the microscopic point of view. (author)

  9. Exploring the Structure of a DNA Hairpin with the Help of NMR Spin-Spin Coupling Constants: An Experimental and Quantum Chemical Investigation

    Czech Academy of Sciences Publication Activity Database

    Sychrovský, Vladimír; Vacek, Jaroslav; Hobza, Pavel; Žídek, L.; Sklenář, V.; Cremer, D.

    2002-01-01

    Roč. 106, - (2002), s. 10242-10250 ISSN 1089-5639 R&D Projects: GA MŠk LN00A032 Institutional research plan: CEZ:AV0Z4040901 Keywords : DNA * help of NMR spin-spin coupling constants * quantum chemical investigation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.765, year: 2002

  10. Distribution of electron density and internal rotation in phospha-alkenes according to data from quantum-chemical calculations by the MNDO method

    International Nuclear Information System (INIS)

    Boldeskul, I.E.; Pen'kovskii, V.V.; Povolotskii, M.I.

    1988-01-01

    A quantum-chemical investigation of the characteristics of the phosphorus-carbon bond and the internal rotation around it in phospha-alkenes has been carried out in the MNDO approximation. The results of the calculation have been compared with experimental dynamic 1 H NMR data

  11. POSSIBLE NATURE OF THE RADIATION-INDUCED SIGNAL IN NAILS: HIGH-FIELD EPR, CONFIRMING CHEMICAL SYNTHESIS, AND QUANTUM CHEMICAL CALCULATIONS.

    Science.gov (United States)

    Tipikin, Dmitriy S; Swarts, Steven G; Sidabras, Jason W; Trompier, François; Swartz, Harold M

    2016-12-01

    Exposure of finger- and toe-nails to ionizing radiation generates an Electron Paramagnetic Resonance (EPR) signal whose intensity is dose dependent and stable at room temperature for several days. The dependency of the radiation-induced signal (RIS) on the received dose may be used as the basis for retrospective dosimetry of an individual's fortuitous exposure to ionizing radiation. Two radiation-induced signals, a quasi-stable (RIS2) and stable signal (RIS5), have been identified in nails irradiated up to a dose of 50 Gy. Using X-band EPR, both RIS signals exhibit a singlet line shape with a line width around 1.0 mT and an apparent g-value of 2.0044. In this work, we seek information on the exact chemical nature of the radiation-induced free radicals underlying the signal. This knowledge may provide insights into the reason for the discrepancy in the stabilities of the two RIS signals and help develop strategies for stabilizing the radicals in nails or devising methods for restoring the radicals after decay. In this work an analysis of high field (94 GHz and 240 GHz) EPR spectra of the RIS using quantum chemical calculations, the oxidation-reduction properties and the pH dependence of the signal intensities are used to show that spectroscopic and chemical properties of the RIS are consistent with a semiquinone-type radical underlying the RIS. It has been suggested that semiquinone radicals formed on trace amounts of melanin in nails are the basis for the RIS signals. However, based on the quantum chemical calculations and chemical properties of the RIS, it is likely that the radicals underlying this signal are generated from the radiolysis of L-3,4-dihydroxyphenylalanine (DOPA) amino acids in the keratin proteins. These DOPA amino acids are likely formed from the exogenous oxidation of tyrosine in keratin by the oxygen from the air prior to irradiation. We show that these DOPA amino acids can work as radical traps, capturing the highly reactive and unstable sulfur

  12. POSSIBLE NATURE OF THE RADIATION-INDUCED SIGNAL IN NAILS: HIGH-FIELD EPR, CONFIRMING CHEMICAL SYNTHESIS, AND QUANTUM CHEMICAL CALCULATIONS

    Science.gov (United States)

    Tipikin, Dmitriy S.; Swarts, Steven G.; Sidabras, Jason W.; Trompier, François; Swartz, Harold M.

    2016-01-01

    Exposure of finger- and toe-nails to ionizing radiation generates an Electron Paramagnetic Resonance (EPR) signal whose intensity is dose dependent and stable at room temperature for several days. The dependency of the radiation-induced signal (RIS) on the received dose may be used as the basis for retrospective dosimetry of an individual's fortuitous exposure to ionizing radiation. Two radiation-induced signals, a quasi-stable (RIS2) and stable signal (RIS5), have been identified in nails irradiated up to a dose of 50 Gy. Using X-band EPR, both RIS signals exhibit a singlet line shape with a line width around 1.0 mT and an apparent g-value of 2.0044. In this work, we seek information on the exact chemical nature of the radiation-induced free radicals underlying the signal. This knowledge may provide insights into the reason for the discrepancy in the stabilities of the two RIS signals and help develop strategies for stabilizing the radicals in nails or devising methods for restoring the radicals after decay. In this work an analysis of high field (94 GHz and 240 GHz) EPR spectra of the RIS using quantum chemical calculations, the oxidation–reduction properties and the pH dependence of the signal intensities are used to show that spectroscopic and chemical properties of the RIS are consistent with a semiquinone-type radical underlying the RIS. It has been suggested that semiquinone radicals formed on trace amounts of melanin in nails are the basis for the RIS signals. However, based on the quantum chemical calculations and chemical properties of the RIS, it is likely that the radicals underlying this signal are generated from the radiolysis of L-3,4-dihydroxyphenylalanine (DOPA) amino acids in the keratin proteins. These DOPA amino acids are likely formed from the exogenous oxidation of tyrosine in keratin by the oxygen from the air prior to irradiation. We show that these DOPA amino acids can work as radical traps, capturing the highly reactive and unstable

  13. Synthesis, vibrational, NMR, quantum chemical and structure-activity relation studies of 2-hydroxy-4-methoxyacetophenone.

    Science.gov (United States)

    Arjunan, V; Devi, L; Subbalakshmi, R; Rani, T; Mohan, S

    2014-09-15

    The stable geometry of 2-hydroxy-4-methoxyacetophenone is optimised by DFT/B3LYP method with 6-311++G(∗∗) and cc-pVTZ basis sets. The structural parameters, thermodynamic properties and vibrational frequencies of the optimised geometry have been determined. The effects of substituents (hydroxyl, methoxy and acetyl groups) on the benzene ring vibrational frequencies are analysed. The vibrational frequencies of the fundamental modes of 2-hydroxy-4-methoxyacetophenone have been precisely assigned and analysed and the theoretical results are compared with the experimental vibrations. 1H and 13C NMR isotropic chemical shifts are calculated and assignments made are compared with the experimental values. The energies of important MO's, the total electron density and electrostatic potential of the compound are determined. Various reactivity and selectivity descriptors such as chemical hardness, chemical potential, softness, electrophilicity, nucleophilicity and the appropriate local quantities are calculated. Copyright © 2014 Elsevier B.V. All rights reserved.

  14. Calibration and use of the polar organic chemical integrative sampler--a critical review.

    Science.gov (United States)

    Harman, Christopher; Allan, Ian John; Vermeirssen, Etiënne L M

    2012-12-01

    The implementation of strict environmental quality standards for polar organic priority pollutants poses a challenge for monitoring programs. The polar organic chemical integrative sampler (POCIS) may help to address the challenge of measuring low and fluctuating trace concentrations of such organic contaminants, offering significant advantages over traditional sampling. In the present review, the authors evaluate POCIS calibration methods and factors affecting sampling rates together with reported environmental applications. Over 300 compounds have been shown to accumulate in POCIS, including pesticides, pharmaceuticals, hormones, and industrial chemicals. Polar organic chemical integrative sampler extracts have been used for both chemical and biological analyses. Several different calibration methods have been described, which makes it difficult to directly compare sampling rates. In addition, despite the fact that some attempts to correlate sampling rates with the properties of target compounds such as log K(OW) have been met with varying success, an overall model that can predict uptake is lacking. Furthermore, temperature, water flow rates, salinity, pH, and fouling have all been shown to affect uptake; however, there is currently no robust method available for adjusting for these differences. Overall, POCIS has been applied to a wide range of sampling environments and scenarios and has been proven to be a useful screening tool. However, based on the existing literature, a more mechanistic approach is required to increase understanding and thus improve the quantitative nature of the measurements. Copyright © 2012 SETAC.

  15. Efficient Implementation of Many-body Quantum Chemical Methods on the Intel Xeon Phi Coprocessor

    Energy Technology Data Exchange (ETDEWEB)

    Apra, Edoardo; Klemm, Michael; Kowalski, Karol

    2014-12-01

    This paper presents the implementation and performance of the highly accurate CCSD(T) quantum chemistry method on the Intel Xeon Phi coprocessor within the context of the NWChem computational chemistry package. The widespread use of highly correlated methods in electronic structure calculations is contingent upon the interplay between advances in theory and the possibility of utilizing the ever-growing computer power of emerging heterogeneous architectures. We discuss the design decisions of our implementation as well as the optimizations applied to the compute kernels and data transfers between host and coprocessor. We show the feasibility of adopting the Intel Many Integrated Core Architecture and the Intel Xeon Phi coprocessor for developing efficient computational chemistry modeling tools. Remarkable scalability is demonstrated by benchmarks. Our solution scales up to a total of 62560 cores with the concurrent utilization of Intel Xeon processors and Intel Xeon Phi coprocessors.

  16. FTIR, FT-Raman, FT-NMR and quantum chemical investigations of 3-acetylcoumarin

    Science.gov (United States)

    Arjunan, V.; Sakiladevi, S.; Marchewka, M. K.; Mohan, S.

    2013-05-01

    3-Acetylcoumarin (3AC) was synthesised by a Knoevenagel reaction. Conformational analysis using the B3LYP method was also carried out to determine the most stable conformation of the compound. FTIR and FT-Raman spectra of 3AC have been recorded in the range 4000-400 and 4000-100 cm-1, respectively. 1H and 13C NMR spectra have also been recorded. The complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the experimental FTIR and FT-Raman data and quantum mechanical studies. The experimental vibrational frequencies were compared with the wavenumbers obtained theoretically from the DFT-B3LYP/B3PW91 gradient calculations employing the standard 6-31G**, high level 6-311++G** and cc-pVTZ basis sets for optimised geometry of the compound. The frontier molecular orbital energies of the compound are determined by DFT method.

  17. Mixed quantum-classical studies of energy partitioning in unimolecular chemical reactions

    Science.gov (United States)

    Bladow, Landon Lowell

    A mixed quantum-classical reaction path Hamiltonian method is utilized to study the dynamics of unimolecular reactions. The method treats motion along the reaction path classically and treats the transverse vibrations quantum mechanically. The theory leads to equations that predict the disposai of the exit-channel potential energy to product translation and vibration. In addition, vibrational state distributions are obtained for the product normal modes. Vibrational excitation results from the curvature of the minimum energy reaction path. The method is applied to six unimolecular reactions: HF elimination from fluoroethane, 1,1-difluoroethane, 1,1-difluoroethene, and trifluoromethane; and HCl elimination from chloroethane and acetyl chloride. The minimum energy paths were calculated at either the MP2 or B3LYP level of theory. In all cases, the majority of the vibrational excitation of the products occurs in the HX fragment. The results are compared to experimental data and other theoretical results, where available. The best agreement between the experimental and calculated HX vibrational distributions is found for the halogenated ethanes, and the experimental deduction that the majority of the HX vibrational excitation arises from the potential energy release is supported. It is believed that the excess energy provided in experiments contributes to the poorer agreement between experiment and theory observed for HF elimination from 1,1-difluoroethene and trifluoromethane. An attempt is described to incorporate a treatment of the excess energy into the present method. However, the sign of the curvature coupling elements is then found to affect the dynamics. Overall, the method appears to be an efficient dynamical tool for modeling the disposal of the exit-channel potential energy in unimolecular reactions.

  18. Diversion of the melanin synthetic pathway by dopamine product scavengers: A quantum chemical modeling of the reaction mechanisms

    Directory of Open Access Journals (Sweden)

    T. B. Demissie

    2017-01-01

    Full Text Available We report the stability and reactivity of the oxidation products as well as L-cysteine and N-acetylcysteine adducts of dopamine studied using quantum chemical calculations. The overall reactions studied were subdivided into four reaction channels. The first reaction channel is the oxidation of dopamine to form dopaminoquinone. The second reaction channel leads to melanin formation through subsequent reactions. The third and fourth reaction channels are reactions leading to the formation of dopaminoquinone adducts which are aimed to divert the synthesis of melanin. The results indicate that L-cysteine and N-acetylcysteine undergo chemical reactions mainly at C5 position of dopaminoquinone. The analyses of the thermodynamic energies indicate that L-cysteine and N-acetylcysteine covalently bind to dopaminoquinone by competing with the internal cyclization reaction of dopaminoquinone which leads to the synthesis of melanin. The analysis of the results, based on the reaction free energies, is also supported by the investigation of the natural bond orbitals of the reactants and products.

  19. Influence of N-Oxide Introduction on the Stability of Nitrogen-Rich Heteroaromatic Rings: A Quantum Chemical Study.

    Science.gov (United States)

    Yuan, Jia; Long, Xinping; Zhang, Chaoyang

    2016-12-01

    N-Oxidization is an important strategy for enhancing the density and energy of energetic materials. Nevertheless, the influence of N + -O - introduction on molecular stability remains relatively unknown. Thus, the present work comprehensively studied 102 basic N-rich ring structures, including azoles, furazans, and azines, as well as their N-oxides by quantum chemical calculations. The introduction of N + -O - weakens molecular stability in most cases because the process elongates chemical bonds, decreases ring aromaticity, narrows the gaps between the highest occupied and lowest unoccupied molecular orbitals, and increases the photochemical reactivity. Besides, the easy H transfer to the neighboring O atom, which forms a N-OH isomer in azoles, renders the stabilization by N-oxide introduction ineffective. However, N-oxide introduction can enhance the molecular stability of 1,2,3,4-tetrazine-1,3-dioxide and tetrazino-tetrazine 1,3,6,8-tetraoxide by promoting σ-π separation and relieving lone-pair repulsion. Moreover, the alternate arrangement of positive and negative charges is another factor stabilizing the 1,2,3,4-tetrazine ring by 1,3-dioxidation. Finally, we assess the accessibility of N-oxidized azoles and azines by regarding N 2 O and H 2 O 2 as oxidizers. We find that all the oxidations were exothermic, thermodynamically spontaneous, and kinetically feasible. After an overall evaluation, we propose 19 N-oxides as basic structures for high-energy materials with considerable stability.

  20. Quantum dots assisted photocatalysis for the chemiluminometric determination of chemical oxygen demand using a single interface flow system

    Energy Technology Data Exchange (ETDEWEB)

    Silvestre, Cristina I.C.; Frigerio, Christian [Requimte, Department of Chemistry, Faculty of Pharmacy, Porto University, Rua Anibal Cunha 164, 4099-030, Porto (Portugal); Santos, Joao L.M., E-mail: joaolms@ff.up.pt [Requimte, Department of Chemistry, Faculty of Pharmacy, Porto University, Rua Anibal Cunha 164, 4099-030, Porto (Portugal); Lima, Jose L.F.C. [Requimte, Department of Chemistry, Faculty of Pharmacy, Porto University, Rua Anibal Cunha 164, 4099-030, Porto (Portugal)

    2011-08-12

    Highlights: {yields} A novel flow method for the determination of chemical oxygen demand is proposed. {yields} CdTe nanocrystals are irradiated with UV light to generate strong oxidizing species. {yields} Reactive species promote a fast catalytic degradation of organic matter. {yields} Luminol is used as a chemiluminescence probe for indirect COD assessment. {yields} A single interface flow system was implemented to automate the assays. - Abstract: A novel flow method for the determination of chemical oxygen demand (COD) is proposed in this work. It relies on the combination of a fully automated single interface flow system, an on-line UV photocatalytic unit and quantum dot (QD) nanotechnology. The developed approach takes advantage of CdTe nanocrystals capacity to generate strong oxidizing species upon irradiation with UV light, which fostered a fast catalytic degradation of the organic compounds. Luminol was used as a chemiluminescence (CL) probe for indirect COD assessment, since it is easily oxidized by the QD generated species yielding a strong CL emission that is quenched in the presence of the organic matter. The proposed methodology allowed the determination of COD concentrations between 1 and 35 mg L{sup -1}, with good precision (R.S.D. < 1.1%, n = 3) and a sampling frequency of about 33 h{sup -1}. The procedure was applied to the determination of COD in wastewater certified reference materials and the obtained results showed an excellent agreement with the certified values.