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Sample records for quantum chemistry study

  1. Quantum chemistry

    CERN Document Server

    Lowe, John P

    1993-01-01

    Praised for its appealing writing style and clear pedagogy, Lowe's Quantum Chemistry is now available in its Second Edition as a text for senior undergraduate- and graduate-level chemistry students. The book assumes little mathematical or physical sophistication and emphasizes an understanding of the techniques and results of quantum chemistry, thus enabling students to comprehend much of the current chemical literature in which quantum chemical methods or concepts are used as tools. The book begins with a six-chapter introduction of standard one-dimensional systems, the hydrogen atom,

  2. Experimental study of quantum simulation for quantum chemistry with a nuclear magnetic resonance simulator.

    Science.gov (United States)

    Lu, Dawei; Xu, Nanyang; Xu, Boruo; Li, Zhaokai; Chen, Hongwei; Peng, Xinhua; Xu, Ruixue; Du, Jiangfeng

    2012-10-13

    Quantum computers have been proved to be able to mimic quantum systems efficiently in polynomial time. Quantum chemistry problems, such as static molecular energy calculations and dynamical chemical reaction simulations, become very intractable on classical computers with scaling up of the system. Therefore, quantum simulation is a feasible and effective approach to tackle quantum chemistry problems. Proof-of-principle experiments have been implemented on the calculation of the hydrogen molecular energies and one-dimensional chemical isomerization reaction dynamics using nuclear magnetic resonance systems. We conclude that quantum simulation will surpass classical computers for quantum chemistry in the near future.

  3. Applications of Quantum Chemistry to the Study of Carbon Nanotubes

    Science.gov (United States)

    Jaffe, Richard L.

    2005-01-01

    For several years, scientists at NASA Ames have been studying the properties of carbon nanotubes using various experimental and computational methods. In this talk, I will compare different strategies for using quantum chemistry calculations to describe the electronic structure, deformation and chemical functionalization of single wall carbon nanotubes (SWNT) and the physisorption of small molecules on nanotube surfaces. The SWNT can be treated as an infinite (periodic) or finite length carbon cylinder or as a polycyclic aromatic hydrocarbon (PAH) molecule with an imposed curvature maintained by external constraints (as if it were cut out of the SWNT surface). Calculations are carried out using DFT and MP2 methods and a variety of atomic orbital basis sets from minimal (STO-3G) to valence triple zeta. The optimal approach is based on the particular SWNT property of interest. Examples to be discussed include: nanotube fluorination and other functionalization reactions; coating of nanotubes by water vapor and low-molecular weight organic molecules; and the nature of the interface between SWNT and liquids such as water and amines. In many cases, the quantum chemistry calculations are used to parameterize or validate force fields for molecular dynamics simulations. The results of these calculations have helped explain experimental data and contributed to the design of novel materials and sensors based on carbon nanotubes. Some of this research is described in the following papers:

  4. A quantum chemistry study of natural gas hydrates.

    Science.gov (United States)

    Atilhan, Mert; Pala, Nezih; Aparicio, Santiago

    2014-04-01

    The structure and properties of natural gas hydrates containing hydrocarbons, CO₂, and N₂ molecules were studied by using computational quantum chemistry methods via the density functional theory approach. All host cages involved in I, II, and H types structures where filled with hydrocarbons up to pentanes, CO₂ and N₂ molecules, depending on their size, and the structures of these host-guest systems optimized. Structural properties, vibrational spectra, and density of states were analyzed together with results from atoms-in-a-molecule and natural bond orbitals methods. The inclusion of dispersion terms in the used functional plays a vital role for obtaining reliable information, and thus, B97D functional was shown to be useful for these systems. Results showed remarkable interaction energies, not strongly affected by the type of host cage, with molecules tending to be placed at the center of the cavities when host cages and guest molecules cavities are of similar size, but with molecules approaching hexagonal faces for larger cages. Vibrational properties show remarkable features in certain regions, with shiftings rising from host-guest interactions, and useful patterns in the terahertz region rising from water surface vibrations strongly coupled with guest molecules. Likewise, calculations on crystal systems for the I and H types were carried out using a pseudopotential approach combined with Grimme's method to take account of dispersion.

  5. Advances in quantum chemistry

    CERN Document Server

    Sabin, John R

    2013-01-01

    Advances in Quantum Chemistry presents surveys of current topics in this rapidly developing field that has emerged at the cross section of the historically established areas of mathematics, physics, chemistry, and biology. It features detailed reviews written by leading international researchers. This volume focuses on the theory of heavy ion physics in medicine.Advances in Quantum Chemistry presents surveys of current topics in this rapidly developing field that has emerged at the cross section of the historically established areas of mathematics, physics, chemistry, and biology. It features

  6. Principles of quantum chemistry

    CERN Document Server

    George, David V

    2013-01-01

    Principles of Quantum Chemistry focuses on the application of quantum mechanics in physical models and experiments of chemical systems.This book describes chemical bonding and its two specific problems - bonding in complexes and in conjugated organic molecules. The very basic theory of spectroscopy is also considered. Other topics include the early development of quantum theory; particle-in-a-box; general formulation of the theory of quantum mechanics; and treatment of angular momentum in quantum mechanics. The examples of solutions of Schroedinger equations; approximation methods in quantum c

  7. A Quantum Chemistry Study on Structural Properties of Petroleum Resin

    Institute of Scientific and Technical Information of China (English)

    Wang Daxi; Pan Yueqiu; Zhang Hongye

    2007-01-01

    The geometries of resins with single-layer (SG), double-layer (DG) and triple-layer (TG) were calculated with the quantum chemistry method. The geometries and net charges of atoms were obtained. The calculated average distances between layers were 0.5348 nm and 0.5051 nm and the action energies were -9.6355 kJ/mol and -32.2803 kJ/mol for resins DG and TG, respectively. Higher electronegative polar atoms can easily form hydrogen bonds with hydrogen atoms of other resin molecules, resulting in resin aggregates. The minimum cross-sectional diameters of resin molecules are too large to enter the pores of zeolite, so they are likely to crack on the surface of zeolite.

  8. Quantum mechanics in chemistry

    CERN Document Server

    Schatz, George C

    2002-01-01

    Intended for graduate and advanced undergraduate students, this text explores quantum mechanical techniques from the viewpoint of chemistry and materials science. Dynamics, symmetry, and formalism are emphasized. An initial review of basic concepts from introductory quantum mechanics is followed by chapters examining symmetry, rotations, and angular momentum addition. Chapter 4 introduces the basic formalism of time-dependent quantum mechanics, emphasizing time-dependent perturbation theory and Fermi's golden rule. Chapter 5 sees this formalism applied to the interaction of radiation and matt

  9. Quantum chemistry an introduction

    CERN Document Server

    Kauzmann, Walter

    2013-01-01

    Quantum Chemistry: An Introduction provides information pertinent to the fundamental aspects of quantum mechanics. This book presents the theory of partial differentiation equations by using the classical theory of vibrations as a means of developing physical insight into this essential branch of mathematics.Organized into five parts encompassing 16 chapters, this book begins with an overview of how quantum mechanical deductions are made. This text then describes the achievements and limitations of the application of quantum mechanics to chemical problems. Other chapters provide a brief survey

  10. Fundamentals of quantum chemistry

    CERN Document Server

    House, J E

    2004-01-01

    An introduction to the principles of quantum mechanics needed in physical chemistry. Mathematical tools are presented and developed as needed and only basic calculus, chemistry, and physics is assumed. Applications include atomic and molecular structure, spectroscopy, alpha decay, tunneling, and superconductivity. New edition includes sections on perturbation theory, orbital symmetry of diatomic molecules, the Huckel MO method and Woodward/Hoffman rules as well as a new chapter on SCF and Hartree-Fock methods. * This revised text clearly presents basic q

  11. Handbook of relativistic quantum chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wenjian (ed.) [Peking Univ., Beijing (China). Center for Computational Science and Engineering

    2017-03-01

    This handbook focuses on the foundations of relativistic quantum mechanics and addresses a number of fundamental issues never covered before in a book. For instance: How can many-body theory be combined with quantum electrodynamics? How can quantum electrodynamics be interfaced with relativistic quantum chemistry? What is the most appropriate relativistic many-electron Hamiltonian? How can we achieve relativistic explicit correlation? How can we formulate relativistic properties? - just to name a few. Since relativistic quantum chemistry is an integral component of computational chemistry, this handbook also supplements the ''Handbook of Computational Chemistry''. Generally speaking, it aims to establish the 'big picture' of relativistic molecular quantum mechanics as the union of quantum electrodynamics and relativistic quantum chemistry. Accordingly, it provides an accessible introduction for readers new to the field, presents advanced methodologies for experts, and discusses possible future perspectives, helping readers understand when/how to apply/develop the methodologies.

  12. STUDY OF GRAFT SITES IN EPOXY GRAFT COPOLYMERS BY QUANTUM CHEMISTRY CALCULATIONS

    Institute of Scientific and Technical Information of China (English)

    Song Chen; Xiao-yu Li

    2009-01-01

    Exploration and characterization of grafting productions by experimental methods are often cumbersome or sometimes impossible. Therefore, quantum chemistry calculations were performed to characterize the graft sites of epoxy resin. According to the Gibbs free energy criterion of the second law of thermodynamic, the reported graft sites were confirmed, and more important, some unreported graft sites were found. In addition, method of increasing the number of graft sites was studied in this article.

  13. Understanding Quantum Numbers in General Chemistry Textbooks

    Science.gov (United States)

    Niaz, Mansoor; Fernandez, Ramon

    2008-01-01

    Quantum numbers and electron configurations form an important part of the general chemistry curriculum and textbooks. The objectives of this study are: (1) Elaboration of a framework based on the following aspects: (a) Origin of the quantum hypothesis, (b) Alternative interpretations of quantum mechanics, (c) Differentiation between an orbital and…

  14. Understanding Quantum Numbers in General Chemistry Textbooks

    Science.gov (United States)

    Niaz, Mansoor; Fernandez, Ramon

    2008-01-01

    Quantum numbers and electron configurations form an important part of the general chemistry curriculum and textbooks. The objectives of this study are: (1) Elaboration of a framework based on the following aspects: (a) Origin of the quantum hypothesis, (b) Alternative interpretations of quantum mechanics, (c) Differentiation between an orbital and…

  15. Real-time Quantum Chemistry

    CERN Document Server

    Haag, Moritz P

    2012-01-01

    Significant progress in the development of efficient and fast algorithms for quantum chemical calculations has been made in the past two decades. The main focus has always been the desire to be able to treat ever larger molecules or molecular assemblies---especially linear and sub-linear scaling techniques are devoted to the accomplishment of this goal. However, as many chemical reactions are rather local, they usually involve only a limited number of atoms so that models of about two hundred (or even less) atoms embedded in a suitable environment are sufficient to study their mechanisms. Thus, the system size does not need to be enlarged, but remains constant for reactions of this type that can be described by less than two hundred atoms. The question then arises how fast one can obtain the quantum chemical results. This question is not directly answered by linear-scaling techniques. In fact, ideas such as haptic quantum chemistry or interactive quantum chemistry require an immediate provision of quantum che...

  16. The use of quantum chemistry in pharmaceutical research as illustrated by case studies of indometacin and carbamazepine

    DEFF Research Database (Denmark)

    Gordon, Keith C; McGoverin, Cushla M; Strachan, Clare J

    2007-01-01

    A number of case studies that illustrate how quantum chemistry may be used in studying pharmaceutical systems are reviewed. A brief introduction to quantum methods is provided and the use of these methods in understanding the structure and properties of indometacin and carbamazepine is discussed....... The use of calculated structures and molecular electrostatic potentials in developing quantitative structure-activity relationships is discussed along with the use of computation chemistry to predict spectroscopic properties....

  17. Quantum Computing for Quantum Chemistry

    Science.gov (United States)

    2010-09-01

    This three-year project consisted on the development and application of quantum computer algorithms for chemical applications. In particular, we developed algorithms for chemical reaction dynamics, electronic structure and protein folding. The first quantum computing for

  18. Elementary quantum chemistry

    CERN Document Server

    Pilar, Frank L

    2003-01-01

    Useful introductory course and reference covers origins of quantum theory, Schrödinger wave equation, quantum mechanics of simple systems, electron spin, quantum states of atoms, Hartree-Fock self-consistent field method, more. 1990 edition.

  19. Relativistic quantum chemistry on quantum computers

    DEFF Research Database (Denmark)

    Veis, L.; Visnak, J.; Fleig, T.

    2012-01-01

    The past few years have witnessed a remarkable interest in the application of quantum computing for solving problems in quantum chemistry more efficiently than classical computers allow. Very recently, proof-of-principle experimental realizations have been reported. However, so far only...... the nonrelativistic regime (i.e., the Schrodinger equation) has been explored, while it is well known that relativistic effects can be very important in chemistry. We present a quantum algorithm for relativistic computations of molecular energies. We show how to efficiently solve the eigenproblem of the Dirac......-Coulomb Hamiltonian on a quantum computer and demonstrate the functionality of the proposed procedure by numerical simulations of computations of the spin-orbit splitting in the SbH molecule. Finally, we propose quantum circuits with three qubits and nine or ten controlled-NOT (CNOT) gates, which implement a proof...

  20. Topological quantum chemistry

    Science.gov (United States)

    Bradlyn, Barry; Elcoro, L.; Cano, Jennifer; Vergniory, M. G.; Wang, Zhijun; Felser, C.; Aroyo, M. I.; Bernevig, B. Andrei

    2017-07-01

    Since the discovery of topological insulators and semimetals, there has been much research into predicting and experimentally discovering distinct classes of these materials, in which the topology of electronic states leads to robust surface states and electromagnetic responses. This apparent success, however, masks a fundamental shortcoming: topological insulators represent only a few hundred of the 200,000 stoichiometric compounds in material databases. However, it is unclear whether this low number is indicative of the esoteric nature of topological insulators or of a fundamental problem with the current approaches to finding them. Here we propose a complete electronic band theory, which builds on the conventional band theory of electrons, highlighting the link between the topology and local chemical bonding. This theory of topological quantum chemistry provides a description of the universal (across materials), global properties of all possible band structures and (weakly correlated) materials, consisting of a graph-theoretic description of momentum (reciprocal) space and a complementary group-theoretic description in real space. For all 230 crystal symmetry groups, we classify the possible band structures that arise from local atomic orbitals, and show which are topologically non-trivial. Our electronic band theory sheds new light on known topological insulators, and can be used to predict many more.

  1. Introducing Relativity into Quantum Chemistry

    Science.gov (United States)

    Li, Wai-Kee; Blinder, S. M.

    2011-01-01

    It is not often realized by chemists that the special theory of relativity is behind several aspects of quantum chemistry. The Schrdinger equation itself is based on relations between space-time and energy-momentum four vectors. Electron spin is, of course, the most obvious manifestation of relativity. The chemistry of some heavy elements is…

  2. Remedial Mathematics for Quantum Chemistry

    Science.gov (United States)

    Koopman, Lodewijk; Brouwer, Natasa; Heck, Andre; Buma, Wybren Jan

    2008-01-01

    Proper mathematical skills are important for every science course and mathematics-intensive chemistry courses rely on a sound mathematical pre-knowledge. In the first-year quantum chemistry course at this university, it was noticed that many students lack basic mathematical knowledge. To tackle the mathematics problem, a remedial mathematics…

  3. Introducing Relativity into Quantum Chemistry

    Science.gov (United States)

    Li, Wai-Kee; Blinder, S. M.

    2011-01-01

    It is not often realized by chemists that the special theory of relativity is behind several aspects of quantum chemistry. The Schrdinger equation itself is based on relations between space-time and energy-momentum four vectors. Electron spin is, of course, the most obvious manifestation of relativity. The chemistry of some heavy elements is…

  4. Problems in Quantum Chemistry and Spectroscopy

    DEFF Research Database (Denmark)

    Spanget-Larsen, Jens

    2015-01-01

    A collection of 22 introductory exercise problems for the course "Quantum Chemistry and Spectroscopy (QCS)".......A collection of 22 introductory exercise problems for the course "Quantum Chemistry and Spectroscopy (QCS)"....

  5. Handbook of computational quantum chemistry

    CERN Document Server

    Cook, David B

    2005-01-01

    Quantum chemistry forms the basis of molecular modeling, a tool widely used to obtain important chemical information and visual images of molecular systems. Recent advances in computing have resulted in considerable developments in molecular modeling, and these developments have led to significant achievements in the design and synthesis of drugs and catalysts. This comprehensive text provides upper-level undergraduates and graduate students with an introduction to the implementation of quantum ideas in molecular modeling, exploring practical applications alongside theoretical explanations.Wri

  6. Students' Levels of Explanations, Models, and Misconceptions in Basic Quantum Chemistry: A Phenomenographic Study

    Science.gov (United States)

    Stefani, Christina; Tsaparlis, Georgios

    2009-01-01

    We investigated students' knowledge constructions of basic quantum chemistry concepts, namely atomic orbitals, the Schrodinger equation, molecular orbitals, hybridization, and chemical bonding. Ausubel's theory of meaningful learning provided the theoretical framework and phenomenography the method of analysis. The semi-structured interview with…

  7. Quantum Chemistry via the Periodic Law.

    Science.gov (United States)

    Blinder, S. M.

    1981-01-01

    Describes an approach to quantum mechanics exploiting the periodic structure of the elements as a foundation for the quantum theory of matter. Indicates that a quantum chemistry course can be developed using this approach. (SK)

  8. Methodology of Parameterization of Molecular Mechanics Force Field From Quantum Chemistry Calculations using Genetic Algorithm: A case study of methanol

    CERN Document Server

    Li, Ying; Chan, Maria K Y; Sankaranarayanan, Subramanian; Rouxb, Benoît

    2016-01-01

    In molecular dynamics (MD) simulation, force field determines the capability of an individual model in capturing physical and chemistry properties. The method for generating proper parameters of the force field form is the key component for computational research in chemistry, biochemistry, and condensed-phase physics. Our study showed that the feasibility to predict experimental condensed phase properties (i.e., density and heat of vaporization) of methanol through problem specific force field from only quantum chemistry information. To acquire the satisfying parameter sets of the force field, the genetic algorithm (GA) is the main optimization method. For electrostatic potential energy, we optimized both the electrostatic parameters of methanol using the GA method, which leads to low deviations of between the quantum mechanics (QM) calculations and the GA optimized parameters. We optimized the van der Waals (vdW) parameters both using GA and guided GA methods by calibrating interaction energy of various met...

  9. Structure and Quantum Chemistry Study on Hexaacetyl D-Mannose Hydrazine

    Institute of Scientific and Technical Information of China (English)

    CAO Rui; LIU Xiao-Hong; CHENG Chang-Mei; WANG Ru-Ji; ZHAO Yu-Fen; WANG Lai-Xi

    2007-01-01

    Hexaacetyl D-mannose hydrazine is one type of important intermediates in saccharide chemistry. In this paper, its single crystal was obtained and furthermore, X-ray diffraction and quantum chemistry calculation were performed. It belongs to orthorhombic system, space group P212121, with a=16.267(3), b=19.263(3), c=7.1948(12)(A), Mr=446.41, Dc=1.315 g/cm3, V=2254.5(6)(A)3 and Z=4. Meanwhile, the experimental results also provide information for designing a kind of molecular switch based on the mannose nitrogenous derivatives.

  10. The structural chemistry of metallocorroles: combined X-ray crystallography and quantum chemistry studies afford unique insights.

    Science.gov (United States)

    Thomas, Kolle E; Alemayehu, Abraham B; Conradie, Jeanet; Beavers, Christine M; Ghosh, Abhik

    2012-08-21

    Although they share some superficial structural similarities with porphyrins, corroles, trianionic ligands with contracted cores, give rise to fundamentally different transition metal complexes in comparison with the dianionic porphyrins. Many metallocorroles are formally high-valent, although a good fraction of them are also noninnocent, with significant corrole radical character. These electronic-structural characteristics result in a variety of fascinating spectroscopic behavior, including highly characteristic, paramagnetically shifted NMR spectra and textbook cases of charge-transfer spectra. Although our early research on corroles focused on spectroscopy, we soon learned that the geometric structures of metallocorroles provide a fascinating window into their electronic-structural characteristics. Thus, we used X-ray structure determinations and quantum chemical studies, chiefly using DFT, to obtain a comprehensive understanding of metallocorrole geometric and electronic structures. This Account describes our studies of the structural chemistry of metallocorroles. At first blush, the planar or mildly domed structure of metallocorroles might appear somewhat uninteresting particularly when compared to metalloporphyrins. Metalloporphyrins, especially sterically hindered ones, are routinely ruffled or saddled, but the missing meso carbon apparently makes the corrole skeleton much more resistant to nonplanar distortions. Ruffling, where the pyrrole rings are alternately twisted about the M-N bonds, is energetically impossible for metallocorroles. Saddling is also uncommon; thus, a number of sterically hindered, fully substituted metallocorroles exhibit almost perfectly planar macrocycle cores. Against this backdrop, copper corroles stand out as an important exception. As a result of an energetically favorable Cu(d(x2-y2))-corrole(π) orbital interaction, copper corroles, even sterically unhindered ones, are inherently saddled. Sterically hindered substituents

  11. Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry

    DEFF Research Database (Denmark)

    Meusinger, Carl; Berhanu, Tesfaye A.; Erbland, Joseph

    2014-01-01

    Post-depositional processes alter nitrate concentration and nitrate isotopic composition in the top layers of snow at sites with low snow accumulation rates, such as Dome C, Antarctica. Available nitrate ice core records can provide input for studying past atmospheres and climate if such processes...... undergoing secondary (recombination) chemistry. Modeled NOx emissions may increase significantly above measured values due to the observed quantum yield in this study. The apparent quantum yield in the 200 nm band was found to be ∼ 1%, much lower than reported for aqueous chemistry. A companion paper...... presents an analysis of the change in isotopic composition of snowpack nitrate based on the same samples as in this study....

  12. Surface chemistry of InP quantum dots: a comprehensive study.

    Science.gov (United States)

    Cros-Gagneux, Arnaud; Delpech, Fabien; Nayral, Céline; Cornejo, Alfonso; Coppel, Yannick; Chaudret, Bruno

    2010-12-29

    Advanced (1)H, (13)C, and (31)P solution and solid-state NMR studies combined with IR spectroscopy were used to probe, at the molecular scale, the composition and the surface chemistry of indium phosphide (InP) quantum dots (QDs) prepared via a non-coordinating solvent strategy. This nanomaterial can be described as a core-multishell object: an InP core, with a zinc blende bulk structure, is surrounded first by a partially oxidized surface shell, which is itself surrounded by an organic coating. This organic passivating layer is composed, in the first coordination sphere, of tightly bound palmitate ligands which display two different bonding modes. A second coordination sphere includes an unexpected dialkyl ketone and residual long-chain non-coordinating solvents (ODE and its isomers) which interact through weak intermolecular bonds with the alkyl chains of the carboxylate ligands. We show that this ketone is formed during the synthesis process via a decarboxylative coupling route and provides oxidative conditions which are responsible for the oxidation of the InP core surface. This phenomenon has a significant impact on the photoluminescence properties of the as-synthesized QDs and probably accounts for the failure of further growth of the InP core.

  13. Programmability of the HPCS Languages: A Case Study with a Quantum Chemistry Kernel

    Energy Technology Data Exchange (ETDEWEB)

    Shet, Aniruddha G [ORNL; Elwasif, Wael R [ORNL; Harrison, Robert J [ORNL; Bernholdt, David E [ORNL

    2008-01-01

    As high-end computer systems present users with rapidly increasing numbers of processors, possibly also incorporating attached co-processors, programmers are increasingly challenged to express the necessary levels of concurrency with the dominant parallel programming model, Fortran+MPI+OpenMP (or minor variations). In this paper, we examine the languages developed under the DARPA High-Productivity Computing Systems (HPCS) program (Chapel, Fortress, and X10) as representatives of a different parallel programming model which might be more effective on coming high-performance systems. The application used in this study is the Hartree-Fock method from quantum chemistry, which combines access to distributed data with a task-parallel algorithm and is characterized by significant irregularity in the computational tasks. We present several different implementation strategies for load balancing of the task parallel computation, as well as distributed array operations, in each of the three languages. We conclude that the HPCS languages provide a wide variety of mechanisms for expressing parallelism, which can be combined at multiple levels, making them quite expressive for this problem.

  14. Programmability of the HPCS Languages: A Case Study with a Quantum Chemistry Kernel (Extended Version)

    Energy Technology Data Exchange (ETDEWEB)

    Shet, Aniruddha G [ORNL; Elwasif, Wael R [ORNL; Harrison, Robert J [ORNL; Bernholdt, David E [ORNL

    2008-04-01

    As high-end computer systems present users with rapidly increasing numbers of processors, possibly also incorporating attached co-processors, programmers are increasingly challenged to express the necessary levels of concurrency with the dominant parallel programming model, Fortran+MPI+OpenMP (or minor variations). In this paper, we examine the languages developed under the DARPA High-Productivity Computing Systems (HPCS) program (Chapel, Fortress, and X10) as representatives of a different parallel programming model which might be more effective on coming high-performance systems. The application used in this study is the Hartree-Fock method from quantum chemistry, which combines access to distributed data with a task-parallel algorithm and is characterized by significant irregularity in the computational tasks. We present several different implementation strategies for load balancing of the task parallel computation, as well as distributed array operations, in each of the three languages. We conclude that the HPCS languages provide a wide variety of mechanisms for expressing parallelism, which can be combined at multiple levels, making them quite expressive for this problem.

  15. First-principles quantum chemistry in the life sciences.

    Science.gov (United States)

    van Mourik, Tanja

    2004-12-15

    The area of computational quantum chemistry, which applies the principles of quantum mechanics to molecular and condensed systems, has developed drastically over the last decades, due to both increased computer power and the efficient implementation of quantum chemical methods in readily available computer programs. Because of this, accurate computational techniques can now be applied to much larger systems than before, bringing the area of biochemistry within the scope of electronic-structure quantum chemical methods. The rapid pace of progress of quantum chemistry makes it a very exciting research field; calculations that are too computationally expensive today may be feasible in a few months' time! This article reviews the current application of 'first-principles' quantum chemistry in biochemical and life sciences research, and discusses its future potential. The current capability of first-principles quantum chemistry is illustrated in a brief examination of computational studies on neurotransmitters, helical peptides, and DNA complexes.

  16. From Physical Chemistry to Quantum Chemistry: How Chemists Dealt with Mathematics

    OpenAIRE

    Kostas Gavroglu; Ana Simões

    2012-01-01

    Discussing the relationship of mathematics to chemistry is closely related to the emergence of physical chemistry and of quantum chemistry. We argue that, perhaps, the most significant issue that the 'mathematization of chemistry' has historically raised is not so much methodological, as it is philosophical: the discussion over the ontological status of theoretical entities which were introduced in the process. A systematic study of such an approach to the mathematization of chemistry may, pe...

  17. Computing protein infrared spectroscopy with quantum chemistry.

    Science.gov (United States)

    Besley, Nicholas A

    2007-12-15

    Quantum chemistry is a field of science that has undergone unprecedented advances in the last 50 years. From the pioneering work of Boys in the 1950s, quantum chemistry has evolved from being regarded as a specialized and esoteric discipline to a widely used tool that underpins much of the current research in chemistry today. This achievement was recognized with the award of the 1998 Nobel Prize in Chemistry to John Pople and Walter Kohn. As the new millennium unfolds, quantum chemistry stands at the forefront of an exciting new era. Quantitative calculations on systems of the magnitude of proteins are becoming a realistic possibility, an achievement that would have been unimaginable to the early pioneers of quantum chemistry. In this article we will describe ongoing work towards this goal, focusing on the calculation of protein infrared amide bands directly with quantum chemical methods.

  18. Quantum Nanobiology and Biophysical Chemistry

    DEFF Research Database (Denmark)

    2013-01-01

    An introduction was provided in the first issue by way of an Editorial to this special two issue volume of Current Physical Chemistry – “Quantum Nanobiology and Biophysical Chemistry” [1]. The Guest Editors would like to thank all the authors and referees who have contributed to this second issue....... demonstrate extremely low detection performance of acyl-homoserine lactone in a biologically relevant system using surface enhanced Raman spectroscopy. Sugihara and Bondar evaluate the influence of methyl-groups and the protein environment on retinal geometries in rhodopsin and bacteriorhodopsin, two...

  19. Exploiting Locality in Quantum Computation for Quantum Chemistry.

    Science.gov (United States)

    McClean, Jarrod R; Babbush, Ryan; Love, Peter J; Aspuru-Guzik, Alán

    2014-12-18

    Accurate prediction of chemical and material properties from first-principles quantum chemistry is a challenging task on traditional computers. Recent developments in quantum computation offer a route toward highly accurate solutions with polynomial cost; however, this solution still carries a large overhead. In this Perspective, we aim to bring together known results about the locality of physical interactions from quantum chemistry with ideas from quantum computation. We show that the utilization of spatial locality combined with the Bravyi-Kitaev transformation offers an improvement in the scaling of known quantum algorithms for quantum chemistry and provides numerical examples to help illustrate this point. We combine these developments to improve the outlook for the future of quantum chemistry on quantum computers.

  20. Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Meusinger, Carl; Johnson, Matthew S. [Department of Chemistry, University of Copenhagen, Copenhagen (Denmark); Berhanu, Tesfaye A.; Erbland, Joseph; Savarino, Joel, E-mail: jsavarino@lgge.obs.ujf-grenoble.fr [Univ. Grenoble Alpes, LGGE, F-38000 Grenoble (France); CNRS, LGGE, F-38000 Grenoble (France)

    2014-06-28

    Post-depositional processes alter nitrate concentration and nitrate isotopic composition in the top layers of snow at sites with low snow accumulation rates, such as Dome C, Antarctica. Available nitrate ice core records can provide input for studying past atmospheres and climate if such processes are understood. It has been shown that photolysis of nitrate in the snowpack plays a major role in nitrate loss and that the photolysis products have a significant influence on the local troposphere as well as on other species in the snow. Reported quantum yields for the main reaction spans orders of magnitude – apparently a result of whether nitrate is located at the air-ice interface or in the ice matrix – constituting the largest uncertainty in models of snowpack NO{sub x} emissions. Here, a laboratory study is presented that uses snow from Dome C and minimizes effects of desorption and recombination by flushing the snow during irradiation with UV light. A selection of UV filters allowed examination of the effects of the 200 and 305 nm absorption bands of nitrate. Nitrate concentration and photon flux were measured in the snow. The quantum yield for loss of nitrate was observed to decrease from 0.44 to 0.003 within what corresponds to days of UV exposure in Antarctica. The superposition of photolysis in two photochemical domains of nitrate in snow is proposed: one of photolabile nitrate, and one of buried nitrate. The difference lies in the ability of reaction products to escape the snow crystal, versus undergoing secondary (recombination) chemistry. Modeled NO{sub x} emissions may increase significantly above measured values due to the observed quantum yield in this study. The apparent quantum yield in the 200 nm band was found to be ∼1%, much lower than reported for aqueous chemistry. A companion paper presents an analysis of the change in isotopic composition of snowpack nitrate based on the same samples as in this study.

  1. Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry.

    Science.gov (United States)

    Meusinger, Carl; Berhanu, Tesfaye A; Erbland, Joseph; Savarino, Joel; Johnson, Matthew S

    2014-06-28

    Post-depositional processes alter nitrate concentration and nitrate isotopic composition in the top layers of snow at sites with low snow accumulation rates, such as Dome C, Antarctica. Available nitrate ice core records can provide input for studying past atmospheres and climate if such processes are understood. It has been shown that photolysis of nitrate in the snowpack plays a major role in nitrate loss and that the photolysis products have a significant influence on the local troposphere as well as on other species in the snow. Reported quantum yields for the main reaction spans orders of magnitude - apparently a result of whether nitrate is located at the air-ice interface or in the ice matrix - constituting the largest uncertainty in models of snowpack NOx emissions. Here, a laboratory study is presented that uses snow from Dome C and minimizes effects of desorption and recombination by flushing the snow during irradiation with UV light. A selection of UV filters allowed examination of the effects of the 200 and 305 nm absorption bands of nitrate. Nitrate concentration and photon flux were measured in the snow. The quantum yield for loss of nitrate was observed to decrease from 0.44 to 0.003 within what corresponds to days of UV exposure in Antarctica. The superposition of photolysis in two photochemical domains of nitrate in snow is proposed: one of photolabile nitrate, and one of buried nitrate. The difference lies in the ability of reaction products to escape the snow crystal, versus undergoing secondary (recombination) chemistry. Modeled NOx emissions may increase significantly above measured values due to the observed quantum yield in this study. The apparent quantum yield in the 200 nm band was found to be ∼1%, much lower than reported for aqueous chemistry. A companion paper presents an analysis of the change in isotopic composition of snowpack nitrate based on the same samples as in this study.

  2. A Quantum Chemistry Concept Inventory for Physical Chemistry Classes

    Science.gov (United States)

    Dick-Perez, Marilu; Luxford, Cynthia J.; Windus, Theresa L.; Holme, Thomas

    2016-01-01

    A 14-item, multiple-choice diagnostic assessment tool, the quantum chemistry concept inventory or QCCI, is presented. Items were developed based on published student misconceptions and content coverage and then piloted and used in advanced physical chemistry undergraduate courses. In addition to the instrument itself, data from both a pretest,…

  3. A Quantum Chemistry Concept Inventory for Physical Chemistry Classes

    Science.gov (United States)

    Dick-Perez, Marilu; Luxford, Cynthia J.; Windus, Theresa L.; Holme, Thomas

    2016-01-01

    A 14-item, multiple-choice diagnostic assessment tool, the quantum chemistry concept inventory or QCCI, is presented. Items were developed based on published student misconceptions and content coverage and then piloted and used in advanced physical chemistry undergraduate courses. In addition to the instrument itself, data from both a pretest,…

  4. Quantum chemistry simulation on quantum computers: theories and experiments.

    Science.gov (United States)

    Lu, Dawei; Xu, Boruo; Xu, Nanyang; Li, Zhaokai; Chen, Hongwei; Peng, Xinhua; Xu, Ruixue; Du, Jiangfeng

    2012-07-14

    It has been claimed that quantum computers can mimic quantum systems efficiently in the polynomial scale. Traditionally, those simulations are carried out numerically on classical computers, which are inevitably confronted with the exponential growth of required resources, with the increasing size of quantum systems. Quantum computers avoid this problem, and thus provide a possible solution for large quantum systems. In this paper, we first discuss the ideas of quantum simulation, the background of quantum simulators, their categories, and the development in both theories and experiments. We then present a brief introduction to quantum chemistry evaluated via classical computers followed by typical procedures of quantum simulation towards quantum chemistry. Reviewed are not only theoretical proposals but also proof-of-principle experimental implementations, via a small quantum computer, which include the evaluation of the static molecular eigenenergy and the simulation of chemical reaction dynamics. Although the experimental development is still behind the theory, we give prospects and suggestions for future experiments. We anticipate that in the near future quantum simulation will become a powerful tool for quantum chemistry over classical computations.

  5. Density functional theory in quantum chemistry

    CERN Document Server

    Tsuneda, Takao

    2014-01-01

    This book examines density functional theory based on the foundation of quantum chemistry. Unconventional in approach, it reviews basic concepts, then describes the physical meanings of state-of-the-art exchange-correlation functionals and their corrections.

  6. The Application of SCC-DV-Xα Computational Method of Quantum Chemistry in Cement Chemistry

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    It has been explored why quantum chemistry is applied to the research field of cement chemistry. The fundamental theory of SCC-DV-Xα computational method of quantum chemistry is synopsized. The results obtained by computational quantum chemistry method in recent years of valence-bond structures and hydration activity of some cement clinker minerals, mechanical strength and stabilization of some hydrates are summarized and evaluated. Finally the prospects of the future application of quantum chemistry to cement chemistry are depicted.

  7. Simulating chemistry using quantum computers

    CERN Document Server

    Kassal, Ivan; Perdomo-Ortiz, Alejandro; Yung, Man-Hong; Aspuru-Guzik, Alán

    2010-01-01

    The difficulty of simulating quantum systems, well-known to quantum chemists, prompted the idea of quantum computation. One can avoid the steep scaling associated with the exact simulation of increasingly large quantum systems on conventional computers, by mapping the quantum system to another, more controllable one. In this review, we discuss to what extent the ideas in quantum computation, now a well-established field, have been applied to chemical problems. We describe algorithms that achieve significant advantages for the electronic-structure problem, the simulation of chemical dynamics, protein folding, and other tasks. Although theory is still ahead of experiment, we outline recent advances that have led to the first chemical calculations on small quantum information processors.

  8. Simulating chemistry using quantum computers.

    Science.gov (United States)

    Kassal, Ivan; Whitfield, James D; Perdomo-Ortiz, Alejandro; Yung, Man-Hong; Aspuru-Guzik, Alán

    2011-01-01

    The difficulty of simulating quantum systems, well known to quantum chemists, prompted the idea of quantum computation. One can avoid the steep scaling associated with the exact simulation of increasingly large quantum systems on conventional computers, by mapping the quantum system to another, more controllable one. In this review, we discuss to what extent the ideas in quantum computation, now a well-established field, have been applied to chemical problems. We describe algorithms that achieve significant advantages for the electronic-structure problem, the simulation of chemical dynamics, protein folding, and other tasks. Although theory is still ahead of experiment, we outline recent advances that have led to the first chemical calculations on small quantum information processors.

  9. Towards quantum chemistry on a quantum computer.

    Science.gov (United States)

    Lanyon, B P; Whitfield, J D; Gillett, G G; Goggin, M E; Almeida, M P; Kassal, I; Biamonte, J D; Mohseni, M; Powell, B J; Barbieri, M; Aspuru-Guzik, A; White, A G

    2010-02-01

    Exact first-principles calculations of molecular properties are currently intractable because their computational cost grows exponentially with both the number of atoms and basis set size. A solution is to move to a radically different model of computing by building a quantum computer, which is a device that uses quantum systems themselves to store and process data. Here we report the application of the latest photonic quantum computer technology to calculate properties of the smallest molecular system: the hydrogen molecule in a minimal basis. We calculate the complete energy spectrum to 20 bits of precision and discuss how the technique can be expanded to solve large-scale chemical problems that lie beyond the reach of modern supercomputers. These results represent an early practical step toward a powerful tool with a broad range of quantum-chemical applications.

  10. Quantum chemistry study of molecular structure and vibrational spectrum of naproxen.

    Science.gov (United States)

    Liu, Lekun; Gao, Hongwei

    2012-02-01

    The purpose of this research was to compare the performance of different DFT methods at different basis sets in predicting geometry and vibrational spectrum of naproxen. The molecular structure and infrared spectrum of naproxen was studied. Quantum chemical calculations using density functional theory (DFT) with functions LSDA, B3LYP, B3PW91, BPV86, mPW1PW91 and PBEPBE at various basis set levels (LANL2DZ, SDD, 3-21G, 6-31G, 6-311G and STO-3G) were performed. The computed result indicates that LSDA/6-311G level is distinctly superior to all the remaining DFT methods in predicting molecular structure of naproxen. The vibrational spectral analysis indicates the LSDA/3-21G level and LSDA/6-311G level are both better than the other methods at all the remaining basis sets.

  11. Alternative algebraic approaches in quantum chemistry

    Science.gov (United States)

    Mezey, Paul G.

    2015-01-01

    Various algebraic approaches of quantum chemistry all follow a common principle: the fundamental properties and interrelations providing the most essential features of a quantum chemical representation of a molecule or a chemical process, such as a reaction, can always be described by algebraic methods. Whereas such algebraic methods often provide precise, even numerical answers, nevertheless their main role is to give a framework that can be elaborated and converted into computational methods by involving alternative mathematical techniques, subject to the constraints and directions provided by algebra. In general, algebra describes sets of interrelations, often phrased in terms of algebraic operations, without much concern with the actual entities exhibiting these interrelations. However, in many instances, the very realizations of two, seemingly unrelated algebraic structures by actual quantum chemical entities or properties play additional roles, and unexpected connections between different algebraic structures are often giving new insight. Here we shall be concerned with two alternative algebraic structures: the fundamental group of reaction mechanisms, based on the energy-dependent topology of potential energy surfaces, and the interrelations among point symmetry groups for various distorted nuclear arrangements of molecules. These two, distinct algebraic structures provide interesting interrelations, which can be exploited in actual studies of molecular conformational and reaction processes. Two relevant theorems will be discussed.

  12. Adiabatic quantum simulation of quantum chemistry.

    Science.gov (United States)

    Babbush, Ryan; Love, Peter J; Aspuru-Guzik, Alán

    2014-10-13

    We show how to apply the quantum adiabatic algorithm directly to the quantum computation of molecular properties. We describe a procedure to map electronic structure Hamiltonians to 2-body qubit Hamiltonians with a small set of physically realizable couplings. By combining the Bravyi-Kitaev construction to map fermions to qubits with perturbative gadgets to reduce the Hamiltonian to 2-body, we obtain precision requirements on the coupling strengths and a number of ancilla qubits that scale polynomially in the problem size. Hence our mapping is efficient. The required set of controllable interactions includes only two types of interaction beyond the Ising interactions required to apply the quantum adiabatic algorithm to combinatorial optimization problems. Our mapping may also be of interest to chemists directly as it defines a dictionary from electronic structure to spin Hamiltonians with physical interactions.

  13. The Study on Application of Quantum Chemistry Software%量子化学软件的应用研究

    Institute of Scientific and Technical Information of China (English)

    郭瑞萍; 刘旭光

    2009-01-01

    量化软件的引入对学生学习、理解、应用起到积极作用,激发了学生的学习动机,便于教师调整教学内容和进度, 优化教学过程.通过变分法在Gaussian软件包中的体现、Gaussian软件计算O2+,O2,和O2-的键长,对比键级的结果以及σ-π反馈键三个具体实例说明量子化学软件在教学中的应用,以及应用中的注意原则.%The introduction of quantum chemistry program into the teaching of Structural Chemistry not only plays a positive role for students to learn, understand and apply the Structural Chemistry course but also stimulates students' motivation.This is helpful for teachers to adjust teaching contents and progresses and optimize teaching procedure.The application and its rules of quantum chemistry program in Structural Chemistry are also illustrated by practical examples.

  14. A quantum chemistry study for ionic liquids applied to gas capture and separation.

    Science.gov (United States)

    Damas, Giane B; Dias, Amina B A; Costa, Luciano T

    2014-07-31

    In recent years, the global climate change is in evidence and it is almost a consensus that it is caused by the greenhouse gases emissions. An alternative to reduce these emissions is carbon capture and storage (CCS), which employs solvents based on amine compounds. In this scene, ionic liquids (IL) have been investigated to a greater extent for this application. In this work, we make an evaluation of interactions between gases (CO2, SO2, and H2S) and anion/cation from IL, as well as cation-anion interactions. For this, quantum calculations under vacuum were performed at the B3LYP/6-311+G** level of theory and using the M06-2X functional, where dispersion effects are considered. Among the well-studied systems based on imidazolium cations and fluorinated anions, we also studied the tetraalkylammonium, tetraalkylphosphonium, ether-functionalized imidazolium based systems, and tetrahexylammonium bis(trifluoromethanesulfonyl)imide, [THA][Tf2N], as a potential prototype. The ion pairs evaluated include [Tf2N](-)-based IL, with alkyl chain varying from [C1mim](+) to [C8mim](+) and [C1mim](+)-based IL. We found that the anion becomes more available to interact with gas with the weakening of the cation-anion interaction. [THA][Tf2N] has a binding energy of -274.89 kJ/mol at the B3LYP/6-311+G** level of theory, which is considered energetically interesting to gas capture applications.

  15. Quantum chemistry and charge transport in biomolecules with superconducting circuits

    Science.gov (United States)

    García-Álvarez, L.; Las Heras, U.; Mezzacapo, A.; Sanz, M.; Solano, E.; Lamata, L.

    2016-06-01

    We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we optimally digitize fermionic models of molecular structure with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects.

  16. Quantum chemistry and charge transport in biomolecules with superconducting circuits

    Science.gov (United States)

    García-Álvarez, L.; Las Heras, U.; Mezzacapo, A.; Sanz, M.; Solano, E.; Lamata, L.

    2016-01-01

    We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we optimally digitize fermionic models of molecular structure with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects. PMID:27324814

  17. Quantum chemistry and charge transport in biomolecules with superconducting circuits.

    Science.gov (United States)

    García-Álvarez, L; Las Heras, U; Mezzacapo, A; Sanz, M; Solano, E; Lamata, L

    2016-06-21

    We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we optimally digitize fermionic models of molecular structure with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects.

  18. Semi-Empirical Quantum Chemistry Method for Pre-Polymerization Rational Design of Ciprofloxacin Imprinted Polymer and Adsorption Studies

    OpenAIRE

    Marestoni,Luiz D.; Wong,Ademar; Feliciano, Gustavo T.; Marchi,Mary R. R.; Tarley, César R. T.; Sotomayor,Maria D. P. T.

    2016-01-01

    It is well known that selectivity of molecularly imprinted polymers (MIPs) depends on adequate choice of functional monomer before the experimental synthesis. Computational simulation seems to be an ideal way to produce selective MIPs. In this work, we have proposed the use of semi-empirical simulation to obtain the best monomer able to strongly interact with ciprofloxacin. Twenty functional monomers were evaluated through semi-empirical quantum chemistry method and three MIPs were synthesize...

  19. Visually impaired researchers get their hands on quantum chemistry: application to a computational study on the isomerization of a sterol.

    Science.gov (United States)

    Lounnas, Valère; Wedler, Henry B; Newman, Timothy; Schaftenaar, Gijs; Harrison, Jason G; Nepomuceno, Gabriella; Pemberton, Ryan; Tantillo, Dean J; Vriend, Gert

    2014-11-01

    In molecular sciences, articles tend to revolve around 2D representations of 3D molecules, and sighted scientists often resort to 3D virtual reality software to study these molecules in detail. Blind and visually impaired (BVI) molecular scientists have access to a series of audio devices that can help them read the text in articles and work with computers. Reading articles published in this journal, though, is nearly impossible for them because they need to generate mental 3D images of molecules, but the article-reading software cannot do that for them. We have previously designed AsteriX, a web server that fully automatically decomposes articles, detects 2D plots of low molecular weight molecules, removes meta data and annotations from these plots, and converts them into 3D atomic coordinates. AsteriX-BVI goes one step further and converts the 3D representation into a 3D printable, haptic-enhanced format that includes Braille annotations. These Braille-annotated physical 3D models allow BVI scientists to generate a complete mental model of the molecule. AsteriX-BVI uses Molden to convert the meta data of quantum chemistry experiments into BVI friendly formats so that the entire line of scientific information that sighted people take for granted-from published articles, via printed results of computational chemistry experiments, to 3D models-is now available to BVI scientists too. The possibilities offered by AsteriX-BVI are illustrated by a project on the isomerization of a sterol, executed by the blind co-author of this article (HBW).

  20. Quantum Mechanics in Chemistry (by Jack Simons and Jeff Nichols)

    Science.gov (United States)

    McCallum, C. Michael

    1998-12-01

    Topics in Physical Chemistry Series. Oxford University Press: New York, 1997. xxiii + 612 pp. Illustrations. ISBN 0-19-508200-1. $75.00. One of the problems faced by graduate-level quantum mechanics courses in chemistry is that there is often little time for studying chemical problems. Students must learn so much matrix algebra and notation that a first-semester course seems more like a math or physics course than chemistry. Another problem is the focus of most graduate texts. Excellent texts, such as those by Sakurai, and older treatments, such as Messiah and Cohen-Tannoudji, offer a comprehensive amount of mathematical rigor to go along with chemistry problems, but it seems the intended audience is hard-core theoretical or physical chemistry students. Requirements that are more general, such as reaction-path dynamics, structure and term symbols, and symmetry in quantum mechanical problems, are often left behind. Schatz and Ratner's Book Quantum Mechanics in Chemistry (Prentice Hall) is one book that fills this gap (at least for second-semester students); Simons and Nichols' new book is another, but it is a book that requires revision before it can be seriously considered.

  1. Quantum theory and chemistry: Two propositions

    Science.gov (United States)

    Aronowitz, S.

    1980-01-01

    Two propositions concerning quantum chemistry are proposed. First, it is proposed that the nonrelativistic Schroedinger equation, where the Hamiltonian operator is associated with an assemblage of nuclei and electrons, can never be arranged to yield specific molecules in the chemists' sense. It is argued that this result is a necessary condition if the Schroedinger has relevancy to chemistry. Second, once a system is in a particular state with regard to interactions among its components (the assemblage of nuclei and electrons), it cannot spontaneously eliminate any of those interactions. This leads to a subtle form of irreversibility.

  2. Orbital entanglement in quantum chemistry

    CERN Document Server

    Boguslawski, Katharina

    2014-01-01

    The basic concepts of orbital entanglement and its application to chemistry are briefly reviewed. The calculation of orbital entanglement measures from correlated wavefunctions is discussed in terms of reduced $n$-particle density matrices. Possible simplifications in their evaluation are highlighted in case of seniority-zero wavefunctions. Specifically, orbital entanglement allows us to dissect electron correlation effects in its strong and weak contributions, to determine bond orders, to assess the quality and stability of active space calculations, to monitor chemical reactions, and to identify points along the reaction coordinate where electronic wavefunctions change drastically. Thus, orbital entanglement represents a useful and intuitive tool to interpret complex electronic wavefunctions and to facilitate a qualitative understanding of electronic structure and how it changes in chemical processes.

  3. Quantum Dots: An Experiment for Physical or Materials Chemistry

    Science.gov (United States)

    Winkler, L. D.; Arceo, J. F.; Hughes, W. C.; DeGraff, B. A.; Augustine, B. H.

    2005-01-01

    An experiment is conducted for obtaining quantum dots for physical or materials chemistry. This experiment serves to both reinforce the basic concept of quantum confinement and providing a useful bridge between the molecular and solid-state world.

  4. Study of photochemical transformations of organic azides by matrix isolation techniques and quantum chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Gritsan, N P [Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

    2007-12-31

    Results of investigations of organic azide photochemistry in inert gas matrices and the most important spectroscopic studies of the last decade, which formed the basis for the modern views on the photochemistry of azides, are analysed. The unique potential of the matrix isolation technique for the reliable identification of reaction intermediates is demonstrated.

  5. Inverse Quantum Chemistry: Concepts and Strategies for Rational Compound Design

    CERN Document Server

    Weymuth, Thomas

    2014-01-01

    The rational design of molecules and materials is becoming more and more important. With the advent of powerful computer systems and sophisticated algorithms, quantum chemistry plays an important role in rational design. While traditional quantum chemical approaches predict the properties of a predefined molecular structure, the goal of inverse quantum chemistry is to find a structure featuring one or more desired properties. Herein, we review inverse quantum chemical approaches proposed so far and discuss their advantages as well as their weaknesses.

  6. Carrier mobility in double-helix DNA and RNA: A quantum chemistry study with Marcus-Hush theory

    Science.gov (United States)

    Wu, Tao; Sun, Lei; Shi, Qi; Deng, Kaiming; Deng, Weiqiao; Lu, Ruifeng

    2016-12-01

    Charge mobilities of six DNAs and RNAs have been computed using quantum chemistry calculation combined with the Marcus-Hush theory. Based on this simulation model, we obtained quite reasonable results when compared with the experiment, and the obtained charge mobility strongly depends on the molecular reorganization and electronic coupling. Besides, we find that hole mobilities are larger than electron mobilities no matter in DNAs or in RNAs, and the hole mobility of 2L8I can reach 1.09 × 10-1 cm2 V-1 s-1 which can be applied in the molecular wire. The findings also show that our theoretical model can be regarded as a promising candidate for screening DNA- and RNA-based molecular electronic devices.

  7. Carrier mobility in double-helix DNA and RNA: A quantum chemistry study with Marcus-Hush theory.

    Science.gov (United States)

    Wu, Tao; Sun, Lei; Shi, Qi; Deng, Kaiming; Deng, Weiqiao; Lu, Ruifeng

    2016-12-21

    Charge mobilities of six DNAs and RNAs have been computed using quantum chemistry calculation combined with the Marcus-Hush theory. Based on this simulation model, we obtained quite reasonable results when compared with the experiment, and the obtained charge mobility strongly depends on the molecular reorganization and electronic coupling. Besides, we find that hole mobilities are larger than electron mobilities no matter in DNAs or in RNAs, and the hole mobility of 2L8I can reach 1.09 × 10(-1) cm(2) V(-1) s(-1) which can be applied in the molecular wire. The findings also show that our theoretical model can be regarded as a promising candidate for screening DNA- and RNA-based molecular electronic devices.

  8. Theoretical study of interactions between human adult hemoglobin and acetate ion by polarizable force field and fragmentation quantum chemistry methods

    Institute of Scientific and Technical Information of China (English)

    YAN XiuFen; JIANG Nan; MA Jing

    2009-01-01

    A series of theoretical approaches,including conventional FF03 and FF03-based polarization model,as well as the generalized energy-based fragmentation (GEBF) quantum chemistry method,have been applied to investigate the interactions between acetate ion (CH_3COO~-) and the α-subunit of human adult hemoglobin (designated as Hb-α) at four binding sites (Lys16,Lys90,Arg92,and Lys127),respectively.The FF03-based polarizable force fields show that the interaction energies between the CH_3COO~-group and Hb-α follow the trend of Arg92>Lys127>Lys90>Lys16.The complexation of CH_3COO~-with Hb-α is governed by the long-range electrostatic interactions and steric effect.

  9. Theoretical study of interactions between human adult hemoglobin and acetate ion by polarizable force field and fragmentation quantum chemistry methods

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    A series of theoretical approaches,including conventional FF03 and FF03-based polarization model,as well as the generalized energy-based fragmentation(GEBF) quantum chemistry method,have been applied to investigate the interactions between acetate ion(CH3COO-) and the α-subunit of human adult hemoglobin(designated as Hb-α) at four binding sites(Lys16,Lys90,Arg92,and Lys127),respectively.The FF03-based polarizable force fields show that the interaction energies between the CH3COO-group and Hb-α follow the trend of Arg92>Lys127>Lys90>Lys16.The complexation of CH3COO-with Hb-α is governed by the long-range electrostatic interactions and steric effect.

  10. Electron diffraction study of the equilibrium structure of hexamethylenetetramine involving data from quantum chemistry and vibrational spectroscopy

    Science.gov (United States)

    Khaikin, L. S.; Grikina, O. E.; Karasev, N. M.; Kovtun, D. M.; Kochikov, I. V.

    2014-04-01

    The equilibrium structure of the urotropine molecule is characterized by means of gas electron diffraction (GED) with the involvement of quantum chemistry and vibrational spectroscopy. A structural analysis of the GED data is performed based on the parameters of the intramolecular potential function using of the program complex SYMM/DISP/ELDIFF/LARGE. The quadratic and cubic force constants of the urotropine molecule were obtained earlier on the basis of calculations at the MP2(full)/cc-pVTZ level and assuming molecular symmetry T d . The values of the equilibrium geometric parameters r e of the urotropine molecule are found. The experimental structural parameters are in good agreement with those calculated at the MP2(full)/cc-pVTZ level.

  11. Primary Reactions of the LOV2 Domain of Phototropin Studied with Ultrafast Mid-Infrared Spectroscopy and Quantum Chemistry

    Science.gov (United States)

    Alexandre, Maxime T.A.; Domratcheva, Tatiana; Bonetti, Cosimo; van Wilderen, Luuk J.G.W.; van Grondelle, Rienk; Groot, Marie-Louise; Hellingwerf, Klaas J.; Kennis, John T.M.

    2009-01-01

    Abstract Phototropins, major blue-light receptors in plants, are sensitive to blue light through a pair of flavin mononucleotide (FMN)-binding light oxygen and voltage (LOV) domains, LOV1 and LOV2. LOV2 undergoes a photocycle involving light-driven covalent adduct formation between a conserved cysteine and the FMN C(4a) atom. Here, the primary reactions of Avena sativa phototropin 1 LOV2 (AsLOV2) were studied using ultrafast mid-infrared spectroscopy and quantum chemistry. The singlet excited state (S1) evolves into the triplet state (T1) with a lifetime of 1.5 ns at a yield of ∼50%. The infrared signature of S1 is characterized by absorption bands at 1657 cm−1, 1495–1415 cm−1, and 1375 cm−1. The T1 state shows infrared bands at 1657 cm−1, 1645 cm−1, 1491–1438 cm−1, and 1390 cm−1. For both electronic states, these bands are assigned principally to C=O, C=N, C-C, and C-N stretch modes. The overall downshifting of C=O and C=N bond stretch modes is consistent with an overall bond-order decrease of the conjugated isoalloxazine system upon a π-π∗ transition. The configuration interaction singles (CIS) method was used to calculate the vibrational spectra of the S1 and T1 excited ππ∗ states, as well as respective electronic energies, structural parameters, electronic dipole moments, and intrinsic force constants. The harmonic frequencies of S1 and T1, as calculated by the CIS method, are in satisfactory agreement with the evident band positions and intensities. On the other hand, CIS calculations of a T1 cation that was protonated at the N(5) site did not reproduce the experimental FMN T1 spectrum. We conclude that the FMN T1 state remains nonprotonated on a nanosecond timescale, which rules out an ionic mechanism for covalent adduct formation involving cysteine-N(5) proton transfer on this timescale. Finally, we observed a heterogeneous population of singly and doubly H-bonded FMN C(4)=O conformers in the dark state, with stretch frequencies

  12. Disciplines, models, and computers: the path to computational quantum chemistry.

    Science.gov (United States)

    Lenhard, Johannes

    2014-12-01

    Many disciplines and scientific fields have undergone a computational turn in the past several decades. This paper analyzes this sort of turn by investigating the case of computational quantum chemistry. The main claim is that the transformation from quantum to computational quantum chemistry involved changes in three dimensions. First, on the side of instrumentation, small computers and a networked infrastructure took over the lead from centralized mainframe architecture. Second, a new conception of computational modeling became feasible and assumed a crucial role. And third, the field of computa- tional quantum chemistry became organized in a market-like fashion and this market is much bigger than the number of quantum theory experts. These claims will be substantiated by an investigation of the so-called density functional theory (DFT), the arguably pivotal theory in the turn to computational quantum chemistry around 1990.

  13. Steps toward fault-tolerant quantum chemistry.

    Energy Technology Data Exchange (ETDEWEB)

    Taube, Andrew Garvin

    2010-05-01

    Developing quantum chemistry programs on the coming generation of exascale computers will be a difficult task. The programs will need to be fault-tolerant and minimize the use of global operations. This work explores the use a task-based model that uses a data-centric approach to allocate work to different processes as it applies to quantum chemistry. After introducing the key problems that appear when trying to parallelize a complicated quantum chemistry method such as coupled-cluster theory, we discuss the implications of that model as it pertains to the computational kernel of a coupled-cluster program - matrix multiplication. Also, we discuss the extensions that would required to build a full coupled-cluster program using the task-based model. Current programming models for high-performance computing are fault-intolerant and use global operations. Those properties are unsustainable as computers scale to millions of CPUs; instead one must recognize that these systems will be hierarchical in structure, prone to constant faults, and global operations will be infeasible. The FAST-OS HARE project is introducing a scale-free computing model to address these issues. This model is hierarchical and fault-tolerant by design, allows for the clean overlap of computation and communication, reducing the network load, does not require checkpointing, and avoids the complexity of many HPC runtimes. Development of an algorithm within this model requires a change in focus from imperative programming to a data-centric approach. Quantum chemistry (QC) algorithms, in particular electronic structure methods, are an ideal test bed for this computing model. These methods describe the distribution of electrons in a molecule, which determine the properties of the molecule. The computational cost of these methods is high, scaling quartically or higher in the size of the molecule, which is why QC applications are major users of HPC resources. The complexity of these algorithms means that

  14. Quantum chemistry-assisted synthesis route development

    Energy Technology Data Exchange (ETDEWEB)

    Hori, Kenji; Sumimoto, Michinori [Graduate School of Science and Engineering, Yamaguchi University, Tokiwadai, Ube, Yamaguchi 755-8611 (Japan); Murafuji, Toshihiro [Graduate School of Medicine, Yamaguchi University, Yamaguchi, Yamaguchi 753-8512 (Japan)

    2015-12-31

    We have been investigating “quantum chemistry-assisted synthesis route development” using in silico screenings and applied the method to several targets. Another example was conducted to develop synthesis routes for a urea derivative, namely 1-(4-(trifluoromethyl)-2-oxo-2H-chromen-7-yl)urea. While five synthesis routes were examined, only three routes passed the second in silico screening. Among them, the reaction of 7-amino-4-(trifluoromethyl)-2H-chromen-2-one and O-methyl carbamate with BF{sub 3} as an additive was ranked as the first choice for synthetic work. We were able to experimentally obtain the target compound even though its yield was as low as 21 %. The theoretical result was thus consistent with that observed. The summary of transition state data base (TSDB) is also provided. TSDB is the key to reducing time of in silico screenings.

  15. Virtually going green: The role of quantum computational chemistry in reducing pollution and toxicity in chemistry

    Science.gov (United States)

    Stevens, Jonathan

    2017-07-01

    Continuing advances in computational chemistry has permitted quantum mechanical calculation to assist in research in green chemistry and to contribute to the greening of chemical practice. Presented here are recent examples illustrating the contribution of computational quantum chemistry to green chemistry, including the possibility of using computation as a green alternative to experiments, but also illustrating contributions to greener catalysis and the search for greener solvents. Examples of applications of computation to ambitious projects for green synthetic chemistry using carbon dioxide are also presented.

  16. From transistor to trapped-ion computers for quantum chemistry.

    Science.gov (United States)

    Yung, M-H; Casanova, J; Mezzacapo, A; McClean, J; Lamata, L; Aspuru-Guzik, A; Solano, E

    2014-01-07

    Over the last few decades, quantum chemistry has progressed through the development of computational methods based on modern digital computers. However, these methods can hardly fulfill the exponentially-growing resource requirements when applied to large quantum systems. As pointed out by Feynman, this restriction is intrinsic to all computational models based on classical physics. Recently, the rapid advancement of trapped-ion technologies has opened new possibilities for quantum control and quantum simulations. Here, we present an efficient toolkit that exploits both the internal and motional degrees of freedom of trapped ions for solving problems in quantum chemistry, including molecular electronic structure, molecular dynamics, and vibronic coupling. We focus on applications that go beyond the capacity of classical computers, but may be realizable on state-of-the-art trapped-ion systems. These results allow us to envision a new paradigm of quantum chemistry that shifts from the current transistor to a near-future trapped-ion-based technology.

  17. Quantum information and computation for chemistry

    CERN Document Server

    Kais, Sabre; Rice, Stuart A

    2014-01-01

    Examines the intersection of quantum information and chemical physics The Advances in Chemical Physics series is dedicated to reviewing new and emerging topics as well as the latest developments in traditional areas of study in the field of chemical physics. Each volume features detailed comprehensive analyses coupled with individual points of view that integrate the many disciplines of science that are needed for a full understanding of chemical physics. This volume of the series explores the latest research findings, applications, and new research paths from the quantum information science

  18. Monte Carlo methods in AB initio quantum chemistry quantum Monte Carlo for molecules

    CERN Document Server

    Lester, William A; Reynolds, PJ

    1994-01-01

    This book presents the basic theory and application of the Monte Carlo method to the electronic structure of atoms and molecules. It assumes no previous knowledge of the subject, only a knowledge of molecular quantum mechanics at the first-year graduate level. A working knowledge of traditional ab initio quantum chemistry is helpful, but not essential.Some distinguishing features of this book are: Clear exposition of the basic theory at a level to facilitate independent study. Discussion of the various versions of the theory: diffusion Monte Carlo, Green's function Monte Carlo, and release n

  19. Solutions to selected exercise problems in quantum chemistry and spectroscopy

    DEFF Research Database (Denmark)

    Spanget-Larsen, Jens

    2016-01-01

    Suggested solutions to a number of problems from the collection "Exercise Problems in Quantum Chemistry and Spectroscopy", previously published on ResearchGate (DOI: 10.13140/RG.2.1.4024.8162).......Suggested solutions to a number of problems from the collection "Exercise Problems in Quantum Chemistry and Spectroscopy", previously published on ResearchGate (DOI: 10.13140/RG.2.1.4024.8162)....

  20. Solutions to selected exercise problems in quantum chemistry and spectroscopy

    DEFF Research Database (Denmark)

    Spanget-Larsen, Jens

    2016-01-01

    Suggested solutions to a number of problems from the collection "Exercise Problems in Quantum Chemistry and Spectroscopy", previously published on ResearchGate (DOI: 10.13140/RG.2.1.4024.8162).......Suggested solutions to a number of problems from the collection "Exercise Problems in Quantum Chemistry and Spectroscopy", previously published on ResearchGate (DOI: 10.13140/RG.2.1.4024.8162)....

  1. Whole-Parts Strategies in Quantum Chemistry: Some Philosophical and Mereological Lessons

    Directory of Open Access Journals (Sweden)

    Jean-Pierre Llored

    2014-12-01

    Full Text Available Philosophers mainly refer to quantum chemistry in order to address questions about the reducibility or autonomy of chemistry relative to quantum physics, and to argue for or against ontological emergence. To make their point, they scrutinize quantum approximations and formalisms as if they were independent of the questions at stake. This paper proposes a return to history and to the laboratory so as to emphasize how quantum chemists never cease to negotiate the relationships between a molecule, its parts, and its environment. This investigation will enable us to draw methodological conclusions about the role of history within philosophical studies, and to examine how quantum chemistry can clarify important philosophical and mereological issues related to the emergence/reduction debate, or to the way instruments and contexts are involved in the material making and the formal description of wholes and parts.

  2. The many roles of quantum chemical predictions in synthetic organic chemistry.

    Science.gov (United States)

    Nguyen, Quynh Nhu N; Tantillo, Dean J

    2014-03-01

    This account discusses representative case studies for various applications of quantum chemical calculations in synthetic organic chemistry. These include confirmation of target structures, methodology development, and catalyst design. These examples demonstrate how predictions from quantum chemical calculations can be utilized to streamline synthetic efforts.

  3. The Dalton quantum chemistry program system

    DEFF Research Database (Denmark)

    Aidas, Kestutis; Angeli, C.; Bak, K.L.

    2014-01-01

    Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree–Fock, Kohn–Sham, multiconfigurational self-consistent-field, Møller–Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide vari......-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from http://www.daltonprogram.org for a number of UNIX platforms....

  4. Fuzzy electron density fragments in macromolecular quantum chemistry, combinatorial quantum chemistry, functional group analysis, and shape-activity relations.

    Science.gov (United States)

    Mezey, Paul G

    2014-09-16

    Conspectus Just as complete molecules have no boundaries and have "fuzzy" electron density clouds approaching zero density exponentially at large distances from the nearest nucleus, a physically justified choice for electron density fragments exhibits similar behavior. Whereas fuzzy electron densities, just as any fuzzy object, such as a thicker cloud on a foggy day, do not lend themselves to easy visualization, one may partially overcome this by using isocontours. Whereas a faithful representation of the complete fuzzy density would need infinitely many such isocontours, nevertheless, by choosing a selected few, one can still obtain a limited pictorial representation. Clearly, such images are of limited value, and one better relies on more complete mathematical representations, using, for example, density matrices of fuzzy fragment densities. A fuzzy density fragmentation can be obtained in an exactly additive way, using the output from any of the common quantum chemical computational techniques, such as Hartree-Fock, MP2, and various density functional approaches. Such "fuzzy" electron density fragments properly represented have proven to be useful in a rather wide range of applications, for example, (a) using them as additive building blocks leading to efficient linear scaling macromolecular quantum chemistry computational techniques, (b) the study of quantum chemical functional groups, (c) using approximate fuzzy fragment information as allowed by the holographic electron density theorem, (d) the study of correlations between local shape and activity, including through-bond and through-space components of interactions between parts of molecules and relations between local molecular shape and substituent effects, (e) using them as tools of density matrix extrapolation in conformational changes, (f) physically valid averaging and statistical distribution of several local electron densities of common stoichiometry, useful in electron density databank mining, for

  5. A quantum chemistry study on the performance of porphyrin-based solar cell sensitisers; Zinc and anchor group position effects

    Science.gov (United States)

    Arkan, Foroogh; Izadyar, Mohammad; Nakhaeipour, Ali

    2015-12-01

    In this work, ten porphyrin derivatives, including free-base zinc-metalised compounds were studied by varying the position of the carboxyl anchoring group and the alkyl substituents length on the remaining three phenyl rings with the aim of the cell efficiency investigation. Theoretical performances of the sensitisers in the dye-sensitised solar cell systems have been discussed by analysis of the optical absorption, the oxidised potential of ground and excited states, light-harvesting efficiency and electron injection efficiency. Due to lower symmetry of free-based porphyrins, they showed broader bands than zinc porphyrins. The second group sensitisers are better than the first one due to the smaller oxidation potential energy, higher open-circuit voltage and light-harvesting efficiency. The influence of long alkyl substituents on the photovoltaic parameters is not perceptible but ortho and meta positions of anchoring group modify the solar cell performance. Finally, some correlations between the quantum reactivity indices and photovoltaic parameters have obtained and discussed.

  6. Design, synthesis and bioactivity of novel ALS enzyme inhibitors (II)——Molecular mechanics, quantum chemistry and structure-activity relationship studies on the herbicidal heterocyclic sulfonamide

    Institute of Scientific and Technical Information of China (English)

    陆荣健; 杨华铮; 尚贞锋; 汪惟为; 潘荫明; 赵学庄

    1996-01-01

    In view of quantum pharmacology, the structure-activity relationships of different kinds of fused heterocydic sulfonamides with the same mode of action were first investigated using molecular mechanics, quantum chemistry and discriminatory analysis. It has been found that the process of the interaction of the fused heterocydic sulfonamide with ALS enzyme involves the electropositive region of the sulfonyl bridge chain and the electronegative region of the heterocydic moiety. The herbicidal activity is related to the potency of electric charge translocation of the related regions.

  7. The density matrix renormalization group for ab initio quantum chemistry

    CERN Document Server

    Wouters, Sebastian

    2014-01-01

    During the past 15 years, the density matrix renormalization group (DMRG) has become increasingly important for ab initio quantum chemistry. Its underlying wavefunction ansatz, the matrix product state (MPS), is a low-rank decomposition of the full configuration interaction tensor. The virtual dimension of the MPS, the rank of the decomposition, controls the size of the corner of the many-body Hilbert space that can be reached with the ansatz. This parameter can be systematically increased until numerical convergence is reached. The MPS ansatz naturally captures exponentially decaying correlation functions. Therefore DMRG works extremely well for noncritical one-dimensional systems. The active orbital spaces in quantum chemistry are however often far from one-dimensional, and relatively large virtual dimensions are required to use DMRG for ab initio quantum chemistry (QC-DMRG). The QC-DMRG algorithm, its computational cost, and its properties are discussed. Two important aspects to reduce the computational co...

  8. Quantum-State-Resolved Ion-Molecule Chemistry

    Science.gov (United States)

    Chen, Gary; Yang, Tiangang; Campbell, Wesley; Hudson, Eric

    2016-05-01

    We propose a method to achieve quantum-state-resolved ion-molecule chemistry by utilizing cryogenic buffer gas cooling techniques and a combination of ion imaging and mass spectrometry of targets in an RF Paul trap. Cold molecular species produced by a cryogenic buffer gas beam (CBGB) are introduced to target ion species in an linear quadrupole trap (LQT) where ion imaging techniques and time of flight mass spectrometry (ToF) are then used to observe the target ions and the charged reaction products [1,2]. By taking advantage of the large ion-neutral interaction cross sections and characteristically long ion trap lifetimes, we can utilize the precision control over quantum states allowed by an ion trap to resolve state-to-state quantum chemical reactions without high-density molecular sample production, well within proposed capabilities. The combination of these two very general cold species production techniques allows for production and observation of a broad range of ion-neutral reactions. We initially plan to study chemical reactions between sympathetically cooled carbon ions (via laser cooled beryllium ions) with buffer gas cooled water. This work is supported by the US Air Force Office of Scientific Research.

  9. Computational quantum chemistry and adaptive ligand modeling in mechanistic QSAR.

    Science.gov (United States)

    De Benedetti, Pier G; Fanelli, Francesca

    2010-10-01

    Drugs are adaptive molecules. They realize this peculiarity by generating different ensembles of prototropic forms and conformers that depend on the environment. Among the impressive amount of available computational drug discovery technologies, quantitative structure-activity relationship approaches that rely on computational quantum chemistry descriptors are the most appropriate to model adaptive drugs. Indeed, computational quantum chemistry descriptors are able to account for the variation of the intramolecular interactions of the training compounds, which reflect their adaptive intermolecular interaction propensities. This enables the development of causative, interpretive and reasonably predictive quantitative structure-activity relationship models, and, hence, sound chemical information finalized to drug design and discovery.

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

    OpenAIRE

    Rappoport, Dmitrij; Galvin, Cooper J.; Zubarev, Dmitry; Aspuru-Guzik, Alan

    2014-01-01

    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 reacti...

  11. Quantum kernel applications in medicinal chemistry.

    Science.gov (United States)

    Huang, Lulu; Massa, Lou

    2012-07-01

    Progress in the quantum mechanics of biological molecules is being driven by computational advances. The notion of quantum kernels can be introduced to simplify the formalism of quantum mechanics, making it especially suitable for parallel computation of very large biological molecules. The essential idea is to mathematically break large biological molecules into smaller kernels that are calculationally tractable, and then to represent the full molecule by a summation over the kernels. The accuracy of the kernel energy method (KEM) is shown by systematic application to a great variety of molecular types found in biology. These include peptides, proteins, DNA and RNA. Examples are given that explore the KEM across a variety of chemical models, and to the outer limits of energy accuracy and molecular size. KEM represents an advance in quantum biology applicable to problems in medicine and drug design.

  12. State of the art in quantum chemistry today

    Science.gov (United States)

    Stepanov, Nikolai F.

    2004-01-01

    Modern quantum chemistry is the quantum theory of structure an dynamics of molecular systems. The development of quantum chemistry for almost 8 decades gave birth to many concepts of modern chemistry and created many calculation technique which are widely used to obtain preliminary as well as high-precision information on molecular properties. In the end of XXth century it becomes the real fundamental base of chemistry and the active tool for the qualitative interpretation of structural features and physical and chemical properties including dynamics of chemical transformations. It turns out to be a very power means to obtaining quantitative results for molecular clusters as well as isolated molecules in free states and in external fields. The computational programs created in the last decades of the XXth century and permanently refined provide the reliable quantitative information on molecular equilibrium configurations, harmonic vibrational frequencies and anharmonic force constants, frequencies and intensities of the first electronic transitions, energies of the formations and potential barriers, the parameters important for interpretation of ESR and NMR spectra, electric and magnetic moments, and many other characteristics of molecular systems. The last two decades turned many quantum chemists to comparatively large molecules especially those with the distinctly pronounced biological activity. Nevertheless, small molecules the calculation results for which can pretend on the highest precision still serve as a strong attractor for the people who deal with methodological as well as applied problems.

  13. Quantum Mechanics and Conceptual Change in High School Chemistry Textbooks.

    Science.gov (United States)

    Shiland, Thomas W.

    1997-01-01

    Examines the presentation of quantum mechanics in eight secondary chemistry texts for elements associated with a conceptual change model: (1) dissatisfaction; (2) intelligibility; (3) plausibility; and (4) fruitfulness. Reports that these elements were not present in sufficient quantities to promote conceptual change. Presents recommendations for…

  14. Quantum chemical study of relative reactivities of a series of amines and nitriles - Relevance to prebiotic chemistry

    Science.gov (United States)

    Loew, G. H.; Berkowitz, D.; Chang, S.

    1975-01-01

    Using the Iterative Extended Huckel Theory (IEHT) calculations of the electron distribution and orbital energies of a series of thirteen amines, nitriles and amino-nitriles relevant to prebiotic and cosmo-chemistry have been carried out. Ground state properties such as the energy and nature of the highest occupied (HOMO) and lowest empty (LEMO) molecular orbitals, net atomic charges and number of nonbonding electrons have been identified as criteria for correlating the relative nucleophilicity of amine and nitrile nitrogens and the electrophilicity of nitrile and other unsaturated carbon atoms. The results of such correlations can be partially verified by known chemical behavior of these compounds and are used to predict and understand their role in prebiotic organic synthesis.

  15. Quantum chemical study of relative reactivities of a series of amines and nitriles - Relevance to prebiotic chemistry

    Science.gov (United States)

    Loew, G. H.; Berkowitz, D.; Chang, S.

    1975-01-01

    Using the Iterative Extended Huckel Theory (IEHT) calculations of the electron distribution and orbital energies of a series of thirteen amines, nitriles and amino-nitriles relevant to prebiotic and cosmo-chemistry have been carried out. Ground state properties such as the energy and nature of the highest occupied (HOMO) and lowest empty (LEMO) molecular orbitals, net atomic charges and number of nonbonding electrons have been identified as criteria for correlating the relative nucleophilicity of amine and nitrile nitrogens and the electrophilicity of nitrile and other unsaturated carbon atoms. The results of such correlations can be partially verified by known chemical behavior of these compounds and are used to predict and understand their role in prebiotic organic synthesis.

  16. NWChem: Quantum Chemistry Simulations at Scale

    Energy Technology Data Exchange (ETDEWEB)

    Apra, Edoardo; Kowalski, Karol; Hammond, Jeff R.; Klemm, Michael

    2015-01-17

    Methods based on quantum mechanics equations have been developed since the 1930's with the purpose of accurately studying the electronic structure of molecules. However, it is only during the last two decades that intense development of new computational algorithms has opened the possibility of performing accurate simulations of challenging molecular processes with high-order many-body methods. A wealth of evidence indicates that the proper inclusion of instantaneous interactions between electrons (or the so-called electron correlation effects) is indispensable for the accurate characterization of chemical reactivity, molecular properties, and interactions of light with matter. The availability of reliable methods for benchmarking of medium-size molecular systems provides also a unique chance to propagate high-level accuracy across spatial scales through the multiscale methodologies. Some of these methods have potential to utilize computational resources in an effi*cient way since they are characterized by high numerical complexity and appropriate level of data granularity, which can be effi*ciently distributed over multi-processor architectures. The broad spectrum of coupled cluster (CC) methods falls into this class of methodologies. Several recent CC implementations clearly demonstrated the scalability of CC formalisms on architectures composed of hundreds thousand computational cores. In this context NWChem provides a collection of Tensor Contraction Engine (TCE) generated parallel implementations of various coupled cluster methods capable of taking advantage of many thousand of cores on leadership class parallel architectures.

  17. Quantum chemistry, band structures and polymers

    Science.gov (United States)

    André, Jean-Marie

    2012-06-01

    A short review of the long way from the first calculations on polyenes after the second world war to the recent electronic devices like Organic Light Emitting Diodes or Photovoltaic Cells is given. It shows how quantum chemical methods on one side and synthesis or experiments have (or should have) interacted as incentives to new methods and technologies.

  18. Optimizing qubit resources for quantum chemistry simulations in second quantization on a quantum computer

    Science.gov (United States)

    Moll, Nikolaj; Fuhrer, Andreas; Staar, Peter; Tavernelli, Ivano

    2016-07-01

    Quantum chemistry simulations on a quantum computer suffer from the overhead needed for encoding the Fermionic problem in a system of qubits. By exploiting the block diagonality of a Fermionic Hamiltonian, we show that the number of required qubits can be reduced while the number of terms in the Hamiltonian will increase. All operations for this reduction can be performed in operator space. The scheme is conceived as a pre-computational step that would be performed prior to the actual quantum simulation. We apply this scheme to reduce the number of qubits necessary to simulate both the Hamiltonian of the two-site Fermi-Hubbard model and the hydrogen molecule. Both quantum systems can then be simulated with a two-qubit quantum computer. Despite the increase in the number of Hamiltonian terms, the scheme still remains a useful tool to reduce the dimensionality of specific quantum systems for quantum simulators with a limited number of resources.

  19. Infrared and Raman spectroscopy and quantum chemistry calculation studies of C H⋯O hydrogen bondings and thermal behavior of biodegradable polyhydroxyalkanoate

    Science.gov (United States)

    Sato, Harumi; Dybal, Jiří; Murakami, Rumi; Noda, Isao; Ozaki, Yukihiro

    2005-06-01

    This review paper reports infrared (IR) and Raman spectroscopy and quantum chemistry calculation studies of C-H⋯O hydrogen bondings and thermal behavior of biodegradable polyhydroxyalkanoates. IR and Raman spectra were measured for poly(3-hydroxybutyrate) (PHB) and a new type of bacterial copolyester, poly(3-hydroxybutyrate- co-3-hydroxyhexanoate), P(HB- co-HHx) (HHx=12 mol%) over a temperature range of 20 °C to higher temperatures (PHB, 200 °C; HHx=12 mol%, 140 °C) to explore their structure and thermal behavior. One of bands due to the CH 3 asymmetric stretching modes appears near 3010 cm -1 in the IR and Raman spectra of PHB and P(HB- co-HHx) at 20 °C. These frequencies of IR and Raman CH 3 asymmetric stretching bands are much higher than usual. These anomalous frequencies of the CH 3 asymmetric stretching bands together with the X-ray crystallographic structure of PHB have suggested that there is an inter- or intra-molecular C-H⋯O hydrogen bond between the C dbnd6 O group in one helical structure and the CH 3 group in the other helical structure in PHB and P(HB- co-HHx). The quantum chemical calculation of model compounds of PHB also has suggested the existence of C-H⋯O hydrogen bonds in PHB and P(HB- co-HHx). It is very likely that a chain of C-H⋯O hydrogen bond pairs link two parallel helical structures in the crystalline parts. The temperature-dependent IR and Raman spectral variations have revealed that the crystallinity of P(HB- co-HHx) (HHx=12 mol%) decreases gradually from a fairly low temperature (about 60 °C), while the crystallinity of PHB remains almost unchanged until just below its melting temperature. It has also been found from the IR and Raman studies that for both PHB and P(HB- co-HHx) the weakening of the C-H⋯O hydrogen bonds starts from just above room temperature, but the deformation of helical structures occurs after the weakening of the C-H⋯O hydrogen bonds advances to some extent.

  20. Control through operators for quantum chemistry

    CERN Document Server

    Laurent, Philippe; Salomon, Julien; Turinici, Gabriel

    2012-01-01

    We consider the problem of operator identification in quantum control. The free Hamiltonian and the dipole moment are searched such that a given target state is reached at a given time. A local existence result is obtained. As a by-product, our works reveals necessary conditions on the laser field to make the identification feasible. In the last part of this work, some algorithms are proposed to compute effectively these operators.

  1. 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.

  2. Quantum Chemistry of Solids LCAO Treatment of Crystals and Nanostructures

    CERN Document Server

    Evarestov, Robert A

    2012-01-01

    Quantum Chemistry of Solids delivers a comprehensive account of the main features and possibilities of LCAO methods for the first principles calculations of electronic structure of periodic systems. The first part describes the basic theory underlying the LCAO methods  applied to periodic systems and the use of Hartree-Fock(HF), Density Function theory(DFT) and hybrid Hamiltonians. The translation and site symmetry consideration is included to establish connection between k-space solid –state physics and real-space quantum chemistry. The inclusion of electron correlation effects for periodic systems is considered on the basis of localized crystalline orbitals. The possibilities of LCAO methods for chemical bonding analysis in periodic systems are discussed. The second part deals with the applications of LCAO methods  for calculations of bulk crystal properties, including magnetic ordering and crystal structure optimization.  In the second edition two new chapters are added in the application part II of t...

  3. Quasi-classical alternatives in quantum chemistry

    CERN Document Server

    Gineityte, V

    2014-01-01

    The article contains an overview of authors achievements in development of alternative quantum-chemical approaches oriented towards revival of the classical tradition of qualitative chemical thinking instead of obtaining numerical results. The above-mentioned tradition is concluded to be based mainly on principles (rules) of additivity, transferability and locality of molecular properties. Accordingly, model Hamiltonian matrices are used in the approaches under development (called quasi-classical alternatives), wherein algebraic parameters play the role of matrix elements and these are assumed to be transferable for similar atoms and/or atomic orbitals in addition. Further, passing to delocalized descriptions of electronic structures (as usual) is expected to be the main origin of difficulties seeking to formulate quasi-classical alternatives. In the framework of the canonical method of molecular orbitals (MOs), delocalization is shown to be partially avoidable by invoking a recently-suggested approach to sec...

  4. Visually impaired researchers get their hands on quantum chemistry: application to a computational study on the isomerization of a sterol

    NARCIS (Netherlands)

    Lounnas, V.; Wedler, H.B.; Newman, T.; Schaftenaar, G.; Harrison, J.G.; Nepomuceno, G.; Pemberton, R.; Tantillo, D.J.; Vriend, G.

    2014-01-01

    In molecular sciences, articles tend to revolve around 2D representations of 3D molecules, and sighted scientists often resort to 3D virtual reality software to study these molecules in detail. Blind and visually impaired (BVI) molecular scientists have access to a series of audio devices that can h

  5. Visually impaired researchers get their hands on quantum chemistry: application to a computational study on the isomerization of a sterol

    NARCIS (Netherlands)

    Lounnas, V.; Wedler, H.B.; Newman, T.; Schaftenaar, G.; Harrison, J.G.; Nepomuceno, G.; Pemberton, R.; Tantillo, D.J.; Vriend, G.

    2014-01-01

    In molecular sciences, articles tend to revolve around 2D representations of 3D molecules, and sighted scientists often resort to 3D virtual reality software to study these molecules in detail. Blind and visually impaired (BVI) molecular scientists have access to a series of audio devices that can

  6. Quantum Chemistry via Walks in Determinant Space

    Energy Technology Data Exchange (ETDEWEB)

    Umrigar, Cyrus J. [Cornell Univ., Ithaca, NY (United States)

    2016-01-05

    There are many chemical questions of practical interest to the DOE that could be answered if there were an electronic structure method that provided consistently accurate results for all systems at an affordable computational cost. The coupled cluster method with single, double and perturbative triple excitations (CCSD(T)) is the most frequently used high-order method, but it has known deficiencies, e.g., in the description of stretched bonds. The full configuration interaction (FCI) method is the most robust method for treating electronic correlations, but it is little used because its computational cost scales exponentially in the size of the system. The largest calculation that has been done to date employed 10 billion determinants. In this regard, there was a major advance in 2010. The Alavi group at Cambridge University developed a stochastic approach to FCI --- combining it with ideas from quantum Monte Carlo (QMC) --- called FCIQMC, that allows one to go to a far larger number of determinants in certain circumstances. The computational cost is exponential in the system and basis size but with a much reduced exponent compared to conventional FCI. In this project Umrigar's group made several major improvements to the FCIQMC method that increased its efficiency by many orders of magnitude. In addition this project resulted in a cross-fertilization of ideas between the FCIQMC method, the older phaseless auxilliary-field quantum Monte Carlo (AFQMC) method developed by Zhang and Krakauer (two of the PI's of this project), and symmetry-restored wavefunctions developed by Scuseria (also a PI of this project).

  7. Let Students Derive, by Themselves, Two-Dimensional Atomic and Molecular Quantum Chemistry from Scratch

    Science.gov (United States)

    Ge, Yingbin

    2016-01-01

    Hands-on exercises are designed for undergraduate physical chemistry students to derive two-dimensional quantum chemistry from scratch for the H atom and H[subscript 2] molecule, both in the ground state and excited states. By reducing the mathematical complexity of the traditional quantum chemistry teaching, these exercises can be completed…

  8. Quantum Chemistry Study of Cycloaddition Pathways for the Reaction of o-Benzyne with Fullerenes and Carbon Nanotubes

    Science.gov (United States)

    Jaffe, Richard; Han, Jie; Langhoff, Stephen R. (Technical Monitor)

    1997-01-01

    Functionalization of fullerenes via the [2+2] cycloaddition reaction with o-benzyne has been demonstrated in the laboratory. In contrast, [2+4) cycloaddition products are formed when benzyne reacts with planar polycyclic aromatic hydrocarbons. Using density functional theory (DFT) calculations with Becke's hybrid functional and small contracted gaussian basis sets, we are able to reproduce these product preferences. The objective of this work is to explore the functionalization of carbon nanotubes. We have studied o-benzyne cycloaddition products with a [14,0] single-walled nanotube. We find both the [2+2] and [2+4] adducts to be stable, with the latter product being somewhat favored.

  9. The molecular electron density distribution meeting place of X-ray diffraction and quantum chemistry intermediate - between theory and experiment

    NARCIS (Netherlands)

    Feil, Dirk

    1992-01-01

    Quantum chemistry and the concepts used daily in chemistry are increasingly growing apart. Among the concepts that are able to bridge the gap between theory and experimental practice, electron density distribution has an important place. The study of this distribution has led to new developments in

  10. Principles of conjugating quantum dots to proteins via carbodiimide chemistry.

    Science.gov (United States)

    Song, Fayi; Chan, Warren C W

    2011-12-09

    The covalent coupling of nanomaterials to bio-recognition molecules is a critical intermediate step in using nanomaterials for biology and medicine. Here we investigate the carbodiimide-mediated conjugation of fluorescent quantum dots to different proteins (e.g., immunoglobulin G, bovine serum albumin, and horseradish peroxidase). To enable these studies, we developed a simple method to isolate quantum dot bioconjugates from unconjugated quantum dots. The results show that the reactant concentrations and protein type will impact the overall number of proteins conjugated onto the surfaces of the quantum dots, homogeneity of the protein-quantum dot conjugate population, quantum efficiency, binding avidity, and enzymatic kinetics. We propose general principles that should be followed for the successful coupling of proteins to quantum dots.

  11. Bond additivity corrections for quantum chemistry methods

    Energy Technology Data Exchange (ETDEWEB)

    C. F. Melius; M. D. Allendorf

    1999-04-01

    In the 1980's, the authors developed a bond-additivity correction procedure for quantum chemical calculations called BAC-MP4, which has proven reliable in calculating the thermochemical properties of molecular species, including radicals as well as stable closed-shell species. New Bond Additivity Correction (BAC) methods have been developed for the G2 method, BAC-G2, as well as for a hybrid DFT/MP2 method, BAC-Hybrid. These BAC methods use a new form of BAC corrections, involving atomic, molecular, and bond-wise additive terms. These terms enable one to treat positive and negative ions as well as neutrals. The BAC-G2 method reduces errors in the G2 method due to nearest-neighbor bonds. The parameters within the BAC-G2 method only depend on atom types. Thus the BAC-G2 method can be used to determine the parameters needed by BAC methods involving lower levels of theory, such as BAC-Hybrid and BAC-MP4. The BAC-Hybrid method should scale well for large molecules. The BAC-Hybrid method uses the differences between the DFT and MP2 as an indicator of the method's accuracy, while the BAC-G2 method uses its internal methods (G1 and G2MP2) to provide an indicator of its accuracy. Indications of the average error as well as worst cases are provided for each of the BAC methods.

  12. Big Data Meets Quantum Chemistry Approximations: The Δ-Machine Learning Approach.

    Science.gov (United States)

    Ramakrishnan, Raghunathan; Dral, Pavlo O; Rupp, Matthias; von Lilienfeld, O Anatole

    2015-05-12

    Chemically accurate and comprehensive studies of the virtual space of all possible molecules are severely limited by the computational cost of quantum chemistry. We introduce a composite strategy that adds machine learning corrections to computationally inexpensive approximate legacy quantum methods. After training, highly accurate predictions of enthalpies, free energies, entropies, and electron correlation energies are possible, for significantly larger molecular sets than used for training. For thermochemical properties of up to 16k isomers of C7H10O2 we present numerical evidence that chemical accuracy can be reached. We also predict electron correlation energy in post Hartree-Fock methods, at the computational cost of Hartree-Fock, and we establish a qualitative relationship between molecular entropy and electron correlation. The transferability of our approach is demonstrated, using semiempirical quantum chemistry and machine learning models trained on 1 and 10% of 134k organic molecules, to reproduce enthalpies of all remaining molecules at density functional theory level of accuracy.

  13. Big Data meets Quantum Chemistry Approximations: The $\\Delta$-Machine Learning Approach

    CERN Document Server

    Ramakrishnan, Raghunathan; Rupp, Matthias; von Lilienfeld, O Anatole

    2015-01-01

    Chemically accurate and comprehensive studies of the virtual space of all possible molecules are severely limited by the computational cost of quantum chemistry. We introduce a composite strategy that adds machine learning corrections to computationally inexpensive approximate legacy quantum methods. After training, highly accurate predictions of enthalpies, free energies, entropies, and electron correlation energies are possible, for significantly larger molecular sets than used for training. For thermochemical properties of up to 16k constitutional isomers of C$_7$H$_{10}$O$_2$ we present numerical evidence that chemical accuracy can be reached. We also predict electron correlation energy in post Hartree-Fock methods, at the computational cost of Hartree-Fock, and we establish a qualitative relationship between molecular entropy and electron correlation. The transferability of our approach is demonstrated, using semi-empirical quantum chemistry and machine learning models trained on 1 and 10\\% of 134k organ...

  14. Industrial Chemistry and School Chemistry: Making Chemistry Studies More Relevant

    Science.gov (United States)

    Hofstein, Avi; Kesner, Miri

    2006-01-01

    In this paper, we present the development and implementation over the period of more than 15 years of learning materials focusing on industrial chemistry as the main theme. The work was conducted in the Department of Science Teaching at the Weizmann Institute of Science, Israel. The project's general goal was to teach chemistry concepts in the…

  15. Block-adaptive quantum mechanics: an adaptive divide-and-conquer approach to interactive quantum chemistry.

    Science.gov (United States)

    Bosson, Maël; Grudinin, Sergei; Redon, Stephane

    2013-03-05

    We present a novel Block-Adaptive Quantum Mechanics (BAQM) approach to interactive quantum chemistry. Although quantum chemistry models are known to be computationally demanding, we achieve interactive rates by focusing computational resources on the most active parts of the system. BAQM is based on a divide-and-conquer technique and constrains some nucleus positions and some electronic degrees of freedom on the fly to simplify the simulation. As a result, each time step may be performed significantly faster, which in turn may accelerate attraction to the neighboring local minima. By applying our approach to the nonself-consistent Atom Superposition and Electron Delocalization Molecular Orbital theory, we demonstrate interactive rates and efficient virtual prototyping for systems containing more than a thousand of atoms on a standard desktop computer.

  16. Teaching the Philosophical Interpretations of Quantum Mechanics and Quantum Chemistry Through Controversies

    Science.gov (United States)

    Garritz, Andoni

    2013-07-01

    This study has the key premise of teaching history and philosophy of physical sciences to illustrate how controversies and rivalries among scientists play a key role in the progress of science and why scientific development is not only founded on the accumulation of experimental data. The author is a defender of teachers who consider philosophical, historical and socio-scientific issues. In particular, the disputes can be used in science teaching to promote students awareness of the "historicity" of science and to facilitate the understanding of scientific progress beyond that of inductive generalizations. The establishment of a theory is accompanied with philosophical interpretations all the way. The author will try to show that it gives excellent results in teaching and learning to bring to the foreground the complexity that surrounds the development of ideas in science, illustrating how controversies, presuppositions, contradictions and inconsistencies find a place in the work of scientists and philosophers alike. In this sense, the case of quantum mechanics and quantum chemistry is very solid because it is historically full of controversies among their heads: Einstein, Bohr, De Broglie, Heisenberg, Schrödinger, Born, Lewis, Langmuir, Bader, Hoffmann and Pauling, at least.

  17. Development of massively parallel quantum chemistry program SMASH

    Energy Technology Data Exchange (ETDEWEB)

    Ishimura, Kazuya [Department of Theoretical and Computational Molecular Science, Institute for Molecular Science 38 Nishigo-Naka, Myodaiji, Okazaki, Aichi 444-8585 (Japan)

    2015-12-31

    A massively parallel program for quantum chemistry calculations SMASH was released under the Apache License 2.0 in September 2014. The SMASH program is written in the Fortran90/95 language with MPI and OpenMP standards for parallelization. Frequently used routines, such as one- and two-electron integral calculations, are modularized to make program developments simple. The speed-up of the B3LYP energy calculation for (C{sub 150}H{sub 30}){sub 2} with the cc-pVDZ basis set (4500 basis functions) was 50,499 on 98,304 cores of the K computer.

  18. Relativistic quantum chemistry the fundamental theory of molecular science

    CERN Document Server

    Reiher, Markus

    2014-01-01

    Einstein proposed his theory of special relativity in 1905. For a long time it was believed that this theory has no significant impact on chemistry. This view changed in the 1970s when it was realized that (nonrelativistic) Schrödinger quantum mechanics yields results on molecular properties that depart significantly from experimental results. Especially when heavy elements are involved, these quantitative deviations can be so large that qualitative chemical reasoning and understanding is affected. For this to grasp the appropriate many-electron theory has rapidly evolved. Nowadays relativist

  19. Photodissociation of a diatomic molecule in the quantum regime reveals ultracold chemistry

    CERN Document Server

    McDonald, M; Apfelbeck, F; Lee, C -H; Majewska, I; Moszynski, R; Zelevinsky, T

    2015-01-01

    Chemical reactions at temperatures near absolute zero require a full quantum description of the reaction pathways and enable enhanced control of the products via quantum state selection. Ultracold molecule experiments have provided initial insight into the quantum nature of basic chemical processes involving diatomic molecules, for example from studies of bimolecular reactions, but complete control over the reactants and products has remained elusive. The "half-collision" process of photodissociation is an indispensable tool in molecular physics and offers significantly more control than the reverse process of photoassociation. Here we reach a fully quantum regime with photodissociation of ultracold $^{88}$Sr$_2$ molecules where the initial bound state of the molecule and the target continuum state of the fragments are strictly controlled. Detection of the photodissociation products via optical absorption imaging reveals the hallmarks of ultracold chemistry: resonant and nonresonant barrier tunneling, importa...

  20. Implementation of replica-exchange umbrella sampling in the DFTB + semiempirical quantum chemistry package

    Science.gov (United States)

    Ito, Shingo; Irle, Stephan; Okamoto, Yuko

    2016-07-01

    The replica-exchange umbrella sampling (REUS) method combines replica-exchange and umbrella sampling methods and allows larger conformational sampling than conventional simulation methods. This method has been used in many studies to understand docking mechanisms and the functions of molecules. However, REUS has not been combined with quantum chemical codes. Therefore, we implemented the REUS simulation technique in the DFTB + quantum chemistry code utilizing approximate density functional theory. We performed REUS simulations of an intra-molecular proton transfer reaction of malonaldehyde and a formation of a phthalocyanine from four phthalonitriles and one iron atom to validate the reliability of our implemented REUS-DFTB + combination.

  1. Expression of results in quantum chemistry physical chemistry division commission on physicochemical symbols, terminology and units

    CERN Document Server

    Whiffen, D H

    2013-01-01

    Expression of Results in Quantum Chemistry recommends the appropriate insertion of physical constants in the output information of a theoretical paper in order to make the numerical end results of theoretical work easily transformed to SI units by the reader. The acceptance of this recommendation would circumvent the need for a set of atomic units each with its own symbol and name. It is the traditional use of the phrase """"atomic units"""" in this area which has obscured the real problem. The four SI dimensions of length, mass, time, and current require four physical constants to be permitte

  2. Few-Qubit Magnetic Resonance Quantum Information Processors: Simulating Chemistry and Physics

    CERN Document Server

    Criger, Ben; Baugh, Jonathan

    2012-01-01

    We review recent progress made in quantum information processing (QIP) which can be applied in the simulation of quantum systems and chemical phenomena. The review is focused on quantum algorithms which are useful for quantum simulation of chemistry and advances in nuclear magnetic resonance (NMR) and electron spin resonance (ESR) QIP. Discussions also include a number of recent experiments demonstrating the current capabilities of the NMR QIP for quantum simulation and prospects for spin-based implementations of QIP.

  3. Formation of Carbon Nanotube Based Gears: Quantum Chemistry and Molecular Mechanics Study of the Electrophilic Addition of o-Benzyne to Fullerenes, Graphene, and Nanotubes

    Science.gov (United States)

    Jaffe, Richard; Han, Jie; Globus, Al; Chancellor, Marisa K. (Technical Monitor)

    1997-01-01

    Considerable progress has been made in recent years in chemical functionalization of fullerene molecules. In some cases, the predominant reaction products are different from those obtained (using the same reactants) from polycyclic aromatic hydrocarbons (PAHs). One such example is the cycloaddition of o-benzyne to C60. It is well established that benzyne adds across one of the rings in naphthalene, anthracene and other PAHs forming the [2+4] cycloaddition product (benzobicyclo[2.2.2.]-octatriene with naphthalene and triptycene with anthracene). However, Hoke et al demonstrated that the only reaction path for o-benzyne with C60 leads to the [2+2] cycloaddition product in which benzyne adds across one of the interpentagonal bonds (forming a cyclobutene ring in the process). Either reaction product results in a loss of aromaticity and distortion of the PAH or fullerene substrate, and in a loss of strain in the benzyne. It is not clear, however, why different products are preferred in these cases. In the current paper, we consider the stability of benzyne-nanotube adducts and the ability of Brenner's potential energy model to describe the structure and stability of these adducts. The Brenner potential has been widely used for describing diamondoid and graphitic carbon. Recently it has also been used for molecular mechanics and molecular dynamics simulations of fullerenes and nanotubes. However, it has not been tested for the case of functionalized fullerenes (especially with highly strained geometries). We use the Brenner potential for our companion nanogear simulations and believe that it should be calibrated to insure that those simulations are physically reasonable. In the present work, Density Functional theory (DFT) calculations are used to determine the preferred geometric structures and energetics for this calibration. The DFT method is a kind of ab initio quantum chemistry method for determining the electronic structure of molecules. For a given basis set

  4. Walking in the woods with quantum chemistry--applications of quantum chemical calculations in natural products research.

    Science.gov (United States)

    Tantillo, Dean J

    2013-08-01

    This Highlight describes applications of quantum chemical calculations to problems in natural products chemistry, including the elucidation of natural product structures (distinguishing between constitutional isomers, distinguishing between diastereomers, and assigning absolute configuration) and determination of reasonable mechanisms for their formation.

  5. Computing UV/vis spectra using a combined molecular dynamics and quantum chemistry approach: bis-triazin-pyridine (BTP) ligands studied in solution.

    Science.gov (United States)

    Höfener, Sebastian; Trumm, Michael; Koke, Carsten; Heuser, Johannes; Ekström, Ulf; Skerencak-Frech, Andrej; Schimmelpfennig, Bernd; Panak, Petra J

    2016-03-21

    We report a combined computational and experimental study to investigate the UV/vis spectra of 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine (BTP) ligands in solution. In order to study molecules in solution using theoretical methods, force-field parameters for the ligand-water interaction are adjusted to ab initio quantum chemical calculations. Based on these parameters, molecular dynamics (MD) simulations are carried out from which snapshots are extracted as input to quantum chemical excitation-energy calculations to obtain UV/vis spectra of BTP ligands in solution using time-dependent density functional theory (TDDFT) employing the Tamm-Dancoff approximation (TDA). The range-separated CAM-B3LYP functional is used to avoid large errors for charge-transfer states occurring in the electronic spectra. In order to study environment effects with theoretical methods, the frozen-density embedding scheme is applied. This computational procedure allows to obtain electronic spectra calculated at the (range-separated) DFT level of theory in solution, revealing solvatochromic shifts upon solvation of up to about 0.6 eV. Comparison to experimental data shows a significantly improved agreement compared to vacuum calculations and enables the analysis of relevant excitations for the line shape in solution.

  6. Going beyond "no-pair relativistic quantum chemistry".

    Science.gov (United States)

    Liu, Wenjian; Lindgren, Ingvar

    2013-07-07

    The current field of relativistic quantum chemistry (RQC) has been built upon the no-pair and no-retardation approximations. While retardation effects must be treated in a time-dependent manner through quantum electrodynamics (QED) and are hence outside RQC, the no-pair approximation (NPA) has to be removed from RQC for it has some fundamental defects. Both configuration space and Fock space formulations have been proposed in the literature to do this. However, the former is simply wrong, whereas the latter is still incomplete. To resolve the old problems pertinent to the NPA itself and new problems beyond the NPA, we propose here an effective many-body (EMB) QED approach that is in full accordance with standard methodologies of electronic structure. As a first application, the full second order energy E2 of a closed-shell many-electron system subject to the instantaneous Coulomb-Breit interaction is derived, both algebraically and diagrammatically. It is shown that the same E2 can be obtained by means of 3 Goldstone-like diagrams through the standard many-body perturbation theory or 28 Feynman diagrams through the S-matrix technique. The NPA arises naturally by retaining only the terms involving the positive energy states. The potential dependence of the NPA can be removed by adding in the QED one-body counter terms involving the negative energy states, thereby leading to a "potential-independent no-pair approximation" (PI-NPA). The NPA, PI-NPA, EMB-QED, and full QED then span a continuous spectrum of relativistic molecular quantum mechanics.

  7. Quantum Chemistry Study on Electronic Structure of Vanadium Hydride%钒氢化物电子结构的量子化学研究

    Institute of Scientific and Technical Information of China (English)

    李荣; 周上祺; 陈昌国; 梁国明; 刘守平; 孔纪兰

    2005-01-01

    利用电荷自洽离散变分Xα(SCC-DV-Xα)方法计算了钒基固溶体中钒氢反应前后钒及其氢化物(VHx,x=0,1,2)、假定原子簇模型VH*x(x=1,2)和VHx′(x=0,1)的电子结构.结果表明:钒与氢气反应生成VH时,化学效应和结构效应都使V 3d和H 1s轨道向低能量方向移动,氢化物VH中V 3d和H 1s轨道重叠最多,V-H之间的相互作用较强.VH再与氢气反应生成VH2时,结构效应使V 3d和H 1s轨道都向高能量方向移动,氢化物VH2中V 3d和H 1s轨道重叠最少,V和H之间的相互作用较弱.氢化物VH和VH2中不仅存在离子性相互作用,而且还存在共价性相互作用.结构效应导致VH2中V-H键的共价性减弱,从而导致VH2中V和H之间的相互作用减弱.氢化物VH的费米能级比VH2的低,说明VH更稳定.%The electronic structure of V and VHx(x=0, 1, 2) in vanadium-based solid solution was calculated by using self-consistent-charge discrete variational (SCC-DV-Xα) method of quantum chemistry. The results demonstrated that the interaction between V and H in VH and VH2 was not only ionic but also covalent; the V-H bond between V and H bands in hydride VH2 was weaker than that in VH. The bonds were due to interaction between the V 4s and H1s in hydride VH, and the interaction between V 4s, V 3d and H1s in VH2. Fermi energy level in VH was lower than in VH2.The results suggested that VH is more stable.

  8. Role of gamma carboxylated Glu47 in connexin 26 hemichannel regulation by extracellular Ca{sup 2+}: Insight from a local quantum chemistry study

    Energy Technology Data Exchange (ETDEWEB)

    Zonta, Francesco [Dipartimento di Fisica e Astronomia “G. Galilei”, Università degli Studi di Padova, 35131 Padova (Italy); Mammano, Fabio, E-mail: fabio.mammano@unipd.it [Dipartimento di Fisica e Astronomia “G. Galilei”, Università degli Studi di Padova, 35131 Padova (Italy); Istituto Veneto di Medicina Molecolare, Fondazione per la Ricerca Biomedica Avanzata, 35129 Padova (Italy); Istituto CNR di Neuroscienze, 35131 Padova (Italy); Torsello, Mauro; Fortunati, Nicola [Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Via Marzolo 1, 35131 Padova (Italy); Orian, Laura, E-mail: laura.orian@unipd.it [Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Via Marzolo 1, 35131 Padova (Italy); Polimeno, Antonino [Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Via Marzolo 1, 35131 Padova (Italy)

    2014-02-28

    Graphical abstract: - Highlights: • QM calculations show that Ca{sup 2+} binds to γGlu47 in connexin hemichannels. • Molecular models of increasing size are employed in hybrid DFT calculations. • Ca{sup 2+} binding affects the interaction between γGlu47 and Arg75, Arg184. • Ca{sup 2+} binding alters the structure in a critical region of connexin hemichannels. - Abstract: Connexin hemichannels are regulated by several gating mechanisms, some of which depend critically on the extracellular Ca{sup 2+} concentration ([Ca{sup 2+}]{sub e}). It is well established that hemichannel activity is inhibited at normal (∼1 mM) [Ca{sup 2+}]{sub e}, whereas lowering [Ca{sup 2+}]{sub e} to micromolar levels fosters hemichannel opening. Atomic force microscopy imaging shows significant and reversible changes of pore diameter at the extracellular mouth of Cx26 hemichannels exposed to different [Ca{sup 2+}]{sub e}, however, the underlying molecular mechanisms are not fully elucidated. Analysis of the crystal structure of connexin 26 (Cx26) gap junction channels, corroborated by molecular dynamics (MD) simulations, suggests that several negatively charged amino acids create a favorable environment for low-affinity Ca{sup 2+} binding within the extracellular vestibule of the Cx26 hemichannel. In particular a highly conserved glutammic acid, found in position 47 in most connexins, is thought to undergo post translational gamma carboxylation (γGlu47), and is thus likely to play an important role in Ca{sup 2+} coordination. γGlu47 may also form salt bridges with two conserved arginines (Arg75 and Arg184 in Cx26), which are considered important in stabilizing the structure of the extracellular region. Using a combination of quantum chemistry methods, we analyzed the interaction between γGlu47, Arg75 and Arg184 in a Cx26 hemichannel model both in the absence and in the presence of Ca{sup 2+}. We show that Ca{sup 2+} imparts significant local structural changes and speculate

  9. Exponentially more precise quantum simulation of fermions I: Quantum chemistry in second quantization

    CERN Document Server

    Babbush, Ryan; Kivlichan, Ian D; Wei, Annie Y; Love, Peter J; Aspuru-Guzik, Alán

    2015-01-01

    We introduce novel algorithms for the quantum simulation of molecular systems which are asymptotically more efficient than those based on the Trotter-Suzuki decomposition. We present the first application of a recently developed technique for simulating Hamiltonian evolution using a truncated Taylor series to obtain logarithmic scaling with the inverse of the desired precision, an exponential improvement over all prior methods. The two algorithms developed in this work rely on a second quantized encoding of the wavefunction in which the state of an $N$ spin-orbital system is encoded in ${\\cal O}(N)$ qubits. Our first algorithm has time complexity $\\widetilde{\\cal O}(N^8 t)$. Our second algorithm involves on-the-fly computation of molecular integrals, in a way that is exponentially more precise than classical sampling methods, by using the truncated Taylor series simulation technique. Our second algorithm has the lowest asymptotic time complexity of any second quantized approach to quantum chemistry simulation...

  10. Dynamical mean-field theory for quantum chemistry.

    Science.gov (United States)

    Lin, Nan; Marianetti, C A; Millis, Andrew J; Reichman, David R

    2011-03-04

    The dynamical mean-field concept of approximating an unsolvable many-body problem in terms of the solution of an auxiliary quantum impurity problem, introduced to study bulk materials with a continuous energy spectrum, is here extended to molecules, i.e., finite systems with a discrete energy spectrum. The application to small clusters of hydrogen atoms yields ground state energies which are competitive with leading quantum chemical approaches at intermediate and large interatomic distances as well as good approximations to the excitation spectrum.

  11. Numerical Studies of Quantum Turbulence

    Science.gov (United States)

    Tsubota, Makoto; Fujimoto, Kazuya; Yui, Satoshi

    2017-09-01

    We review numerical studies of quantum turbulence. Quantum turbulence is currently one of the most important problems in low temperature physics and is actively studied for superfluid helium and atomic Bose-Einstein condensates. A key aspect of quantum turbulence is the dynamics of condensates and quantized vortices. The dynamics of quantized vortices in superfluid helium are described by the vortex filament model, while the dynamics of condensates are described by the Gross-Pitaevskii model. Both of these models are nonlinear, and the quantum turbulent states of interest are far from equilibrium. Hence, numerical studies have been indispensable for studying quantum turbulence. In fact, numerical studies have contributed to revealing the various problems of quantum turbulence. This article reviews the recent developments in numerical studies of quantum turbulence. We start with the motivation and the basics of quantum turbulence and invite readers to the frontier of this research. Though there are many important topics in the quantum turbulence of superfluid helium, this article focuses on inhomogeneous quantum turbulence in a channel, which has been motivated by recent visualization experiments. Atomic Bose-Einstein condensates are a modern issue in quantum turbulence, and this article reviews a variety of topics in the quantum turbulence of condensates, e.g., two-dimensional quantum turbulence, weak wave turbulence, turbulence in a spinor condensate, some of which have not been addressed in superfluid helium and paves the novel way for quantum turbulence researches. Finally, we discuss open problems.

  12. Solved and unsolved problems in relativistic quantum chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Kutzelnigg, Werner, E-mail: werner.kutzelnigg@rub.de [Lehrstuhl fuer Theoretische Chemie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

    2012-02-20

    Graphical abstract: The graphical abstract represents the Dirac-Coulomb Hamiltonian in Fock space in a diagrammatic notation. A line (vertical or slanted) with an upgoing arrow represents an eletron, with a downgoing arrow a positron. A cross in the first line means the potential created by a nucleus, a broken line represents the Coulomb interaction between electrons and positrons. Highlights: Black-Right-Pointing-Pointer Relativistic many-electron theory needs a Fock space and a field-dependent vacuum. Black-Right-Pointing-Pointer A good starting point is QED in Coulomb gauge without transversal photons. Black-Right-Pointing-Pointer The Dirac underworld picture is obsolete. Black-Right-Pointing-Pointer A kinetically balanced even-tempered Gaussian basis is complete. Black-Right-Pointing-Pointer 'Quantum chemistry in Fock space is preferable over QED. - Abstract: A hierarchy of approximations in relativistic many-electron theory is discussed that starts with the Dirac equation and its expansion in a kinetically balanced basis, via a formulation of non-interacting electrons in Fock space (which is the only consistent way to deal with negative-energy states). The most straightforward approximate Hamiltonian for interacting electrons is derived from quantum electrodynamics (QED) in Coulomb gauge with the neglect of transversal photons. This allows an exact (non-perturbative) decoupling of the electromagnetic field from the fermionic field. The electric interaction of the fermions is non-retarded and non-quantized. The quantization of the fermionic field leads to a polarizable vacuum. The simplest (but somewhat problematic) approximation is a no-pair projected theory with external-field projectors. The Dirac-Coulomb operator in configuration space (first quantization) is not acceptable, even if the Brown-Ravenhall disease is much less virulent than often claimed. Effects of transversal photons, such as the Breit interaction and renormalized self-interaction can be

  13. Quantum Chemistry Meets Rotational Spectroscopy for Astrochemistry: Increasing Molecular Complexity

    Science.gov (United States)

    Puzzarini, Cristina

    2016-06-01

    For many years, scientists suspected that the interstellar medium was too hostile for organic species and that only a few simple molecules could be formed under such extreme conditions. However, the detection of approximately 180 molecules in interstellar or circumstellar environments in recent decades has changed this view dramatically. A rich chemistry has emerged, and relatively complex molecules such as C60 and C70 are formed. Recently, researchers have also detected complex organic and potentially prebiotic molecules, such as amino acids, in meteorites and in other space environments. Those discoveries have further stimulated the debate on the origin of the building blocks of life in the universe. Rotational spectroscopy plays a crucial role in the investigation of planetary atmosphere and the interstellar medium. Increasingly these astrochemical investigations are assisted by quantum-mechanical calculations of structures as well as spectroscopic and thermodynamic properties to guide and support observations, line assignments, and data analysis in these new and chemically complicated situations. However, it has proved challenging to extend accurate quantum-chemical computational approaches to larger systems because of the unfavorable scaling with the number of degrees of freedom (both electronic and nuclear). In this contribution, it is demonstrated that it is now possible to compute physicochemical properties of building blocks of biomolecules with an accuracy rivaling that of the most sophisticated experimental techniques. We analyze the spectroscopic properties of representative building blocks of DNA bases (uracil and thiouracil), of proteins (glycine and glycine dipeptide analogue), and also of PAH (phenalenyl radical and cation). V. Barone, M. Biczysko, C. Puzzarini 2015, Acc. Chem. Res., 48, 1413

  14. Quantum Chemistry, and Eclectic Mix: From Silicon Carbide to Size Consistency

    Energy Technology Data Exchange (ETDEWEB)

    Rintelman, Jamie Marie [Iowa State Univ., Ames, IA (United States)

    2004-12-19

    Chemistry is a field of great breadth and variety. It is this diversity that makes for both an interesting and challenging field. My interests have spanned three major areas of theoretical chemistry: applications, method development, and method evaluation. The topics presented in this thesis are as follows: (1) a multi-reference study of the geometries and relative energies of four atom silicon carbide clusters in the gas phase; (2) the reaction of acetylene on the Si(100)-(2x1) surface; (3) an improvement to the Effective Fragment Potential (EFP) solvent model to enable the study of reactions in both aqueous and nonaqueous solution; and (4) an evaluation of the size consistency of Multireference Perturbation Theory (MRPT). In the following section, the author briefly discusses two topics central to, and present throughout, this thesis: Multi-reference methods and Quantum Mechanics/Molecular Mechanics (QM/MM) methods.

  15. A Student Guide to Studying General Chemistry.

    Science.gov (United States)

    Schlenker, Richard M.

    This is a guide for introductory college chemistry students who are new to the subject of chemistry and who have been exposed to linear and second-order algebra equations and the concept of slope. The guide presents directions on the following topics: (1) How to prepare for lectures and take notes; (2) How to study chemistry outside of class using…

  16. A Study of Quantum Algorithms and Quantum Cryptography

    OpenAIRE

    小柴, 健史

    2007-01-01

    This report describes properties of basic cryptographic primitives (quantum public-key cryptosystmes and quantum one-way functions) in the quantum world where quantum computers are available. Some quantum public-key cryptosystems have already proposed. However, the security requirements for quantum public-key cryptosystems are not studied well. We propose several security notions for quantum public-key cryptosystems and discuss relation among them. In the classical setting, the notion of one-...

  17. Study of the lithiated phenylacetonitrile monoanions and dianions formed according to the lithiated base used (LHMDS, LDA, or n-BuLi). 2. Alkylation and deuteriation mechanism study by vibrational and NMR spectroscopy and quantum chemistry calculations.

    Science.gov (United States)

    Strzalko, Tekla; Wartski, Lya; Corset, Jacques; Castellà-Ventura, Martine; Froment, Françoise

    2012-08-01

    Mechanisms of alkylation by PhCH(2)Cl or CH(3)I in THF and of deuteriation by DCl (4 N in D(2)O) in THF or THF-toluene of lithiated phenylacetonitrile monoanions and dianions obtained with LHMDS, LDA, or n-BuLi are studied by vibrational and NMR spectroscopy and quantum chemistry calculations. Dialkylation of the three dilithio dianions generated with n-BuLi (2.0-2.7 equiv, THF-hexane) depends on their structure: N-lithio (PhCCNLi)(-)Li(+) and (C,N)-dilithio PhCLiCNLi dianions afford PhCR(2)CN (R = PhCH(2), CH(3)) from the intermediate N-lithio monoalkylated monoanion PhCRCNLi 10; C-lithio dianion (PhCLiCN)(-)Li(+) leads to a carbenoid species, the C-lithio monoalkylated nitrile PhCLiRCN 11, which either eliminates carbene Ph-C-R and different LiCN species or isomerizes to PhCRCNLi in the presence of LiX (X = Cl, I). Dialkylation or dideuteriation of monoanions (monomers, dimers, and heterodimers [PhCHCNLi·LiR'], R' = (SiMe(3))(2)N, (i-Pr)(2)N) obtained with LHMDS or LDA (2.4 equiv, THF) proceeds via a sequential mechanism involving monometalation-monoalkylation (or monodeuteriation) reactions. Some carbene and (LiCNLi)(+) are also observed, and explained by another mechanism implying the C-lithio monoalkylated monoanion PhCLiRCN 9 in the presence of LiX. These results show the ambiphilic behavior of PhCLiRCN as a carbenoid (11) or a carbanion (9) and the importance of LiX formed in situ in the first alkylation step.

  18. Extraction Behaviors of Heavy Rare Earths with Organophosphoric Extractants: The Contribution of Extractant Dimer Dissociation, Acid Ionization, and Complexation. A Quantum Chemistry Study.

    Science.gov (United States)

    Jing, Yu; Chen, Ji; Chen, Li; Su, Wenrou; Liu, Yu; Li, Deqian

    2017-03-30

    Heavy rare earths (HREs), namely Ho(3+), Er(3+), Tm(3+), Yb(3+) and Lu(3+), are rarer and more exceptional than light rare earths, due to the stronger extraction capacity for 100 000 extractions. Therefore, their incomplete stripping and high acidity of stripping become problems for HRE separation by organophosphoric extractants. However, the theories of extractant structure-performance relationship and molecular design method of novel HRE extractants are still not perfect. Beyond the coordination chemistry of the HRE-extracted complex, the extractant dimer dissociation, acid ionization, and complexation behaviors can be crucial to HRE extraction and reactivity of ionic species for understanding and further improving the extraction performance. To address the above issues, three primary fundamental processes, including extractant dimer dissociation, acid ionization, and HRE complexation, were identified and investigated systematically. The intrinsic extraction performances of HRE cations with four acidic organophosphoric extractants (P507, P204, P227 and Cyanex 272) were studied by using relativistic energy-consistent 4f core pseudopotentials, combined with density functional theory and a solvation model. Four acidic organophosphoric extractants have been qualified quantitatively from microscopic structures to chemical properties. It has been found that the Gibbs free energy changes of the overall extraction process (sequence: P204 > P227 > P507 > Cyanex 272) and their differences as a function of HREs (sequence: Ho/Er > Er/Tm > Tm/Yb > Yb/Lu) are in good agreement with the experimental maximum extraction capacities and separation factors. These results could provide an important approach to evaluate HRE extractants by the comprehensive consideration of dimer dissociation, acid ionization, and complexation processes. This paper also demonstrates the importance of the P-O bond, the P-C bond, isomer substituent, and solvation effects on the structure

  19. Quantum Diffusion-Controlled Chemistry: Reactions of Atomic Hydrogen with Nitric Oxide in Solid Parahydrogen.

    Science.gov (United States)

    Ruzi, Mahmut; Anderson, David T

    2015-12-17

    Our group has been working to develop parahydrogen (pH2) matrix isolation spectroscopy as a method to study low-temperature condensed-phase reactions of atomic hydrogen with various reaction partners. Guided by the well-defined studies of cold atom chemistry in rare-gas solids, the special properties of quantum hosts such as solid pH2 afford new opportunities to study the analogous chemical reactions under quantum diffusion conditions in hopes of discovering new types of chemical reaction mechanisms. In this study, we present Fourier transform infrared spectroscopic studies of the 193 nm photoinduced chemistry of nitric oxide (NO) isolated in solid pH2 over the 1.8 to 4.3 K temperature range. Upon short-term in situ irradiation the NO readily undergoes photolysis to yield HNO, NOH, NH, NH3, H2O, and H atoms. We map the postphotolysis reactions of mobile H atoms with NO and document first-order growth in HNO and NOH reaction products for up to 5 h after photolysis. We perform three experiments at 4.3 K and one at 1.8 K to permit the temperature dependence of the reaction kinetics to be quantified. We observe Arrhenius-type behavior with a pre-exponential factor of A = 0.036(2) min(-1) and Ea = 2.39(1) cm(-1). This is in sharp contrast to previous H atom reactions we have studied in solid pH2 that display definitively non-Arrhenius behavior. The contrasting temperature dependence measured for the H + NO reaction is likely related to the details of H atom quantum diffusion in solid pH2 and deserves further study.

  20. Interactive quantum chemistry: a divide-and-conquer ASED-MO method.

    Science.gov (United States)

    Bosson, Mäel; Richard, Caroline; Plet, Antoine; Grudinin, Sergei; Redon, Stephane

    2012-03-15

    We present interactive quantum chemistry simulation at the atom superposition and electron delocalization molecular orbital (ASED-MO) level of theory. Our method is based on the divide-and-conquer (D&C) approach, which we show is accurate and efficient for this non-self-consistent semiempirical theory. The method has a linear complexity in the number of atoms, scales well with the number of cores, and has a small prefactor. The time cost is completely controllable, as all steps are performed with direct algorithms, i.e., no iterative schemes are used. We discuss the errors induced by the D&C approach, first empirically on a few examples, and then via a theoretical study of two toy models that can be analytically solved for any number of atoms. Thanks to the precision and speed of the D&C approach, we are able to demonstrate interactive quantum chemistry simulations for systems up to a few hundred atoms on a current multicore desktop computer. When drawing and editing molecular systems, interactive simulations provide immediate, intuitive feedback on chemical structures. As the number of cores on personal computers increases, and larger and larger systems can be dealt with, we believe such interactive simulations-even at lower levels of theory-should thus prove most useful to effectively understand, design and prototype molecules, devices and materials.

  1. Study of Quantum Computing

    Directory of Open Access Journals (Sweden)

    Prashant Anil Patil

    2012-04-01

    Full Text Available This paper gives the detailed information about Quantum computer, and difference between quantum computer and traditional computers, the basis of Quantum computers which are slightly similar but still different from traditional computer. Many research groups are working towards the highly technological goal of building a quantum computer, which would dramatically improve computational power for particular tasks. Quantum computer is very much use full for computation purpose in field of Science and Research. Large amount of data and information will be computed, processing, storing, retrieving, transmitting and displaying information in less time with that much of accuracy which is not provided by traditional computers.

  2. Case Study: The Chemistry of Cocaine

    Science.gov (United States)

    Dewprashad, Brahmadeo

    2011-01-01

    This column provides original articles on innovations in case study teaching, assessment of the method, as well as case studies with teaching notes. This month's case study focuses on the chemistry of cocaine to teach a number of core concepts in organic chemistry. It also requires that students read and analyze an original research paper on…

  3. Case Study: The Chemistry of Cocaine

    Science.gov (United States)

    Dewprashad, Brahmadeo

    2011-01-01

    This column provides original articles on innovations in case study teaching, assessment of the method, as well as case studies with teaching notes. This month's case study focuses on the chemistry of cocaine to teach a number of core concepts in organic chemistry. It also requires that students read and analyze an original research paper on…

  4. Human development VIII: a theory of "deep" quantum chemistry and cell consciousness: quantum chemistry controls genes and biochemistry to give cells and higher organisms consciousness and complex behavior.

    Science.gov (United States)

    Ventegodt, Søren; Hermansen, Tyge Dahl; Flensborg-Madsen, Trine; Nielsen, Maj Lyck; Merrick, Joav

    2006-11-14

    Deep quantum chemistry is a theory of deeply structured quantum fields carrying the biological information of the cell, making it able to remember, intend, represent the inner and outer world for comparison, understand what it "sees", and make choices on its structure, form, behavior and division. We suggest that deep quantum chemistry gives the cell consciousness and all the qualities and abilities related to consciousness. We use geometric symbolism, which is a pre-mathematical and philosophical approach to problems that cannot yet be handled mathematically. Using Occam's razor we have started with the simplest model that works; we presume this to be a many-dimensional, spiral fractal. We suggest that all the electrons of the large biological molecules' orbitals make one huge "cell-orbital", which is structured according to the spiral fractal nature of quantum fields. Consciousness of single cells, multi cellular structures as e.g. organs, multi-cellular organisms and multi-individual colonies (like ants) and human societies can thus be explained by deep quantum chemistry. When biochemical activity is strictly controlled by the quantum-mechanical super-orbital of the cell, this orbital can deliver energetic quanta as biological information, distributed through many fractal levels of the cell to guide form and behavior of an individual single or a multi-cellular organism. The top level of information is the consciousness of the cell or organism, which controls all the biochemical processes. By this speculative work inspired by Penrose and Hameroff we hope to inspire other researchers to formulate more strict and mathematically correct hypothesis on the complex and coherence nature of matter, life and consciousness.

  5. Quantum Chemistry in Nanoscale Environments: Insights on Surface-Enhanced Raman Scattering and Organic Photovoltaics

    Science.gov (United States)

    Olivares-Amaya, Roberto

    The understanding of molecular effects in nanoscale environments is becoming increasingly relevant for various emerging fields. These include spectroscopy for molecular identification as well as in finding molecules for energy harvesting. Theoretical quantum chemistry has been increasingly useful to address these phenomena to yield an understanding of these effects. In the first part of this dissertation, we study the chemical effect of surface-enhanced Raman scattering (SERS). We use quantum chemistry simulations to study the metal-molecule interactions present in these systems. We find that the excitations that provide a chemical enhancement contain a mixed contribution from the metal and the molecule. Moreover, using atomistic studies we propose an additional source of enhancement, where a transition metal dopant surface could provide an additional enhancement. We also develop methods to study the electrostatic effects of molecules in metallic environments. We study the importance of image-charge effects, as well as field-bias to molecules interacting with perfect conductors. The atomistic modeling and the electrostatic approximation enable us to study the effects of the metal interacting with the molecule in a complementary fashion, which provides a better understanding of the complex effects present in SERS. In the second part of this dissertation, we present the Harvard Clean Energy Project, a high-throughput approach for a large-scale computational screening and design of organic photovoltaic materials. We create molecular libraries to search for candidates structures and use quantum chemistry, machine learning and cheminformatics methods to characterize these systems and find structure-property relations. The scale of this study requires an equally large computational resource. We rely on distributed volunteer computing to obtain these properties. In the third part of this dissertation we present our work related to the acceleration of electronic structure

  6. Problems and solutions in quantum chemistry and physics

    CERN Document Server

    Johnson, Charles S

    1988-01-01

    Unusually varied problems, with detailed solutions, cover quantum mechanics, wave mechanics, angular momentum, molecular spectroscopy, scattering theory, more. 280 problems, plus 139 supplementary exercises.

  7. A Synthesis of Fluid Dynamics and Quantum Chemistry for the Design of Nanoelectronics

    Science.gov (United States)

    MacDougall, Preston J.

    1998-01-01

    In 1959, during a famous lecture entitled "There's Plenty of Room at the Bottom", Richard Feynman focused on the startling technical possibilities that would exist at the limit of miniaturization, that being atomically precise devices with dimensions in the nanometer range. A nanometer is both a convenient unit of length for medium to large sized molecules, and the root of the name of the new interdisciplinary field of "nanotechnology". Essentially, "nanoelectronics" denotes the goal of shrinking electronic devices, such as diodes and transistors, as well as integrated circuits of such devices that can perform logical operations, down to dimensions in the range of 100 nanometers. The thirty-year hiatus in the development of nanotechnology can figuratively be seen as a period of waiting for the bottom-up and atomically precise construction skills of synthetic chemistry to meet the top-down reductionist aspirations of device physics. The sub-nanometer domain of nineteenth-century classical chemistry has steadily grown, and state-of-the-art supramolecular chemistry can achieve atomic precision in non-repeating molecular assemblies of the size desired for nanotechnology. For nanoelectronics in particular, a basic understanding of the electron transport properties of molecules must also be developed. Quantum chemistry provides powerful computational methods that can accurately predict the properties of small to medium sized molecules on a desktop workstation, and those of large molecules if one has access to a supercomputer. Of the many properties of a molecule that quantum chemistry routinely predicts, the ability to carry a current is one that had not even been considered until recently. "Currently", there is a controversy over just how to define this key property. Reminiscent of the situation in high-Tc superconductivity, much of the difficulty arises from the different models that are used to simplify the complex electronic structure of real materials. A model

  8. Atoms and molecules in cavities, from weak to strong coupling in quantum-electrodynamics (QED) chemistry.

    Science.gov (United States)

    Flick, Johannes; Ruggenthaler, Michael; Appel, Heiko; Rubio, Angel

    2017-03-21

    In this work, we provide an overview of how well-established concepts in the fields of quantum chemistry and material sciences have to be adapted when the quantum nature of light becomes important in correlated matter-photon problems. We analyze model systems in optical cavities, where the matter-photon interaction is considered from the weak- to the strong-coupling limit and for individual photon modes as well as for the multimode case. We identify fundamental changes in Born-Oppenheimer surfaces, spectroscopic quantities, conical intersections, and efficiency for quantum control. We conclude by applying our recently developed quantum-electrodynamical density-functional theory to spontaneous emission and show how a straightforward approximation accurately describes the correlated electron-photon dynamics. This work paves the way to describe matter-photon interactions from first principles and addresses the emergence of new states of matter in chemistry and material science.

  9. Photoelectron Imaging as a Quantum Chemistry Visualization Tool

    Science.gov (United States)

    Grumbling, Emily R.; Pichugin, Kostyantyn; Mabbs, Richard; Sanov, Andrei

    2011-01-01

    An overview and simple example of photoelectron imaging is presented, highlighting its efficacy as a pedagogical tool for visualizing quantum phenomena. Specifically, photoelectron imaging of H[superscript -] (the simplest negative ion) is used to demonstrate several quantum mechanical principles. This example could be incorporated into an…

  10. Linear-scaling and parallelizable algorithms for stochastic quantum chemistry

    CERN Document Server

    Booth, George H; Alavi, Ali

    2013-01-01

    For many decades, quantum chemical method development has been dominated by algorithms which involve increasingly complex series of tensor contractions over one-electron orbital spaces. Procedures for their derivation and implementation have evolved to require the minimum amount of logic and rely heavily on computationally efficient library-based matrix algebra and optimized paging schemes. In this regard, the recent development of exact stochastic quantum chemical algorithms to reduce computational scaling and memory overhead requires a contrasting algorithmic philosophy, but one which when implemented efficiently can often achieve higher accuracy/cost ratios with small random errors. Additionally, they can exploit the continuing trend for massive parallelization which hinders the progress of deterministic high-level quantum chemical algorithms. In the Quantum Monte Carlo community, stochastic algorithms are ubiquitous but the discrete Fock space of quantum chemical methods is often unfamiliar, and the metho...

  11. Studies in quantum information theory

    Science.gov (United States)

    Menicucci, Nicolas C.

    potential for use as generic quantum systems over which the experimenter has exquisite control and which can be used to simulate other quantum systems and also study generic quantum phenomena. This is followed by a proposal for using a trapped ion as a time-dependent harmonic oscillator---a quantum system that is common in theoretical literature but of which few laboratory examples are known. A second project studies the way that quantum fluctuations in the vibrational state of a chain of ions influence correlations in optical measurements made on the ions. The final part looks at quantum information theory in a relativistic setting. An introduction discusses the interface between quantum information theory and relativity in general, including the nonclassical notion of entanglement and the peculiar features of curved-space quantum field theory. An original gedankenexperiment combines these ideas and examines whether entanglement---a quantum information-theoretic concept and physical resource---can be used to distinguish universes of different curvature in a situation where local measurements would show no difference. These three parts are followed by a personal (and possibly controversial) conclusion, which describes my fascination with---and ultimately my reason for pursuing---studies in quantum information theory.

  12. Quantum chemistry calculation-aided structural optimization of combretastatin A-4-like tubulin polymerization inhibitors: improved stability and biological activity.

    Science.gov (United States)

    Jiang, Junhang; Zheng, Canhui; Zhu, Kongkai; Liu, Jia; Sun, Nannan; Wang, Chongqing; Jiang, Hualiang; Zhu, Ju; Luo, Cheng; Zhou, Youjun

    2015-03-12

    A potent combretastatin A-4 (CA-4) like tubulin polymerization inhibitor 22b was found with strong antitumor activity previously. However, it easily undergoes cis-trans isomerization under natural light, and the resulting decrease in activity limits its further applications. In this study, we used quantum chemistry calculations to explore the molecular basis of its instability. Aided by the calculations, two rounds of structural optimization of 22b were conducted. Accelerated quantitative light stability testing confirmed that the stability of these designed compounds was significantly improved as predicted. Among them, compounds 1 and 3b displayed more potent inhibitory activity on tumor cell growth than 22b. In addition, the potent in vivo antitumor activity of compound 1 was confirmed. Quantum chemistry calculations were used in the optimization of stilbene-like molecules, providing new insight into stilbenoid optimization and important implications for the future development of novel CA-4-like tubulin polymerization inhibitors.

  13. Langmuir adsorption study of the interaction of CdSe/ZnS quantum dots with model substrates: influence of substrate surface chemistry and pH.

    Science.gov (United States)

    Park, Jung Jin; Lacerda, Silvia H De Paoli; Stanley, Scott K; Vogel, Brandon M; Kim, Sangcheol; Douglas, Jack F; Raghavan, Dharmaraj; Karim, Alamgir

    2009-01-06

    We investigate the utility of Langmuir adsorption measurements for characterizing nanoparticle-substrate interactions. Spherical CdSe/ZnS core-shell nanoparticles were chosen as representative particles because of their widespread use in biological labeling measurements and their relatively monodisperse dimensions. In particular, the quantum dots were functionalized with 11-mercaptoundecanoic acid, and we utilized an amine-terminated self-assembled monolayer (SAM) as a model substrate. SAMs with different end-groups (-CH(3) and -COOH) were also considered to contrast with the adsorption behavior on the amine-terminated SAM substrates. We followed the kinetics of nanoparticle adsorption on the aminosilane layer by quartz crystal microgravimetry (QCM) over a range of particle concentrations and determined the corresponding Langmuir adsorption isotherms. Analysis of both equilibrium adsorption and kinetic adsorption data allowed us to determine a consistent value of the Langmuir adsorption equilibrium constant for the amine-terminated SAM at room temperature (K(L) approximately 2.7 (micromol/L)(-1)), providing a useful characterization of the nanoparticle-substrate interaction. The effect of varying solution pH on Langmuir adsorption was also investigated in order to gain insight into the role of electrostatic interactions on nanoparticle adsorption. The equilibrium extent of adsorption was found to be maximum at about pH 7. These changes of nanoparticle adsorption were further quantified and validated by X-ray photoelectron spectroscopy (XPS) and confocal fluorescence microscopy measurements. We conclude that Langmuir adsorption measurements provide a promising approach for quantifying nanoparticle-substrate interactions.

  14. Influence of Force Fields and Quantum Chemistry Approach on Spectral Densities of BChl a in Solution and in FMO Proteins.

    Science.gov (United States)

    Chandrasekaran, Suryanarayanan; Aghtar, Mortaza; Valleau, Stéphanie; Aspuru-Guzik, Alán; Kleinekathöfer, Ulrich

    2015-08-06

    Studies on light-harvesting (LH) systems have attracted much attention after the finding of long-lived quantum coherences in the exciton dynamics of the Fenna-Matthews-Olson (FMO) complex. In this complex, excitation energy transfer occurs between the bacteriochlorophyll a (BChl a) pigments. Two quantum mechanics/molecular mechanics (QM/MM) studies, each with a different force-field and quantum chemistry approach, reported different excitation energy distributions for the FMO complex. To understand the reasons for these differences in the predicted excitation energies, we have carried out a comparative study between the simulations using the CHARMM and AMBER force field and the Zerner intermediate neglect of differential orbital (ZINDO)/S and time-dependent density functional theory (TDDFT) quantum chemistry methods. The calculations using the CHARMM force field together with ZINDO/S or TDDFT always show a wider spread in the energy distribution compared to those using the AMBER force field. High- or low-energy tails in these energy distributions result in larger values for the spectral density at low frequencies. A detailed study on individual BChl a molecules in solution shows that without the environment, the density of states is the same for both force field sets. Including the environmental point charges, however, the excitation energy distribution gets broader and, depending on the applied methods, also asymmetric. The excitation energy distribution predicted using TDDFT together with the AMBER force field shows a symmetric, Gaussian-like distribution.

  15. Neural Network Based on Quantum Chemistry for Predicting Melting Point of Organic Compounds

    Institute of Scientific and Technical Information of China (English)

    Juan A. Lazzús

    2009-01-01

    The melting points of organic compounds were estimated using a combined method that includes a backpropagation neural network and quantitative structure property relationship (QSPR) parameters in quantum chemistry. Eleven descriptors that reflect the intermolec-ular forces and molecular symmetry were used as input variables. QSPR parameters were calculated using molecular modeling and PM3 semi-empirical molecular orbital theories. A total of 260 compounds were used to train the network, which was developed using MatLab. Then, the melting points of 73 other compounds were predicted and results were compared to experimental data from the literature. The study shows that the chosen artificial neural network and the quantitative structure property relationships method present an excellent alternative for the estimation of the melting point of an organic compound, with average absolute deviation of 5%.

  16. Bridging the Gap Between Quantum Chemistry and Classical Simulations for CO2 Capture

    Energy Technology Data Exchange (ETDEWEB)

    Gagliardi, Laura [Univ. of Minnesota, Minneapolis, MN (United States)

    2015-09-17

    We have developed a systematic procedure to generate transferable force fields to simulate the behavior of CO2 and other gases in open-metal-site metal organic frameworks using high-level quantum chemical calculations. Monte Carlo simulations based on an ab initio force field for CO2 in the Mg2(dobpdc) material have been employed to describe the interactions of CO2 with open metals. Our study has shed some light on the interpretation of thermodynamic data of flue gas in Mg2(dobpdc). This force field accurately describes the chemistry of the open metal sites, and is transferable to other structures.

  17. Many-body quantum chemistry for the electron gas: convergent perturbative theories

    CERN Document Server

    Shepherd, James J

    2013-01-01

    We investigate the accuracy of a number of wavefunction based methods at the heart of quantum chemistry for metallic systems. Using Hartree-Fock as a reference, perturbative (M{\\o}ller-Plesset, MP) and coupled cluster (CC) theories are used to study the uniform electron gas model. Our findings suggest that non-perturbative coupled cluster theories are acceptable for modelling electronic interactions in metals whilst perturbative coupled cluster theories are not. Using screened interactions, we propose a simple modification to the widely-used coupled-cluster singles and doubles plus perturbative triples method (CCSD(T)) that lifts the divergent behaviour and is shown to give very accurate correlation energies for the homogeneous electron gas.

  18. Molecular Orbitals of NO, NO[superscript+], and NO[superscript-]: A Computational Quantum Chemistry Experiment

    Science.gov (United States)

    Orenha, Renato P.; Galembeck, Sérgio E.

    2014-01-01

    This computational experiment presents qualitative molecular orbital (QMO) and computational quantum chemistry exercises of NO, NO[superscript+], and NO[superscript-]. Initially students explore several properties of the target molecules by Lewis diagrams and the QMO theory. Then, they compare qualitative conclusions with EHT and DFT calculations…

  19. The Relationships between PCK Components: The Case of Quantum Chemistry Professors

    Science.gov (United States)

    Padilla, Kira; Van Driel, Jan

    2011-01-01

    The purpose of this paper is to capture the pedagogical content knowledge (PCK) of university professors about quantum chemistry. More specifically, we aimed to identify and analyze relationships between specific PCK components, using an adapted version of the model of PCK of Magnusson "et al.". A sample of university professors (n = 6)…

  20. Ab Initio Studies of Stratospheric Ozone Depletion Chemistry

    Science.gov (United States)

    Lee, Timothy J.; Head-Gordon, Martin; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    An overview of the current understanding of ozone depletion chemistry, particularly with regards the formation of the so-called Antarctic ozone hole, will be presented together with an outline as to how ab initio quantum chemistry can be used to further our understanding of stratospheric chemistry. The ability of modern state-of-the art ab initio quantum chemical techniques to characterize reliably the gas-phase molecular structure, vibrational spectrum, electronic spectrum, and thermal stability of fluorine, chlorine, bromine and nitrogen oxide species will be demonstrated by presentation of some example studies. The ab initio results will be shown to be in excellent agreement with the available experimental data, and where the experimental data are either not known or are inconclusive, the theoretical results are shown to fill in the gaps and to resolve experimental controversies. In addition, ab initio studies in which the electronic spectra and the characterization of excited electronic states of halogen oxide species will also be presented. Again where available, the ab initio results are compared to experimental observations, and are used to aid in the interpretation of experimental studies.

  1. Quantum Chemistry Study on Paralytic Shellfish Poisoning Toxins%麻痹性贝毒素生物毒性的量子化学研究

    Institute of Scientific and Technical Information of China (English)

    张永清; 刁宁

    2011-01-01

    Quantum chemical descriptors computed with density functional theory at the B3LYP/6-31G (d) level and the modified ant colony algorithm with amended Cp statistical quantity as an objective function were used to set up QSAR models for the natural logarithm of semi-lethal doses of 17 paralytic shellfish poisoning (PSP) toxins. The model with high correlation coefficients (R2=0.968) and a high cross-validation test result (q2=0.858) shows that the model has high precision and good prediction capacity. The jackknife method is also used to test the model's stability and reliability. Among the descriptors investigated, the eigenvalue of the highest occupied molecular orbital plays the most important role in the lethal dose of PSP toxins, and the next highest occupied molecular orbital plays an important role in the medium lethal dose of PSP toxins. Thus it is concluded that the interaction of molecular orbitals and the molecule's reactivity have decisive influence on the biotoxicity of PSP toxins.%运用密度泛函(DFT)理论在B3LYP/6-31G(d)水平下计算了17种麻痹性贝毒素的量子化学结构描述符,采用修正Cp统计量为目标函数的改进蚁群算法进行变量选择,建立了麻痹性贝毒素的半数致死浓度与其量化参数之间的QSAR模型;模型的决定系数R2为0.968,交叉验证系数q2为0.858,表明模型具备良好的拟合效果和较好的预测能力;同时使用"jackknife法"检验模型,相关系数R有16个落在0.982-0.987之间,占总数的94.1%,表明模型具有较强的稳健性.在所考察的诸多参数中,分子最高占有轨道特征值EHOMO对麻痹性贝类毒素的半数致死剂量影响最大,其次为分子的次高占据轨道能量ENHOMO,说明分子的轨道相互作用和反应活性对麻痹性贝毒素的生物毒性具有决定性的影响.

  2. Industrial Chemistry Option in MSc Studies in Chemistry.

    Science.gov (United States)

    Shani, Arnon

    1982-01-01

    Discusses the rationale for and development of an industrial chemistry program in chemistry at Ben-Gurion University of the Negev in Israel. Includes an outline of the recommended 2-year curriculum and list of courses in this industrial chemistry option leading to a master of science degree. (Author/JN)

  3. GPU Linear Algebra Libraries and GPGPU Programming for Accelerating MOPAC Semiempirical Quantum Chemistry Calculations.

    Science.gov (United States)

    Maia, Julio Daniel Carvalho; Urquiza Carvalho, Gabriel Aires; Mangueira, Carlos Peixoto; Santana, Sidney Ramos; Cabral, Lucidio Anjos Formiga; Rocha, Gerd B

    2012-09-11

    In this study, we present some modifications in the semiempirical quantum chemistry MOPAC2009 code that accelerate single-point energy calculations (1SCF) of medium-size (up to 2500 atoms) molecular systems using GPU coprocessors and multithreaded shared-memory CPUs. Our modifications consisted of using a combination of highly optimized linear algebra libraries for both CPU (LAPACK and BLAS from Intel MKL) and GPU (MAGMA and CUBLAS) to hasten time-consuming parts of MOPAC such as the pseudodiagonalization, full diagonalization, and density matrix assembling. We have shown that it is possible to obtain large speedups just by using CPU serial linear algebra libraries in the MOPAC code. As a special case, we show a speedup of up to 14 times for a methanol simulation box containing 2400 atoms and 4800 basis functions, with even greater gains in performance when using multithreaded CPUs (2.1 times in relation to the single-threaded CPU code using linear algebra libraries) and GPUs (3.8 times). This degree of acceleration opens new perspectives for modeling larger structures which appear in inorganic chemistry (such as zeolites and MOFs), biochemistry (such as polysaccharides, small proteins, and DNA fragments), and materials science (such as nanotubes and fullerenes). In addition, we believe that this parallel (GPU-GPU) MOPAC code will make it feasible to use semiempirical methods in lengthy molecular simulations using both hybrid QM/MM and QM/QM potentials.

  4. 树状分子聚酰胺胺(PAMAM)的量子化学研究%Quantum chemistry study of the PAMAM dendrimer

    Institute of Scientific and Technical Information of China (English)

    胡姣姣; 李海琴; 周朝昕; 杨祥; 陈婷; 房晓燕

    2009-01-01

    The molecular structure of EDA-cored 1.0G polyamidoamine (PAMAM) was fully geometrical optimized using the density functional theory (DFT) B3LYP method, as well as Hartree-Fock method at both 3-21G and 6-31G* level. The results obtained at various levels were discussed and compared with each other and with the available experimental datas. It was shown that the calculations performed at B3LYP/6-31G * level could produce more reliable results. The results derived at B3LYP/6-31G * level were studied. The steady conformation was not entirely symmetrical, and the four branches were basically on the same plane. The primary amine, tertiary and secondary amine brought about by the decreasing number of negative charge, and the highest occupied molecular orbital concentrated on the nuclear.%采用传统的Hartree-Fock(HF)从头算和密度泛函B3LYP方法,选择不同的基组水平(3-21G,6-31G*)对以乙二胺为核的1.0代PAMAM分子进行全几何优化,并对结果进行比较,同时与实验值进行对照.结果表明,B3LYP/6-31G*方法得到的结果更可靠.B3LYP/6.31G*计算结果表明,1.0代PAMAM分子构象不完全对称,4个支链基本在一个平面上,伯胺,仲胺和叔胺上的N原子所带负电荷数逐渐减少,HOMO轨道主要集中在核上,核极易发挥供电子作用.

  5. Electronic Properties of Two Series of Blue-Emitting Conjugated Oligomers and Polymers Based on Cyanostilbene:A Quantum Chemistry Study

    Institute of Scientific and Technical Information of China (English)

    YANG, Li; FENG, Ji-Kang; REN, Ai-Min

    2007-01-01

    One of the drawbacks of the electroluminescence (EL) polymers is that they are usually much better at accepting and transporting holes than electrons due to their inherent richness of π-electrons. One approach improving electron injection and transport in conjugatel polymers is to incorporate moieties with high electron affinities. In this theoretical work, to gain an insight into the chemical structure-property relationships was aimed by controllable modification of the main chain structures. Two cyanovinylene derivatives with 2,7-fluorenylene and p-phenylene moieties in the main chains, namely, poly{(2,5-dimethoxy-p-phenylene-1,4-ylene)-alt-[1,2-bis(p-phenylene)-1-cyanovinylene]} (PPhCN) and poly{[9,9-dimethyl-2,7-fluorenylene]-alt-[1,2-bis(p-phenylene)-1-cyanovinylene]}(PFCN), were studied employing density functional theory (DFT) and time dependent density functional theory (TD-DFT) with B3LYP functional. The electronic properties of the neutral molecules, extrapolated ionization potentials (IP) and electron affinities (EA), and energy gaps were investigated in comparison with pristine poly(2,7-fluorenylene). From comparison with poly(2,7-fluorenylene) (PF), the 1,2-bis(p-phenylene)-1-cyanovi- nylene unit was found to be a good electron-withdrawing moiety for electronic materials and the incorporation of 1,2-bis(pphenylene)-1-cyanovinylene resulted in a narrow band gap and ared shift of both the absorption and photoluminescence emission peaks. Most importantly, the LUMO energies of PFCN are around 1 eV lower than those of PF,which results in the decrement of EA about 0.9 eV, indicating that the 1,2-bis(p-phenylene)-1-cyanovinylene unit has significantly improved the electron-accepting properties of the copolymer PFCN. Substitution of 2,5-dimeth-oxy-p-phenylene for 9,9-dimethyl-2,7-fluorenylene induced larger band gaps and thus a blue-shift in absorption and emission peaks, which can be attributed to the better conjugated backbone in PFCN.

  6. Test of quantum chemistry in vibrationally-hot hydrogen molecules

    CERN Document Server

    Niu, M L; Ubachs, W

    2015-01-01

    Precision measurements are performed on highly excited vibrational quantum states of molecular hydrogen. The $v=12, J=0-3$ rovibrational levels of H$_2$ ($X^1\\Sigma_g^+$), lying only $2000$ cm$^{-1}$ below the first dissociation limit, were populated by photodissociation of H$_2$S and their level energies were accurately determined by two-photon Doppler-free spectroscopy. A comparison between the experimental results on $v=12$ level energies with the best \\textit{ab initio} calculations shows good agreement, where the present experimental accuracy of $3.5 \\times10^{-3}$ cm$^{-1}$ is more precise than theory, hence providing a gateway to further test theoretical advances in this benchmark quantum system.

  7. A Química Quântica na compreensão de teorias de Química Orgânica The Quantum Chemistry in the understanding of theories of Organic Chemistry

    Directory of Open Access Journals (Sweden)

    Régis Casimiro Leal

    2010-01-01

    Full Text Available Quantum chemical calculations were performed in order to obtain molecular properties such as electronic density, dipole moment, atomic charges, and bond lengths, which were compared to qualitative results based on the theories of the organic chemistry. The quantum chemistry computational can be a useful tool to support the main theories of the organic chemistry.

  8. Determination of Quantum Chemistry Based Force Fields for Molecular Dynamics Simulations of Aromatic Polymers

    Science.gov (United States)

    Jaffe, Richard; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    Ab initio quantum chemistry calculations for model molecules can be used to parameterize force fields for molecular dynamics simulations of polymers. Emphasis in our research group is on using quantum chemistry-based force fields for molecular dynamics simulations of organic polymers in the melt and glassy states, but the methodology is applicable to simulations of small molecules, multicomponent systems and solutions. Special attention is paid to deriving reliable descriptions of the non-bonded and electrostatic interactions. Several procedures have been developed for deriving and calibrating these parameters. Our force fields for aromatic polyimide simulations will be described. In this application, the intermolecular interactions are the critical factor in determining many properties of the polymer (including its color).

  9. Quantum Chemistry of Solids The LCAO First Principles Treatment of Crystals

    CERN Document Server

    Evarestov, Robert A

    2007-01-01

    Quantum Chemistry of Solids delivers a comprehensive account of the main features and possibilities of LCAO methods for the first principles calculations of electronic structure of periodic systems. The first part describes the basic theory underlying the LCAO methods applied to periodic systems and the use of wave-function-based (Hartree-Fock), density-based (DFT) and hybrid hamiltonians. The translation and site symmetry consideration is included to establish connection between k-space solid-state physics and real-space quantum chemistry methods in the framework of cyclic model of an infinite crystal. The inclusion of electron correlation effects for periodic systems is considered on the basis of localized crystalline orbitals. The possibilities of LCAO methods for chemical bonding analysis in periodic systems are discussed. The second part deals with the applications of LCAO methods for calculations of bulk crystal properties, including magnetic ordering and crystal structure optimization. The discussion o...

  10. Liquefaction chemistry and kinetics: Hydrogen utilization studies

    Energy Technology Data Exchange (ETDEWEB)

    Rothenberger, K.S.; Warzinski, R.P.; Cugini, A.V. [Pittsburgh Energy Technology Center, PA (United States)] [and others

    1995-12-31

    The objectives of this project are to investigate the chemistry and kinetics that occur in the initial stages of coal liquefaction and to determine the effects of hydrogen pressure, catalyst activity, and solvent type on the quantity and quality of the products produced. The project comprises three tasks: (1) preconversion chemistry and kinetics, (2) hydrogen utilization studies, and (3) assessment of kinetic models for liquefaction. The hydrogen utilization studies work will be the main topic of this report. However, the other tasks are briefly described.

  11. A Need to Reassess Physical-Organic Curricula: A Course Enhancement Using Readily Available Quantum Chemistry Programs.

    Science.gov (United States)

    Lipkowitz, Kenny B.

    1982-01-01

    Describes a graduate-level course in physical-organic chemistry in which students learn to solve problems using computer programs available through the Quantum Chemistry Program Exchange. Includes condensed syllabus and time line showing where various computational programs are introduced. (Author/JN)

  12. On the applicability of one- and many-electron quantum chemistry models for hydrated electron clusters.

    Science.gov (United States)

    Turi, László

    2016-04-21

    We evaluate the applicability of a hierarchy of quantum models in characterizing the binding energy of excess electrons to water clusters. In particular, we calculate the vertical detachment energy of an excess electron from water cluster anions with methods that include one-electron pseudopotential calculations, density functional theory(DFT) based calculations, and ab initio quantum chemistry using MP2 and eom-EA-CCSD levels of theory. The examined clusters range from the smallest cluster size (n = 2) up to nearly nanosize clusters with n = 1000 molecules. The examined cluster configurations are extracted from mixed quantum-classical molecular dynamics trajectories of cluster anions with n = 1000 water molecules using two different one-electron pseudopotenial models. We find that while MP2 calculations with large diffuse basis set provide a reasonable description for the hydrated electron system, DFT methods should be used with precaution and only after careful benchmarking. Strictly tested one-electron psudopotentials can still be considered as reasonable alternatives to DFT methods, especially in large systems. The results of quantum chemistry calculations performed on configurations, that represent possible excess electron binding motifs in the clusters, appear to be consistent with the results using a cavitystructure preferring one-electron pseudopotential for the hydrated electron, while they are in sharp disagreement with the structural predictions of a non-cavity model.

  13. Benzoxazoles and oxazolopyridines in medicinal chemistry studies

    DEFF Research Database (Denmark)

    Demmer, Charles S; Bunch, Lennart

    2015-01-01

    and the use of benzoxazole as a bioisostere are discussed. The review is extended to cover structure-activity relationship studies of 2-substituted benzoxazoles, 2-substituted oxazolopyridines, and in perspective, application of the recently published novel heterocycle oxazolopyrazine in medicinal chemistry...

  14. Surface Chemistry of Semiconducting Quantum Dots: Theoretical Perspectives.

    Science.gov (United States)

    Kilina, Svetlana V; Tamukong, Patrick K; Kilin, Dmitri S

    2016-10-18

    Colloidal quantum dots (QDs) are near-ideal nanomaterials for energy conversion and lighting technologies. However, their photophysics exhibits supreme sensitivity to surface passivation and defects, of which control is problematic. The role of passivating ligands in photodynamics remains questionable and is a focus of ongoing research. The optically forbidden nature of surface-associated states makes direct measurements on them challenging. Therefore, computational modeling is imperative for insights into surface passivation and its impact on light-driven processes in QDs. This Account discusses challenges and recent progress in understanding surface effects on the photophysics of QDs addressed via quantum-chemical calculations. We overview different methods, including the effective mass approximation (EMA), time-dependent density functional theory (TDDFT), and multiconfiguration approaches, considering their strengths and weaknesses relevant to modeling of QDs with a complicated surface. We focus on CdSe, PbSe, and Si QDs, where calculations successfully explain experimental trends sensitive to surface defects, doping, and ligands. We show that the EMA accurately describes both linear and nonlinear optical properties of large-sized CdSe QDs (>2.5 nm), while TDDFT is required for smaller QDs where surface effects dominate. Both approaches confirm efficient two-photon absorption enabling applications of QDs as nonlinear optical materials. TDDFT also describes the effects of morphology on the optical response of QDs: the photophysics of stoichiometric, magic-sized XnYn (X = Cd, Pb; Y = S, Se) QDs is less sensitive to their passivation compared with nonstoichiometric Xn≠mYm QDs. In the latter, surface-driven optically inactive midgap states can be eliminated by anionic ligands, explaining the better emission of metal-enriched QDs compared with nonmetal-enriched QDs. Ideal passivation of magic-sized QDs by amines and phosphine oxides leaves lower-energy transitions

  15. A study on quantum similarity in the phase space

    Science.gov (United States)

    Sellier, J. M.; Ivanova, D. Y.; Dimov, I.

    2016-10-01

    Quantum similarity represents an important concept in the context of many applied disciplines such as physical and quantum chemistry. Nowadays, two definitions exist based, respectively, on the real and the phase spaces. In this paper, we focus on the second one, which was presented recently, and investigate it. In particular, being its mathematical definition dependent on a given integer s, we study the influence of this parameter on the similarity between two systems. To keep this investigation comprehensible, while still meaningful, we focus on a very simple quantum system represented by a hydrogen atom in the ground and excited states corresponding to the quantum numbers (n , l , m) =(1 , 0 , 0) and (n , l , m) =(2 , 0 , 0) .

  16. Student and Teacher Perceptions of Industrial Chemistry Case Studies.

    Science.gov (United States)

    Kesner, Miri; Hofstein, Avi; Ben-Zvi, Ruth

    1997-01-01

    Describes a study conducted in Israel that focuses on how studying industrial-chemistry case studies affects students' perceptions of their learning environment and their interest in chemistry studies. Contains 18 references. (DDR)

  17. 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 ...

  18. NATO Advanced Study Institute on Fundamental and Technological Aspects of Organo-f-Element Chemistry

    CERN Document Server

    Fragalà, Ignazio

    1985-01-01

    The past decade has seen a dramatic acceleration of activity and interest in phenomena surrounding lanthanide and actinide organo­ metallic compounds. Around the world, active research in organo-f­ element synthesis, chemistry, catalysis, crystallography, and quantum chemistry is in progress. This activity has spanned a remarkably wide range of disciplines, from synthetic/mechanistic inorganic and organic chemistry to radiochemistry, catalytic chemistry, spectroscopy (vibra­ tional, optical, magnetic resonance, photoelectron, Mossbauer), X-ray and neutron diffraction structural analysis, as well as to crystal field and molecular orbital theoretical studies at the interface of chemistry and physics. These investigations have been motivated both by fundamental and applied goals. The evidence that f-element organo­ metallic compounds have unique chemical and physical properties which cannot be duplicated by organometallic compounds of d-block elements has suggested many new areas of endeavor and application....

  19. Glycoconjugated amphiphilic polymers via click-chemistry for the encapsulation of quantum dots.

    Science.gov (United States)

    Schmidtke, Christian; Kreuziger, Anna-Marlena; Alpers, Dirk; Jacobsen, Anna; Leshch, Yevgeniy; Eggers, Robin; Kloust, Hauke; Tran, Huong; Ostermann, Johannes; Schotten, Theo; Thiem, Joachim; Thimm, Julian; Weller, Horst

    2013-10-08

    Herein, we present a strategy for the glycoconjugation of nanoparticles (NPs), with a special focus on fluorescent quantum dots (QDs), recently described by us as "preassembly" approach. Therein, prior to the encapsulation of diverse nanoparticles by an amphiphilic poly(isoprene)-b-poly(ethylene glycol) diblock copolymer (PI-b-PEG), the terminal PEG appendage was modified by covalently attaching a carbohydrate moiety using Huisgen-type click-chemistry. Successful functionalization was proven by NMR spectroscopy. The terminally glycoconjugated polymers were subsequently used for the encapsulation of QDs in a phase transfer process, which fully preserved fluorescence properties. Binding of these nanoconstructs to the lectin Concanavalin A (Con A) was studied via surface plasmon resonance (SPR). Depending on the carbohydrate moiety, namely, D-manno-heptulose, D-glucose, D-galactose, 2-deoxy-2-{[methylamino)carbonyl]amino}-D-glucopyranose ("des(nitroso)-streptozotocin"), or D-maltose, the glycoconjugated QDs showed enhanced affinity constants due to multivalent binding effects. None of the constructs showed toxicity from 0.001 to 1 μM (particle concentration) using standard WST and LDH assays on A549 cells.

  20. Quantum chemistry investigation on the reaction mechanism of the elemental mercury, chlorine, bromine and ozone system.

    Science.gov (United States)

    Gao, Zhengyang; Lv, Shaokun; Yang, Weijie; Yang, Pengfei; Ji, Shuo; Meng, Xinxin

    2015-06-01

    Ab initio calculations were performed to study the quantum chemistry reactions mechanisms among Hg(0), elemental halogen and O3. The geometry of reactions, transition states (TS), intermediates (M) and products were optimized using the MP2 method at the SDD basis function level for Hg, and using 6-311++G (3df, 3pd) for other species. Molecular energies were calculated at QCISD (T) level with zero point energy. Activation energies were calculated along with pre-exponential factors . The reaction rate constants within 298-1800 K were calculated according to transition state theory (TST). The influences of O3 on the reaction of Hg(0) with halogen are discussed. Hg(0) can be oxidized to Hg(1+) by halogen and O3, and halogen and O3 can be arranged in decreasing order as: Br2 > BrO > O3 > Br > Cl, BrCl > HBr > HCl, Br2 > Cl2 according to reaction rate constants. When O3 is presented, Br2, HBr, BrCl, Cl2 and HCl react with O3 and are initially converted to BrO and ClO. O3 is unfavorable for oxidation of Hg(0) by Br2. The mixture of HBr and O3 has better oxidizing Hg(0) performance than HBr and O3. Cl is less effective than Br for oxidation of Hg(0).

  1. Theoretical Studies of Silicon Chemistry

    Science.gov (United States)

    1990-02-01

    Molecular and Electronic Structure of Silyl Nitrene , M.S. Gordon, Chem. Phys. Lett., 146, 148 (1988). 18. A Theoretical Study of the Three-Membered Rings...phase and crystal structures. Of course, all three possibilities may contribute. B. The Electronic and Molecular Structure of Silyl Nitrene , M.S...a silaimine. An interesting question regarding the primary process is whether the silyl nitrene , R3SiN, is formed as an intermediate. As a first step

  2. Synthetic Studies in Phytochrome Chemistry.

    Science.gov (United States)

    Jacobi, Peter A; Adel Odeh, Imad M; Buddhu, Subhas C; Cai, Guolin; Rajeswari, Sundaramoorthi; Fry, Douglas; Zheng, Wanjun; Desimone, Robert W; Guo, Jiasheng; Coutts, Lisa D; Hauck, Sheila I; Leung, Sam H; Ghosh, Indranath; Pippin, Douglas

    2005-01-01

    An account is given of the author's several approaches to the synthesis of the parent chromophore of phytochrome (1), a protein-bound linear tetrapyrrole derivative that controls photomorphogenesis in higher plants. These studies culminated in enantioselective syntheses of both 2R- and 2S-phytochromobilin (4), as well as several (13)C-labeled derivatives designed to probe the site of Z,E-isomerization during photoexcitation. When reacted in vitro, synthetic 2R-4 and recombinant-derived phytochrome apoprotein N-C produced a protein-bound chromophore with identical difference spectra to naturally occurring 1.

  3. [Electroanalytical chemistry study of pilocarpine].

    Science.gov (United States)

    Wang, N X; Chen, J M; Lu, R C; Zhang, X L; Deng, J Q

    1990-01-01

    The electrochemical behaviour of pilocarpine was investigated by differential pulse polarography and cyclic voltammetry. The optimum conditions for the determination of pilocarpine were as follows: The electrolyte was 0.4 mol/L HAc-NaAc(pH 4.0) buffer solution, Zn (II) 1.0 x 10(-3) mol/L; initial potential -0.80 V (vs Ag-AgCl), final potential -1.30 V (vs Ag-AgCl), and voltage sweep rate 5 mV/s. A fair reproducibility in the above procedure and a good relationship between peak current and pilocarpine concentration (4.0 x 10(-6)-4.0 x 10(-5) mol/L) were achieved. The detection limit was 8.0 x 10(-7) mol/L. This paper also reports that the application of cyclic voltammetry to study electrode process behavior has been established. The PVC membrane ion-selective electrode for pilocarpine also was studied. It is based on the use of tetraphenylborate pilocarpine ion pair complex as the active material. The PVC membrane electrode showed Nernstian response over the pilocarpine concentration range from 1.0 x 10(-2) to 3.0 x 10(-5) mol/L, with a slope of 36 mV/decade, the detection limit being 3.0 x 10(-6) mol/L. The electrode gave fast response and good reproducibility. This method provides a rapid and simple way to the determination of pilocarpine in pharmaceutical preparations.

  4. On the Use of Quantum Chemistry for the Determination of Propagation, Copolymerization, and Secondary Reaction Kinetics in Free Radical Polymerization

    Directory of Open Access Journals (Sweden)

    Evangelos Mavroudakis

    2015-09-01

    Full Text Available Throughout the last 25 years, computational chemistry based on quantum mechanics has been applied to the investigation of reaction kinetics in free radical polymerization (FRP with growing interest. Nowadays, quantum chemistry (QC can be considered a powerful and cost-effective tool for the kinetic characterization of many individual reactions in FRP, especially those that cannot yet be fully analyzed through experiments. The recent focus on copolymers and systems where secondary reactions play a major role has emphasized this feature due to the increased complexity of these kinetic schemes. QC calculations are well-suited to support and guide the experimental investigation of FRP kinetics as well as to deepen the understanding of polymerization mechanisms. This paper is intended to provide an overview of the most relevant QC results obtained so far from the investigation of FRP. A comparison between computational results and experimental data is given, whenever possible, to emphasize the performances of the two approaches in the prediction of kinetic data. This work provides a comprehensive database of reaction rate parameters of FRP to assist in the development of advanced models of polymerization and experimental studies on the topic.

  5. Uquantchem: A versatile and easy to use Quantum Chemistry Computational Software

    CERN Document Server

    Souvatzis, Petros

    2013-01-01

    In this paper we present the Uppsala Quantum Chemistry package (UQUANTCHEM), a new and versatile computational platform with capabilities ranging from simple Hartree-Fock calculations to state of the art First principles Extended Lagrangian Born Oppenheimer Molecular Dynamics (XL- BOMD) and diffusion quantum Monte Carlo (DMC). The UQUANTCHEM package is distributed under the general public license and can be directly downloaded from the code web-site. Together with a presentation of the different capabilities of the uquantchem code and a more technical discus- sion on how these capabilities have been implemented, a presentation of the user-friendly aspect of the package on the basis of the large number of default settings will also be presented. Furthermore, since the code has been parallelized within the framework of the message passing interface (MPI), the timing of some benchmark calculations are reported to illustrate how the code scales with the number of computational nodes for different levels of chemic...

  6. Green chemistry for large-scale synthesis of semiconductor quantum dots.

    Science.gov (United States)

    Liu, Jin-Hua; Fan, Jun-Bing; Gu, Zheng; Cui, Jing; Xu, Xiao-Bo; Liang, Zhi-Wu; Luo, Sheng-Lian; Zhu, Ming-Qiang

    2008-05-20

    Large-scale synthesis of semiconductor nanocrystals or quantum dots (QDs) with high concentration and high yield through simultaneously increasing the precursor concentration was introduced. This synthetic route conducted in diesel has produced gram-scale CdSe semiconductor quantum dots (In optimal scale-up synthetic condition, the one-pot yield of QDs is up to 9.6g). The reaction has been conducted in open air and at relatively low temperature at 190-230 degrees C in the absence of expensive organic phosphine ligands, aliphatic amine and octadecene, which is really green chemistry without high energy cost for high temperature reaction and unessential toxic chemicals except for Cd, which is the essential building block for QDs.

  7. Plasma chemistry study of PLAD processes

    Energy Technology Data Exchange (ETDEWEB)

    Qin Shu; Brumfield, Kyle; Liu, Lequn Jennifer; Hu, Yongjun Jeff; McTeer, Allen; Hsu, Wei Hui; Wang Maoying [Nanya Technology Inc., Santa Clara, CA 95054 (United States); Micron Technology Inc., Boise, ID 83707 (United States)

    2012-11-06

    Plasma doping (PLAD) shows very different impurity profiles compared to the conventional beam-line-based ion implantations due to its non-mass separation property and plasma environment. There is no simulation for PLAD process so far due to a lack of a dopant profile model. Several factors determine impurity profiles of PLAD process. The most significant factors are: plasma chemistry and deposition/etching characteristics of multi-ion species plasmas. In this paper, we present plasma chemistry and deposition/etching characteristics of PLAD processes versus co-gas dilutions. Four dopant plasmas including B{sub 2}H{sub 6}, BF{sub 3}, AsH{sub 3}, and PH{sub 3}, and two non-dopant plasmas including CH{sub 4} and GeH{sub 4} are studied and demonstrated.

  8. Quantum chemistry investigation of fluorinated polymer systems of industrial interest.

    Science.gov (United States)

    Mavroudakis, Evangelos; Cuccato, Danilo; Dossi, Marco; Comino, Giovanni; Moscatelli, Davide

    2014-01-09

    In this work, the free-radical polymerization (FRP) of widely used fluorinated monomers was investigated. Computational studies were conducted to assess the FRP kinetics of each binary copolymerization between vinylidene fluoride (VDF), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). More specifically, all calculations were performed using density functional theory (DFT), and the B3LYP level of theory was used to optimize structures and determine absolute minimum energy geometries, whereas the electronic energies were estimated using B3LYP/6-31G(d,p) as well as a higher level of theory, MPWB1K/6-31G(d,p). Transition state theory was employed to determine kinetic parameters according to the terminal model of copolymerization. The homopolymerization of VDF and all of its corresponding copolymerizations were investigated by taking into account every possible propagation reaction (head to head, head to tail, tail to tail, head to monomer, tail to monomer, etc.) to estimate the Arrhenius parameters for each system. This study provides the estimation of a large set of rate coefficients, which gives detailed pictures of the specific copolymerization systems examined and is highly valuable to generate a comprehensive overview of the polymerization kinetics of relevant fluorinated monomers.

  9. Quantum-chemistry calculations of hydrogen adsorption in MOF-5.

    Science.gov (United States)

    Gomez, Diego A; Combariza, Aldo F; Sastre, German

    2009-10-28

    High concentrations of molecular hydrogen adsorption on MOF-5 were evaluated at the semiempirical PM6 (periodic and cluster) and ab initio MP2 (cluster) theoretical levels. From the semiempirical calculations, an uptake of 3.9% weight on the inorganic building unit of MOF-5 was estimated, in good agreement with a recent accurate estimation of 4.5-5.2%. Although PM6 allows a correct estimation of the maximum uptake, the adsorption energy was overestimated and hence ab initio calculations, including a correlation treatment at the MP2 level as well as corrections for basis set superposition error, were performed with full optimisation, including the 6-31G basis set, which rendered an adsorption energy (per hydrogen molecule) of -0.14 kcal mol(-1). The crucial role of the quality of the basis set, as well as the importance of simulating high hydrogen loading (resembling experimental measurements), are remarked. Single point calculations (using the 6-31G geometry) with improved basis sets 6-31G(d,p) and 6-31++G(d,p) yielded adsorption energies of -0.33 and -0.57 kcal mol(-1), the latter in reasonable agreement with a recent experimental estimation of -1.0 kcal mol(-1). The role of the intermolecular hydrogen interactions is highlighted in this study, since many previous computational studies were performed at low hydrogen loadings, far from the experimental uptake conditions.

  10. Quantum Chemistry Calculations on the Interaction Between Kaolinite and Gold

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The density function and discrete variation method (DFT-DVM) is used to study the interaction between kaolinite and gold. The correlation among the structure, chemical bond and stability is discussed. Several models are selected without gold and with gold in different directions and sites. The results show that the models with gold on the edge of kaolinite basal layer are more stable than those with gold above or under the layer, the models with gold near to [AlO2(OH)4] octahedra are more stable than those with gold near to the vacancy without aluminium. The interaction between gold and the surface ions of kaolinite is strong enough to form the surface complexes.

  11. Controlling the Photophysical Properties of Semiconductor Quantum Dot Arrays by Strategically Altering Their Surface Chemistry

    Science.gov (United States)

    Marshall, Ashley R.

    Semiconductor quantum dots (QDs) are interesting materials that, after less than 40 years of research, are used in commercial products. QDs are now found in displays, such as Samsung televisions and the Kindle Fire, and have applications in lighting, bio-imaging, quantum computing, and photovoltaics. They offer a large range of desirable properties: a controllable band gap, solution processability, controlled energy levels, and are currently the best materials for multiple exciton generation. The tunable optoelectronic properties of QDs can be controlled using size, shape, composition, and surface treatments--as shown here. Due to the quasi-spherical shape of QDs the surface to volume ratio is high, i.e. many of the constituent atoms are found on the QD surface. This makes QDs highly sensitive to surface chemistry modifications. This thesis encompasses the effects of surface treatments for QDs of two semiconducting materials: lead chalcogenides and CsPbI3. Our group developed a new synthetic technique for lead chalcogenide QDs via the cation exchange of cadmium chalcogenides. An in-depth chemical analysis is paired with optical and electrical studies and we find that metal halide residue contributes to the oxidative stability and decreased trap state density in cation-exchanged PbS QDs. We exploit these properties to make air-stable QD photovoltaic devices from both PbS and PbSe QD materials. Beyond the effects of residual atoms left from the synthetic technique, I investigated how to controllably add atoms onto the surface of QDs. I found that by introducing metal halides as a post-treatment in an electronically coupled array I am able to control the performance parameters in QD photovoltaic devices. These treatments fully infiltrate the assembled film, even under short exposure times and allow me to add controlled quantities of surface atoms to study their effects on film properties and photovoltaic device performance. Finally, I sought to apply the knowledge of

  12. Quantum Chemistry Study on Cluster NixZry (x:y=1∶2 or 2∶1)%NixZry(x:y=1∶2或2∶1)团簇的量子化学研究

    Institute of Scientific and Technical Information of China (English)

    董昆明; 王艺平; 林梦海; 莫亦荣; 吴玮; 张乾二

    2001-01-01

    According to chemical bond theory and topological principle, 46 non-crystalline clusters NixZry (x:y=1∶2 or 2∶1, x+y≤9) have been examined and optimized by using quantum chemistry ab initio method. The calculation results show that for NixZry (x:y=1∶2) the lower-symmetry plane configurations are more stable than solid tri-prism configuration, and for NixZry (x:y=2∶1) it is reverse. The difference may be due to diverse valence electrons of transition metals∶ There is only 4 valence electrons in zirconium, so it enjoys at plane configuration of lower coordination number, and nickel (4d23d8) more fits to solid configuration.%根据化学键理论和拓扑学原理,设计了非晶态团簇NixZry(x:y=1∶2 或2∶1, x+y≤9)的几十种可能的构型,并应用量子化学从头算方法对它们的几何构型进行了优化,分析比较了这些构型的能量和稳定性。结果表明对于NixZry(x:y=1∶2)低对称性的平面构型最稳定,而NixZry(x:y=2∶1)三棱柱构型最稳定。这可能是由于两者外层价电子的数量差异所致: Zr仅有4个价电子,较适宜配位数低的平面构型,而Ni(4s23d8),更适宜立体构型。

  13. A study of Quantum Correlations in Open Quantum Systems

    CERN Document Server

    Chakrabarty, Indranil; Siddharth, Nana

    2010-01-01

    In this work, we study quantum correlations in mixed states. The states studied are modelled by a two-qubit system interacting with its environment via a quantum nondemolition (purely dephasing) as well as dissipative type of interaction. The entanglement dynamics of this two qubit system is analyzed and the existence of entangled states which do not violate Bell's inequality, but can still be useful as a potential resource for teleportation are reported. In addition, a comparative study of various measures of quantum correlations, like Concurrence, Bell's inequality, Discord and Teleportation fidelity, is made on these states, generated by the above evolutions. Interestingly, examples are found, of states, where entanglement is vanishing, but discord is non-vanishing, bringing out the fact that entanglement is a subset of quantum correlations.

  14. Code interoperability and standard data formats in quantum chemistry and quantum dynamics: The Q5/D5Cost data model.

    Science.gov (United States)

    Rossi, Elda; Evangelisti, Stefano; Laganà, Antonio; Monari, Antonio; Rampino, Sergio; Verdicchio, Marco; Baldridge, Kim K; Bendazzoli, Gian Luigi; Borini, Stefano; Cimiraglia, Renzo; Angeli, Celestino; Kallay, Peter; Lüthi, Hans P; Ruud, Kenneth; Sanchez-Marin, José; Scemama, Anthony; Szalay, Peter G; Tajti, Attila

    2014-03-30

    Code interoperability and the search for domain-specific standard data formats represent critical issues in many areas of computational science. The advent of novel computing infrastructures such as computational grids and clouds make these issues even more urgent. The design and implementation of a common data format for quantum chemistry (QC) and quantum dynamics (QD) computer programs is discussed with reference to the research performed in the course of two Collaboration in Science and Technology Actions. The specific data models adopted, Q5Cost and D5Cost, are shown to work for a number of interoperating codes, regardless of the type and amount of information (small or large datasets) to be exchanged. The codes are either interfaced directly, or transfer data by means of wrappers; both types of data exchange are supported by the Q5/D5Cost library. Further, the exchange of data between QC and QD codes is addressed. As a proof of concept, the H + H2 reaction is discussed. The proposed scheme is shown to provide an excellent basis for cooperative code development, even across domain boundaries. Moreover, the scheme presented is found to be useful also as a production tool in the grid distributed computing environment.

  15. Benzoxazoles and oxazolopyridines in medicinal chemistry studies.

    Science.gov (United States)

    Demmer, Charles S; Bunch, Lennart

    2015-06-05

    The benzoxazole heterocycle is often found in ligands targeting a plethora of receptors and enzymes. By analysis of published X-ray structures, this review aims at highlighting key interactions which the benzoxazole may engage in with its host protein. Furthermore, bioavailability, metabolism and the use of benzoxazole as a bioisostere are discussed. The review is extended to cover structure-activity relationship studies of 2-substituted benzoxazoles, 2-substituted oxazolopyridines, and in perspective, application of the recently published novel heterocycle oxazolopyrazine in medicinal chemistry studies.

  16. Mapping of the interaction sites of galanthamine: a quantitative analysis through pairwise potentials and quantum chemistry

    Science.gov (United States)

    Galland, Nicolas; Kone, Soleymane; Le Questel, Jean-Yves

    2012-10-01

    A quantitative analysis of the interaction sites of the anti-Alzheimer drug galanthamine with molecular probes (water and benzene molecules) representative of its surroundings in the binding site of acetylcholinesterase (AChE) has been realized through pairwise potentials calculations and quantum chemistry. This strategy allows a full and accurate exploration of the galanthamine potential energy surface of interaction. Significantly different results are obtained according to the distances of approaches between the various molecular fragments and the conformation of the galanthamine N-methyl substituent. The geometry of the most relevant complexes has then been fully optimized through MPWB1K/6-31 + G(d,p) calculations, final energies being recomputed at the LMP2/aug-cc-pVTZ(-f) level of theory. Unexpectedly, galanthamine is found to interact mainly from its hydrogen-bond donor groups. Among those, CH groups in the vicinity of the ammonium group are prominent. The trends obtained provide rationales to the predilection of the equatorial orientation of the galanthamine N-methyl substituent for binding to AChE. The analysis of the interaction energies pointed out the independence between the various interaction sites and the rigid character of galanthamine. The comparison between the cluster calculations and the crystallographic observations in galanthamine-AChE co-crystals allows the validation of the theoretical methodology. In particular, the positions of several water molecules appearing as strongly conserved in galanthamine-AChE co-crystals are predicted by the calculations. Moreover, the experimental position and orientation of lateral chains of functionally important aminoacid residues are in close agreement with the ones predicted theoretically. Our study provides relevant information for a rational drug design of galanthamine based AChE inhibitors.

  17. Mapping of the interaction sites of galanthamine: a quantitative analysis through pairwise potentials and quantum chemistry.

    Science.gov (United States)

    Galland, Nicolas; Kone, Soleymane; Le Questel, Jean-Yves

    2012-10-01

    A quantitative analysis of the interaction sites of the anti-Alzheimer drug galanthamine with molecular probes (water and benzene molecules) representative of its surroundings in the binding site of acetylcholinesterase (AChE) has been realized through pairwise potentials calculations and quantum chemistry. This strategy allows a full and accurate exploration of the galanthamine potential energy surface of interaction. Significantly different results are obtained according to the distances of approaches between the various molecular fragments and the conformation of the galanthamine N-methyl substituent. The geometry of the most relevant complexes has then been fully optimized through MPWB1K/6-31 + G(d,p) calculations, final energies being recomputed at the LMP2/aug-cc-pVTZ(-f) level of theory. Unexpectedly, galanthamine is found to interact mainly from its hydrogen-bond donor groups. Among those, CH groups in the vicinity of the ammonium group are prominent. The trends obtained provide rationales to the predilection of the equatorial orientation of the galanthamine N-methyl substituent for binding to AChE. The analysis of the interaction energies pointed out the independence between the various interaction sites and the rigid character of galanthamine. The comparison between the cluster calculations and the crystallographic observations in galanthamine-AChE co-crystals allows the validation of the theoretical methodology. In particular, the positions of several water molecules appearing as strongly conserved in galanthamine-AChE co-crystals are predicted by the calculations. Moreover, the experimental position and orientation of lateral chains of functionally important aminoacid residues are in close agreement with the ones predicted theoretically. Our study provides relevant information for a rational drug design of galanthamine based AChE inhibitors.

  18. Are fragment-based quantum chemistry methods applicable to medium-sized water clusters?

    Science.gov (United States)

    Yuan, Dandan; Shen, Xiaoling; Li, Wei; Li, Shuhua

    2016-06-28

    Fragment-based quantum chemistry methods are either based on the many-body expansion or the inclusion-exclusion principle. To compare the applicability of these two categories of methods, we have systematically evaluated the performance of the generalized energy based fragmentation (GEBF) method (J. Phys. Chem. A, 2007, 111, 2193) and the electrostatically embedded many-body (EE-MB) method (J. Chem. Theory Comput., 2007, 3, 46) for medium-sized water clusters (H2O)n (n = 10, 20, 30). Our calculations demonstrate that the GEBF method provides uniformly accurate ground-state energies for 10 low-energy isomers of three water clusters under study at a series of theory levels, while the EE-MB method (with one water molecule as a fragment and without using the cutoff distance) shows a poor convergence for (H2O)20 and (H2O)30 when the basis set contains diffuse functions. Our analysis shows that the neglect of the basis set superposition error for each subsystem has little effect on the accuracy of the GEBF method, but leads to much less accurate results for the EE-MB method. The accuracy of the EE-MB method can be dramatically improved by using an appropriate cutoff distance and using two water molecules as a fragment. For (H2O)30, the average deviation of the EE-MB method truncated up to the three-body level calculated using this strategy (relative to the conventional energies) is about 0.003 hartree at the M06-2X/6-311++G** level, while the deviation of the GEBF method with a similar computational cost is less than 0.001 hartree. The GEBF method is demonstrated to be applicable for electronic structure calculations of water clusters at any basis set.

  19. Exponentially more precise quantum simulation of fermions II: Quantum chemistry in the CI matrix representation

    CERN Document Server

    Babbush, Ryan; Kivlichan, Ian D; Wei, Annie Y; Love, Peter J; Aspuru-Guzik, Alán

    2015-01-01

    We present a quantum algorithm for the simulation of molecular systems that is asymptotically more efficient than all previous algorithms in the literature. As in the first paper of this series \\cite{BabbushSparse1}, we employ a recently developed technique for simulating Hamiltonian evolution using a truncated Taylor series to obtain logarithmic scaling with the inverse of the desired precision, which is an exponential improvement over methods based on the Trotter-Suzuki decomposition. The algorithm of this paper involves simulation under an oracle for the sparse, first quantized representation of the Hamiltonian known as the configuration interaction (CI) matrix. We construct and query the CI matrix oracle to allow for on-the-fly computation of molecular integrals in a way that is exponentially more efficient than classical numerical methods. Whereas second quantized representations of the wavefunction require $\\widetilde{\\cal O}(N)$ qubits, where $N$ is the number of single-particle spin-orbitals, the CI m...

  20. Shielding of quantum dots using diblock copolymers: implementing copper catalyzed click chemistry to fluorescent quantum dots

    Science.gov (United States)

    Merkl, Jan-Philip; Ostermann, Johannes; Schmidtke, Christian; Kloust, Hauke; Eggers, Robin; Feld, Artur; Wolter, Christopher; Kreuziger, Anna-Marlena; Flessau, Sandra; Mattoussi, Hedi; Weller, Horst

    2014-03-01

    We describe the design and optimization of an amphiphilic diblock copolymer and its use to provide surface functionalization of colloidal semiconductor nanoparticles (quantum dots, QDs). This polymer coating promotes hydrophilicity of the nanocrystals while providing numerous functional groups ideally suited for biofunctionalization of the QDs using copper-catalyzed azide alkyne Husigen 1,3-cyloaddition (i.e., cupper catalyzed "click" reaction). Copper ions are known to quench the fluorescence of QDs in solution. Thus effective shielding of the nanocrystal surface is essential to apply copper-catalyzed reactions to luminescent QDs without drastically quenching their emission. We have applied a strategy based on micellar encapsulation within poly(isoprene-block- ethylene oxide) diblock-copolymers (PI-b-PEO), where three critical factors promote and control the effectiveness of the shielding of copper ion penetration: 1) The excess of PI-b-PEO, 2) the size of PI-b-PEO and 3) insertion of an additional PS-shell grown via seeded emulsion polymerization (EP) reaction. Due to the amphiphilic character of the block-copolymer, this approach provides a shielding layer surrounding the particles, preventing metal ions from reaching the QD surfaces and maintaining high photoluminescence. The effective shielding allowed the use of copper-catalyzed azide-alkyne 1,3-cycloaddition (CuAAC) to hydrophilic and highly fluorescent QDs, opening up great possibilities for the bio functionalization of QDs.

  1. Picture this: The value of multiple visual representations for student learning of quantum concepts in general chemistry

    Science.gov (United States)

    Allen, Emily Christine

    Mental models for scientific learning are often defined as, "cognitive tools situated between experiments and theories" (Duschl & Grandy, 2012). In learning, these cognitive tools are used to not only take in new information, but to help problem solve in new contexts. Nancy Nersessian (2008) describes a mental model as being "[loosely] characterized as a representation of a system with interactive parts with representations of those interactions. Models can be qualitative, quantitative, and/or simulative (mental, physical, computational)" (p. 63). If conceptual parts used by the students in science education are inaccurate, then the resulting model will not be useful. Students in college general chemistry courses are presented with multiple abstract topics and often struggle to fit these parts into complete models. This is especially true for topics that are founded on quantum concepts, such as atomic structure and molecular bonding taught in college general chemistry. The objectives of this study were focused on how students use visual tools introduced during instruction to reason with atomic and molecular structure, what misconceptions may be associated with these visual tools, and how visual modeling skills may be taught to support students' use of visual tools for reasoning. The research questions for this study follow from Gilbert's (2008) theory that experts use multiple representations when reasoning and modeling a system, and Kozma and Russell's (2005) theory of representational competence levels. This study finds that as students developed greater command of their understanding of abstract quantum concepts, they spontaneously provided additional representations to describe their more sophisticated models of atomic and molecular structure during interviews. This suggests that when visual modeling with multiple representations is taught, along with the limitations of the representations, it can assist students in the development of models for reasoning about

  2. The successful merger of theoretical thermochemistry with fragment-based methods in quantum chemistry.

    Science.gov (United States)

    Ramabhadran, Raghunath O; Raghavachari, Krishnan

    2014-12-16

    CONSPECTUS: Quantum chemistry and electronic structure theory have proven to be essential tools to the experimental chemist, in terms of both a priori predictions that pave the way for designing new experiments and rationalizing experimental observations a posteriori. Translating the well-established success of electronic structure theory in obtaining the structures and energies of small chemical systems to increasingly larger molecules is an exciting and ongoing central theme of research in quantum chemistry. However, the prohibitive computational scaling of highly accurate ab initio electronic structure methods poses a fundamental challenge to this research endeavor. This scenario necessitates an indirect fragment-based approach wherein a large molecule is divided into small fragments and is subsequently reassembled to compute its energy accurately. In our quest to further reduce the computational expense associated with the fragment-based methods and overall enhance the applicability of electronic structure methods to large molecules, we realized that the broad ideas involved in a different area, theoretical thermochemistry, are transferable to the area of fragment-based methods. This Account focuses on the effective merger of these two disparate frontiers in quantum chemistry and how new concepts inspired by theoretical thermochemistry significantly reduce the total number of electronic structure calculations needed to be performed as part of a fragment-based method without any appreciable loss of accuracy. Throughout, the generalized connectivity based hierarchy (CBH), which we developed to solve a long-standing problem in theoretical thermochemistry, serves as the linchpin in this merger. The accuracy of our method is based on two strong foundations: (a) the apt utilization of systematic and sophisticated error-canceling schemes via CBH that result in an optimal cutting scheme at any given level of fragmentation and (b) the use of a less expensive second

  3. Comparison of Chain Conformation of Poly(vinyl alcohol) in Solutions and Melts from Quantum Chemistry Based Molecular Dynamics Simulations

    Science.gov (United States)

    Jaffe, Richard; Han, Jie; Matsuda, Tsunetoshi; Yoon, Do; Langhoff, Stephen R. (Technical Monitor)

    1997-01-01

    Confirmations of 2,4-dihydroxypentane (DHP), a model molecule for poly(vinyl alcohol), have been studied by quantum chemistry (QC) calculations and molecular dynamics (MD) simulations. QC calculations at the 6-311G MP2 level show the meso tt conformer to be lowest in energy followed by the racemic tg, due to intramolecular hydrogen bond between the hydroxy groups. The Dreiding force field has been modified to reproduce the QC conformer energies for DHP. MD simulations using this force field have been carried out for DHP molecules in the gas phase, melt, and CHCl3 and water solutions. Extensive intramolecular hydrogen bonding is observed for the gas phase and CHCl3 solution, but not for the melt or aqueous solution, Such a condensed phase effect due to intermolecular interactions results in a drastic change in chain conformations, in agreement with experiments.

  4. Ion chemistry in the early universe: revisiting the role of HeH+ with new quantum calculations

    CERN Document Server

    Bovino, Stefano; Gianturco, Francesco A; Galli, Daniele

    2011-01-01

    The role of HeH+ has been newly assessed with the aid of newly calculated rates which use entirely ab initio methods, thereby allowing us to compute more accurately the relevant abundances within the global chemical network of the early universe. A comparison with the similar role of the ionic molecule LiH+ is also presented. Quantum calculations have been carried out for the gas-phase reaction of HeH+ with H atoms with our new in-house code, based on the negative imaginary potential method. Integral cross sections and reactive rate coefficients obtained under the general conditions of early universe chemistry are presented and discussed. With the new reaction rate, the abundance of HeH+ in the early universe is more than one order of magnitude larger than in previous studies. Our more accurate findings further buttress the possibility to detect cosmological signatures of HeH+.

  5. Coupled effects of solution chemistry and hydrodynamics on the mobility and transport of quantum dot nanomaterials in the Vadose Zone

    Science.gov (United States)

    To investigate the coupled effects of solution chemistry and vadose zone processes on the mobility of quantum dot (QD) nanoparticles, laboratory scale transport experiments were performed. The complex coupled effects of ionic strength, size of QD aggregates, surface tension, contact angle, infiltrat...

  6. Two-electron reduction of ethylene carbonate: a quantum chemistry re-examination of mechanisms

    CERN Document Server

    Leung, Kevin

    2013-01-01

    Passivating solid-electrolyte interphase (SEI) films arising from electrolyte decomposition on low-voltage lithium ion battery anode surfaces are critical for battery operations. We review the recent theoretical literature on electrolyte decomposition and emphasize the modeling work on two-electron reduction of ethylene carbonate (EC, a key battery organic solvent). One of the two-electron pathways, which releases CO gas, is re-examined using simple quantum chemistry calculations. Excess electrons are shown to preferentially attack EC in the order (broken EC^-) > (intact EC^-) > EC. This confirms the viability of two electron processes and emphasizes that they need to be considered when interpreting SEI experiments. An estimate of the crossover between one- and two-electron regimes under a homogeneous reaction zone approximation is proposed.

  7. Sulfobetaine-Vinylimidazole Block Copolymers: A Robust Quantum Dot Surface Chemistry Expanding Bioimaging's Horizons.

    Science.gov (United States)

    Tasso, Mariana; Giovanelli, Emerson; Zala, Diana; Bouccara, Sophie; Fragola, Alexandra; Hanafi, Mohamed; Lenkei, Zsolt; Pons, Thomas; Lequeux, Nicolas

    2015-11-24

    Long-term inspection of biological phenomena requires probes of elevated intra- and extracellular stability and target biospecificity. The high fluorescence and photostability of quantum dot (QD) nanoparticles contributed to foster their promise as bioimaging tools that could overcome limitations associated with traditional fluorophores. However, QDs' potential as a bioimaging platform relies upon a precise control over the surface chemistry modifications of these nano-objects. Here, a zwitterion-vinylimidazole block copolymer ligand was synthesized, which regroups all anchoring groups in one compact terminal block, while the rest of the chain is endowed with antifouling and bioconjugation moieties. By further application of an oriented bioconjugation approach with whole IgG antibodies, QD nanobioconjugates were obtained that display outstanding intra- and extracellular stability as well as biorecognition capacity. Imaging the internalization and intracellular dynamics of a transmembrane cell receptor, the CB1 brain cannabinoid receptor, both in HEK293 cells and in neurons, illustrates the breadth of potential applications of these nanoprobes.

  8. Multireference quantum chemistry through a joint density matrix renormalization group and canonical transformation theory

    Science.gov (United States)

    Yanai, Takeshi; Kurashige, Yuki; Neuscamman, Eric; Chan, Garnet Kin-Lic

    2010-01-01

    We describe the joint application of the density matrix renormalization group and canonical transformation theory to multireference quantum chemistry. The density matrix renormalization group provides the ability to describe static correlation in large active spaces, while the canonical transformation theory provides a high-order description of the dynamic correlation effects. We demonstrate the joint theory in two benchmark systems designed to test the dynamic and static correlation capabilities of the methods, namely, (i) total correlation energies in long polyenes and (ii) the isomerization curve of the [Cu2O2]2+ core. The largest complete active spaces and atomic orbital basis sets treated by the joint DMRG-CT theory in these systems correspond to a (24e,24o) active space and 268 atomic orbitals in the polyenes and a (28e,32o) active space and 278 atomic orbitals in [Cu2O2]2+.

  9. The Quixote project: Collaborative and Open Quantum Chemistry data management in the Internet age

    Directory of Open Access Journals (Sweden)

    Adams Sam

    2011-10-01

    Full Text Available Abstract Computational Quantum Chemistry has developed into a powerful, efficient, reliable and increasingly routine tool for exploring the structure and properties of small to medium sized molecules. Many thousands of calculations are performed every day, some offering results which approach experimental accuracy. However, in contrast to other disciplines, such as crystallography, or bioinformatics, where standard formats and well-known, unified databases exist, this QC data is generally destined to remain locally held in files which are not designed to be machine-readable. Only a very small subset of these results will become accessible to the wider community through publication. In this paper we describe how the Quixote Project is developing the infrastructure required to convert output from a number of different molecular quantum chemistry packages to a common semantically rich, machine-readable format and to build respositories of QC results. Such an infrastructure offers benefits at many levels. The standardised representation of the results will facilitate software interoperability, for example making it easier for analysis tools to take data from different QC packages, and will also help with archival and deposition of results. The repository infrastructure, which is lightweight and built using Open software components, can be implemented at individual researcher, project, organisation or community level, offering the exciting possibility that in future many of these QC results can be made publically available, to be searched and interpreted just as crystallography and bioinformatics results are today. Although we believe that quantum chemists will appreciate the contribution the Quixote infrastructure can make to the organisation and and exchange of their results, we anticipate that greater rewards will come from enabling their results to be consumed by a wider community. As the respositories grow they will become a valuable source of

  10. A COURSE OF STUDY IN CHEMISTRY.

    Science.gov (United States)

    HELWIG, G. ALFRED; AND OTHERS

    AN ELECTIVE CHEMISTRY COURSE IS DESIGNED TO BE EQUALLY VALUABLE TO BOTH FUTURE SCIENTISTS AND NONSCIENTISTS. THE EMPHASIS IS PLACED ON FUNDAMENTAL CONCEPTS AND RELATIONSHIPS RATHER THAN ON DESCRIPTIVE AND APPLIED CHEMISTRY. MAJOR OBJECTIVES ARE--TO SURVEY THE PRESENT STATE OF CHEMICAL KNOWLEDGE, TO EXAMINE IN SOME DEPTH CENTRAL CHEMICAL CONCEPTS…

  11. Linear and nonlinear optical properties of functionalized CdSe quantum dots prepared by plasma sputtering and wet chemistry.

    Science.gov (United States)

    Humbert, Christophe; Dahi, Abdellatif; Dalstein, Laetitia; Busson, Bertrand; Lismont, Marjorie; Colson, Pierre; Dreesen, Laurent

    2015-05-01

    We develop an innovative manufacturing process, based on radio-frequency magnetron sputtering (RFMS), to prepare neat CdSe quantum dots (QDs) on glass and silicon substrates and further chemically functionalize them. In order to validate the fabrication protocol, their optical properties are compared with those of QDs obtained from commercial solutions and deposited by wet chemistry on the substrates. Firstly, AFM measurements attest that nano-objects with a mean diameter around 13 nm are located on the substrate after RFMS treatment. Secondly, the UV-Vis absorption study of this deposited layer shows a specific optical absorption band, located at 550 nm, which is related to a discrete energy level of QDs. Thirdly, by using two-color sum-frequency generation (2C-SFG) nonlinear optical spectroscopy, we show experimentally the functionalization efficiency of the RFMS CdSe QDs layer with thiol derived molecules, which is not possible on the QDs layer prepared by wet chemistry due to the surfactant molecules from the native solution. Finally, 2C-SFG spectroscopy, performed at different visible wavelengths, highlights modifications of the vibration mode shape whatever the QDs deposition method, which is correlated to the discrete energy level of the QDs.

  12. Fast Quantum Molecular Dynamics Simulations of Shock-induced Chemistry in Organic Liquids

    Science.gov (United States)

    Cawkwell, Marc

    2014-03-01

    The responses of liquid formic acid and phenylacetylene to shock compression have been investigated via quantum-based molecular dynamics simulations with the self-consistent tight-binding code LATTE. Microcanonical Born-Oppenheimer trajectories with precise conservation of the total energy were computed without relying on an iterative self-consistent field optimization of the electronic degrees of freedom at each time step via the Fast Quantum Mechanical Molecular Dynamics formalism [A. M. N. Niklasson and M. J. Cawkwell, Phys. Rev. B, 86, 174308 (2012)]. The conservation of the total energy in our trajectories was pivotal for the capture of adiabatic shock heating as well as temperature changes arising from endo- or exothermic chemistry. Our self-consistent tight-binding parameterizations yielded very good predictions for the gas-phase geometries of formic acid and phenylacetylene molecules and the principal Hugoniots of the liquids. In accord with recent flyer-plate impact experiments, our simulations revealed i) that formic acid reacts at relatively low impact pressures but with no change in volume between products and reactants, and ii) a two-step polymerization process for phenylacetylene. Furthermore, the evolution of the HOMO-LUMO gap tracked on-the-fly during our simulations could be correlated with changes transient absorption measured during laser-driven shock compression experiments on these liquids.

  13. International journal of quantum chemistry. Quantum Chemistry Symposium Number 27: Proceedings of the International Symposium on Atomic, Molecular, and Condensed Matter Theory and Computational Methods

    Science.gov (United States)

    Lowdin, Per-Olov; Ohrn, N. Y.; Sabin, John R.; Zerner, Michael C.

    1993-03-01

    The topics covered at the 33rd annual Sanibel Symposium, organized by the faculty and staff of the Quantum Theory Project of the University of Florida, and held March 13 - 20, 1993, include advanced scientific computing, interaction of photons and matter, quantum molecular dynamics, electronic structure methods, polymeric systems, and quantum chemical methods for extended systems.

  14. A Review of Solution Chemistry Studies: Insights into Students' Conceptions

    Science.gov (United States)

    Calyk, Muammer; Ayas, Alipa; Ebenezer, Jazlin V.

    2005-01-01

    This study has reviewed the last two decades of student conception research in solution chemistry pertaining to aims, methods of exploring students' conception, general knowledge claims, students' conceptions and difficulties, and conceptual change studies. The aims of solution chemistry studies have been to assess students' understanding level of…

  15. Human Development VIII: A Theory of “Deep” Quantum Chemistry and Cell Consciousness: Quantum Chemistry Controls Genes and Biochemistry to Give Cells and Higher Organisms Consciousness and Complex Behavior

    Directory of Open Access Journals (Sweden)

    Søren Ventegodt

    2006-01-01

    Full Text Available Deep quantum chemistry is a theory of deeply structured quantum fields carrying the biological information of the cell, making it able to remember, intend, represent the inner and outer world for comparison, understand what it “sees”, and make choices on its structure, form, behavior and division. We suggest that deep quantum chemistry gives the cell consciousness and all the qualities and abilities related to consciousness. We use geometric symbolism, which is a pre-mathematical and philosophical approach to problems that cannot yet be handled mathematically. Using Occam’s razor we have started with the simplest model that works; we presume this to be a many-dimensional, spiral fractal. We suggest that all the electrons of the large biological molecules’ orbitals make one huge “cell-orbital”, which is structured according to the spiral fractal nature of quantum fields. Consciousness of single cells, multi cellular structures as e.g. organs, multi-cellular organisms and multi-individual colonies (like ants and human societies can thus be explained by deep quantum chemistry. When biochemical activity is strictly controlled by the quantum-mechanical super-orbital of the cell, this orbital can deliver energetic quanta as biological information, distributed through many fractal levels of the cell to guide form and behavior of an individual single or a multi-cellular organism. The top level of information is the consciousness of the cell or organism, which controls all the biochemical processes. By this speculative work inspired by Penrose and Hameroff we hope to inspire other researchers to formulate more strict and mathematically correct hypothesis on the complex and coherence nature of matter, life and consciousness.

  16. Spectroscopic Studies of Atmospheric Aerosol Chemistry

    Science.gov (United States)

    Wamsley, R.; Leather, K.; Horn, A. B.; Percival, C.

    2008-12-01

    Particles are ubiquitous in the troposphere and are involved in chemical and physical processes affecting the composition of the atmosphere, climate, cloud albedo and human health (Finlayson-Pitts and Pitts, 2000). Organic species, such as alcohols, carboxylic acids, ketones, aldehydes, aromatics, alkenes and alkanes, originate both from anthropogenic and natural sources and comprise a large component of atmospheric particles. Gas-phase species, such as ozone, can oxidize these organics, changing the particle's oxygen-to carbon ratio and potentially altering its hygroscopicity, viscosity, morphology and reactivity. One reaction in particular, that between ozone and oleic acid, has been the focus of several recent studies and extensively researched by Ziemann (2005). Oleic acid reacts readily with ozone and has a low vapor pressure making this reaction convenient to study in the laboratory and has become the benchmark for studying heterogeneous reactions representing the oxidative processing of atmospheric organic aerosols. A critical source of uncertainty in reactivity estimates is a lack of understanding of the mechanism through which some VOCs are oxidized. This knowledge gap is especially critical for aromatic compounds. Because the intermediate reaction steps and products of aromatics oxidation are unknown, chemical mechanisms incorporate parameters estimated from environmental chamber experiments to represent their overall contribution to ozone formation, e.g. Volkamer et al. ( 2006). Previous studies of uncertainties in incremental reactivity estimates for VOCs found that the representation of aromatics chemistry contributed significantly to the estimated 40 - 50% uncertainties in the incremental reactivities of common aromatic compounds Carter et al. (2002). This study shows development of an effective IR method that can monitor the reaction and hence obtain the kinetics of the ozonolysis of an aromatic compound in the aerosol phase. The development of such

  17. Research for the advancement of green chemistry practice: Studies in atmospheric and educational chemistry

    Science.gov (United States)

    Cullipher, Steven Gene

    Green chemistry is a philosophy of chemistry that emphasizes a decreasing dependence on limited non-renewable resources and an increasing focus on preventing pollution byproducts of the chemical industry. In short, it is the discipline of chemistry practiced through the lens of environmental stewardship. In an effort to advance the practice of green chemistry, three studies will be described that have ramifications for the practice. The first study examines the atmospheric oxidation of a hydrofluorinated ether, a third-generation CFC replacement compound with primarily unknown atmospheric degradation products. Determination of these products has the potential to impact decisions on refrigerant usage in the future. The second study examines chemistry students' development of understanding benefits-costs-risks analysis when presented with two real-world scenarios: refrigerant choice and fuel choice. By studying how benefits-costs-risks thinking develops, curricular materials and instructional approaches can be designed to better foster the development of an ability that is both necessary for green chemists and important in daily decision-making for non-chemists. The final study uses eye tracking technology to examine students' abilities to interpret molecular properties from structural information in the context of global warming. Such abilities are fundamental if chemists are to appropriately assess risks and hazards of chemistry practice.

  18. Teaching the Philosophical Interpretations of Quantum Mechanics and Quantum Chemistry through Controversies

    Science.gov (United States)

    Garritz, Andoni

    2013-01-01

    This study has the key premise of teaching history and philosophy of physical sciences to illustrate how controversies and rivalries among scientists play a key role in the progress of science and why scientific development is not only founded on the accumulation of experimental data. The author is a defender of teachers who consider…

  19. Teaching the Philosophical Interpretations of Quantum Mechanics and Quantum Chemistry through Controversies

    Science.gov (United States)

    Garritz, Andoni

    2013-01-01

    This study has the key premise of teaching history and philosophy of physical sciences to illustrate how controversies and rivalries among scientists play a key role in the progress of science and why scientific development is not only founded on the accumulation of experimental data. The author is a defender of teachers who consider…

  20. Quantum Chemistry Meets Spectroscopy for Astrochemistry: Increasing Complexity toward Prebiotic Molecules.

    Science.gov (United States)

    Barone, Vincenzo; Biczysko, Malgorzata; Puzzarini, Cristina

    2015-05-19

    For many years, scientists suspected that the interstellar medium was too hostile for organic species and that only a few simple molecules could be formed under such extreme conditions. However, the detection of approximately 180 molecules in interstellar or circumstellar environments in recent decades has changed this view dramatically. A rich chemistry has emerged, and relatively complex molecules such as C60 and C70 are formed. Recently, researchers have also detected complex organic and potentially prebiotic molecules, such as amino acids, in meteorites and in other space environments. Those discoveries have further stimulated the debate on the origin of the building blocks of life in the universe. Many efforts continue to focus on the physical, chemical, and astrophysical processes by which prebiotic molecules can be formed in the interstellar dust and dispersed to Earth or to other planets.Spectroscopic techniques, which are widely used to infer information about molecular structure and dynamics, play a crucial role in the investigation of planetary atmosphere and the interstellar medium. Increasingly these astrochemical investigations are assisted by quantum-mechanical calculations of structures as well as spectroscopic and thermodynamic properties, such as transition frequencies and reaction enthalpies, to guide and support observations, line assignments, and data analysis in these new and chemically complicated situations. However, it has proved challenging to extend accurate quantum-chemical computational approaches to larger systems because of the unfavorable scaling with the number of degrees of freedom (both electronic and nuclear).In this Account, we show that it is now possible to compute physicochemical properties of building blocks of biomolecules with an accuracy rivaling that of the most sophisticated experimental techniques, and we summarize specific contributions from our groups. As a test case, we present the underlying computational machinery

  1. Transfer in chemistry: a study of students' abilities in transferring mathematical knowledge to chemistry

    Science.gov (United States)

    Hoban, Richard A.; Finlayson, Odilla E.; Nolan, Brien C.

    2013-01-01

    It is recognized that there is a mathematics problem in chemistry, whereby, for example, undergraduate students appear to be unable to utilize basic calculus knowledge in a chemistry context - calculus knowledge - which would have been taught to these students in a mathematics context. However, there appears to be a scarcity of literature addressing the possible reasons for this problem. This dearth of literature has spurred the following two questions: (1) Can students transfer mathematical knowledge to chemistry?; and (2) What are the possible factors associated with students being able to successfully transfer mathematical knowledge to a chemistry context? These questions were investigated in relation to the basic mathematical knowledge which chemistry students need for chemical kinetics and thermodynamics, using the traditional view of the transfer of learning. Two studies were undertaken amongst two samples of undergraduate students attending Dublin City University. Findings suggest that the mathematical difficulties which students encounter in a chemistry context may not be because of an inability to transfer the knowledge, but may instead be due to insufficient mathematical understanding and/or knowledge of mathematical concepts relevant to chemical kinetics and thermodynamics.

  2. Art and Chemistry: Designing a Study-Abroad Course

    Science.gov (United States)

    Smieja, Joanne A.; D'Ambruoso, Gemma D.; Richman, Robert M.

    2010-01-01

    Three related courses examining the connection between chemistry and art have been developed for study-abroad programs in Florence, Italy, by faculty members at Gonzaga University and Mount Saint Mary's University. These courses are described with the intent of providing a general framework for the development of chemistry and art courses in other…

  3. A Component Approach to Collaborative Scientific Software Development: Tools and Techniques Utilized by the Quantum Chemistry Science Application Partnership

    Directory of Open Access Journals (Sweden)

    Joseph P. Kenny

    2008-01-01

    Full Text Available Cutting-edge scientific computing software is complex, increasingly involving the coupling of multiple packages to combine advanced algorithms or simulations at multiple physical scales. Component-based software engineering (CBSE has been advanced as a technique for managing this complexity, and complex component applications have been created in the quantum chemistry domain, as well as several other simulation areas, using the component model advocated by the Common Component Architecture (CCA Forum. While programming models do indeed enable sound software engineering practices, the selection of programming model is just one building block in a comprehensive approach to large-scale collaborative development which must also address interface and data standardization, and language and package interoperability. We provide an overview of the development approach utilized within the Quantum Chemistry Science Application Partnership, identifying design challenges, describing the techniques which we have adopted to address these challenges and highlighting the advantages which the CCA approach offers for collaborative development.

  4. Proceedings of the meeting on tunneling reaction and low temperature chemistry, 97 October. Tunneling reaction and quantum medium

    Energy Technology Data Exchange (ETDEWEB)

    Miyazaki, Tetsuo; Aratono, Yasuyuki; Ichikawa, Tsuneki; Shiotani, Masaru [eds.

    1998-02-01

    Present report is the proceedings of the 3rd Meeting on Tunneling Reaction and Low Temperature Chemistry held in Oct. 13 and 14, 1997. The main subject of the meeting is `Tunneling Reaction and Quantum Medium`. In the meeting, the physical and chemical phenomena in the liquid helium such as quantum nucleation, spectroscopy of atoms and molecules, and tunneling abstraction reaction of tritium atom were discussed as the main topics as well as the tunneling reactions in the solid hydrogen and organic compounds. Through the meetings held in 1995, 1996, and 1997, the tunneling phenomena proceeding at various temperatures (room temperature to mK) in the wide fields of chemistry, biology, and physics were discussed intensively and the importance of the tunneling phenomena in the science has been getting clear. The 12 of the presented papers are indexed individually. (J.P.N.)

  5. Proceedings of the meeting on tunneling reaction and low temperature chemistry, 97 October. Tunneling reaction and quantum medium

    Energy Technology Data Exchange (ETDEWEB)

    Miyazaki, Tetsuo; Aratono, Yasuyuki; Ichikawa, Tsuneki; Shiotani, Masaru [eds.

    1998-02-01

    Present report is the proceedings of the 3rd Meeting on Tunneling Reaction and Low Temperature Chemistry held in Oct. 13 and 14, 1997. The main subject of the meeting is `Tunneling Reaction and Quantum Medium`. In the meeting, the physical and chemical phenomena in the liquid helium such as quantum nucleation, spectroscopy of atoms and molecules, and tunneling abstraction reaction of tritium atom were discussed as the main topics as well as the tunneling reactions in the solid hydrogen and organic compounds. Through the meetings held in 1995, 1996, and 1997, the tunneling phenomena proceeding at various temperatures (room temperature to mK) in the wide fields of chemistry, biology, and physics were discussed intensively and the importance of the tunneling phenomena in the science has been getting clear. The 12 of the presented papers are indexed individually. (J.P.N.)

  6. Comparison of Oxygen Gauche Effects in Poly(Oxyethylene) and Poly(ethylene terephtylene) Based on Quantum Chemistry Calculations

    Science.gov (United States)

    Jaffe, Richard; Han, Jie; Yoon, Do; Langhoff, Stephen R. (Technical Monitor)

    1997-01-01

    The so-called oxygen gauche effect in poly(oxyethylene) (POE) and its model molecules such as 1,2-dimethoxyethane (DME) and diglyme (CH3OC2H4OC2H4OCH3) is manifested in the preference for gauche C-C bond conformations over trans. This has also been observed for poly(ethylene terephthalate) (PET). Our previous quantum chemistry calculations demonstrated that the large C-C gauche population in DME is due, in part, to a low-lying tg +/- g+ conformer that exhibits a substantial 1,5 CH ... O attraction. New calculations will be described that demonstrate the accuracy of the original quantum chemistry calculations. In addition, an extension of this work to model molecules for PET will be presented. It is seen that the C-C gauche preference is much stronger in 1,2 diacetoxyethane than in DME. In addition, there exist low-lying tg +/- g+/- and g+/-g+/-g+/- conformers that exhibit 1,5 CH ... O attractions involving the carbonyl oxygens. It is expected that the -O-C-C-O- torsional properties will be quite different in these two polymers. The quantum chemistry results are used to parameterize rotational isomeric states models (RIS) and force fields for molecular dynamics simulations of these polymers.

  7. Computational Chemistry Studies on the Carbene Hydroxymethylene

    Science.gov (United States)

    Marzzacco, Charles J.; Baum, J. Clayton

    2011-01-01

    A density functional theory computational chemistry exercise on the structure and vibrational spectrum of the carbene hydroxymethylene is presented. The potential energy curve for the decomposition reaction of the carbene to formaldehyde and the geometry of the transition state are explored. The results are in good agreement with recent…

  8. Nonperturbative Studies of Quantum Gravity

    CERN Document Server

    Beirl, W; Riedler, J; Beirl, Wolfgang; Markum, Harald; Riedler, Juergen

    1993-01-01

    We investigate quantum gravity in the path integral formulation using the Regge calculus. Restricting the quadratic link lengths of the originally triangular lattice the path integral can be transformed to the partition function of a spin system with higher couplings on a Kagome lattice. Various measures acting as external field were considered. Extensions to matter fields and higher dimensions are discussed.

  9. From ab initio quantum chemistry to molecular dynamics: The delicate case of hydrogen bonding in ammonia

    CERN Document Server

    Boese, A D; Martin, J M L; Marx, D; Chandra, Amalendu; Martin, Jan M.L.; Marx, Dominik

    2003-01-01

    The ammonia dimer (NH3)2 has been investigated using high--level ab initio quantum chemistry methods and density functional theory (DFT). The structure and energetics of important isomers is obtained to unprecedented accuracy without resorting to experiment. The global minimum of eclipsed C_s symmetry is characterized by a significantly bent hydrogen bond which deviates from linearity by about 20 degrees. In addition, the so-called cyclic C_{2h} structure is extremely close in energy on an overall flat potential energy surface. It is demonstrated that none of the currently available (GGA, meta--GGA, and hybrid) density functionals satisfactorily describe the structure and relative energies of this nonlinear hydrogen bond. We present a novel density functional, HCTH/407+, designed to describe this sort of hydrogen bond quantitatively on the level of the dimer, contrary to e.g. the widely used BLYP functional. This improved functional is employed in Car-Parrinello ab initio molecular dynamics simulations of liq...

  10. Solving a quantum chemistry equations and high-temperature superconductivity problems

    CERN Document Server

    Liverts, E Z

    2000-01-01

    The conventional technique for solving the equation of quantum chemistry (of solids) is unusually extended to the structures possessing certain symmetries. The extension proposed gives a chance to find unoccupied electronic states located lower than the Fermi level of the ground state of a specific system. Such states can be treated as 'spectral holes'. Application of this technique, in particular, when calculating the electronic structure of the HTSC-compound YBa sub 2 Cu sub 3 O sub 7 sub - subdelta (0<= delta<=1) results in the following. For all versions of the examined charge distributions over a crystal lattice, spectral holes of high spatial localization are found. The 'spatial spectral holes' are mainly located at the p sub y -orbitals of the apex oxygens. These orbitals overlap and form linear chains which are parallel too but do not coincide with the known Cu(1)-O chains which disappear when delta is close tio 1. One can suppose that these linear chains of the overlapping hole states from a su...

  11. Investigation of adsorption of surfactant at the air-water interface with quantum chemistry method

    Institute of Scientific and Technical Information of China (English)

    CHEN MeiLing; WANG ZhengWu; WANG HaiJun; ZHANG GeXin; TAO FuMing

    2007-01-01

    Density functional theory (DFT) of quantum chemistry was used to optimize the configuration of the anionic surfactant complexes CH3(CH2)7OSO-3(H2O)n (n=0-6) and calculate their molecular frequencies at the B3LYP/6-311+G* level. The interaction of CH3(CH2)7OSO-3 with 1 to 6 water molecules was investigated at the air-water interface with DFT. The results revealed that the hydration shell was formed in the form of H-bond between the hydrophilic group of CH3(CH2)7OSO-3 and 6 waters. The strength of H-bonds belongs to medium. Binding free energy revealed that the hydration shell was stable. The increase of the number of water molecules will cause increases of the total charge of hydrophilic group and S10-O9-C8 bond angle, but decreases of the alkyl chain length and the bond lengths of S10-O11,S10-O12 as well as S10-O13, respectively.

  12. Manipulating the Surface Chemistry of Quantum Dots for Sensitive Ratiometric Fluorescence Detection of Sulfur Dioxide.

    Science.gov (United States)

    Li, Huihui; Zhu, Houjuan; Sun, Mingtai; Yan, Yehan; Zhang, Kui; Huang, Dejian; Wang, Suhua

    2015-08-11

    Herein, we report a novel approach to the rapid visual detection of gaseous sulfur dioxide (SO2) by manipulating the surface chemistry of 3-aminopropyltriethoxysilane (APTS)-modified quantum dots (QDs) using fluorescent coumarin-3-carboxylic acid (CCA) for specific reaction with SO2. The CCA molecules are attached to the surface amino groups of the QDs through electrostatic attraction, thus the fluorescence of CCA is greatly suppressed because of the formation of an ion-pair complex between the ATPS-modified QDs and CCA. Such an interaction is vulnerable to SO2 because SO2 can readily react with surface amino groups to form strong charge-transfer complexes and subsequently release the strongly fluorescent CCA molecules. The mechanism has been carefully verified through a series of control experiments. Upon exposure to different amounts of SO2, the fluorescent color of the nanoparticle-based sensor displays continuously changes from red to blue. Most importantly, the approach owns high selectivity for SO2 and a tolerance of interference, which enables the sensor to detect SO2 in a practical application. Using this fluorescence-based sensing method, we have achieved a visual detection limit of 6 ppb for gaseous SO2.

  13. An efficient solver for large structured eigenvalue problems in relativistic quantum chemistry

    CERN Document Server

    Shiozaki, Toru

    2015-01-01

    We report an efficient program for computing the eigenvalues and symmetry-adapted eigenvectors of very large quaternionic (or Hermitian skew-Hamiltonian) matrices, using which structure-preserving diagonalization of matrices of dimension N > 10000 is now routine on a single computer node. Such matrices appear frequently in relativistic quantum chemistry owing to the time-reversal symmetry. The implementation is based on a blocked version of the Paige-Van Loan algorithm [D. Kressner, BIT 43, 775 (2003)], which allows us to use the Level 3 BLAS subroutines for most of the computations. Taking advantage of the symmetry, the program is faster by up to a factor of two than state-of-the-art implementations of complex Hermitian diagonalization; diagonalizing a 12800 x 12800 matrix took 42.8 (9.5) and 85.6 (12.6) minutes with 1 CPU core (16 CPU cores) using our symmetry-adapted solver and Intel MKL's ZHEEV that is not structure-preserving, respectively. The source code is publicly available under the FreeBSD license.

  14. Performance optimization of tensor contraction expressions for many-body methods in quantum chemistry.

    Science.gov (United States)

    Hartono, Albert; Lu, Qingda; Henretty, Thomas; Krishnamoorthy, Sriram; Zhang, Huaijian; Baumgartner, Gerald; Bernholdt, David E; Nooijen, Marcel; Pitzer, Russell; Ramanujam, J; Sadayappan, P

    2009-11-12

    Complex tensor contraction expressions arise in accurate electronic structure models in quantum chemistry, such as the coupled cluster method. This paper addresses two complementary aspects of performance optimization of such tensor contraction expressions. Transformations using algebraic properties of commutativity and associativity can be used to significantly decrease the number of arithmetic operations required for evaluation of these expressions. The identification of common subexpressions among a set of tensor contraction expressions can result in a reduction of the total number of operations required to evaluate the tensor contractions. The first part of the paper describes an effective algorithm for operation minimization with common subexpression identification and demonstrates its effectiveness on tensor contraction expressions for coupled cluster equations. The second part of the paper highlights the importance of data layout transformation in the optimization of tensor contraction computations on modern processors. A number of considerations, such as minimization of cache misses and utilization of multimedia vector instructions, are discussed. A library for efficient index permutation of multidimensional tensors is described, and experimental performance data is provided that demonstrates its effectiveness.

  15. Performance Optimization of Tensor Contraction Expressions for Many Body Methods in Quantum Chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Hartono, Albert; Lu, Qingda; henretty, thomas; Krishnamoorthy, Sriram; zhang, huaijian; Baumgartner, Gerald; Bernholdt, David E.; Nooijen, Marcel; Pitzer, Russell M.; Ramanujam, J.; Sadayappan, Ponnuswamy

    2009-11-12

    Complex tensor contraction expressions arise in accurate electronic structure models in quantum chemistry, such as the coupled cluster method. This paper addresses two complementary aspects of performance optimization of such tensor contraction expressions. Transformations using algebraic properties of commutativity and associativity can be used to significantly decrease the number of arithmetic operations required for evaluation of these expressions. The identification of common subexpressions among a set of tensor contraction expressions can result in a reduction of the total number of operations required to evaluate the tensor contractions. The first part of the paper describes an effective algorithm for operation minimization with common subexpression identification and demonstrates its effectiveness on tensor contraction expressions for coupled cluster equations. The second part of the paper highlights the importance of data layout transformation in the optimization of tensor contraction computations on modern processors. A number of considerations such as minimization of cache misses and utilization of multimedia vector instructions are discussed. A library for efficient index permutation of multi-dimensional tensors is described and experimental performance data is provided that demonstrates its effectiveness.

  16. Group theory and chemistry

    CERN Document Server

    Bishop, David M

    1993-01-01

    Group theoretical principles are an integral part of modern chemistry. Not only do they help account for a wide variety of chemical phenomena, they simplify quantum chemical calculations. Indeed, knowledge of their application to chemical problems is essential for students of chemistry. This complete, self-contained study, written for advanced undergraduate-level and graduate-level chemistry students, clearly and concisely introduces the subject of group theory and demonstrates its application to chemical problems.To assist chemistry students with the mathematics involved, Professor Bishop ha

  17. Quantum science in secondary chemistry: Influence of teachers' beliefs and knowledge on the use of interactive computer models

    Science.gov (United States)

    Robblee, Karen M.

    Current science education reform efforts promote inquiry-based learning, a goal that requires appropriate tools and instructional approaches. This study investigated the influence of the beliefs and knowledge of four experienced secondary chemistry teachers in their use of new instructional software that generates models of atoms and molecules based on quantum mechanics. The software, which was developed through a National Science Foundation funded project, Quantum Science Across Disciplines (QSAD), was designed to promote inquiry learning. Qualitative research methods were used for this multiple case study. Data from surveys, interviews, and extended classroom observations revealed a close correlation between a teacher's model of the learner and his or her model of teaching. Combined models of learner and teacher had the greatest influence on their decisions about implementing QSAD software. Teachers who espoused a constructivist model of learning and related models of teaching used the software to promote student investigations and inductive approaches to learning. Other factors that appeared to support the use of inquiry methods included sufficient time for students to investigate phenomena, the extent of the teacher's pedagogical content knowledge, and the amount of training using QSAD software. The Views-On-Science-Technology-Society (VOSTS) instrument was used to compare the informants' beliefs about the epistemology of science to their classroom practices. Data related to the role of teachers' beliefs about scientific knowledge were inconclusive, and VOSTS results were inconsistent with the informants' stated beliefs. All four cases revealed that the teachers acted as agents of the school culture. In schools that promoted development of critical thinking, questioning, and self-direction in students, teachers were more likely to use a variety of instructional methods and emphasize construction of knowledge. These findings suggest that educational reform

  18. General Chemistry Courses That Can Affect Achievement: An Action Research Study in Developing a Plan to Improve Undergraduate Chemistry Courses

    Science.gov (United States)

    Shweikeh, Eman

    2014-01-01

    Over the past 50 years, considerable research has been dedicated to chemistry education. In evaluating principal chemistry courses in higher education, educators have noted the learning process for first-year general chemistry courses may be challenging. The current study investigated perceptions of faculty, students and administrators on…

  19. General Chemistry Courses That Can Affect Achievement: An Action Research Study in Developing a Plan to Improve Undergraduate Chemistry Courses

    Science.gov (United States)

    Shweikeh, Eman

    2014-01-01

    Over the past 50 years, considerable research has been dedicated to chemistry education. In evaluating principal chemistry courses in higher education, educators have noted the learning process for first-year general chemistry courses may be challenging. The current study investigated perceptions of faculty, students and administrators on…

  20. Extending Halogen-based Medicinal Chemistry to Proteins: IODO-INSULIN AS A CASE STUDY.

    Science.gov (United States)

    El Hage, Krystel; Pandyarajan, Vijay; Phillips, Nelson B; Smith, Brian J; Menting, John G; Whittaker, Jonathan; Lawrence, Michael C; Meuwly, Markus; Weiss, Michael A

    2016-12-30

    Insulin, a protein critical for metabolic homeostasis, provides a classical model for protein design with application to human health. Recent efforts to improve its pharmaceutical formulation demonstrated that iodination of a conserved tyrosine (Tyr(B26)) enhances key properties of a rapid-acting clinical analog. Moreover, the broad utility of halogens in medicinal chemistry has motivated the use of hybrid quantum- and molecular-mechanical methods to study proteins. Here, we (i) undertook quantitative atomistic simulations of 3-[iodo-Tyr(B26)]insulin to predict its structural features, and (ii) tested these predictions by X-ray crystallography. Using an electrostatic model of the modified aromatic ring based on quantum chemistry, the calculations suggested that the analog, as a dimer and hexamer, exhibits subtle differences in aromatic-aromatic interactions at the dimer interface. Aromatic rings (Tyr(B16), Phe(B24), Phe(B25), 3-I-Tyr(B26), and their symmetry-related mates) at this interface adjust to enable packing of the hydrophobic iodine atoms within the core of each monomer. Strikingly, these features were observed in the crystal structure of a 3-[iodo-Tyr(B26)]insulin analog (determined as an R6 zinc hexamer). Given that residues B24-B30 detach from the core on receptor binding, the environment of 3-I-Tyr(B26) in a receptor complex must differ from that in the free hormone. Based on the recent structure of a "micro-receptor" complex, we predict that 3-I-Tyr(B26) engages the receptor via directional halogen bonding and halogen-directed hydrogen bonding as follows: favorable electrostatic interactions exploiting, respectively, the halogen's electron-deficient σ-hole and electronegative equatorial band. Inspired by quantum chemistry and molecular dynamics, such "halogen engineering" promises to extend principles of medicinal chemistry to proteins.

  1. On quantum statistical mechanics; A study guide

    OpenAIRE

    Majewski, W. A.

    2016-01-01

    These notes are intended as an introduction to a study of applications of noncommutative calculus to quantum statistical mechanics. Centered on noncommutative calculus we describe the physical concepts and mathematical structures appearing in the analysis of large quantum systems, and their consequences. These include the emergence of algebraic approach and the necessity of employment of infinite dimensional structures. As an illustration, a quantization of stochastic processes, new formalism...

  2. Quantum catastrophes: a case study

    Science.gov (United States)

    Znojil, Miloslav

    2012-11-01

    The bound-state spectrum of a Hamiltonian H is assumed real in a non-empty domain D of physical values of parameters. This means that for these parameters, H may be called crypto-Hermitian, i.e. made Hermitian via an ad hoc choice of the inner product in the physical Hilbert space of quantum bound states (i.e. via an ad hoc construction of the operator Θ called the metric). The name quantum catastrophe is then assigned to the N-tuple-exceptional-point crossing, i.e. to the scenario in which we leave the domain D along such a path that at the boundary of D, an N-plet of bound-state energies degenerates and, subsequently, complexifies. At any fixed N ⩾ 2, this process is simulated via an N × N benchmark effective matrix Hamiltonian H. It is being assigned such a closed-form metric which is made unique via an N-extrapolation-friendliness requirement. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.

  3. Accuracy of color prediction of anthraquinone dyes in methanol solution estimated from first principle quantum chemistry computations.

    Science.gov (United States)

    Cysewski, Piotr; Jeliński, Tomasz

    2013-10-01

    The electronic spectrum of four different anthraquinones (1,2-dihydroxyanthraquinone, 1-aminoanthraquinone, 2-aminoanthraquinone and 1-amino-2-methylanthraquinone) in methanol solution was measured and used as reference data for theoretical color prediction. The visible part of the spectrum was modeled according to TD-DFT framework with a broad range of DFT functionals. The convoluted theoretical spectra were validated against experimental data by a direct color comparison in terms of CIE XYZ and CIE Lab tristimulus model color. It was found, that the 6-31G** basis set provides the most accurate color prediction and there is no need to extend the basis set since it does not improve the prediction of color. Although different functionals were found to give the most accurate color prediction for different anthraquinones, it is possible to apply the same DFT approach for the whole set of analyzed dyes. Especially three functionals seem to be valuable, namely mPW1LYP, B1LYP and PBE0 due to very similar spectra predictions. The major source of discrepancies between theoretical and experimental spectra comes from L values, representing the lightness, and the a parameter, depicting the position on green→magenta axis. Fortunately, the agreement between computed and observed blue→yellow axis (parameter b) is very precise in the case of studied anthraquinone dyes in methanol solution. Despite discussed shortcomings, color prediction from first principle quantum chemistry computations can lead to quite satisfactory results, expressed in terms of color space parameters.

  4. Mechanism of Magnetostructural Transitions in Copper-Nitroxide-Based Switchable Molecular Magnets: Insights from ab Initio Quantum Chemistry Calculations.

    Science.gov (United States)

    Jung, Julie; Guennic, Boris Le; Fedin, Matvey V; Ovcharenko, Victor I; Calzado, Carmen J

    2015-07-20

    The gradual magnetostructural transition in breathing crystals based on copper(II) and pyrazolyl-substituted nitronyl nitroxides has been analyzed by means of DDCI quantum chemistry calculations. The magnetic coupling constants (J) within the spin triads of Cu(hfac)2L(Bu)·0.5C8H18 have been evaluated for the X-ray structures reported at different temperatures. The coupling is strongly antiferromagnetic at low temperature and becomes ferromagnetic when the temperature increases. The intercluster magnetic coupling (J') is antiferromagnetic and shows a marked dependence on temperature. The magnetostructural transition can be reproduced using the calculated J values for each structure in the simulation of the magnetic susceptibility. However, the μ(T) curve can be improved nicely by considering the coexistence of two phases in the transition region, whose ratio varies with temperature corresponding to both the weakly and strongly coupled spin states. These results complement a recent VT-FTIR study on the parent Cu(hfac)2L(Pr) compound with a gradual magnetostructural transition.

  5. Yb-based heavy fermion compounds and field tuned quantum chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Mun, Eundeok [Iowa State Univ., Ames, IA (United States)

    2010-01-01

    The motivation of this dissertation was to advance the study of Yb-based heavy fermion (HF) compounds especially ones related to quantum phase transitions. One of the topics of this work was the investigation of the interaction between the Kondo and crystalline electric field (CEF) energy scales in Yb-based HF systems by means of thermoelectric power (TEP) measurements. In these systems, the Kondo interaction and CEF excitations generally give rise to large anomalies such as maxima in ρ(T) and as minima in S(T). The TEP data were use to determine the evolution of Kondo and CEF energy scales upon varying transition metals for YbT2Zn20 (T = Fe, Ru, Os, Ir, Rh, and Co) compounds and applying magnetic fields for YbAgGe and YbPtBi. For YbT2Zn20 and YbPtBi, the Kondo and CEF energy scales could not be well separated in S(T), presumably because of small CEF level splittings. A similar effect was observed for the magnetic contribution to the resistivity. For YbAgGe, S(T) has been successfully applied to determine the Kondo and CEF energy scales due to the clear separation between the ground state and thermally excited CEF states. The Kondo temperature, TK, inferred from the local maximum in S(T), remains finite as magnetic field increases up to 140 kOe. In this dissertation we have examined the heavy quasi-particle behavior, found near the field tuned AFM quantum critical point (QCP), with YbAgGe and YbPtBi. Although the observed nFL behaviors in the vicinity of the QCP are different between YbAgGe and YbPtBi, the constructed H-T phase diagram including the two crossovers are similar. For both YbAgGe and YbPtBi, the details of the quantum criticality turn out to be complicated. We expect that YbPtBi will provide an additional example of field tuned quantum criticality, but clearly there are further experimental investigations left and more ideas needed to understand the basic physics of field-induced quantum

  6. Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling

    Science.gov (United States)

    Peng, Zhe; Day, Douglas A.; Ortega, Amber M.; Palm, Brett B.; Hu, Weiwei; Stark, Harald; Li, Rui; Tsigaridis, Kostas; Brune, William H.; Jimenez, Jose L.

    2016-04-01

    Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H2O) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define "riskier OFR conditions" as those with either low H2O ( 200 s-1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O3, similarly to the troposphere. Working under low O2 (volume mixing

  7. Quantum Mechanical Studies of DNA and LNA

    DEFF Research Database (Denmark)

    Koch, Troels; Shim, Irene; Lindow, Morten;

    2014-01-01

    Quantum mechanical (QM) methodology has been employed to study the structure activity relations of DNA and locked nucleic acid (LNA). The QM calculations provide the basis for construction of molecular structure and electrostatic surface potentials from molecular orbitals. The topologies of the e......Quantum mechanical (QM) methodology has been employed to study the structure activity relations of DNA and locked nucleic acid (LNA). The QM calculations provide the basis for construction of molecular structure and electrostatic surface potentials from molecular orbitals. The topologies...

  8. Automated quantum chemistry based molecular dynamics simulations of electron ionization induced fragmentations of the nucleobases Uracil, Thymine, Cytosine, and Guanine.

    Science.gov (United States)

    Grimme, Stefan; Bauer, Christopher Alexander

    2015-01-01

    The gas-phase decomposition pathways of electron ionization (EI)-induced radical cations of the nucleobases uracil, thymine, cytosine, and guanine are investigated by means of mixed quantum-classical molecular dynamics. No preconceived fragmentation channels are used in the calculations. The results compare well to a plethora of experimental and theoretical data for these important biomolecules. With our combined stochastic and dynamic approach, one can access in an unbiased way the energetically available decomposition mechanisms. Additionally, we are able to separate the EI mass spectra of different tautomers of cytosine and guanine. Our method (previously termed quantum chemistry electron ionization mass spectra) reproduces free nucleobase experimental mass spectra well and provides detailed mechanistic in-sight into high-energy unimolecular decomposition processes.

  9. Nobel Prizes in Physics and Chemistry 2014: Celebrating the International Year of Light 2015, commemorating the Old Quantum Theory

    Science.gov (United States)

    Shi, Yu

    2015-01-01

    2015 is the International Year of Light and Light-based Technologies (IYL), while the physics and chemistry Nobel Prizes 2014 are both about light. The work leading to the two prizes share the same basic theoretical foundation: when an electron jumps from a higher energy level to a lower energy level, the energy difference is transformed into a photon. This basic way of light generation is a key part of the Old Quantum Theory. Interestingly, the date of announcing the 2014 Nobel Prize for physics coincided with the birthdays of Niels Bohr and, especially, of Planck's blackbody radiation formula. In connection with the two 2014 Nobel Prizes, we recall the development of the Old Quantum Theory by Planck, Einstein and Bohr.

  10. Quantum Monte Carlo study of the protonated water dimer

    CERN Document Server

    Dagrada, Mario; Saitta, Antonino M; Sorella, Sandro; Mauri, Francesco

    2013-01-01

    We report an extensive theoretical study of the protonated water dimer (Zundel ion) by means of the highly correlated variational Monte Carlo and lattice regularized Monte Carlo approaches. This system represents the simplest model for proton transfer (PT) and a correct description of its properties is essential in order to understand the PT mechanism in more complex acqueous systems. Our Jastrow correlated AGP wave function ensures an accurate treatment of electron correlations. Exploiting the advantages of contracting the primitive basis set over atomic hybrid orbitals, we are able to limit dramatically the number of variational parameters with a systematic control on the numerical precision, crucial in order to simulate larger systems. We investigate energetics and geometrical properties of the Zundel ion as a function of the oxygen-oxygen distance, taken as reaction coordinate. In both cases, our QMC results are found in excellent agreement with coupled cluster CCSD(T) technique, the quantum chemistry "go...

  11. A Thematic Review of Studies into the Effectiveness of Context-Based Chemistry Curricula

    Science.gov (United States)

    Ultay, Neslihan; Calik, Muammer

    2012-01-01

    Context-based chemistry education aims at making connections between real life and the scientific content of chemistry courses. The purpose of this study was to evaluate context-based chemistry studies. In looking for the context-based chemistry studies, the authors entered the keywords "context-based", "contextual learning" and "chemistry…

  12. From C60 to Infinity: Large-Scale Quantum Chemistry Calculations of the Heats of Formation of Higher Fullerenes.

    Science.gov (United States)

    Chan, Bun; Kawashima, Yukio; Katouda, Michio; Nakajima, Takahito; Hirao, Kimihiko

    2016-02-03

    We have carried out large-scale computational quantum chemistry calculations on the K computer to obtain heats of formation for C60 and some higher fullerenes with the DSD-PBE-PBE/cc-pVQZ double-hybrid density functional theory method. Our best estimated values are 2520.0 ± 20.7 (C60), 2683.4 ± 17.7 (C70), 2862.0 ± 18.5 (C76), 2878.8 ± 13.3 (C78), 2946.4 ± 14.5 (C84), 3067.3 ± 15.4 (C90), 3156.6 ± 16.2 (C96), 3967.7 ± 33.4 (C180), 4364 (C240) and 5415 (C320) kJ mol(-1). In our assessment, we also find that the B3-PW91-D3BJ and BMK-D3(BJ) functionals perform reasonably well. Using the convergence behavior for the calculated per-atom heats of formation, we obtained the formula ΔfH per carbon = 722n(-0.72) + 5.2 kJ mol(-1) (n = the number of carbon atoms), which enables an estimation of ΔfH for higher fullerenes more generally. A slow convergence to the graphene limit is observed, which we attribute to the relatively small proportion of fullerene carbons that are in "low-strain" regions. We further propose that it would take tens, if not hundreds, of thousands of carbons for a fullerene to roughly approach the limit. Such a distinction may be a contributing factor to the discrete properties between the two types of nanomaterials. During the course of our study, we also observe a fairly reliable means for the theoretical calculation of heats of formation for medium-sized fullerenes. This involves the use of isodesmic-type reactions with fullerenes of similar sizes to provide a good balance of the chemistry and to minimize the use of accompanying species.

  13. Quantum confined Stark effect in Gaussian quantum wells: A tight-binding study

    Energy Technology Data Exchange (ETDEWEB)

    Ramírez-Morales, A.; Martínez-Orozco, J. C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad Esquina Con Paseo La Bufa S/N, 98060 Zacatecas, Zac. (Mexico)

    2014-05-15

    The main characteristics of the quantum confined Stark effect (QCSE) are studied theoretically in quantum wells of Gaussian profile. The semi-empirical tight-binding model and the Green function formalism are applied in the numerical calculations. A comparison of the QCSE in quantum wells with different kinds of confining potential is presented.

  14. Efficient tree tensor network states (TTNS) for quantum chemistry: generalizations of the density matrix renormalization group algorithm.

    Science.gov (United States)

    Nakatani, Naoki; Chan, Garnet Kin-Lic

    2013-04-07

    We investigate tree tensor network states for quantum chemistry. Tree tensor network states represent one of the simplest generalizations of matrix product states and the density matrix renormalization group. While matrix product states encode a one-dimensional entanglement structure, tree tensor network states encode a tree entanglement structure, allowing for a more flexible description of general molecules. We describe an optimal tree tensor network state algorithm for quantum chemistry. We introduce the concept of half-renormalization which greatly improves the efficiency of the calculations. Using our efficient formulation we demonstrate the strengths and weaknesses of tree tensor network states versus matrix product states. We carry out benchmark calculations both on tree systems (hydrogen trees and π-conjugated dendrimers) as well as non-tree molecules (hydrogen chains, nitrogen dimer, and chromium dimer). In general, tree tensor network states require much fewer renormalized states to achieve the same accuracy as matrix product states. In non-tree molecules, whether this translates into a computational savings is system dependent, due to the higher prefactor and computational scaling associated with tree algorithms. In tree like molecules, tree network states are easily superior to matrix product states. As an illustration, our largest dendrimer calculation with tree tensor network states correlates 110 electrons in 110 active orbitals.

  15. Accurate and efficient quantum chemistry calculations for noncovalent interactions in many-body systems: the XSAPT family of methods.

    Science.gov (United States)

    Lao, Ka Un; Herbert, John M

    2015-01-15

    We present an overview of "XSAPT", a family of quantum chemistry methods for noncovalent interactions. These methods combine an efficient, iterative, monomer-based approach to computing many-body polarization interactions with a two-body version of symmetry-adapted perturbation theory (SAPT). The result is an efficient method for computing accurate intermolecular interaction energies in large noncovalent assemblies such as molecular and ionic clusters, molecular crystals, clathrates, or protein-ligand complexes. As in traditional SAPT, the XSAPT energy is decomposable into physically meaningful components. Dispersion interactions are problematic in traditional low-order SAPT, and two new approaches are introduced here in an attempt to improve this situation: (1) third-generation empirical atom-atom dispersion potentials, and (2) an empirically scaled version of second-order SAPT dispersion. Comparison to high-level ab initio benchmarks for dimers, water clusters, halide-water clusters, a methane clathrate hydrate, and a DNA intercalation complex illustrate both the accuracy of XSAPT-based methods as well as their limitations. The computational cost of XSAPT scales as O(N(3))-O(N(5)) with respect to monomer size, N, depending upon the particular version that is employed, but the accuracy is typically superior to alternative ab initio methods with similar scaling. Moreover, the monomer-based nature of XSAPT calculations makes them trivially parallelizable, such that wall times scale linearly with respect to the number of monomer units. XSAPT-based methods thus open the door to both qualitative and quantitative studies of noncovalent interactions in clusters, biomolecules, and condensed-phase systems.

  16. General chemistry courses that can affect achievement: An action research study in developing a plan to improve undergraduate chemistry courses

    Science.gov (United States)

    Shweikeh, Eman

    Over the past 50 years, considerable research has been dedicated to chemistry education. In evaluating principal chemistry courses in higher education, educators have noted the learning process for first-year general chemistry courses may be challenging. The current study investigated perceptions of faculty, students and administrators on chemistry education at three institutions in Southern California. Via action research, the study sought to develop a plan to improve student engagement in general chemistry courses. A mixed method was utilized to analyze different perceptions on key factors determining the level of commitment and engagement in general chemistry education. The approach to chemistry learning from both a faculty and student perspective was examined including good practices, experiences and extent of active participation. The research study considered well-known measures of effective education with an emphasis on two key components: educational practices and student behavior. Institutional culture was inclusively assessed where cognitive expectations of chemistry teaching and learning were communicated. First, the extent in which faculty members are utilizing the "Seven Principles for Good Practice in Undergraduate Education" in their instruction was explored. Second, student attitudes and approaches toward chemistry learning were examined. The focus was on investigating student understanding of the learning process and the structure of chemistry knowledge. The seven categories used to measure students' expectations for learning chemistry were: effort, concepts, math link, reality link, outcome, laboratory, and visualization. This analysis represents the views of 16 faculty and 140 students. The results validated the assertion that students need some competencies and skills to tackle the challenges of the chemistry learning process to deeply engage in learning. A mismatch exists between the expectations of students and those of the faculty

  17. Teaching introductory quantum physics and chemistry: caveats from the history of science and science teaching to the training of modern chemists

    OpenAIRE

    Greca Dufranc, Ileana María; Freire Junior, Olival

    2014-01-01

    Finding the best ways to introduce quantum physics to undergraduate students in all scientific areas, in particular for chemistry students, is a pressing, but hardly a simple task. In this paper, we discuss the relevance of taking into account lessons from the history of the discipline and the ongoing controversy over its interpretations and foundations in the search for new ways of improving the teaching of quantum physics. We also review and discuss the recent research in science education ...

  18. Exploring Strong Interactions in Proteins with Quantum Chemistry and Examples of Their Applications in Drug Design.

    Directory of Open Access Journals (Sweden)

    Neng-Zhong Xie

    Full Text Available Three strong interactions between amino acid side chains (salt bridge, cation-π, and amide bridge are studied that are stronger than (or comparable to the common hydrogen bond interactions, and play important roles in protein-protein interactions.Quantum chemical methods MP2 and CCSD(T are used in calculations of interaction energies and structural optimizations.The energies of three types of amino acid side chain interactions in gaseous phase and in aqueous solutions are calculated using high level quantum chemical methods and basis sets. Typical examples of amino acid salt bridge, cation-π, and amide bridge interactions are analyzed, including the inhibitor design targeting neuraminidase (NA enzyme of influenza A virus, and the ligand binding interactions in the HCV p7 ion channel. The inhibition mechanism of the M2 proton channel in the influenza A virus is analyzed based on strong amino acid interactions.(1 The salt bridge interactions between acidic amino acids (Glu- and Asp- and alkaline amino acids (Arg+, Lys+ and His+ are the strongest residue-residue interactions. However, this type of interaction may be weakened by solvation effects and broken by lower pH conditions. (2 The cation- interactions between protonated amino acids (Arg+, Lys+ and His+ and aromatic amino acids (Phe, Tyr, Trp and His are 2.5 to 5-fold stronger than common hydrogen bond interactions and are less affected by the solvation environment. (3 The amide bridge interactions between the two amide-containing amino acids (Asn and Gln are three times stronger than hydrogen bond interactions, which are less influenced by the pH of the solution. (4 Ten of the twenty natural amino acids are involved in salt bridge, or cation-, or amide bridge interactions that often play important roles in protein-protein, protein-peptide, protein-ligand, and protein-DNA interactions.

  19. Quantum Chemistry on Quantum Computers: A Polynomial-Time Quantum Algorithm for Constructing the Wave Functions of Open-Shell Molecules.

    Science.gov (United States)

    Sugisaki, Kenji; Yamamoto, Satoru; Nakazawa, Shigeaki; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Takui, Takeji

    2016-08-18

    Quantum computers are capable to efficiently perform full configuration interaction (FCI) calculations of atoms and molecules by using the quantum phase estimation (QPE) algorithm. Because the success probability of the QPE depends on the overlap between approximate and exact wave functions, efficient methods to prepare accurate initial guess wave functions enough to have sufficiently large overlap with the exact ones are highly desired. Here, we propose a quantum algorithm to construct the wave function consisting of one configuration state function, which is suitable for the initial guess wave function in QPE-based FCI calculations of open-shell molecules, based on the addition theorem of angular momentum. The proposed quantum algorithm enables us to prepare the wave function consisting of an exponential number of Slater determinants only by a polynomial number of quantum operations.

  20. InAs Colloidal Quantum Dots Synthesis via Aminopnictogen Precursor Chemistry.

    Science.gov (United States)

    Grigel, Valeriia; Dupont, Dorian; De Nolf, Kim; Hens, Zeger; Tessier, Mickael D

    2016-10-05

    Despite their various potential applications, InAs colloidal quantum dots have attracted considerably less attention than more classical II-VI materials because of their complex syntheses that require hazardous precursors. Recently, amino-phosphine has been introduced as a cheap, easy-to-use and efficient phosphorus precursor to synthesize InP quantum dots. Here, we use aminopnictogen precursors to implement a similar approach for synthesizing InAs quantum dots. We develop a two-step method based on the combination of aminoarsine as the arsenic precursor and aminophosphine as the reducing agent. This results in state-of-the-art InAs quantum dots with respect to the size dispersion and band-gap range. Moreover, we present shell coating procedures that lead to the formation of InAs/ZnS(e) core/shell quantum dots that emit in the infrared region. This innovative synthesis approach can greatly facilitate the research on InAs quantum dots and may lead to synthesis protocols for a wide range of III-V quantum dots.

  1. A Surface Chemistry Approach to Enhancing Colloidal Quantum Dot Solids for Photovoltaics

    Science.gov (United States)

    Carey, Graham Hamilton

    Colloidal quantum dot (CQD) photovoltaic devices have improved rapidly over the past decade of research. By taking advantage of the quantum confinement effect, solar cells constructed using films of infrared-bandgap nanoparticles are able to capture previously untapped ranges of the solar energy spectrum. Additionally, films are fabricated using simple, cheap, reproducible solution processing techniques, enabling the creation of low-cost, flexible photovoltaic devices. A key factor limiting the creation of high efficiency CQD solar cells is the short charge carrier diffusion length in films. Driven by a combination of limited carrier mobility, poor nanoparticle surface passivation, and the presence of unexamined electrically active impurities throughout the film, the poor diffusion length limits the active layer thickness in CQD solar cells, leading to lower-than-desired light absorption, and curtailing the photocurrent generated by such devices. This thesis seeks to address poor diffusion length by addressing each of the limiting factors in turn. Electrical transport in quantum dot solids is examined in the context of improved quantum dot packing; methods are developed to improve packing by using actively densifying components, or by dramatically lowering the volume change required between quantum dots in solution and in solid state. Quantum dot surface passivation is improved by introducing a crucial secondary, small halide ligand source, and by surveying the impact of the processing environment on the final quality of the quantum dot surface. A heretofore unidentified impurity present in quantum dot solids is identified, characterized, and chemically eliminated. Finally, lessons learned through these experiments are combined into a single, novel materials system, leading to quantum dot devices with a significantly improved diffusion length (enhanced from 70 to 230 nm). This enabled thick, high current density (30 mA cm -2, compared to typical values in the 20

  2. Theoretical Study of Quantum Bit Rate in Free-Space Quantum Cryptography

    Institute of Scientific and Technical Information of China (English)

    MA Jing; ZHANG Guang-Yu; TAN Li-Ying

    2006-01-01

    The quantum bit rate is an important operating parameter in free-space quantum key distribution. We introduce the measuring factor and the sifting factor, and present the expressions of the quantum bit rate based on the ideal single-photon sources and the single-photon sources with Poisson distribution. The quantum bit rate is studied in the numerical simulation for the laser links between a ground station and a satellite in a low earth orbit. The results show that it is feasible to implement quantum key distribution between a ground station and a satellite in a low earth orbit.

  3. N4H4分子取代基效应的量子化学研究%Quantum chemistry study on the substituent effect of N4H4

    Institute of Scientific and Technical Information of China (English)

    毛双; 谭英雄; 蒲雪梅; 李来才; 田安民

    2012-01-01

    Studies on substituent effects of the methyl and hydroxyl group on 1-tetrazene and 2-tetrazene were performed. For 1-tetrazene derivatives substituted, the length of N = N double bond was shortened while the length of N—N single bond was increased. But no obvious variation on the bond length was observed for the 2-tetrazene derivatives substituted. The total energy and formation heat were decreased with the addition of substituents. A good correlation was respectively found between the total energy and the formation heat and the number of substituent. In addition, the hyperconjugation from the lone-pair electrons of atom N to the N—C(N — O) bond was increased by the introduction of substituent.%本文计算了甲基(-CH3),羟基(-OH)对1-丁氮烯和2-丁氮烯的取代基效应.1-丁氮烯引入取代基后,N=N双键的键长变短,而N-N单键的键长增长.异构体2-丁氮烯的键长变化较小.引入甲基或羟基后,N原子的孤对电子会与相应的N- C(N- O)键之间发生相互作用,使整个分子的超共轭作用增强.随着取代基数目的增多,总能量和生成热就会降低,取代基数目与分子能量(生成热)之间具有很好的相关性.

  4. Study on Quantum Chemistry of Structure and Properties of A Novel High Energetic Density Compound BNFDAONAB%新型高能量密度化合物BNFDAONAB的结构与性能量子化学研究

    Institute of Scientific and Technical Information of China (English)

    荆苏明; 刘玉存; 刘登程; 郭嘉昒

    2015-01-01

    A novel high energetic density compound N,N′-Bis(4-nitrofuzan-3-yl-)-4,4′-diamino-2、2′,3、3′,5、5′,6、6′-octanitroazobenzene(BNFDAONAB)was designed. The stable geometry was completely optimized at B3LYP/6-31G+G**theoretical level of density functional theory (DFT), and its IR spectrum was obtained. The heat formation of 865.79kJ/mol and theoretical density of 2.08g/cm3 were obtained via isodesmic reaction and Monte-Carlo method, respectively. The detonation velocity, detonation pressure and explosion heat were predicted by the formula of Kamlet-Jacobs, based on the theoretical density. The impact sensitivity was predicted by the formula of Keshavarz. In addition, the reaction route was design by a retro synthesis analysis method. The results showed that BNFDAONAB could meet the requirements of high energetic materials with detonation velocity of 9.13km/s, detonation pressure of 39.03GPa and explosion heat of 4 487.44J/g, predicted value of H 50 was 1.06cm in addition. The study showed that the compound was a potential green primary explosive.%设计了一种新型高能量密度化合物(HEDC)—N,N、-二(4-硝基呋咱基-3-基-)-4,4´-二氨基-2、2´,3、3´,5、5´,6、6´-八硝基偶氮苯(BNFDAONAB),采用密度泛函理论(DFT)方法,在B3LYP/6-31+G**基组水平下对其结构进行优化并计算获得了其红外(IR)光谱;采用Monte-Carlo方法预测了BNFDAONAB的理论密度为2.08g/cm3;设计等键反应计算了生成焓为865.79kJ/mol;运用Klmet-Jacobs公式预测了BNFDAONAB的爆速、爆压和爆热值分别为9.13km/s、39.03GPa和4487.44J/g;运用Keshavarz公式预测撞击感度H50为1.06cm;并利用逆合成分析法设计了其合成路线。结果表明,该化合物主要性能的预测值基本达到了HEDC的要求,是一种潜在的绿色起爆药。

  5. Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study

    Directory of Open Access Journals (Sweden)

    Stephan Michael

    2016-05-01

    Full Text Available In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. Here, we study the influence of two important quantum-dot material parameters, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density can compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. However, by minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory.

  6. Studies of Quantum Chromodynamics at the LHC

    CERN Document Server

    Carli, Tancredi; Schumann, Steffen

    2015-01-01

    A successful description of hadron-hadron collision data demands a profound understanding of quantum chromodynamics. Inevitably, the complexity of strong-interaction phenomena requires the use of a large variety of theoretical techniques -- from perturbative cross-section calculations up to the modelling of exclusive hadronic final states. Together with the unprecedented precision of the data provided by the experiments in the first running period of the LHC, a solid foundation of hadron-hadron collision physics at the TeV scale could be established that allowed the discovery of the Higgs boson and that is vital for estimating the background in searches for new phenomena. This chapter on studies of quantum chromodynamics at the LHC is part of a recent book on the results of LHC Run 1 and presents the advances in theoretical methods side-by-side with related key measurements in an integrated approach.

  7. Elementary and brief introduction of hadronic chemistry

    Science.gov (United States)

    Tangde, Vijay M.

    2013-10-01

    The discipline, today known as Quantum Chemistry for atomic and subatomic level interactions has no doubt made a significant historical contributions to the society. Despite of its significant achievements, quantum chemistry is also known for its widespread denial of insufficiencies it inherits. An Italian-American Scientist Professor Ruggero Maria Santilli during his more than five decades of dedicated and sustained research has denounced the fact that quantum chemistry is mostly based on mere nomenclatures without any quantitative scientific contents. Professor R M Santilli first formulated the iso-, geno- and hyper-mathematics [1-4] that helped in understanding numerous diversified problems and removing inadequacies in most of the established and celebrated theories of 20th century physics and chemistry. This involves the isotopic, genotopic, etc. lifting of Lie algebra that generated Lie admissible mathematics to properly describe irreversible processes. The studies on Hadronic Mechanics in general and chemistry in particular based on Santilli's mathematics[3-5] for the first time has removed the very fundamental limitations of quantum chemistry [2, 6-8]. In the present discussion, we have briefly reviewed the conceptual foundations of Hadronic Chemistry that imparts the completeness to the Quantum Chemistry via an addition of effects at distances of the order of 1 fm (only) which are assumed to be Non-linear, Non-local, Non-potential, Non-hamiltonian and thus Non-unitary and its application in development of a new chemical species called Magnecules.

  8. Green Synthesis, Spectrofluorometric Characterization and Antibacterial Activity of Heterocyclic Compound from Chalcone on the Basis of in Vitro and Quantum Chemistry Calculation.

    Science.gov (United States)

    Khan, Salman A

    2017-02-08

    2-amino-4-(4-bromophenyl)-8-methoxy-5,6-dihydrobenzo[h]quinoline-3-carbonitrile (ABDC) was synthesized by the reaction of (2E)-2-(4 bromobenzylidene) - 6 -methoxy-3,4-dihydronaphthalen-1(2H)-one (Chalcone) with malononitrile and ammonium acetate under microwave irradiation. Chalcone was synthesised by the reaction 4-bromobenzaldehyd, 6-methoxy-1,2,3,4-tetrahydro-naphthalin-1-one under the same condition. Structure of ABDC was conformed by (1)H and (13)C NMR, FT-IR, EI-MS spectral studies and elemental analysis. The electronic absorption and fluorescence spectra of ABDC have been studied in solvents of different polarities, and the data were used to study the solvatochromic properties such as excitation coefficient, stokes shift, oscillator strength, transition dipole moment and fluorescence quantum yield. The absorption maximum and fluorescence emission maximum was observed red shift when increase solvent polarity n-Hexane to DMSO. ABDC undergoes solubilization in different micelles and may be used as a probe and quencher to determine the critical micelle concentration (CMC) of CTAB and SDS. The anti-bacterial activity of chalcone and its cyclized product ABDC was tested in vitro by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria was determined with the reference of standard drug Tetracycline. Results showed that the ABDC is better anti-bacterial agent as compared to chalcone. The anti-bacterial activity was further supported by the quantum chemistry calculation.

  9. Radiation Chemistry Studies on Chemotherapeutic Agents

    DEFF Research Database (Denmark)

    Gohn, M.; Getoff, N.; Bjergbakke, Erling

    1977-01-01

    Adrenalin has been studied as a model radiation protective agent by means of pulse radiolysis in aqueous solutions. The rate constants for the reactions of adrenalin with e–aq and OH were determined : k(e–aq+ adr—NH+2)= 7.5 × 108 dm3 mol–1 s–1, k(e–aq+ adr—NH)= 2.5 × 108 dm3 mol–1 s–1, and k...

  10. Role of Wigner function in studying quantum correlations

    Science.gov (United States)

    Siyouri, F.; El Baz, M.; Hassouni, Y.

    2016-09-01

    In this paper, we investigate the possibility to use the Wigner function to detect and quantify quantum correlations in general. We study these quantum correlations for two quasi-Werner states formed with two general bipartite superposed squeezed states. We find then that the Wigner function is not sensitive to all kinds of quantum correlations but it only witnesses entanglement.

  11. Studies of coal structure using carbene chemistry

    Energy Technology Data Exchange (ETDEWEB)

    1990-01-01

    The object of this grant was to react coal, derivatized forms of coal, and solvent swelled coal with carbenes (divalent carbon species) under mild conditions. These carbenes were to be prepared by treating the coal with several diazo compounds and then thermally decomposing them at relatively low temperatures (80--130{degree}C). The carbenes were to be chosen to show varying selectively toward aromatic rings containing heteroatom functionalities and toward polynuclear aromatic systems. In some instances, where selectivities toward aromatic and heteroaromatic ring systems were not known, model studies were to be carried out. Because of the generally mild conditions employed and the good selectivity anticipated, and actually observed with one particular system, it was expected that this methodology would provide structural information about the coal, along with data on the extent of occurrence and type of aromatic systems. After carbene reactions, treatment of the coal samples was to include extractions and thermolysis. Physical studies included thermogravimetric analysis, diffuse reflectance FT-IR spectroscopy, NMR ({sup 1}H and {sup 13}C) spectroscopy, gas chromatography, GC/MS and GC/FT-IR. 7 figs., 10 tabs.

  12. Experimental and Analytical Studies of Solar System Chemistry

    Science.gov (United States)

    Burnett, Donald S.

    2003-01-01

    The cosmochemistry research funded by this grant resulted in the publications given in the attached Publication List. The research focused in three areas: (1) Experimental studies of trace element partitioning. (2) Studies of the minor element chemistry and O isotopic compositions of MgAlO4 spinels from Ca-Al-Rich Inclusions in carbonaceous chondrite meteorites, and (3) The abundances and chemical fractionations of Th and U in chondritic meteorites.

  13. A Writing and Ethics Component for a Quantum Mechanics, Physical Chemistry Course

    Science.gov (United States)

    Reilly, John T.; Strickland, Michael

    2010-01-01

    A writing-across-the-curriculum and ethics component is presented for a second-semester, physical chemistry course. The activity involves introducing ethical issues pertinent to scientists. Students are asked to read additional material, participate in discussions, and write essays and a paper on an ethical issue. The writing and discussion…

  14. The Essential Role for Laboratory Studies in Atmospheric Chemistry.

    Science.gov (United States)

    Burkholder, James B; Abbatt, Jonathan P D; Barnes, Ian; Roberts, James M; Melamed, Megan L; Ammann, Markus; Bertram, Allan K; Cappa, Christopher D; Carlton, Annmarie G; Carpenter, Lucy J; Crowley, John N; Dubowski, Yael; George, Christian; Heard, Dwayne E; Herrmann, Hartmut; Keutsch, Frank N; Kroll, Jesse H; McNeill, V Faye; Ng, Nga Lee; Nizkorodov, Sergey A; Orlando, John J; Percival, Carl J; Picquet-Varrault, Bénédicte; Rudich, Yinon; Seakins, Paul W; Surratt, Jason D; Tanimoto, Hiroshi; Thornton, Joel A; Tong, Zhu; Tyndall, Geoffrey S; Wahner, Andreas; Weschler, Charles J; Wilson, Kevin R; Ziemann, Paul J

    2017-03-07

    Laboratory studies of atmospheric chemistry characterize the nature of atmospherically relevant processes down to the molecular level, providing fundamental information used to assess how human activities drive environmental phenomena such as climate change, urban air pollution, ecosystem health, indoor air quality, and stratospheric ozone depletion. Laboratory studies have a central role in addressing the incomplete fundamental knowledge of atmospheric chemistry. This article highlights the evolving science needs for this community and emphasizes how our knowledge is far from complete, hindering our ability to predict the future state of our atmosphere and to respond to emerging global environmental change issues. Laboratory studies provide rich opportunities to expand our understanding of the atmosphere via collaborative research with the modeling and field measurement communities, and with neighboring disciplines.

  15. The Essential Role for Laboratory Studies in Atmospheric Chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Burkholder, James B. [National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States); Abbatt, Jonathan P. D. [Univ. of Toronto, ON (Canada); Barnes, Ian [Univ. of Wuppertal (Germany); Roberts, James M. [National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States); Melamed, Megan L. [Univ. of Colorado, Boulder, CO (United States); Ammann, Markus [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Bertram, Allan K. [Univ. of British Columbia, Vancouver, BC (Canada); Cappa, Christopher D. [Univ. of California, Davis, CA (United States); Carlton, Annmarie G. [Univ. of California, Irvine, CA (United States); Carpenter, Lucy J. [Univ. of York (United Kingdom); Crowley, John N. [Max Planck Inst. of Chemistry, Mainz (Germany); Dubowski, Yael [Technion-Israel Inst. of Tech., Haifa (Israel); George, Christian [Univ. of Lyon (France); Heard, Dwayne E. [Univ. of Leeds (United Kingdom); Herrmann, Hartmut [Leibniz Inst. for Tropospheric Research (ITR), Leipzig (Germany); Keutsch, Frank N. [Harvard Univ., Cambridge, MA (United States); Kroll, Jesse H. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); McNeill, V. Faye [Columbia Univ., New York, NY (United States); Ng, Nga Lee [Georgia Inst. of Technology, Atlanta, GA (United States); Nizkorodov, Sergey A. [Univ. of California, Irvine, CA (United States); Orlando, John J. [National Center for Atmospheric Research, Boulder, CO (United States); Percival, Carl J. [Univ. of Manchester (United Kingdom); Picquet-Varrault, Bénédicte [Inst. Pierre-Simon Laplace, Creteil (France); Rudich, Yinon [Weizmann Inst. of Science, Rehovot (Israel); Seakins, Paul W. [Univ. of Leeds (United Kingdom); Surratt, Jason D. [Univ. of North Carolina, Chapel Hill, NC (United States); Tanimoto, Hiroshi [National Inst. for Environmental Studies, Tsukuba (Japan); Thornton, Joel A. [Univ. of Washington, Seattle, WA (United States); Tong, Zhu [Peking Univ., Beijing (China); Tyndall, Geoffrey S. [National Center for Atmospheric Research, Boulder, CO (United States); Wahner, Andreas [Forschungszentrum Julich (Germany); Weschler, Charles J. [Rutgers Univ., Piscataway, NJ (United States); Wilson, Kevin R. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Ziemann, Paul J. [Univ. of Colorado, Boulder, CO (United States)

    2017-02-07

    Laboratory studies of atmospheric chemistry characterize the nature of atmospherically relevant processes down to the molecular level, providing fundamental information used to assess how human activities drive environmental phenomena such as climate change, urban air pollution, ecosystem health, indoor air quality, and stratospheric ozone depletion. Laboratory studies have a central role in addressing the incomplete fundamental knowledge of atmospheric chemistry. This paper highlights the evolving science needs for this community and emphasizes how our knowledge is far from complete, hindering our ability to predict the future state of our atmosphere and to respond to emerging global environmental change issues. Finally, laboratory studies provide rich opportunities to expand our understanding of the atmosphere via collaborative research with the modeling and field measurement communities, and with neighboring disciplines.

  16. Surface chemistry studies of phosphate glasses

    Science.gov (United States)

    Barnes, Amy Suzanne

    This research examined the surface of an undoped and rare-earth doped sodium alumino metaphosphate glass after fracture or surface finishing and subsequent exposure to humid and aqueous environments. In addition, the adsorption of aminopropyl triethoxysilane (APS), and the dominant parameters controlling the structure of the deposited film, were studied. Typically, commercial glasses must be cut and polished into optical components for engineering applications. This process involves a series of aqueous treatments in both acidic and basic media. The experiments performed here on aluminophosphate glass showed that this results in dissolution, surface composition changes (depletion of Na) and surface pitting. In both alkaline detergent and acid etching solution, dissolution at a rate of approximately 4 x 10 -3 mol/m2/hr (0.2 mum/hr) occurs along with a drastic alteration of the surface morphology. When exposed to an environment of elevated humidity and temperature for an extended period of time, this aluminophosphate glass was observed to break down, forming a soluble phosphate gel that dissolves away from the surface. Simultaneously, the surface became enriched in silica, a trace contaminant in the glass, which eventually precipitated and coalesced into a dendritic pattern that covered the surface. The freshly powdered phosphate glass was found to contain surface hydroxyls weakly associated with one another, and some bound by a stronger hydrogen bond, likely to adjacent non-bridging oxygens. Most of these hydroxyls could be desorbed upon heating above the glass transition temperature to leave only a small concentration of weakly associated hydroxyls and free hydroxyls on the surface. The characterization of hydroxyls and water on the phosphate glass surface was used to understand the adsorption of aminopropyl tri-ethoxysilane (APS) also through the use of in-situ DRIFTS. The concentration of adsorbed APS was found to be independent of solution pH, but the measured

  17. Interfacial chemistry and the design of solid-phase nucleic acid hybridization assays using immobilized quantum dots as donors in fluorescence resonance energy transfer.

    Science.gov (United States)

    Algar, W Russ; Krull, Ulrich J

    2011-01-01

    The use of quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) offer several advantages for the development of multiplexed solid-phase QD-FRET nucleic acid hybridization assays. Designs for multiplexing have been demonstrated, but important challenges remain in the optimization of these systems. In this work, we identify several strategies based on the design of interfacial chemistry for improving sensitivity, obtaining lower limits of detection (LOD) and enabling the regeneration and reuse of solid-phase QD-FRET hybridization assays. FRET-sensitized emission from acceptor dyes associated with hybridization events at immobilized QD donors provides the analytical signal in these assays. The minimization of active sensing area reduces background from QD donor PL and allows the resolution of smaller amounts of acceptor emission, thus lowering the LOD. The association of multiple acceptor dyes with each hybridization event can enhance FRET efficiency, thereby improving sensitivity. Many previous studies have used interfacial protein layers to generate selectivity; however, transient destabilization of these layers is shown to prevent efficient regeneration. To this end, we report a protein-free interfacial chemistry and demonstrate the specific detection of as little as 2 pmol of target, as well as an improved capacity for regeneration.

  18. Interfacial Atmospheric Chemistry: Quantum Chemical Calculations on the Mechanism of Protonation and Oligomerization of Isoprene on Aqueous Surfaces

    Science.gov (United States)

    Mishra, H.; Colussi, A. J.; Enami, S.; Nielsen, R. J.; Hoffmann, M. R.; Goddard, W. A.

    2012-12-01

    It has become increasingly apparent that atmospheric chemistry involves more than gas-phase reactions. Key processes, such as the decay of NO2 in urban plumes and the associated daytime formation of HONO, and the rapid chemistries observed in and over forest canopies at nighttime defy explanation by conventional atmospheric chemistry mechanisms. We have recently reported experimental results on several gas-liquid reactions of atmospheric interest, such as the facile protonation of gaseous isoprene on mildly acidic (pH bioenergetics coupling, 'on-water' catalysis, self-assembly and molecular recognition, little is known about the molecular mechanisms of such reactions. Herein we apply quantum mechanics to investigate how biogenic or anthropogenic olefins may get protonated and undergo oligomerization at the air-water interface by performing model calculations on small water clusters carrying an excess proton as surrogates for the surface of mildly acidic water as sensed by gaseous isoprene (ISO). We find that ISO binds weakly to the surface of water and accepts a proton from H+(H2O)3, leading to ISOH+ via a proton transfer hindered by a ΔG1‡ = 5.6 kcal mol-1 kinetic barrier. Subsequently, another ISO attaches loosely to this ensemble, before being attacked by the ISOH+. This process, which represents the first step of the cationic polymerization of ISO, is hindered by a similar ΔG2‡ = 5.7 kcal mol-1 barrier. Our theoretical results are consistent with experimental (~ 10-4) uptake coefficients for ISO measured on acidic water.

  19. What can quantum chemistry tell us about Pa(V) hydration and hydrolysis?

    Energy Technology Data Exchange (ETDEWEB)

    Siboulet, B. [CEA Marcoule, Lab. de Conception des Architectures Moleculaires (DRCP/SCPS), 30 (France); Marsden, C.J. [Universite P. Sabatier, Lab. de Physique Quantique, CNRS-UMR 5626, 31 - Toulouse (France); Vitorge, P. [CEA Saclay, Lab. de Speciation des Radionucleides et Molecules (UMR 8587DPC/SECR), 91 - Gif-sur-Yvette (France)

    2008-12-15

    Published liquid-liquid extraction studies of Pa(V) were interpreted with aqueous mono-, di- and tri cations. B3LYP DFT is applied here to such cations surrounded by two explicit hydration layers: Linear or tetrahedral geometries are found for the Pa(V) aquo ions. PaO{sub 2}{sup +} is similar to the other AnO{sub 2}{sup +} cations, but has strong apical bonds, resulting from the highly negative O{sub yl} charge, which decreases along the An(V) series. This explains the instability of PaO{sub 2}{sup +} in water, and the differences with the heavier An(V). PaO{sub 2}{sup +} di-protonates to give Pa(OH){sub 2}{sup 3+} and can further di-hydrolyze to give T{sub d}-Pa(OH){sub 4}{sup +}, which might very well be the most stable Pa(V) mono cation. PaOOH{sup 2+} is confirmed to be the Pa(V) aqueous di cation invoked in the literature for pH{<=} 1.4 {+-} 0.7. PaO{sup 3+} is confirmed in sulfate solution, with a bond length close to 180 pm. Pa(OH){sub 2}{sup 3+} cannot be excluded in other conditions. The strong influence of the solvent was not fully taken into account in most previous theoretical studies that focused only on bare or partially solvated PaO{sub 2}{sup +}. Toraishi et al. have studied hydrated Pa(V) and our work confirms this study and its qualitative interpretation. The new tetrahedral Pa(OH){sub 4}{sup +} geometry that is shown here to be important opens the field to further quantum chemical studies of Pa(V) and other f-elements. As a test for the two-shell model approach for Pa(V), fluoride coordination to Pa(V) is studied and compared with published EXAFS data: an excellent fit is obtained with the well-established species PaF{sub 7}{sup 2-}, but most other stoichiometries tested are precluded. (authors)

  20. Merging Structural Information from X-ray Crystallography, Quantum Chemistry, and EXAFS Spectra: The Oxygen-Evolving Complex in PSII.

    Science.gov (United States)

    Chernev, Petko; Zaharieva, Ivelina; Rossini, Emanuele; Galstyan, Artur; Dau, Holger; Knapp, Ernst-Walter

    2016-10-12

    Structural data of the oxygen-evolving complex (OEC) in photosystem II (PSII) determined by X-ray crystallography, quantum chemistry (QC), and extended X-ray absorption fine structure (EXAFS) analyses are presently inconsistent. Therefore, a detailed study of what information can be gained about the OEC through a comparison of QC and crystallographic structure information combined with the information from range-extended EXAFS spectra was undertaken. An analysis for determining the precision of the atomic coordinates of the OEC by QC is carried out. OEC model structures based on crystallographic data that are obtained by QC from different research groups are compared with one another and with structures obtained by high-resolution crystallography. The theory of EXAFS spectra is summarized, and the application of EXAFS spectra to the experimental determination of the structure of the OEC is detailed. We discriminate three types of parameters entering the formula for the EXAFS spectrum: (1) model-independent, predefined, and fixed; (2) model-dependent that can be computed or adjusted; and (3) model-dependent that must be adjusted. The information content of EXAFS spectra is estimated and is related to the precision of atomic coordinates and resolution power to discriminate different atom-pair distances of the OEC. It is demonstrated how a precise adjustment of atomic coordinates can yield a nearly perfect representation of the experimental OEC EXAFS spectrum, but at the expense of overfitting and losing the knowledge of the initial OEC model structure. Introducing a novel type of penalty function, it is shown that moderate adjustment of atomic coordinates to the EXAFS spectrum limited by constraints avoids overfitting and can be used to validate different OEC model structures. This technique is used to identify the OEC model structures whose computed OEC EXAFS spectra agree best with the measured spectrum. In this way, the most likely S-state and protonation pattern

  1. IMPLEMENTATION OF REACTION FIELD METHODS IN QUANTUM-CHEMISTRY COMPUTER CODES

    NARCIS (Netherlands)

    DEVRIES, AH; VANDUIJNEN, PT; JUFFER, AH; RULLMANN, JAC; DIJKMAN, JP; MERENGA, H; THOLE, BT

    1995-01-01

    The embedding of a quantum mechanically described subsystem by classical representations of its surroundings is reviewed. The choices for a distributed monopole representation and a distributed (group) polarizability representation, as well as the continuum approach to model bulk effects, are discus

  2. The Variation Theorem Applied to H-2+: A Simple Quantum Chemistry Computer Project

    Science.gov (United States)

    Robiette, Alan G.

    1975-01-01

    Describes a student project which requires limited knowledge of Fortran and only minimal computing resources. The results illustrate such important principles of quantum mechanics as the variation theorem and the virial theorem. Presents sample calculations and the subprogram for energy calculations. (GS)

  3. Enhancing Quantum Dots for Bioimaging using Advanced Surface Chemistry and Advanced Optical Microscopy: Application to Silicon Quantum Dots (SiQDs).

    Science.gov (United States)

    Cheng, Xiaoyu; Hinde, Elizabeth; Owen, Dylan M; Lowe, Stuart B; Reece, Peter J; Gaus, Katharina; Gooding, J Justin

    2015-10-28

    Fluorescence lifetime imaging microscopy is successfully demonstrated in both one- and two-photon cases with surface modified, nanocrystalline silicon quantum dots in the context of bioimaging. The technique is further demonstrated in combination with Förster resonance energy transfer studies where the color of the nanoparticles is tuned by using organic dye acceptors directly conjugated onto the nanoparticle surface.

  4. Learning beyond the Classroom: Using Text Messages to Measure General Chemistry Students' Study Habits

    Science.gov (United States)

    Ye, Li; Oueini, Razanne; Dickerson, Austin P.; Lewis, Scott E.

    2015-01-01

    This study used a series of text message inquiries sent to General Chemistry students asking: "Have you studied for General Chemistry I in the past 48 hours? If so, how did you study?" This method for collecting data is novel to chemistry education research so the first research goals were to investigate the feasibility of the technique…

  5. Learning beyond the Classroom: Using Text Messages to Measure General Chemistry Students' Study Habits

    Science.gov (United States)

    Ye, Li; Oueini, Razanne; Dickerson, Austin P.; Lewis, Scott E.

    2015-01-01

    This study used a series of text message inquiries sent to General Chemistry students asking: "Have you studied for General Chemistry I in the past 48 hours? If so, how did you study?" This method for collecting data is novel to chemistry education research so the first research goals were to investigate the feasibility of the technique…

  6. Dynamics of the Chemistry of Electronically Excited Atoms in Defined Quantum States.

    Science.gov (United States)

    1978-05-01

    laser development . In essence, this research concerns itself with the elucidation of the role of electronic energy in affecting the chemistry or photochemistry of excited halogen atoms and molecules. While much is known about the dynamics of chemical and physical processes which are carried out on the lowest potential energy hypersurface correlating with reactants and products in their electronic ground state, relatively little is known about the dynamics of such phenomena as energy transfer and chemical reactivity on higher-lying potential

  7. Quantum mechanical studies of carbon structures

    Energy Technology Data Exchange (ETDEWEB)

    Bartelt, Norman Charles [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Ward, Donald [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Zhou, Xiaowang [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Foster, Michael E. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Schultz, Peter A. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Wang, Bryan M. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Univ. of California, Riverside, CA (United States); McCarty, Kevin F. [Sandia National Lab. (SNL-CA), Livermore, CA (United States)

    2015-10-01

    Carbon nanostructures, such as nanotubes and graphene, are of considerable interest due to their unique mechanical and electrical properties. The materials exhibit extremely high strength and conductivity when defects created during synthesis are minimized. Atomistic modeling is one technique for high resolution studies of defect formation and mitigation. To enable simulations of the mechanical behavior and growth mechanisms of C nanostructures, a high-fidelity analytical bond-order potential for the C is needed. To generate inputs for developing such a potential, we performed quantum mechanical calculations of various C structures.

  8. Photoluminescence studies of single InGaAs quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1999-01-01

    Semiconductor quantum dots are considered a promising material system for future optical devices and quantum computers. We have studied the low-temperature photoluminescence properties of single InGaAs quantum dots embedded in GaAs. The high spatial resolution required for resolving single dots...... to resolve luminescence lines from individual quantum dots, revealing an atomic-like spectrum of sharp transition lines. A parameter of fundamental importance is the intrinsic linewidth of these transitions. Using high-resolution spectroscopy we have determined the linewidth and investigated its dependence...... on temperature, which gives information about how the exciton confined to the quantum dot interacts with the surrounding lattice....

  9. Accelerating Wave Function Convergence in Interactive Quantum Chemical Reactivity Studies

    CERN Document Server

    Mühlbach, Adrian H; Reiher, Markus

    2015-01-01

    The inherently high computational cost of iterative self-consistent-field (SCF) methods proves to be a critical issue delaying visual and haptic feedback in real-time quantum chemistry. In this work, we introduce two schemes for SCF acceleration. They provide a guess for the initial density matrix of the SCF procedure generated by extrapolation techniques. SCF optimizations then converge in fewer iterations, which decreases the execution time of the SCF optimization procedure. To benchmark the proposed propagation schemes, we developed a test bed for performing quantum chemical calculations on sequences of molecular structures mimicking real-time quantum chemical explorations. Explorations of a set of six model reactions employing the semi-empirical methods PM6 and DFTB3 in this testing environment showed that the proposed propagation schemes achieved speedups of up to thirty percent as a consequence of a reduced number of SCF iterations.

  10. Assessing Advanced High School and Undergraduate Students' Thinking Skills: The Chemistry--From the Nanoscale to Microelectronics Module

    Science.gov (United States)

    Dori, Yehudit Judy; Dangur, Vered; Avargil, Shirly; Peskin, Uri

    2014-01-01

    Chemistry students in Israel have two options for studying chemistry: basic or honors (advanced placement). For instruction in high school honors chemistry courses, we developed a module focusing on abstract topics in quantum mechanics: Chemistry--From the Nanoscale to Microelectronics. The module adopts a visual-conceptual approach, which…

  11. Assessing Advanced High School and Undergraduate Students' Thinking Skills: The Chemistry--From the Nanoscale to Microelectronics Module

    Science.gov (United States)

    Dori, Yehudit Judy; Dangur, Vered; Avargil, Shirly; Peskin, Uri

    2014-01-01

    Chemistry students in Israel have two options for studying chemistry: basic or honors (advanced placement). For instruction in high school honors chemistry courses, we developed a module focusing on abstract topics in quantum mechanics: Chemistry--From the Nanoscale to Microelectronics. The module adopts a visual-conceptual approach, which…

  12. One-Step Synthesis of Boron Nitride Quantum Dots: Simple Chemistry Meets Delicate Nanotechnology.

    Science.gov (United States)

    Liu, Bingping; Yan, Shihai; Song, Zhongqian; Liu, Mengli; Ji, Xuqiang; Yang, Wenrong; Liu, Jingquan

    2016-12-23

    Herein, a conceptually new and straightforward aqueous route is described for the synthesis of hydroxyl- and amino-functionalized boron nitride quantum dots (BNQDs) with quantum yields (QY) as high as 18.3 % by using a facile bottom-up approach, in which a mixture of boric acid and ammonia solution was hydrothermally treated in one pot at 200 °C for 12 h. The functionalized BNQDs, with excellent photoluminescence properties, could be easily dispersed in an aqueous medium and applied as fluorescent probes for the detection of ferrous (Fe(2+) ) and ferric (Fe(3+) ) ions with excellent selectivity and low detection limits. The mechanisms for the hydrothermal reaction and fluorescence quenching were also simulated by using density functional theory (DFT), which confirmed the feasibility and advantages of this strategy. It provides a scalable and eco-friendly method for preparation of BNQDs with good dispersability and could also be generalized to the synthesis of other 2D quantum dots and nanoplates.

  13. Study of metallothionein-quantum dots interactions.

    Science.gov (United States)

    Tmejova, Katerina; Hynek, David; Kopel, Pavel; Krizkova, Sona; Blazkova, Iva; Trnkova, Libuse; Adam, Vojtech; Kizek, Rene

    2014-05-01

    Nanoparticles have gained increasing interest in medical and in vivo applications. Metallothionein (MT) is well known as a maintainer of metal ions balance in intracellular space. This is due to high affinity of this protein to any reactive species including metals and reactive oxygen species. The purpose of this study was to determine the metallothionein-quantum dots interactions that were investigated by spectral and electrochemical techniques. CuS, CdS, PbS, and CdTe quantum dots (QDs) were analysed. The highest intensity was shown for CdTe, than for CdS measured by fluorescence. These results were supported by statistical analysis and considered as significant. Further, these interactions were analysed using gel electrophoresis, where MT aggregates forming after interactions with QDs were detected. Using differential pulse voltammetry Brdicka reaction, QDs and MT were studied. This method allowed us to confirm spectral results and, moreover, to observe the changes in MT structure causing new voltammetric peaks called X and Y, which enhanced with the prolonged time of interaction up to 6 h.

  14. Prêmio Nobel de Química em 1998: Walter Kohn e John A. Pople 1998 Nobel Prize in Chemistry: Walter Kohn and John A. Pople

    Directory of Open Access Journals (Sweden)

    Luiz Carlos Gomide Freitas

    1999-04-01

    Full Text Available A résumé of the evolution of quantum chemistry methodologies is presented. The pioneering contributions of John A. Pople and Water Kohn, the 1998 Nobel Prize Laureates in Chemistry, to the development of quantum chemistry computational methods for studying the properties of molecules and their interaction is discussed.

  15. Stability of gas-phase tartaric acid anions investigated by quantum chemistry, mass spectrometry, and infrared spectroscopy

    NARCIS (Netherlands)

    R. Tonner; P. Schwerdtfeger; A. L. May; J.D. Steill; G. Berden; J. Oomens; S. R. Campagna; R.N. Compton

    2012-01-01

    In an effort to understand the chemical factors that stabilize dianions, experimental and theoretical studies on the stability of the tartrate dianion were performed. Quantum chemical calculations at the coupled cluster level reveal only a metastable state with a possible decomposition pathway (O2C-

  16. Stability of Gas-Phase Tartaric Acid Anions Investigated by Quantum Chemistry, Mass Spectrometry, and Infrared Spectroscopy

    NARCIS (Netherlands)

    Tonner, R.; Schwerdtfeger, P.; May, A. L.; Steill, J. D.; G. Berden,; Oomens, J.; Campagna, S. R.; Compton, R. N.

    2012-01-01

    In an effort to understand the chemical factors that stabilize dianions, experimental and theoretical studies on the stability of the tartrate dianion were performed. Quantum chemical calculations at the coupled cluster level reveal only a metastable state with a possible decomposition pathway (O2C-

  17. Stability of Gas-Phase Tartaric Acid Anions Investigated by Quantum Chemistry, Mass Spectrometry, and Infrared Spectroscopy

    NARCIS (Netherlands)

    Tonner, R.; Schwerdtfeger, P.; May, A. L.; Steill, J. D.; G. Berden,; Oomens, J.; Campagna, S. R.; Compton, R. N.

    2012-01-01

    In an effort to understand the chemical factors that stabilize dianions, experimental and theoretical studies on the stability of the tartrate dianion were performed. Quantum chemical calculations at the coupled cluster level reveal only a metastable state with a possible decomposition pathway

  18. Stability of gas-phase tartaric acid anions investigated by quantum chemistry, mass spectrometry, and infrared spectroscopy

    NARCIS (Netherlands)

    Tonner, R.; Schwerdtfeger, P.; May, A. L.; Steill, J.D.; Berden, G.; Oomens, J.; Campagna, S. R.; Compton, R.N.

    2012-01-01

    In an effort to understand the chemical factors that stabilize dianions, experimental and theoretical studies on the stability of the tartrate dianion were performed. Quantum chemical calculations at the coupled cluster level reveal only a metastable state with a possible decomposition pathway

  19. Spectroscopic accuracy directly from quantum chemistry: application to ground and excited states of beryllium dimer

    CERN Document Server

    Sharma, Sandeep; Booth, George H; Umrigar, C J; Chan, Garnet Kin-Lic

    2014-01-01

    We combine explicit correlation via the canonical transcorrelation approach with the density matrix renormalization group and initiator full configuration interaction quantum Monte Carlo methods to compute a near-exact beryllium dimer curve, {\\it without} the use of composite methods. In particular, our direct density matrix renormalization group calculations produce a well-depth of $D_e$=931.2 cm$^{-1}$ which agrees very well with recent experimentally derived estimates $D_e$=929.7$\\pm 2$~cm$^{-1}$ [Science, 324, 1548 (2009)] and $D_e$=934.6~cm$^{-1}$ [Science, 326, 1382 (2009)

  20. QED-SCF, MCSCF and Coupled-cluster Methods in Quantum Chemistry

    OpenAIRE

    Ohsaku, Tadafumi; Yamaguchi, Kizashi

    2001-01-01

    We investigate the method to combine the techniques of quantum chemisty with QED. In our theory, we treat the N-electron system and the Dirac sea on an equal footing; we regard both of them as the dynamical degrees of freedom of a many-body system. After the introduction of our QED-SCF method, the QED-SCF solutions are classified into several classes on the basis of group-theoretical operations such as time reversal, parity and O(3) rotational symmetry. The natural orbitals of general QED-SCF...

  1. Studies of silicon quantum dots prepared at different substrate temperatures

    Science.gov (United States)

    Al-Agel, Faisal A.; Suleiman, Jamal; Khan, Shamshad A.

    2017-03-01

    In this research work, we have synthesized silicon quantum dots at different substrate temperatures 193, 153 and 123 K at a fixed working pressure 5 Torr. of Argon gas. The structural studies of these silicon quantum dots have been undertaken using X-ray diffraction, Field Emission Scanning Electron Microscopy (FESEM) and High Resolution Transmission Electron Microscopy (HRTEM). The optical and electrical properties have been studied using UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Fluorescence spectroscopy and I-V measurement system. X-ray diffraction pattern of Si quantum dots prepared at different temperatures show the amorphous nature except for the quantum dots synthesized at 193 K which shows polycrystalline nature. FESEM images of samples suggest that the size of quantum dots varies from 2 to 8 nm. On the basis of UV-visible spectroscopy measurements, a direct band gap has been observed for Si quantum dots. FTIR spectra suggest that as-grown Si quantum dots are partially oxidized which is due exposure of as-prepared samples to air after taking out from the chamber. PL spectra of the synthesized silicon quantum dots show an intense peak at 444 nm, which may be attributed to the formation of Si quantum dots. Temperature dependence of dc conductivity suggests that the dc conductivity enhances exponentially by raising the temperature. On the basis above properties i.e. direct band gap, high absorption coefficient and high conductivity, these silicon quantum dots will be useful for the fabrication of solar cells.

  2. Organic Chemistry Educators' Perspectives on Fundamental Concepts and Misconceptions: An Exploratory Study

    Science.gov (United States)

    Duis, Jennifer M.

    2011-01-01

    An exploratory study was conducted with 23 organic chemistry educators to discover what general chemistry concepts they typically review, the concepts they believe are fundamental to introductory organic chemistry, the topics students find most difficult in the subject, and the misconceptions they observe in undergraduate organic chemistry…

  3. Organic Chemistry Educators' Perspectives on Fundamental Concepts and Misconceptions: An Exploratory Study

    Science.gov (United States)

    Duis, Jennifer M.

    2011-01-01

    An exploratory study was conducted with 23 organic chemistry educators to discover what general chemistry concepts they typically review, the concepts they believe are fundamental to introductory organic chemistry, the topics students find most difficult in the subject, and the misconceptions they observe in undergraduate organic chemistry…

  4. Periodic quantum chemical studies on anhydrous and hydrated acid clinoptilolite.

    Science.gov (United States)

    Valdiviés Cruz, Karell; Lam, Anabel; Zicovich-Wilson, Claudio M

    2014-08-07

    Periodic quantum chemistry methods as implemented in the crystal09 code were considered to study acid clinoptilolite (HEU framework type), both anhydrous and hydrated. The most probable location of acid sites and water molecules together with other structural details has been the object of particular attention. Calculations were performed at hybrid and pristine DFT levels of theory with a VDZP quality basis set in order to compare performances. It arises that PBE0 provides the best agreement with experimental data as concerns structural features and the most stable Al distribution in the framework. The role of the water molecule distribution in the stability of the systems, the most probable structure that they induce in the material, and their eventual influence on further chemical modification processes, such as dealumination, are discussed in detail. Results show that, apart from the usually considered interactions of water molecules with the zeolite framework, that is, a H-bond with Brönsted acid sites and coordination with framework Al as Lewis ones, it is necessary to consider cooperation of other weaker effects so as to fully understand the hydration effect in this kind of materials.

  5. Atmospheric Chemistry of the Carbon Capture Solvent Monoethanolamine (MEA): A Theoretical Study

    Science.gov (United States)

    da Silva, G.

    2012-12-01

    The development of amine solvent technology for carbon capture and storage has the potential to create large new sources of amines to the atmosphere. The atmospheric chemistry of amines generally, and carbon capture solvents in particular, is not well understood. We have used quantum chemistry and master equation modelling to investigate the OH radical initiated oxidation of monoethanolamine (NH2CH2CH2OH), or MEA, the archetypal carbon capture solvent. The OH radical can abstract H atoms from either carbon atom in MEA, with negative reaction barriers. Treating these reactions with a two transition state model can reliably reproduce experimental rate constants and their temperature dependence. The products of the MEA + OH reaction, the NH2CHCH2OH and NH2CH2CHOH radicals, undergo subsequent reaction with O2, which has also been studied. In both cases chemically activated reactions that bypass peroxyl radical intermediates dominate, producing 2-iminoethanol + HO2 (from NH2CHCH2OH) or aminoacetaldehyde + HO2 (from NH2CH2CHOH), making the process HOx-neutral. The operation of chemically activated reaction mechanisms has implications for the ozone forming potential of MEA. The products of MEA photo-oxidation are proposed as important species in the formation of both organic and inorganic secondary aerosols, particularly through uptake of the imine 2-iminoethanol and subsequent hydrolysis to ammonia and glycolaldehyde.

  6. Interfacial Chemistry and the Design of Solid-Phase Nucleic Acid Hybridization Assays Using Immobilized Quantum Dots as Donors in Fluorescence Resonance Energy Transfer

    OpenAIRE

    Krull, Ulrich J.; W. Russ Algar

    2011-01-01

    The use of quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) offer several advantages for the development of multiplexed solid-phase QD-FRET nucleic acid hybridization assays. Designs for multiplexing have been demonstrated, but important challenges remain in the optimization of these systems. In this work, we identify several strategies based on the design of interfacial chemistry for improving sensitivity, obtaining lower limits of detection (LOD) and enabling th...

  7. A Thematic Review of Studies into the Effectiveness of Context-Based Chemistry Curricula

    Science.gov (United States)

    Ültay, Neslihan; Çalık, Muammer

    2012-12-01

    Context-based chemistry education aims at making connections between real life and the scientific content of chemistry courses. The purpose of this study was to evaluate context-based chemistry studies. In looking for the context-based chemistry studies, the authors entered the keywords `context-based', `contextual learning' and `chemistry education' in well-known databases (i.e. Academic Search Complete, Education Research Complete, ERIC, Springer LINK Contemporary). Further, in case the computer search by key words may have missed a rather substantial part of the important literature in the area, the authors also conducted a hand search of the related journals. To present a detailed thematic review of context-based chemistry studies, a matrix was used to summarize the findings by focusing on insights derived from the related studies. The matrix incorporates the following themes: needs, aims, methodologies, general knowledge claims, and implications for teaching and learning, implications for curriculum development and suggestions for future research. The general knowledge claims investigated in this paper were: (a) positive effects of the context-based chemistry studies; (b) caveats, both are examined in terms of students' attitudes and students' understanding/cognition. Implications were investigated for practice in context- based chemistry studies, for future research in context- based chemistry studies, and for curriculum developers in context- based chemistry studies. Teachers of context-based courses claimed that the application of the context-based learning approach in chemistry education improved students' motivation and interest in the subject. This seems to have generated an increase in the number of the students who wish to continue chemistry education at higher levels. However, despite the fact that the majority of the studies have reported advantages of context-based chemistry studies, some of them have also referred to pitfalls, i.e. dominant

  8. Quantum control study of ultrafast optical responses in semiconductor quantum dot devices.

    Science.gov (United States)

    Huang, Jung Y; Lin, Chien Y; Liu, Wei-Sheng; Chyi, Jen-Inn

    2014-12-15

    Two quantum control spectroscopic techniques were applied to study InAs quantum dot (QD) devices, which contain different strain-reducing layers. By adaptively control light matter interaction, a delayed resonant response from the InAs QDs was found to be encoded into the optimal phase profile of ultrafast optical pulse used. We verified the delayed resonant response to originate from excitons coupled to acoustic phonons of InAs QDs with two-dimensional coherent spectroscopy. Our study yields valuable dynamical information that can deepen our understanding of the coherent coupling process of exciton in the quantum-confined systems.

  9. Optical studies of capped quantum dots

    NARCIS (Netherlands)

    Wuister, S.F.

    2005-01-01

    This thesis describes the synthesis and spectroscopy of CdSe and CdTe semiconductor quantum dots (QDs). The first chapter gives an introduction into the unique size dependent properties of semiconductor quantum dots. Highly luminescent QDs of CdSe and CdTe were prepared via a high temperature method

  10. The unimolecular chemistry of protonated and deprotonated 2,2-dinitroethene-1,1-diamine (FOX-7) studied by tandem mass spectrometry and computational chemistry.

    Science.gov (United States)

    Žabka, Ján; Šimková, Ludmila; Jalový, Zdeněk; Polášek, Miroslav

    2014-01-01

    2,2-Dinitroethene-1,1-diamine (FOX-7) was studied by means of electrospray ionization (ESI) and chemical ionization (CI) mass spectrometry in both positive and negative ion mode. Detailed mechanisms of unimolecular fragmentations of protonated and deprotonated FOX-7 were investigated using high- and low- energy collision-induced dissociation (CID) mass spectrometry, neutral fragment reionization mass spectrometry and quantum chemistry calculations. In deprotonated FOX-7, elimination of the carbodiimide molecule was identified as the energetically most favored fragmentation channel, closely resembling the base hydrolysis of FOX-7. The dinitromethanide ion is formed during this fragmentation as revealed by comparison with CID mass spectra of an isobaric ion prepared by the ESI of authentic sodium dinitromethanide. The proton affinity of FOX-7 was estimated as 855 kJ mo(-1) by high-accuracy quantum chemistry calculations. This value corresponds to protonation at the C-2 position, though the oxygen-protonated tautomer was found to be nearly isoenergetic in the gas phase. In acetonitrile, the nitro group-protonated FOX-7 was found to be significantly less stable then its C-2 tautomer. These theoretical findings are clearly reflected in differences in fragmentations of ESI- and CI-generated [M+H(]+) ions. Interestingly, the consecutive losses of OH∙ and NO2∙ radicals instead of a whole HNO3 molecule were found to account for the most abundant fragment ion in the positive ESI CID mass spectra. In the CI-generated [M+H](+) and [M+D](+) ions, substantial internal energy effects upon the CID were observed.

  11. Quantum Chemistry for Solvated Molecules on Graphical Processing Units (GPUs)using Polarizable Continuum Models

    CERN Document Server

    Liu, Fang; Kulik, Heather J; Martínez, Todd J

    2015-01-01

    The conductor-like polarization model (C-PCM) with switching/Gaussian smooth discretization is a widely used implicit solvation model in chemical simulations. However, its application in quantum mechanical calculations of large-scale biomolecular systems can be limited by computational expense of both the gas phase electronic structure and the solvation interaction. We have previously used graphical processing units (GPUs) to accelerate the first of these steps. Here, we extend the use of GPUs to accelerate electronic structure calculations including C-PCM solvation. Implementation on the GPU leads to significant acceleration of the generation of the required integrals for C-PCM. We further propose two strategies to improve the solution of the required linear equations: a dynamic convergence threshold and a randomized block-Jacobi preconditioner. These strategies are not specific to GPUs and are expected to be beneficial for both CPU and GPU implementations. We benchmark the performance of the new implementat...

  12. Quantum Chemistry on the time axis: electron correlations and rearrangements on femtosecond and attosecond scales

    CERN Document Server

    Nicolaides, Cleanthes A

    2015-01-01

    Recent developments toward the production and laboratory use of pulses of high intensity, and/or of very high frequency, and/or of ultrashort duration, make possible experiments which can produce time-resolved data on ultrafast transformations involving motions of electrons. The formulation, quantitative understanding and prediction of related new phenomena entail the possibility of computing and applying solutions of the many-electron time-dependent Schroedinger equation, for arbitrary electronic structures, including the dominant effects of Rydberg series, of multiply excited states and of the multi-channel continuous spectrum. To this purpose, we have proposed and applied to many prototypical cases the state-specific expansion approach (SSEA). (Mercouris, Komninos and Nicolaides, Adv. Quantum Chem. 60, 333 (2010)). The paper explains briefly the SSEA, and outlines four of its applications to recently formulated problems concerning time-resolved electronic processes, where electron correlations are crucial....

  13. High-throughput quantum chemistry and virtual screening for OLED material components

    Science.gov (United States)

    Halls, Mathew D.; Giesen, David J.; Hughes, Thomas F.; Goldberg, Alexander; Cao, Yixiang

    2013-09-01

    Computational structure enumeration, analysis using an automated simulation workflow and filtering of large chemical structure libraries to identify lead systems, has become a central paradigm in drug discovery research. Transferring this paradigm to challenges in materials science is now possible due to advances in the speed of computational resources and the efficiency and stability of chemical simulation packages. State-of-the-art software tools that have been developed for drug discovery can be applied to efficiently explore the chemical design space to identify solutions for problems such as organic light-emitting diode material components. In this work, virtual screening for OLED materials based on intrinsic quantum mechanical properties is illustrated. Also, a new approach to more reliably identify candidate systems is introduced that is based on the chemical reaction energetics of defect pathways for OLED materials.

  14. Spectral methods in chemistry and physics applications to kinetic theory and quantum mechanics

    CERN Document Server

    Shizgal, Bernard

    2015-01-01

    This book is a pedagogical presentation of the application of spectral and pseudospectral methods to kinetic theory and quantum mechanics. There are additional applications to astrophysics, engineering, biology and many other fields. The main objective of this book is to provide the basic concepts to enable the use of spectral and pseudospectral methods to solve problems in diverse fields of interest and to a wide audience. While spectral methods are generally based on Fourier Series or Chebychev polynomials, non-classical polynomials and associated quadratures are used for many of the applications presented in the book. Fourier series methods are summarized with a discussion of the resolution of the Gibbs phenomenon. Classical and non-classical quadratures are used for the evaluation of integrals in reaction dynamics including nuclear fusion, radial integrals in density functional theory, in elastic scattering theory and other applications. The subject matter includes the calculation of transport coefficient...

  15. Synthesis, Crystal Structure and Quantum Chemistry Calculation of a Bis(dafone) Di(dmf) Copper(Ⅱ) Complex

    Institute of Scientific and Technical Information of China (English)

    REN Yong-Gang; CHEN Zhi-Rong; LI Hao-Hong; ZHAO Bin; HUANG Chang-Cang; LI Jun-Qian

    2005-01-01

    The title compound [Cu(dafone)2(DMF)2](2ClO4 1 (dafone = 4,5-diazafluoren- 9-one, dmf = N,N(A)-dimethyl formamide) was synthesized by the reaction of Cu(ClO4 )2 and dafone in DMF solution at room temperature with pH = 3.0.The single-crystal X-ray analysis has revealed that 1 crystallizes in monoclinic, space group P21/n with a = 8.4853(8), b = 13.1520 (14), c = 14.3866(12) (A), β = 102.629(3)o, V = 1566.7(3) (A)3, C28H26Cl2CuN6O12, Mr = 773.00, Z = 2, Dc = 1.639 g/cm3 , F(000) = 790, μ = 0.942 mm-1, the final R = 0.0438 and wR = 0.1214 for 3165 obser- ved reflections with I > 2σ(I).X-ray analysis shows that compound 1 has unsymmetric chelation of dafone with one Cu-N bond being much longer than the other.Coordination geometry of Cu is a highly distorted octahedron and the whole structure is stabilized by π-π stacking and static attractive forces from [ClO4]- anions.Based on the crystal data, quantum chemistry calculation at the DFT/ B3LPY level was used to reveal the electronic structure of 1.

  16. A quantum-quantum Metropolis algorithm.

    Science.gov (United States)

    Yung, Man-Hong; Aspuru-Guzik, Alán

    2012-01-17

    The classical Metropolis sampling method is a cornerstone of many statistical modeling applications that range from physics, chemistry, and biology to economics. This method is particularly suitable for sampling the thermal distributions of classical systems. The challenge of extending this method to the simulation of arbitrary quantum systems is that, in general, eigenstates of quantum Hamiltonians cannot be obtained efficiently with a classical computer. However, this challenge can be overcome by quantum computers. Here, we present a quantum algorithm which fully generalizes the classical Metropolis algorithm to the quantum domain. The meaning of quantum generalization is twofold: The proposed algorithm is not only applicable to both classical and quantum systems, but also offers a quantum speedup relative to the classical counterpart. Furthermore, unlike the classical method of quantum Monte Carlo, this quantum algorithm does not suffer from the negative-sign problem associated with fermionic systems. Applications of this algorithm include the study of low-temperature properties of quantum systems, such as the Hubbard model, and preparing the thermal states of sizable molecules to simulate, for example, chemical reactions at an arbitrary temperature.

  17. High-resolution photoluminescence studies of single semiconductor quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis

    2000-01-01

    Semiconductor quantum dots, especially those formed by self-organized growth, are considered a promising material system for future optical devices [1] and the optical properties of quantum dot ensembles have been investigated in detail over the past years. Recently, considerable interest has...... developed in the study of single quantum dots, characterized by sharp atomic-like transition lines revealing their zero-dimensional density of states. Substantial information about the fundamental properties of individual quantum dots, as well as their interactions with other dots and the host lattice, can...

  18. Toward an Understanding of the Oxidation Process of Methionine Enkephalin: A Combined Electrochemistry, Quantum Chemistry and Quantum Chemical Topology Analysis.

    Science.gov (United States)

    Bergès, Jacqueline; Kamar, Amanda; de Oliveira, Pedro; Pilmé, Julien; Luppi, Eleonora; Houée-Levin, Chantal

    2015-06-11

    Recent experimental results about the oxidation of methionine enkephalin by ·OH radicals indicated an intramolecular electron transfer between the C-terminal methionine radical cation and the tyrosine N-terminus too fast to be observed. We have investigated the thermodynamic possibility of this intramolecular electron transfer by calculating the one-electron redox potentials of both residues for several conformations of the peptide, extracted from the experimental data of the Protein Data Bank (1PLW). Using a QM/MM approach, we show that the redox potential of the Met(•+)/Met couple is higher than that of the TyrOH(•+)/TyrOH one (tyrosine is denoted as TyrOH) for all conformations. The intramolecular electron transfer between both residues (from TyrOH to Met(•+)) is thus always thermodynamically allowed. Previously, we had performed topological studies on the intramolecular electron transfer which predicted this charge transfer. A study by cyclic voltammetry pointed out that the wave belonging to methionine is not present when methionine enkephalin is oxidized and only the direct involvement of the tyrosine residue is observed.

  19. Studies of Novel Quantum Phenomena in Ruthenates

    Energy Technology Data Exchange (ETDEWEB)

    Mao, Zhiqiang

    2011-04-08

    Strongly correlated oxides have been the subject of intense study in contemporary condensed matter physics, and perovskite ruthenates (Sr,Ca)n+1RunO3n+1 have become a new focus in this field. One of important characteristics of ruthenates is that both lattice and orbital degrees of freedom are active and are strongly coupled to charge and spin degrees of freedom. Such a complex interplay of multiple degrees of freedom causes the properties of ruthenates to exhibit a gigantic response to external stimuli under certain circumstances. Magnetic field, pressure, and chemical composition all have been demonstrated to be effective in inducing electronic/magnetic phase transitions in ruthenates. Therefore, ruthenates are ideal candidates for searching for novel quantum phenomena through controlling external parameters. The objective of this project is to search for novel quantum phenomena in ruthenate materials using high-quality single crystals grown by the floating-zone technique, and investigate the underlying physics. The following summarizes our accomplishments. We have focused on trilayered Sr4Ru3O10 and bilayered (Ca1-xSrx)3Ru2O7. We have succeeded in growing high-quality single crystals of these materials using the floating-zone technique and performed systematic studies on their electronic and magnetic properties through a variety of measurements, including resistivity, Hall coefficient, angle-resolved magnetoresistivity, Hall probe microscopy, and specific heat. We have also studied microscopic magnetic properties for some of these materials using neutron scattering in collaboration with Los Alamos National Laboratory. We have observed a number of unusual exotic quantum phenomena through these studies, such as an orbital selective metamagnetic transition, bulk spin valve effect, and a heavy-mass nearly ferromagnetic state with a surprisingly large Wilson ratio. Our work has also revealed underlying physics of these exotic phenomena. Exotic phenomena of correlated

  20. New algorithms for iterative matrix-free eigensolvers in quantum chemistry.

    Science.gov (United States)

    Zuev, Dmitry; Vecharynski, Eugene; Yang, Chao; Orms, Natalie; Krylov, Anna I

    2015-02-15

    New algorithms for iterative diagonalization procedures that solve for a small set of eigen-states of a large matrix are described. The performance of the algorithms is illustrated by calculations of low and high-lying ionized and electronically excited states using equation-of-motion coupled-cluster methods with single and double substitutions (EOM-IP-CCSD and EOM-EE-CCSD). We present two algorithms suitable for calculating excited states that are close to a specified energy shift (interior eigenvalues). One solver is based on the Davidson algorithm, a diagonalization procedure commonly used in quantum-chemical calculations. The second is a recently developed solver, called the "Generalized Preconditioned Locally Harmonic Residual (GPLHR) method." We also present a modification of the Davidson procedure that allows one to solve for a specific transition. The details of the algorithms, their computational scaling, and memory requirements are described. The new algorithms are implemented within the EOM-CC suite of methods in the Q-Chem electronic structure program.

  1. Inactivation of ovine cyclooxygenase-1 by bromoaspirin and aspirin: a quantum chemistry description.

    Science.gov (United States)

    Barroso-Neto, Ito L; Marques, João Paulo C; da Costa, Roner F; Caetano, Ewerton W S; Cavada, Benildo S; Gottfried, Carmem; Freire, Valder N

    2012-03-15

    The resulting noncovalent bonding of the salicylic acid to ovine COX-1 after bromoaspirin and aspirin acetylation by Ser530 is investigated within the scope of density functional theory considering a 6.5 Å radius binding pocket. We have not only took full advantage of published X-ray structural data for the ovine COX-1 cocrystallized with bromoaspirin, but we also have improved that data through computation, finding good estimates for the hydrogen atom positions at the residues of the binding pocket, and repositioning the Ser530Ac[Br;H] lateral chain and salicylic acid by total energy minimization procedures employing LDA and GGA+D exchange-correlation functionals. Using bromoaspirin as a template, we have simulated the positioning of aspirin in the binding pocket, estimating its interaction energy with each of its neighbor COX-1 residues. We demonstrate that the binding energies of bromoaspirin and aspirin to COX-1 are very close when second-order quantum refinements of the structural data are performed, which points to an explanation on why the IC(50) values for the 126 μM COX-1 activity of both bromoaspirin and aspirin are practically the same. Attracting and repelling residues were identified, being shown that Arg120 is the most effective residue attracting the salicylic acid, followed by Ala527, Leu531, Leu359, and Ser353. On the other hand, Glu524 was found the most effective repulsive residue (strength interaction comparable to Arg120). © 2012 American Chemical Society

  2. Molecular structure and ring tunneling of phenyl formate as observed by microwave spectroscopy and quantum chemistry

    Science.gov (United States)

    Ferres, Lynn; Mouhib, Halima; Stahl, Wolfgang; Schwell, Martin; Nguyen, Ha Vinh Lam

    2017-07-01

    Phenyl formate has been investigated by molecular jet Fourier-transform microwave spectroscopy in the frequency range from 2 to 26.5 GHz. Quantum chemical calculations at the MP2/6-311++G(d,p) level of theory indicate that this molecule does not have a plane of symmetry at equilibrium, and that the phenyl ring performs a large amplitude tunneling motion from one side of the Cs configuration to the other. The tilt angle of the ring out of the Hsbnd (Cdbnd O)O plane is ±70° and the calculated tunneling barrier is only 28 cm-1. The two lowest torsional states vt = 0 and 1 are assigned in the experimental spectrum and fitted using the program SPFIT/SPCAT. The Coriolis splitting ΔE between these states is 46.2231(25) GHz, very close to the value of 48.24 GHz calculated using a simple two-top torsional Hamiltonian of the formate group and the phenyl ring.

  3. A spin-adapted Density Matrix Renormalization Group algorithm for quantum chemistry

    CERN Document Server

    Sharma, Sandeep

    2014-01-01

    We extend the spin-adapted density matrix renormalization group (DMRG) algorithm of McCulloch and Gulacsi [Europhys. Lett.57, 852 (2002)] to quantum chemical Hamiltonians. This involves two key modifications to the non-spin-adapted DMRG algorithm: the use of a quasi-density matrix to ensure that the renormalised DMRG states are eigenvalues of $S^2$ , and the use of the Wigner-Eckart theorem to greatly reduce the overall storage and computational cost. We argue that the advantages of the spin-adapted DMRG algorithm are greatest for low spin states. Consequently, we also implement the singlet-embedding strategy of Nishino et al [Phys. Rev. E61, 3199 (2000)] which allows us to target high spin states as a component of a mixed system which is overall held in a singlet state. We evaluate our algorithm on benchmark calculations on the Fe$_2$S$_2$ and Cr$_2$ transition metal systems. By calculating the full spin ladder of Fe$_2$S$_2$ , we show that the spin-adapted DMRG algorithm can target very closely spaced spin ...

  4. Towards ab initio self-energy embedding theory in quantum chemistry

    CERN Document Server

    Lan, Tran Nguyen; Zgid, Dominika

    2015-01-01

    The self-energy embedding theory (SEET), in which the active space self-energy is embedded in the self-energy obtained from a perturbative method treating the non-local correlation effects, was recently developed in our group. In SEET the double counting problem does not appear and the accuracy can be improved either by increasing the perturbation order or by enlarging the active space. This method was first calibrated for the 2D Hubbard lattice showing promising results. In this paper, we report an extension of SEET to quantum chemical ab initio Hamiltonians for applications to molecular systems. The self-consistent second-order Green's function (GF2) method is used to describe the non-local correlations, while the full configuration interaction (FCI) method is carried out to capture strong correlation within the active space. Using few proof-of-concept examples, we show that SEET yields results of comparable quality to $n-$electron valence state second-order perturbation theory (NEVPT2) with the same active...

  5. Communication: Towards ab initio self-energy embedding theory in quantum chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Lan, Tran Nguyen, E-mail: latran@umich.edu [Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Kananenka, Alexei A.; Zgid, Dominika [Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    2015-12-28

    The self-energy embedding theory (SEET), in which the active space self-energy is embedded in the self-energy obtained from a perturbative method treating the non-local correlation effects, was recently developed in our group. In SEET, the double counting problem does not appear and the accuracy can be improved either by increasing the perturbation order or by enlarging the active space. This method was first calibrated for the 2D Hubbard lattice showing promising results. In this paper, we report an extension of SEET to quantum chemical ab initio Hamiltonians for applications to molecular systems. The self-consistent second-order Green’s function method is used to describe the non-local correlations, while the full configuration interaction method is carried out to capture strong correlation within the active space. Using few proof-of-concept examples, we show that SEET yields results of comparable quality to n-electron valence state second-order perturbation theory with the same active space, and furthermore, the full active space can be split into smaller active spaces without further implementation. Moreover, SEET avoids intruder states and does not require any high-order reduced density matrices. These advantages show that SEET is a promising method to describe physical and chemical properties of challenging molecules requiring large active spaces.

  6. Quantum dot surface chemistry and functionalization for cell targeting and imaging.

    Science.gov (United States)

    Bilan, Regina; Fleury, Fabrice; Nabiev, Igor; Sukhanova, Alyona

    2015-04-15

    Quantum dots (QDs) are highly fluorescent nanoscale crystals with size-dependent emission spectra. Due to their excellent photophysical properties, QDs are a promising alternative to organic fluorescent dyes and fluorescent proteins for cell targeting, imaging, and drug delivery. For biomedical applications, QDs should be chemically modified to be stable in aqueous solutions and tagged with the recognition molecules or drugs. Here, we review surface modification approaches to, and strategies for, conjugation of bioactive molecules with QDs. There are a variety of methods of QD surface modification and QD incorporation into larger delivery systems that yield fluorescent nanocarriers from 10 nm to several micrometers. Conjugates of QDs with peptides, proteins, antibodies, oligonucleotides, and small molecules have been used for fluorescent targeting, tracking, and imaging both in vitro and in vivo. Due to an extremely high stability to photobleaching, QDs were used for long-term visualization. QD applications pave the way for new generations of ultrasensitive detection, diagnostic systems, as well as drug delivery approaches, combining accurate targeting, delivery, and imaging in a single assay.

  7. Communication: Towards ab initio self-energy embedding theory in quantum chemistry.

    Science.gov (United States)

    Lan, Tran Nguyen; Kananenka, Alexei A; Zgid, Dominika

    2015-12-28

    The self-energy embedding theory (SEET), in which the active space self-energy is embedded in the self-energy obtained from a perturbative method treating the non-local correlation effects, was recently developed in our group. In SEET, the double counting problem does not appear and the accuracy can be improved either by increasing the perturbation order or by enlarging the active space. This method was first calibrated for the 2D Hubbard lattice showing promising results. In this paper, we report an extension of SEET to quantum chemical ab initio Hamiltonians for applications to molecular systems. The self-consistent second-order Green's function method is used to describe the non-local correlations, while the full configuration interaction method is carried out to capture strong correlation within the active space. Using few proof-of-concept examples, we show that SEET yields results of comparable quality to n-electron valence state second-order perturbation theory with the same active space, and furthermore, the full active space can be split into smaller active spaces without further implementation. Moreover, SEET avoids intruder states and does not require any high-order reduced density matrices. These advantages show that SEET is a promising method to describe physical and chemical properties of challenging molecules requiring large active spaces.

  8. RM1 Semiempirical Quantum Chemistry: Parameters for Trivalent Lanthanum, Cerium and Praseodymium.

    Directory of Open Access Journals (Sweden)

    José Diogo L Dutra

    Full Text Available The RM1 model for the lanthanides is parameterized for complexes of the trications of lanthanum, cerium, and praseodymium. The semiempirical quantum chemical model core stands for the [Xe]4fn electronic configuration, with n =0,1,2 for La(III, Ce(III, and Pr(III, respectively. In addition, the valence shell is described by three electrons in a set of 5d, 6s, and 6p orbitals. Results indicate that the present model is more accurate than the previous sparkle models, although these are still very good methods provided the ligands only possess oxygen or nitrogen atoms directly coordinated to the lanthanide ion. For all other different types of coordination, the present RM1 model for the lanthanides is much superior and must definitely be used. Overall, the accuracy of the model is of the order of 0.07Å for La(III and Pr(III, and 0.08Å for Ce(III for lanthanide-ligand atom distances which lie mostly around the 2.3Å to 2.6Å interval, implying an error around 3% only.

  9. Aggregation and growth of ZnO quantum dots prepared from sol-gel chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Santilli, C.V.; Pulcinelli, S.H.; Caetano, B.L. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Araraquara, SP (Brazil); Briois, V.B [Synchrotron SOLEIL, Saint-Aubin (France)

    2016-07-01

    Full text: Herein we discuss in depth the mechanisms of growth control of ZnO quantum dots (Q-dot) prepared from the zinc oxy-acetate ethanolic solution by the addition of LiOH. Through in situ monitoring of Q-dot radii and of aggregation index calculated from UV-Vis absorption spectra and small-angle X-ray scattering (SAXS) the aggregation and growth of ZnO nanocrystal was well described from two kinetic models: during the first step (t< 50 min) the structural evolution is controlled by the coalescence caused by the oriented attachment between the nanocrystal aggregates while at the advanced time (t> 50 min) the Q-dot coarsening follows the Ostwald ripening (OR) mechanism. From the higher oriented attachment efficiency observed here as compared with early reported synthesis using NaOH and KOH, we propose an universal mechanism to control coalescence and coarsening of ZnO nanocrystal provided from the shield caused by the adsorption of the alkali cation. From X-ray diffraction and transmission electron microscopy results we demonstrate that this mechanism is also useful to prepare Q-dot powders with controlled size. (author)

  10. Measuring Meaningful Learning in the Undergraduate General Chemistry and Organic Chemistry Laboratories: A Longitudinal Study

    Science.gov (United States)

    Galloway, Kelli R.; Bretz, Stacey Lowery

    2015-01-01

    Understanding how students learn in the undergraduate chemistry teaching laboratory is an essential component to developing evidence-based laboratory curricula. The Meaningful Learning in the Laboratory Instrument (MLLI) was developed to measure students' cognitive and affective expectations and experiences for learning in the chemistry…

  11. Measuring Meaningful Learning in the Undergraduate General Chemistry and Organic Chemistry Laboratories: A Longitudinal Study

    Science.gov (United States)

    Galloway, Kelli R.; Bretz, Stacey Lowery

    2015-01-01

    Understanding how students learn in the undergraduate chemistry teaching laboratory is an essential component to developing evidence-based laboratory curricula. The Meaningful Learning in the Laboratory Instrument (MLLI) was developed to measure students' cognitive and affective expectations and experiences for learning in the chemistry…

  12. Colour Chemistry

    Science.gov (United States)

    Griffiths, J.; Rattee, I. D.

    1973-01-01

    Discusses the course offerings in pure color chemistry at two universities and the three main aspects of study: dyestuff chemistry, color measurement, and color application. Indicates that there exists a constant challenge to ingenuity in the subject discipline. (CC)

  13. Real-Time Monitoring Surface Chemistry-Dependent In Vivo Behaviors of Protein Nanocages via Encapsulating an NIR-II Ag2S Quantum Dot.

    Science.gov (United States)

    Li, Chunyan; Li, Feng; Zhang, Yejun; Zhang, Wenjing; Zhang, Xian-En; Wang, Qiangbin

    2015-12-22

    Protein nanocages (PNCs) have been recognized as a promising platform for nanomedicine innovation. Real-time in vivo tracking of PNCs can provide critically important information for the development of PNC-based diagnostics and therapeutics. Here we demonstrate a general strategy for monitoring the behaviors of PNCs in vivo by encapsulating a Ag2S quantum dot (QD) with fluorescence in the second near-infrared window (NIR-II, 1000-1700 nm) inside the PNC, using simian virus 40 (SV40) PNC (PNCSV40) as a model. Benefiting from the high spatiotemporal resolution and deep tissue penetration of NIR-II fluorescence imaging, the dynamic distribution of the PNCSV40 in living mice was tracked in real time with high fidelity, and adopting the PEGylation strategy, surface chemistry-dependent in vivo behaviors of PNCSV40 were clearly revealed. This study represents the first evidence of real-time tracking of the intrinsic behaviors of PNCs in vivo without interference in PNC-host interactions by encapsulating nanoprobes inside. The as-described imaging strategy will facilitate the study of interactions between exogenously introduced PNCs and host body and prompt the development of future protein-based drugs, sensors, and high-efficacy targeted delivery systems.

  14. Phenol-benzene complexation dynamics: quantum chemistry calculation, molecular dynamics simulations, and two dimensional IR spectroscopy.

    Science.gov (United States)

    Kwac, Kijeong; Lee, Chewook; Jung, Yousung; Han, Jaebeom; Kwak, Kyungwon; Zheng, Junrong; Fayer, M D; Cho, Minhaeng

    2006-12-28

    Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared vibrational echo spectrum as a function of time, which directly displays the formation and dissociation of the complex through the growth of off-diagonal peaks, and the linear absorption spectrum, which displays two hydroxyl stretch peaks, one for the complex and one for the free phenol. The results of the simulations are compared to previously reported experimental data and are found to be in quite reasonable agreement. The electronic structure calculations show that the complex is T shaped. The classical potential used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level of the electronic structure calculations. A variety of other features is extracted from the simulations including the relationship between the structure and the projection of the electric field on the hydroxyl group. The fluctuating electric field is used to determine the hydroxyl stretch frequency-frequency correlation function (FFCF). The simulations are also used to examine the number distribution of benzene and CCl4 molecules in the first solvent shell around the phenol. It is found that the distribution is not that of the solvent mole fraction of benzene. There are substantial probabilities of finding a phenol in either a pure benzene environment or a pure CCl4 environment. A conjecture is made that relates the FFCF to the local number of benzene molecules in phenol's first solvent shell.

  15. Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling

    Directory of Open Access Journals (Sweden)

    Z. Peng

    2016-04-01

    secondary organic aerosol (SOA samples is estimated to be significant (> 20 % under the upper limit assumption of unity quantum yield at medium (1 × 1013 and 1.5 × 1015 photons cm−2 s−1 at 185 and 254 nm, respectively or higher UV flux settings. The need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors.

  16. Quantum chemical studies of trace gas adsorption on ice nanoparticles

    Science.gov (United States)

    Schrems, Otto; Ignatov, Stanislav K.; Gadzhiev, Oleg B.; Masunov, Artem E.

    2013-04-01

    We have investigated the interaction of atmospheric trace gases with crystalline water ice particles of nanoscale size by modern quantum chemical methods. Small ice particles which can be formed in different altitudes play an important role in chemistry and physics of the Earth atmosphere. Knowledge about the uptake and incorporation of atmospheric trace gases in ice particles as well as their interactions with water molecules is very important for the understanding of processes at the air/ice interface. The interaction of the atmospheric trace gases with atmospheric ice nanoparticles is also an important issue for the development of modern physicochemical models. Usually, the interactions between trace gases and small particles considered theoretically apply small-size model complexes or the surface models representing only fragments of the ideal surface. Ice particles consisting of 48, 72, 216 and 270 water molecules with a distorted structure of hexagonal water ice Ih were studied using the new SCC-DFTBA method combining well the advantages of the DFT theory and semiempirical methods of quantum chemistry. The largest clusters correspond to the minimal nanoparticle size which are considered to be crystalline as determined experimentally. The clusters up to (H2O)72 were studied at the B3LYP/6-31++G(d,p) and B3LYP/6-311++G(2d,2p) levels. The larger clusters were studied using DFTBA and DFTB+ methods. Several adsorption complexes for the (H2O)270 water ice cluster were optimized at the RI-BLYP/6-31+G(d) theory level to verify the DFTB+ results. Trace gas molecules were coordinated on different sites of the nanoparticles corresponding to different ice Ih crystal planes: (0001), (10-10), (11-20). As atmospheric trace gases we have chosen CO, CO2, HCO*, HCOH*, HCHO, HCOOH and (HCO)2. which are the possible products and intermediates of the UV photolysis of organic molecules such as HCHCHO adsorbed on the ice surface. The structures of the corresponding coordination

  17. A Quantum Chemistry Study on the Electronic Structure of Mercapto Flotation Reagents and Its Coordination with Metal Ions%巯基类浮选药剂电子结构及其与金属离子作用的量子化学研究

    Institute of Scientific and Technical Information of China (English)

    杨刚; 龙翔云

    2001-01-01

    用量子化学程序MOAN计算了巯基类浮选剂MBT,MBO和MBM的电子结构,讨论了其硫醇形式与硫酮形式的稳定性及与过渡金属离子Cu(I)的配位模式和配体的活性位置;研究了五元杂环中N,O,S是否参与配位和分子中苯环的作用及配位原子周围不同的化学环境对配位作用的影响,得到了螯合剂MAT,MBO和MAM与Pt,Pb,Fe,Zn,Cu金属离子作用的强弱顺序,解释了一些基本的实验事实.%The electronic structure of mercapto flotation reagents MBT,MBO,MBM was calculated by use of a quantum chemistry program package,MOAN.As a results,the experiment factors for the stability of isomers of these flotation reagents were explained: the activity site and the role played by benzene ring were discussed and some reasons for that N,O,S on pentahetero ring do not act as a reaction site when coordinating with M(Ⅱ) were also found.Furthermore,the interactions between species above and Pb(Ⅱ),Zn(Ⅱ) as well as some of transition metal ions,Pt (Ⅱ),Fe (Ⅱ),Cu(Ⅱ),were also calculated and discussed here.

  18. Computational studies of thermal and quantum phase transitions approached through non-equilibrium quenching

    Science.gov (United States)

    Liu, Cheng-Wei

    Phase transitions and their associated critical phenomena are of fundamental importance and play a crucial role in the development of statistical physics for both classical and quantum systems. Phase transitions embody diverse aspects of physics and also have numerous applications outside physics, e.g., in chemistry, biology, and combinatorial optimization problems in computer science. Many problems can be reduced to a system consisting of a large number of interacting agents, which under some circumstances (e.g., changes of external parameters) exhibit collective behavior; this type of scenario also underlies phase transitions. The theoretical understanding of equilibrium phase transitions was put on a solid footing with the establishment of the renormalization group. In contrast, non-equilibrium phase transition are relatively less understood and currently a very active research topic. One important milestone here is the Kibble-Zurek (KZ) mechanism, which provides a useful framework for describing a system with a transition point approached through a non-equilibrium quench process. I developed two efficient Monte Carlo techniques for studying phase transitions, one is for classical phase transition and the other is for quantum phase transitions, both are under the framework of KZ scaling. For classical phase transition, I develop a non-equilibrium quench (NEQ) simulation that can completely avoid the critical slowing down problem. For quantum phase transitions, I develop a new algorithm, named quasi-adiabatic quantum Monte Carlo (QAQMC) algorithm for studying quantum quenches. I demonstrate the utility of QAQMC quantum Ising model and obtain high-precision results at the transition point, in particular showing generalized dynamic scaling in the quantum system. To further extend the methods, I study more complex systems such as spin-glasses and random graphs. The techniques allow us to investigate the problems efficiently. From the classical perspective, using the

  19. Biological Actions of Artemisinin: Insights from Medicinal Chemistry Studies

    Directory of Open Access Journals (Sweden)

    Jian Li

    2010-03-01

    Full Text Available Artemisinins have become essential antimalarial drugs for increasingly widespread drug-resistant malaria strains. Although tremendous efforts have been devoted to decipher how this class of molecules works, their exact antimalarial mechanism is still an enigma. Several hypotheses have been proposed to explain their actions, including alkylation of heme by carbon-centered free radicals, interference with proteins such as the sarcoplasmic/endoplasmic calcium ATPase (SERCA, as well as damaging of normal mitochondrial functions. Besides artemisinins, other endoperoxides with various backbones have also been synthesized, some of which showed comparable or even higher antimalarial effects. It is noteworthy that among these artemisinin derivatives, some enantiomers displayed similar in vitro malaria killing efficacy. In this article, the proposed mechanisms of action of artemisinins are reviewed in light of medicinal chemistry findings characterized by efficacy-structure studies, with the hope of gaining more insight into how these potent drugs work.

  20. Soil Studies: Applying Acid-Base Chemistry to Environmental Analysis.

    Science.gov (United States)

    West, Donna M.; Sterling, Donna R.

    2001-01-01

    Laboratory activities for chemistry students focus attention on the use of acid-base chemistry to examine environmental conditions. After using standard laboratory procedures to analyze soil and rainwater samples, students use web-based resources to interpret their findings. Uses CBL probes and graphing calculators to gather and analyze data and…

  1. Soil Studies: Applying Acid-Base Chemistry to Environmental Analysis.

    Science.gov (United States)

    West, Donna M.; Sterling, Donna R.

    2001-01-01

    Laboratory activities for chemistry students focus attention on the use of acid-base chemistry to examine environmental conditions. After using standard laboratory procedures to analyze soil and rainwater samples, students use web-based resources to interpret their findings. Uses CBL probes and graphing calculators to gather and analyze data and…

  2. Information carriers and (reading them through) information theory in quantum chemistry.

    Science.gov (United States)

    Geerlings, Paul; Borgoo, Alex

    2011-01-21

    This Perspective discusses the reduction of the electronic wave function via the second-order reduced density matrix to the electron density ρ(r), which is the key ingredient in density functional theory (DFT) as a basic carrier of information. Simplifying further, the 1-normalized density function turns out to contain essentially the same information as ρ(r) and is even of preferred use as an information carrier when discussing the periodic properties along Mendeleev's table where essentially the valence electrons are at stake. The Kullback-Leibler information deficiency turns out to be the most interesting choice to obtain information on the differences in ρ(r) or σ(r) between two systems. To put it otherwise: when looking for the construction of a functional F(AB) = F[ζ(A)(r),ζ(B)(r)] for extracting differences in information from an information carrier ζ(r) (i.e. ρ(r), σ(r)) for two systems A and B the Kullback-Leibler information measure ΔS is a particularly adequate choice. Examples are given, varying from atoms, to molecules and molecular interactions. Quantum similarity of atoms indicates that the shape function based KL information deficiency is the most appropriate tool to retrieve periodicity in the Periodic Table. The dissimilarity of enantiomers for which different information measures are presented at global and local (i.e. molecular and atomic) level leads to an extension of Mezey's holographic density theorem and shows numerical evidence that in a chiral molecule the whole molecule is pervaded by chirality. Finally Kullback-Leibler information profiles are discussed for intra- and intermolecular proton transfer reactions and a simple S(N)2 reaction indicating that the theoretical information profile can be used as a companion to the energy based Hammond postulate to discuss the early or late transition state character of a reaction. All in all this Perspective's answer is positive to the question of whether an even simpler carrier of

  3. Spectroscopic studies in open quantum systems

    Science.gov (United States)

    Rotter; Persson; Pichugin; Seba

    2000-07-01

    The Hamiltonian H of an open quantum system is non-Hermitian. Its complex eigenvalues E(R) are the poles of the S matrix and provide both the energies and widths of the states. We illustrate the interplay between Re(H) and Im(H) by means of the different interference phenomena between two neighboring resonance states. Level repulsion may occur along the real or imaginary axis (the latter is called resonance trapping). In any case, the eigenvalues of the two states avoid crossing in the complex plane. We then calculate the poles of the S matrix and the corresponding wave functions for a rectangular microwave resonator with a scatter as a function of the area of the resonator as well as of the degree of opening to a waveguide. The calculations are performed by using the method of exterior complex scaling. Re(H) and Im(H) cause changes in the structure of the wave functions which are permanent, as a rule. The resonance picture obtained from the microwave resonator shows all the characteristic features known from the study of many-body systems in spite of the absence of two-body forces. The effects arising from the interplay between resonance trapping and level repulsion along the real axis are not involved in the statistical theory (random matrix theory).

  4. The role of surface chemistry in determining in vivo biodistribution and toxicity of CdSe/ZnS core-shell quantum dots.

    Science.gov (United States)

    Tang, Yuan; Han, Songling; Liu, Hongmei; Chen, Xin; Huang, Li; Li, Xiaohui; Zhang, Jianxiang

    2013-11-01

    To examine the effect of surface chemistry and surface charge on in vivo biodistribution and toxicity of CdSe/ZnS core-shell quantum dots (QDs), QDs with positive, negative, or PEG coating are used in this study for in vivo evaluation in a mouse model. The results suggest that QDs coated with cationic polydiallyldimethylammonium chloride (PDDA) preferentially deposit in the lung other than in the liver, while the negative and PEGylated QDs render abundant accumulation in the liver. At higher doses positive QDs with PDDA coating show severe acute toxicity due to pulmonary embolism. Independent of their surface coatings, all QDs cause injuries in specific tissues like liver, spleen, lung, and kidney, after acute and long-term exposure, and the degree of injuries is dominated by their surface properties. For the positively charged QDs, the acute phase toxicity is primarily contributed by the coating material PDDA, while coating on QDs may amplify both in vitro and in vivo toxicity of PDDA. PEGylated QDs display the slightest chronic injuries in the long-term toxicity examination in comparison to positive or negative ones.

  5. Prediction of logP for Pt(II) and Pt(IV) complexes: Comparison of statistical and quantum-chemistry based approaches.

    Science.gov (United States)

    Tetko, Igor V; Varbanov, Hristo P; Galanski, Markus; Talmaciu, Mona; Platts, James A; Ravera, Mauro; Gabano, Elisabetta

    2016-03-01

    The octanol/water partition coefficient, logP, is one of the most important physico-chemical parameters for the development of new metal-based anticancer drugs with improved pharmacokinetic properties. This study addresses an issue with the absence of publicly available models to predict logP of Pt(IV) complexes. Following data collection and subsequent development of models based on 187 complexes from literature, we validate new and previously published models on a new set of 11 Pt(II) and 35 Pt(IV) complexes, which were kept blind during the model development step. The error of the consensus model, 0.65 for Pt(IV) and 0.37 for Pt(II) complexes, indicates its good accuracy of predictions. The lower accuracy for Pt(IV) complexes was attributed to experimental difficulties with logP measurements for some poorly-soluble compounds. This model was developed using general-purpose descriptors such as extended functional groups, molecular fragments and E-state indices. Surprisingly, models based on quantum-chemistry calculations provided lower prediction accuracy. We also found that all the developed models strongly overestimate logP values for the three complexes measured in the presence of DMSO. Considering that DMSO is frequently used as a solvent to store chemicals, its effect should not be overlooked when logP measurements by means of the shake flask method are performed. The final models are freely available at http://ochem.eu/article/76903.

  6. Intrinsic Folding Proclivities in Cyclic β-Peptide Building Blocks: Configuration and Heteroatom Effects Analyzed by Conformer-Selective Spectroscopy and Quantum Chemistry.

    Science.gov (United States)

    Alauddin, Mohammad; Gloaguen, Eric; Brenner, Valérie; Tardivel, Benjamin; Mons, Michel; Zehnacker-Rentien, Anne; Declerck, Valérie; Aitken, David J

    2015-11-09

    This work describes the use of conformer-selective laser spectroscopy following supersonic expansion to probe the local folding proclivities of four-membered ring cyclic β-amino acid building blocks. Emphasis is placed on stereochemical effects as well as on the structural changes induced by the replacement of a carbon atom of the cycle by a nitrogen atom. The amide A IR spectra are obtained and interpreted with the help of quantum chemistry structure calculations. Results provide evidence that the building block with a trans-substituted cyclobutane ring has a predilection to form strong C8 hydrogen bonds. Nitrogen-atom substitution in the ring induces the formation of the hydrazino turn, with a related but distinct hydrogen-bonding network: the structure is best viewed as a bifurcated C8/C5 bond with the N heteroatom lone electron pair playing a significant acceptor role, which supports recent observations on the hydrazino turn structure in solution. Surprisingly, this study shows that the cis-substituted cyclobutane ring derivative also gives rise predominantly to a C8 hydrogen bond, although weaker than in the two former cases, a feature that is not often encountered for this building block.

  7. Stacked and H-Bonded Cytosine Dimers. Analysis of the Intermolecular Interaction Energies by Parallel Quantum Chemistry and Polarizable Molecular Mechanics.

    Science.gov (United States)

    Gresh, Nohad; Sponer, Judit E; Devereux, Mike; Gkionis, Konstantinos; de Courcy, Benoit; Piquemal, Jean-Philip; Sponer, Jiri

    2015-07-30

    Until now, atomistic simulations of DNA and RNA and their complexes have been executed using well calibrated but conceptually simple pair-additive empirical potentials (force fields). Although such simulations provided many valuable results, it is well established that simple force fields also introduce errors into the description, underlying the need for development of alternative anisotropic, polarizable molecular mechanics (APMM) potentials. One of the most abundant forces in all kinds of nucleic acids topologies is base stacking. Intra- and interstrand stacking is assumed to be the most essential factor affecting local conformational variations of B-DNA. However, stacking also contributes to formation of all kinds of noncanonical nucleic acids structures, such as quadruplexes or folded RNAs. The present study focuses on 14 stacked cytosine (Cyt) dimers and the doubly H-bonded dimer. We evaluate the extent to which an APMM procedure, SIBFA, could account quantitatively for the results of high-level quantum chemistry (QC) on the total interaction energies, and the individual energy contributions and their nonisotropic behaviors. Good agreements are found at both uncorrelated HF and correlated DFT and CCSD(T) levels. Resorting in SIBFA to distributed QC multipoles and to an explicit representation of the lone pairs is essential to respectively account for the anisotropies of the Coulomb and of the exchange-repulsion QC contributions.

  8. 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.

  9. Embedded Mathematics in Chemistry: A Case Study of Students' Attitudes and Mastery

    Science.gov (United States)

    Preininger, Anita M.

    2017-02-01

    There are many factors that shape students' attitudes toward science, technology, engineering and mathematics. This exploratory study of high school students examined the effect of enriching chemistry with math on chemistry students' attitudes toward math and careers involving math. To measure student attitudes, a survey was administered before and after the 18-week chemistry class; results from the chemistry class were compared to survey results from students in an elective science class that did not emphasize mathematics. At the end of the 18-week period, only the chemistry students exhibited more positive views toward their abilities in mathematics and careers that involve mathematics, as compared to their views at the outset of the course. To ensure that chemistry mastery was not hindered by the additional emphasis on math, and that mastery on state end-of-course examinations reflected knowledge acquired during the math-intensive chemistry class, a chemistry progress test was administered at the start and end of the term. This exploratory study suggests that emphasizing mathematical approaches in chemistry may positively influence attitudes toward math in general, as well as foster mastery of chemistry content.

  10. Embedded Mathematics in Chemistry: A Case Study of Students' Attitudes and Mastery

    Science.gov (United States)

    Preininger, Anita M.

    2016-09-01

    There are many factors that shape students' attitudes toward science, technology, engineering and mathematics. This exploratory study of high school students examined the effect of enriching chemistry with math on chemistry students' attitudes toward math and careers involving math. To measure student attitudes, a survey was administered before and after the 18-week chemistry class; results from the chemistry class were compared to survey results from students in an elective science class that did not emphasize mathematics. At the end of the 18-week period, only the chemistry students exhibited more positive views toward their abilities in mathematics and careers that involve mathematics, as compared to their views at the outset of the course. To ensure that chemistry mastery was not hindered by the additional emphasis on math, and that mastery on state end-of-course examinations reflected knowledge acquired during the math-intensive chemistry class, a chemistry progress test was administered at the start and end of the term. This exploratory study suggests that emphasizing mathematical approaches in chemistry may positively influence attitudes toward math in general, as well as foster mastery of chemistry content.

  11. Support vector machine regression (LS-SVM)--an alternative to artificial neural networks (ANNs) for the analysis of quantum chemistry data?

    Science.gov (United States)

    Balabin, Roman M; Lomakina, Ekaterina I

    2011-06-28

    A multilayer feed-forward artificial neural network (MLP-ANN) with a single, hidden layer that contains a finite number of neurons can be regarded as a universal non-linear approximator. Today, the ANN method and linear regression (MLR) model are widely used for quantum chemistry (QC) data analysis (e.g., thermochemistry) to improve their accuracy (e.g., Gaussian G2-G4, B3LYP/B3-LYP, X1, or W1 theoretical methods). In this study, an alternative approach based on support vector machines (SVMs) is used, the least squares support vector machine (LS-SVM) regression. It has been applied to ab initio (first principle) and density functional theory (DFT) quantum chemistry data. So, QC + SVM methodology is an alternative to QC + ANN one. The task of the study was to estimate the Møller-Plesset (MPn) or DFT (B3LYP, BLYP, BMK) energies calculated with large basis sets (e.g., 6-311G(3df,3pd)) using smaller ones (6-311G, 6-311G*, 6-311G**) plus molecular descriptors. A molecular set (BRM-208) containing a total of 208 organic molecules was constructed and used for the LS-SVM training, cross-validation, and testing. MP2, MP3, MP4(DQ), MP4(SDQ), and MP4/MP4(SDTQ) ab initio methods were tested. Hartree-Fock (HF/SCF) results were also reported for comparison. Furthermore, constitutional (CD: total number of atoms and mole fractions of different atoms) and quantum-chemical (QD: HOMO-LUMO gap, dipole moment, average polarizability, and quadrupole moment) molecular descriptors were used for the building of the LS-SVM calibration model. Prediction accuracies (MADs) of 1.62 ± 0.51 and 0.85 ± 0.24 kcal mol(-1) (1 kcal mol(-1) = 4.184 kJ mol(-1)) were reached for SVM-based approximations of ab initio and DFT energies, respectively. The LS-SVM model was more accurate than the MLR model. A comparison with the artificial neural network approach shows that the accuracy of the LS-SVM method is similar to the accuracy of ANN. The extrapolation and interpolation results show that LS-SVM is

  12. A study of how precursor key concepts for organic chemistry success are understood by general chemistry students

    Science.gov (United States)

    Meyer, Patrick Gerard

    This study examines college student understanding of key concepts that will support future organic chemistry success as determined by university instructors. During four one-hour individual interviews the sixteen subjects attempted to solve general chemistry problems. A think-aloud protocol was used along with a whiteboard where the students could draw and illustrate their ideas. The protocols for the interviews were adapted from the Covalent Structure and Bonding two-tiered multiple choice diagnostic instrument (Peterson, Treagust, & Garnett, 1989) and augmented by the Geometry and Polarity of Molecules single-tiered multiple choice instrument (Furio & Calatayud, 1996). The interviews were videotaped, transcribed, and coded for analysis to determine the subjects' understanding of the key ideas. The subjects displayed many misconceptions that were summarized into nine assertions about student conceptualization of chemistry. (1) Many students misunderstand the location and nature of intermolecular forces. (2) Some think electronegativity differences among atoms in a molecule are sufficient to make the molecule polar, regardless of spatial arrangement. (3) Most know that higher phase change temperatures imply stronger intermolecular attractions, but many do not understand the difference between covalent molecular and covalent network substances. (4) Many have difficulty deciding whether a molecule is polar or non-polar, often confusing bilateral symmetry with spatial symmetry in all three dimensions. (5) Many cannot reliably draw correct Lewis structures due to carelessness and overuse of flawed algorithms. (6) Many are confused by how electrons can both repel one other and facilitate bonding between atoms via orbitals---this seems oxymoronic to them. (7) Many cannot explain why the atoms of certain elements do not follow the octet rule and some believe the octet rule alone can determine the shape of a molecule. (8) Most do know that electronegativity and polarity

  13. Temperature Studies of Single InP Quantum Dots

    Science.gov (United States)

    1999-06-18

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP012858 TITLE: Temperature Studies of Single InP Quantum Dots DISTRIBUTION...34 QWR/QD.07 St Petersburg, Russia, June 14-18, 1999 © 1999 loffe Institute Temperature studies of single InP quantum dots Valdry Zwiller, Mats-Erik...Information on the size and geometry of our self-assembled InP Quantum Dots grown on GamnP lattice matched to GaAs has been published elsewhere -I

  14. Pre-Service Chemistry Teachers' Competencies in the Laboratory: A Cross-Grade Study in Solution Preparation

    Science.gov (United States)

    Karatas, F. O.

    2016-01-01

    One of the prerequisites for chemistry teacher candidates is to demonstrate certain laboratory skills. This article aims to determine and discuss the competencies of pre-service chemistry teachers in a chemistry laboratory context working with solution chemistry content. The participants in this study consisted of a group of pre-service chemistry…

  15. Quantum-chemical studies on porphyrins, fullerenes and carbon nanostructures

    CERN Document Server

    Loboda, Oleksandr

    2014-01-01

    ​This book presents theoretical studies of electronic structure, optical and spectroscopic properties of a number of compounds. It presents new, faster calculation methods for applications in quantum-chemical theory of electronic structures.

  16. Laboratory experiments in the study of the chemistry of the outer planets

    Science.gov (United States)

    Scattergood, T. W.

    It is shown that much information about planetary chemistry and physics can be gained through laboratory work. The types of experiments relevant to planetary research concern fundamental properties, spectral/optical properties, 'Miller-Urey' syntheses, and detailed syntheses. Specific examples of studies of the chemistry in the atmosphere of Titan are described with attention given to gas phase chemistry in the troposphere and the composition of model Titan aerosols. A list of work that still needs to be done is provided.

  17. SOME QUANTUM CHEMICAL STUDY ON THE STRUCTURAL ...

    African Journals Online (AJOL)

    Preferred Customer

    Formula. Formula weight. (gmol-1) ... Quantum chemical calculations (Density Functional Theory, B3LYP/6-31G (d)) were used to purposed the ... correlation functional [B3LYP/6-31G(d)]) calculations were done by using Gaussian 03 program ...

  18. Photoluminescence studies of single InGaAs quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1999-01-01

    Semiconductor quantum dots are considered a promising material system for future optical devices and quantum computers. We have studied the low-temperature photoluminescence properties of single InGaAs quantum dots embedded in GaAs. The high spatial resolution required for resolving single dots...... is obtained by exciting and detecting the photoluminescence through a microscope objective which is located inside the cryostat. Furthermore, e-beam lithography and mesa etching have been used to reduce the size of the detection area to a few hundred nanometers in diameter. These techniques allow us...

  19. Laboratory studies of nitrate radical chemistry - application to atmospheric processes

    Energy Technology Data Exchange (ETDEWEB)

    Noremsaune, Ingse

    1997-12-31

    This thesis studies atmospheric chemistry and tries in particular to fill gaps in the data base of atmospheric reactions. It studies the nitrate radical reactions with chloroethenes and with but-2-yne (2-butyne). The mechanisms and rate coefficients for the NO{sub 3}-initiated degradation of the chloroethenes and 2-butyne were investigated by means of the static reaction chamber and the fast flow-discharge technique. The reactions between the nitrate radical and the chloroethenes were studied at atmospheric pressure in a reaction chamber with synthetic air as bath gas. FTIR (Fourier Transform InfraRed spectroscopy) spectroscopy was used to follow the reactions and to identify the products. Products were observed for the reactions with (E)-1,2-dichloroethene and tetrachloroethene, although the absorption bands are weak. The alkyl peroxynitrate and nitrate compounds form very strong and characteristic absorption bands. The rate coefficients for the reactions between NO{sub 3} and the chloroethenes were investigated at room temperature by three different methods. The results are given in tables. 132 refs., 44 figs., 21 tabs.

  20. Quantum-chemistry based calibration of the alkali metal cation series (Li(+)-Cs(+)) for large-scale polarizable molecular mechanics/dynamics simulations.

    Science.gov (United States)

    Dudev, Todor; Devereux, Mike; Meuwly, Markus; Lim, Carmay; Piquemal, Jean-Philip; Gresh, Nohad

    2015-02-15

    The alkali metal cations in the series Li(+)-Cs(+) act as major partners in a diversity of biological processes and in bioinorganic chemistry. In this article, we present the results of their calibration in the context of the SIBFA polarizable molecular mechanics/dynamics procedure. It relies on quantum-chemistry (QC) energy-decomposition analyses of their monoligated complexes with representative O-, N-, S-, and Se- ligands, performed with the aug-cc-pVTZ(-f) basis set at the Hartree-Fock level. Close agreement with QC is obtained for each individual contribution, even though the calibration involves only a limited set of cation-specific parameters. This agreement is preserved in tests on polyligated complexes with four and six O- ligands, water and formamide, indicating the transferability of the procedure. Preliminary extensions to density functional theory calculations are reported.

  1. Superheavy Elements Challenge Experimental and Theoretical Chemistry

    CERN Document Server

    Zvára, I

    2003-01-01

    When reflecting on the story of superheavy elements, the an experimenter, acknowledges the role, which the predictions of nuclear and chemical theories have played in ongoing studies. Today, the problems of major interest for experimental chemistry are the studies of elements 112 and 114 including their chemical identification. Advanced quantum chemistry calculations of atoms and molecules would be of much help. First experiments with element 112 evidence that the metal is much more volatile and inert than mercury.

  2. A Cross-Age Study of Science Student Teachers' Chemistry Attitudes

    Science.gov (United States)

    Çalik, Muammer; Ültay, Neslihan; Kolomuç, Ali; Aytar, Ayse

    2015-01-01

    The aim of this study is to investigate the effects of some variables (gender and year of study) on science student teachers' (SSTs) chemistry attitudes. An adapted version of Chemistry Attitudes and Experiences Questionnaire was administered to 983 SSTs drawn from four different universities in the region of Eastern Black Sea, Turkey. Significant…

  3. Controlling Multivalent Binding through Surface Chemistry: Model Study on Streptavidin

    Science.gov (United States)

    2017-01-01

    Although multivalent binding to surfaces is an important tool in nanotechnology, quantitative information about the residual valency and orientation of surface-bound molecules is missing. To address these questions, we study streptavidin (SAv) binding to commonly used biotinylated surfaces such as supported lipid bilayers (SLBs) and self-assembled monolayers (SAMs). Stability and kinetics of SAv binding are characterized by quartz crystal microbalance with dissipation monitoring, while the residual valency of immobilized SAv is quantified using spectroscopic ellipsometry by monitoring binding of biotinylated probes. Purpose-designed SAv constructs having controlled valencies (mono-, di-, trivalent in terms of biotin-binding sites) are studied to rationalize the results obtained on regular (tetravalent) SAv. We find that divalent interaction of SAv with biotinylated surfaces is a strict requirement for stable immobilization, while monovalent attachment is reversible and, in the case of SLBs, leads to the extraction of biotinylated lipids from the bilayer. The surface density and lateral mobility of biotin, and the SAv surface coverage are all found to influence the average orientation and residual valency of SAv on a biotinylated surface. We demonstrate how the residual valency can be adjusted to one or two biotin binding sites per immobilized SAv by choosing appropriate surface chemistry. The obtained results provide means for the rational design of surface-confined supramolecular architectures involving specific biointeractions at tunable valency. This knowledge can be used for the development of well-defined bioactive coatings, biosensors and biomimetic model systems. PMID:28234007

  4. Recent progresses at IENGF on studies on quantum information

    Science.gov (United States)

    Brida, G.; Cagliero, E.; Genovese, M.; Gramegna, M.; Predazzi, E.

    2005-08-01

    In this proceeding we present the most recent studies performed at IEN "Galileo Ferraris" on quantum information by using quantum optical states. After a general summary of the most recent studies, among them we will present in some details the results of two recent experiments. The first was addressed to tomographic reconstruction of a quantum state by using an innovative theoretical scheme based on a variable quantum efficiency of the detector. This scheme has been applied to Fock (PDC heralded photons), coherent (attenuated laser beam) and thermal states, for which experimental results will be presented. The second was pointed to experimentally investigate the effects of fibre propagation of PDC light produced in a type II crystal and, in particular, to the restoration of entanglement due to wave packet dispersion. Also in this case we will present and discuss our most recent data. Finally, we will shortly acknowledge of realisation of a heralded photon source with strong spectral selection.

  5. Combustion chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Brown, N.J. [Lawrence Berkeley Laboratory, CA (United States)

    1993-12-01

    This research is concerned with the development and use of sensitivity analysis tools to probe the response of dependent variables to model input variables. Sensitivity analysis is important at all levels of combustion modeling. This group`s research continues to be focused on elucidating the interrelationship between features in the underlying potential energy surface (obtained from ab initio quantum chemistry calculations) and their responses in the quantum dynamics, e.g., reactive transition probabilities, cross sections, and thermal rate coefficients. The goals of this research are: (i) to provide feedback information to quantum chemists in their potential surface refinement efforts, and (ii) to gain a better understanding of how various regions in the potential influence the dynamics. These investigations are carried out with the methodology of quantum functional sensitivity analysis (QFSA).

  6. Quantum Chemistry Calculation on Oxygen and Nitrogen Adsorption in Carbon Nanotude

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Oxygen and nitrogen adsorption in single-walled carbon nanotube (SWCNT) is studied by density function and discrete variational (DFT-DVM) method.The models of O2 and N2 adsorption in the SWCNT are optimized based on the energy minimization.The calculated results of density of state,populations and energy gaps of the molecular orbitals show that oxygen adsorption in SWCNT increases the carbon nanotube`s electrical conductivity more notably than nitrogen adsorption,which is consistent with the experiment.

  7. Pharmacokinetic study with computational tools in the medicinal chemistry course

    Directory of Open Access Journals (Sweden)

    Monique Araújo de Brito

    2011-12-01

    Full Text Available To improve the teaching-learning process in the Medicinal Chemistry course, new strategies have been incorporated into practical classes of this fundamental discipline of the pharmaceutical curriculum. Many changes and improvements have been made in the area of medicinal chemistry so far, and students should be prepared for these new approaches with the use of technological resources in this field. Practical activities using computational techniques have been directed to the evaluation of chemical and physicochemical properties that affect the pharmacokinetics of drugs. Their objectives were to allow students to know these tools, to learn how to access them, to search for the structures of drugs and to analyze results. To the best of our knowledge, this is the first study in Brazil to demonstrate the use of computational practices in teaching pharmacokinetics. Practical classes using Osiris and Molinspiration were attractive to students, who developed the activities easily and acquired better theoretical knowledge.Para melhorar o processo ensino-aprendizagem no curso de Química Medicinal novas estratégias estão sendo incorporadas às aulas práticas desta disciplina fundamental do currículo farmacêutico. Muitas mudanças e melhorias vêm marcando a área de química medicinal e por isso é importante que os alunos sejam colocados nestas novas abordagens na área, com a utilização de recursos tecnológicos. As atividades práticas foram direcionadas para a avaliação dos dados químicos e físico-químicos de fármacos que influenciam as propriedades farmacocinéticas com o auxílio de técnicas computacionais. Os objetivos foram permitir aos alunos conhecer essas ferramentas, saber como acessá-las, procurar as estruturas de fármacos e analisar os resultados. Este é o primeiro estudo publicado no Brasil que apresenta aula prática computacional sobre o tema farmacocinética. As aulas práticas utilizando os servidores Osiris e

  8. Organic analogues of diluted magnetic semiconductors: bridging quantum chemistry to condensed matter physics

    Science.gov (United States)

    Furis, Madalina; Rawat, Naveen; Cherian, Judy G.; Wetherby, Anthony; Waterman, Rory; McGill, Stephen

    2015-09-01

    The selective coupling between polarized photons and electronic states in materials enables polarization-resolved spectroscopy studies of exchange interactions, spin dynamics, and collective magnetic behavior of conduction electrons in semiconductors. Here we report on Magnetic Circular Dichroism (MCD) studies of magnetic properties of electrons in crystalline thin films of small molecule organic semiconductors. Specifically, the focus was on the magnetic exchange interaction properties of d-shell ions (Cu2+, Co2+ and Mn2+) metal phthalocyanine (Pc) thin films that one may think of as organic analogues of diluted magnetic semiconductors (DMS). These films were deposited in-house using a recently developed pen-writing method that results in crystalline films with macroscopic long range ordering and improved electronic properties, ideally suited for spectroscopy techniques. Our experiments reveal that, in analogy to DMS, the extended π-orbitals of the Pc molecule mediate the spin exchange between highly localized d-like unpaired spins. We established that exchange mechanisms involve different electronic states in each species and/or hybridization between d-like orbitals and certain delocalized π-orbitals. Unprecedented 25T MCD and PL conducted in the unique 25T Split Florida HELIX magnet at the National High Magnetic Field Laboratory (NHMFL) will prove useful in probing these exchange interactions.

  9. Crystals for neutron scattering studies of quantum magnetism

    Energy Technology Data Exchange (ETDEWEB)

    Yankova, Tantiana [ETH Zurich, Switzerland; Hüvonen, Dan [ETH Zurich, Switzerland; Mühlbauer, Sebastian [ETH Zurich, Switzerland; Schmidiger, David [ETH Zurich, Switzerland; Wulf, Erik [ETH Zurich, Switzerland; Hong, Tao [ORNL; Garlea, Vasile O [ORNL; Custelcean, Radu [ORNL; Ehlers, Georg [ORNL

    2012-01-01

    We review a strategy for targeted synthesis of large single crystal samples of prototype quantum magnets for inelastic neutron scattering experiments. Four case studies of organic copper halogenide S = 1/2 systems are presented. They are meant to illustrate that exciting experimental results pertaining to the forefront of many-body quantum physics can be obtained on samples grown using very simple techniques, standard laboratory equipment, and almost no experience in advanced crystal growth techniques.

  10. Quantum study of Foldy-Wouthuysen-Tani theory on lattice

    Institute of Scientific and Technical Information of China (English)

    Liu Da-Qing

    2007-01-01

    We study here a quantum version of Foldy-Wouthuysen-Tani (FWT) transformation and compare the similarities and differences between the quantum and the classic FWT theories. Then the improvement of action on lattice is discussed. The result shows that it is not necessary to improve the covariant difference along the time direction on lattice. Finally we discuss briefly the structure of physical vacuum and give a model independent of field condensate.

  11. Quantum chemistry and excited states: First investigations on pyrene-like molecules

    Science.gov (United States)

    Parisel, Olivier; Ellinger, Y.

    1994-01-01

    Although the calculations are expected to be accurate within 10%, it follows then that there cannot be proposed unquestionable one-to-one attribution due to the density of the DIB's (Diffuse Interstellar Bands). Nevertheless, it has been shown that if one is interested in the experimental study of methyl-pyrene cations, for example, then, the most promising candidate is the 1-methyl isomer: this isomer has been investigated by d'Hendecourt and Leger (1993,1994) and their spectrum shows very striking features in very good agreement with both our calculations and a few DIB's. However, 1-methyl-pyrene cation is not the only product susceptible of being formed in this experiment, and further investigations are in progress to give a complete interpretations of the results. This preliminary report on pyrene-like molecules illustrates the role that theoretical calculations can ply in both the design and the interpretation of experiments.

  12. Substitution Structures of Large Molecules and Medium Range Correlations in Quantum Chemistry Calculations

    Science.gov (United States)

    Evangelisti, Luca; Pate, Brooks

    2017-06-01

    A study of the minimally exciting topic of agreement between experimental and measured rotational constants of molecules was performed on a set of large molecules with 16-18 heavy atoms (carbon and oxygen). The molecules are: nootkatone (C_{15}H_{22}O), cedrol (C_{15}H_{26}O), ambroxide (C_{16}H_{28}O), sclareolide (C_{16}H_{22}O_{2}), and dihydroartemisinic acid (C_{15}H_{24}O_{2}). For this set of molecules we obtained 13C-subsitution structures for six molecules (this includes two conformers of nootkatone). A comparison of theoretical structures and experimental substitution structures was performed in the spirit of the recent work of Grimme and Steinmetz.[1] Our analysis focused the center-of-mass distance of the carbon atoms in the molecules. Four different computational methods were studied: standard DFT (B3LYP), dispersion corrected DFT (B3LYP-D3BJ), hybrid DFT with dispersion correction (B2PLYP-D3), and MP2. A significant difference in these theories is how they handle medium range correlation of electrons that produce dispersion forces. For larger molecules, these dispersion forces produce an overall contraction of the molecule around the center-of-mass. DFT poorly treats this effect and produces structures that are too expanded. MP2 calculations overestimate the correction and produce structures that are too compact. Both dispersion corrected DFT methods produce structures in excellent agreement with experiment. The analysis shows that the difference in computational methods can be described by a linear error in the center-of-mass distance. This makes it possible to correct poorer performing calculations with a single scale factor. We also reexamine the issue of the "Costain error" in substitution structures and show that it is significantly larger in these systems than in the smaller molecules used by Costain to establish the error limits. [1] Stefan Grimme and Marc Steinmetz, "Effects of London dispersion correction in density functional theory on

  13. Unified approach to study quantum properties of primordial black holes, wormholes and of quantum cosmology

    CERN Document Server

    Nojiri, S; Odintsov, S D

    1999-01-01

    We review the anomaly induced effective action for dilaton coupled spinors and scalars in large N and s-wave approximation. It may be applied to study the following fundamental problems: construction of quantum corrected black holes (BHs), inducing of primordial wormholes in the early Universe (this effect is confirmed) and the solution of initial singularity problem. The recently discovered anti-evaporation of multiple horizon BHs is discussed. The existance of such primordial BHs may be interpreted as SUSY manifestation. Quantum corrections to BHs thermodynamics maybe also discussed within such scheme.

  14. The Quantum Chemistry Calculation and Thermoelectrics of Bi-Sb-Te Series

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The density function theory and discrete variation method(DFT-DVM) was used to study correlation between composition, structure, chemical bond,and property of thermoelectrics of Bi-Sb-Te series.8 models of Bi20-xSbxTe32(x=0,2,6,8,12,14,18 and 20) were calculated.The results show that there is less difference in the ionic bonds between Te(Ⅰ)-Bi(Sb) and Te(Ⅱ)-Bi(Sb), but the covalent bond of Te(Ⅰ)-Bi(Sb) is stronger than that of Te(Ⅱ)-Bi(Sb).The interaction between Te(Ⅰ) and Te(Ⅰ) in different layers is the weakest and the interaction should be Van Der Waals power.The charge of Sb is lower than that of Bi,and the ionic bond of Te-Sb is weaker than that of Te-Bi.The covalent bond of Te-Sb is also weaker than that of Te-Bi.Therefore,the thermoelectric property may be improved by adjusting the electrical conductivity and thermal conductivity through changing the composition in the compounds of Bi-Sb-Te. The calculated results are consistent with the experiments.

  15. STURCTURAL CHARACTERISTICS AND QUANTUM CHEMISTRY CALCULATION OF Al-DOPED BORON CARBIDES

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Structural characteristics, chemical bonds and thermoelectric properties of Al-doped boron carbides are studied through calculations of various structural unit models by using a self-consistent-field discrete variation Xα method. The calculations show that Al atom doped in boron carbide is in preference to substituting B or C atoms on the end of boron carbide chain, and then may occupy interstitial sites, but it is difficult for Al to substitute B or C atom in the centers of the chain or in the icosahedra. A representative structural unit containing an Al atom is [C-B-Al]ε+-[B11C]ε-, while the structural unit without Al is [C-B-B(C)]ε--[B11C]ε+, and the coexistence of these two different structural units makes the electrical conductivity increased. As the covalent bond of Al-B or Al-C is weaker than that of B-B or B-C, the thermal conductivity decreases when Al is added into boron carbides. With the electrical conductivity increasing and the thermal conductivity decreases, Al doping has significant effect on thermoelectric properties of boron carbides.

  16. Coupled effects of solution chemistry and hydrodynamics on the mobility and transport of quantum dot nanomaterials in the vadose zone

    Science.gov (United States)

    Uyusur, Burcu; Darnault, Christophe J. G.; Snee, Preston T.; Kokën, Emre; Jacobson, Astrid R.; Wells, Robert R.

    2010-11-01

    To investigate the coupled effects of solution chemistry and hydrodynamics on the mobility of quantum dot (QD) nanoparticles in the vadose zone, laboratory scale transport experiments involving single and/or sequential infiltrations of QDs in unsaturated and saturated porous media, and computations of total interaction and capillary potential energies were performed. As ionic strength increased, QD retention in the unsaturated porous media increased; however, this retention was significantly suppressed in the presence of a non-ionic surfactant in the infiltration suspensions as indicated by surfactant enhanced transport of QDs. In the vadose zone, the non-ionic surfactant limited the formation of QD aggregates, enhanced QD mobility and transport, and lowered the solution surface tension, which resulted in a decrease in capillary forces that not only led to a reduction in the removal of QDs, but also impacted the vadose zone flow processes. When chemical transport conditions were favorable (ionic strength of 5 × 10 -4 M and 5 × 10 -3 M, or ionic strengths of 5 × 10 -2 M and 0.5 M with surfactant), the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were meso-scale processes, where infiltration by preferential flow results in the rapid transport of QDs. When chemical transport conditions were unfavorable (ionic strength of 5 × 10 -2 M and 0.5 M) the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were pore-scale processes governed by gas-water interfaces (GWI) that impact the mobility of QDs. The addition of surfactant enhanced the transport of QDs both in favorable and unfavorable chemical transport conditions. The mobility and retention of QDs was controlled by interaction and capillary forces, with the latter being the most influential. GWI were found to be the dominant mechanism and site for QD removal compared with solid-water interfaces (SWI) and pore straining. Additionally

  17. The use of quantum molecular calculations to guide a genetic algorithm: a way to search for new chemistry.

    Science.gov (United States)

    Durrant, Marcus C

    2007-01-01

    The process of gene-based molecular evolution has been simulated in silico by using massively parallel density functional theory quantum calculations, coupled with a genetic algorithm, to test for fitness with respect to a target chemical reaction in populations of genetically encoded molecules. The goal of this study was the identification of transition-metal complexes capable of mediating a known reaction, namely the cleavage of N(2) to give the metal nitride. Each complex within the search space was uniquely specified by a nanogene consisting of an eight-digit number. Propagation of an individual nanogene into successive generations was determined by the fitness of its phenotypic molecule to perform the target reaction and new generations were created by recombination and mutation of surviving nanogenes. In its simplest implementation, the quantum-directed genetic algorithm (QDGA) quickly located a local minimum on the evolutionary fitness hypersurface, but proved incapable of progressing towards the global minimum. A strategy for progressing beyond local minima consistent with the Darwinian paradigm by the use of environmental variations coupled with mass extinctions was therefore developed. This allowed for the identification of nitriding complexes that are very closely related to known examples from the chemical literature. Examples of mutations that appear to be beneficial at the genetic level but prove to be harmful at the phenotypic level are described. As well as revealing fundamental aspects of molecular evolution, QDGA appears to be a powerful tool for the identification of lead compounds capable of carrying out a target chemical reaction.

  18. Competitive Lithium Solvation of Linear and Cyclic Carbonates from Quantum Chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Borodin, Oleg; Olguin, Marco; Ganesh, P.; Kent, Paul; Allen, Joshua S.; Henderson, Wesley A.

    2015-11-17

    The composition of the lithium cation (Li+) solvation shell in mixed linear and cyclic carbonate-based electrolytes has been re-examined using Born–Oppenheimer molecular dynamics (BOMD) as a function of salt concentration with ethylene carbonate:dimethyl carbonate (EC:DMC)-LiPF6 as a model system. A slight coordination preference for EC over DMC to a Li+ was found at low salt concentrations, while a slightly higher preference for DMC over EC was found at high salt concentrations. Analysis of the relative binding energies of the (EC)n(DMC)m-Li+ and (EC)n(DMC)m-LiPF6 solvates in the gas-phase and for an implicit solvent (as a function of the solvent dielectric constant) indicated that the DMC-containing Li+ solvates were stabilized relative to (EC4)-Li+ and (EC)3-LiPF6 by immersing them in the implicit solvent. Such stabilization was more pronounced in the implicit solvents with a high dielectric constant. Results from previous Raman and IR experiments were reanalyzed and reconciled by correcting them for changes of the Raman activities, IR intensities and band shifts for the solvents which occur upon Li+ coordination. After these correction factors were applied to the results of BOMD simulations, the composition of the Li+ solvation shell from the BOMD simulations was found to agree well with the solvation numbers extracted from Raman experiments. Finally, the mechanism of the Li+ diffusion in the (EC:DMC)LiPF6 mixed solvent electrolyte was studied using the BOMD simulations.

  19. Analytical studies of spectrum broadcast structures in quantum Brownian motion

    Science.gov (United States)

    Tuziemski, J.; Korbicz, J. K.

    2016-11-01

    Spectrum broadcast structures are a new and fresh concept in the quantum-to-classical transition, introduced recently in the context of decoherence and the appearance of objective features in quantum mechanics. These are specific quantum state structures, responsible for the objectivization of the decohered state of a system. Recently, they have been demonstrated by means of the well-known quantum Brownian motion model of the recoilless limit (infinitely massive central system), as the principal interest lies in information transfer from the system to the environment. However, a final analysis relied on numerics. Here, after a presentation of the main concepts, we perform analytical studies of the model, showing the timescales and the efficiency of the spectrum broadcast structure formation. We consider a somewhat simplified environment, being random with a uniform distribution of frequencies.

  20. Learning and Studying Strategies Used by General Chemistry Students with Different Affective Characteristics

    Science.gov (United States)

    Chan, Julia Y. K.; Bauer, Christopher F.

    2016-01-01

    Students in general chemistry were partitioned into three groups by cluster analysis of six affective characteristics (emotional satisfaction, intellectual accessibility, chemistry self-concept, math self-concept, self-efficacy, and test anxiety). The at-home study strategies for exam preparation and in-class learning strategies differed among the…

  1. Embedded Mathematics in Chemistry: A Case Study of Students' Attitudes and Mastery

    Science.gov (United States)

    Preininger, Anita M.

    2017-01-01

    There are many factors that shape students' attitudes toward science, technology, engineering and mathematics. This exploratory study of high school students examined the effect of enriching chemistry with math on chemistry students' attitudes toward math and careers involving math. To measure student attitudes, a survey was administered before…

  2. Computational Chemistry in the Undergraduate Laboratory: A Mechanistic Study of the Wittig Reaction

    Science.gov (United States)

    Albrecht, Birgit

    2014-01-01

    The Wittig reaction is one of the most useful reactions in organic chemistry. Despite its prominence early in the organic chemistry curriculum, the exact mechanism of this reaction is still under debate, and this controversy is often neglected in the classroom. Introducing a simple computational study of the Wittig reaction illustrates the…

  3. Embedded Mathematics in Chemistry: A Case Study of Students' Attitudes and Mastery

    Science.gov (United States)

    Preininger, Anita M.

    2017-01-01

    There are many factors that shape students' attitudes toward science, technology, engineering and mathematics. This exploratory study of high school students examined the effect of enriching chemistry with math on chemistry students' attitudes toward math and careers involving math. To measure student attitudes, a survey was administered before…

  4. Learning and Studying Strategies Used by General Chemistry Students with Different Affective Characteristics

    Science.gov (United States)

    Chan, Julia Y. K.; Bauer, Christopher F.

    2016-01-01

    Students in general chemistry were partitioned into three groups by cluster analysis of six affective characteristics (emotional satisfaction, intellectual accessibility, chemistry self-concept, math self-concept, self-efficacy, and test anxiety). The at-home study strategies for exam preparation and in-class learning strategies differed among the…

  5. Assessing clinical prospects of silicon quantum dots: studies in mice and monkeys.

    Science.gov (United States)

    Liu, Jianwei; Erogbogbo, Folarin; Yong, Ken-Tye; Ye, Ling; Liu, Jing; Hu, Rui; Chen, Hongyan; Hu, Yazhuo; Yang, Yi; Yang, Jinghui; Roy, Indrajit; Karker, Nicholas A; Swihart, Mark T; Prasad, Paras N

    2013-08-27

    Silicon nanocrystals can provide the outstanding imaging capabilities of toxic heavy-metal-based quantum dots without employing heavy metals and have potential for rapid progression to the clinic. Understanding the toxicity of silicon quantum dots (SiQDs) is essential to realizing this potential. However, existing studies of SiQD biocompatibility are limited, with no systematic progression from small-animal to large-animal studies that are more clinically relevant. Here, we test the response of both mice and monkeys to high intravenous doses of a nanoconstruct created using only SiQDs and FDA-approved materials. We show that (1) neither mice nor monkeys show overt signs of toxicity reflected in their behavior, body mass, or blood chemistry, even at a dose of 200 mg/kg. (2) This formulation did not biodegrade as expected. Elevated levels of silicon were present in the liver and spleen of mice three months post-treatment. (3) Histopathology three months after treatment showed adverse effects of the nanoformulation in the livers of mice, but showed no such effects in monkeys. This investigation reveals that the systemic reactions of the two animal models may have some differences and there are no signs of toxicity clearly attributable to silicon quantum dots.

  6. Quantum Effects in Biological Systems

    CERN Document Server

    2016-01-01

    Since the last decade the study of quantum mechanical phenomena in biological systems has become a vibrant field of research. Initially sparked by evidence of quantum effects in energy transport that is instrumental for photosynthesis, quantum biology asks the question of how methods and models from quantum theory can help us to understand fundamental mechanisms in living organisms. This approach entails a paradigm change challenging the related disciplines: The successful framework of quantum theory is taken out of its low-temperature, microscopic regimes and applied to hot and dense macroscopic environments, thereby extending the toolbox of biology and biochemistry at the same time. The Quantum Effects in Biological Systems conference is a platform for researchers from biology, chemistry and physics to present and discuss the latest developments in the field of quantum biology. After meetings in Lisbon (2009), Harvard (2010), Ulm (2011), Berkeley (2012), Vienna (2013), Singapore (2014) and Florence (2015),...

  7. Size distributions and geometries of alkali halide nanoclusters probed using ESI FT-ICR mass spectrometry and quantum chemistry

    Science.gov (United States)

    Lemke, K.; Sadjadi, S.; Seward, T.

    2010-12-01

    The structures and energetic properties of ionic alkali metal halide clusters play a significant role in our understanding of aqueous geochemical processes such as salt dissolution, precipitation and neutralization reactions. Mass spectrometric and quantum chemical studies of such systems offer new opportunities to study the size-dependent evolution of cluster structures, the occurrence of magic number species as well as their fundamental properties. The work here presents new results for the stability, abundance and structure of pure [Na(NaClm)]+ , [K(KCl)m]+ and mixed [Na(NaCl)p(KCl)q]+ metal halide clusters with mQB3 and G4 methods and comment on the onset of the doubly charged cluster series. FT-ICR mass spectra for [Na(NaCl)n]+ clusters generated from 1mM NaCl in 20%H2O 80% acetonitrile in positive ion mode.

  8. Ferritin Diversity: Mechanistic Studies, Disease Implications, and Materials Chemistry

    Science.gov (United States)

    Hilton, Robert J.

    2011-07-01

    The study of ferritin includes a rich history of discoveries and scientific progress. Initially, the composition of ferritin was determined. Soon, it was shown that ferritin is a spherical, hollow protein. Eventually, over several decades of research, the structure and some function of this interesting protein was elucidated. However, the ferritin field was not completely satisfied. Today, for example, researchers are interested in refining the details of ferritin function, in discovering the role of ferritin in a variety of diseases, and in using ferritin for materials chemistry applications. The work presented in this dissertation highlights the progress that we have made in each of these three areas: (1) Mechanistic studies: The buffer used during horse spleen ferritin iron loading significantly influences the mineralization process and the quantity of iron deposited in ferritin. The ferrihydrite core of ferritin is crystalline and ordered when iron is loaded into ferritin in the presence of imidazole buffer. On the other hand, when iron is loaded into ferritin in the presence of MOPS buffer, the ferrihydrite core is less crystalline and less ordered, and a smaller amount of total iron is loaded in ferritin. We also show that iron can be released from the ferritin core in a non-reductive manner. The rate of Fe3+ release from horse spleen ferritin was measured using the Fe3+-specific chelator desferoxamine. We show that iron release occurs by three kinetic events. (2) Disease studies: In order to better understand iron disruption during disease states, we performed in vitro assays that mimicked chronic kidney disease. We tested the hypothesis that elevated levels of serum phosphate interrupted normal iron binding by transferrin and ferritin. Results show that phosphate competes for iron, forming an iron(III)-phosphate complex that is inaccessible to either transferrin or ferritin. Ferritin samples separated from the iron(III)-phosphate complex shows that as the

  9. Mathematics for quantum chemistry

    CERN Document Server

    Anderson, Jay Martin

    2005-01-01

    This concise volume offers undergraduates an introduction to mathematical formalism in problems of molecular structure and motion. The main topics cover the calculus of orthogonal functions, algebra of vector spaces, and Lagrangian and Hamiltonian formulation of classical mechanics and applications to molecular motion. Answers to problems. 1966 edition.

  10. Hydrothermal chemistry, structures, and luminescence studies of alkali hafnium fluorides.

    Science.gov (United States)

    Underwood, Christopher C; McMillen, Colin D; Chen, Hongyu; Anker, Jeffery N; Kolis, Joseph W

    2013-01-07

    This paper describes the hydrothermal chemistry of alkali hafnium fluorides, including the synthesis and structural characterization of five new alkali hafnium fluorides. Two ternary alkali hafnium fluorides are described: Li(2)HfF(6) in space group P31m with a = 4.9748(7) Å and c = 4.6449(9) Å and Na(5)Hf(2)F(13) in space group C2/m with a = 11.627(2) Å, b = 5.5159(11) Å, and c = 8.4317(17) Å. Three new alkali hafnium oxyfluorides are also described: two fluoroelpasolites, K(3)HfOF(5) and (NH(4))(3)HfOF(5), in space group Fm3m with a = 8.9766(10) and 9.4144(11) Å, respectively, and K(2)Hf(3)OF(12) in space group R3m with a = 7.6486(11) Å and c = 28.802(6) Å. Infrared (IR) spectra were obtained for the title solids to confirm the structure solutions. Comparison of these materials was made based on their structures and synthesis conditions. The formation of these species in hydrothermal fluids appears to be dependent upon both the concentration of the alkali fluoride mineralizer solution and the reaction temperature. Both X-ray and visible fluorescence studies were conducted on compounds synthesized in this study and showed that fluorescence was affected by a variety of factors, such as alkali metal size, the presence/absence of oxygen in the compound, and the coordination environment of Hf(4+).

  11. Laboratory Studies of Methane and Its Relationship to Prebiotic Chemistry

    Science.gov (United States)

    Kobayashi, Kensei; Geppert, Wolf D.; Carrasco, Nathalie; Holm, Nils G.; Mousis, Olivier; Palumbo, Maria Elisabetta; Waite, J. Hunter; Watanabe, Naoki; Ziurys, Lucy M.

    2017-08-01

    To examine how prebiotic chemical evolution took place on Earth prior to the emergence of life, laboratory experiments have been conducted since the 1950s. Methane has been one of the key molecules in these investigations. In earlier studies, strongly reducing gas mixtures containing methane and ammonia were used to simulate possible reactions in the primitive atmosphere of Earth, producing amino acids and other organic compounds. Since Earth's early atmosphere is now considered to be less reducing, the contribution of extraterrestrial organics to chemical evolution has taken on an important role. Such organic molecules may have come from molecular clouds and regions of star formation that created protoplanetary disks, planets, asteroids, and comets. The interstellar origin of organics has been examined both experimentally and theoretically, including laboratory investigations that simulate interstellar molecular reactions. Endogenous and exogenous organics could also have been supplied to the primitive ocean, making submarine hydrothermal systems plausible sites of the generation of life. Experiments that simulate such hydrothermal systems where methane played an important role have consequently been conducted. Processes that occur in other Solar System bodies offer clues to the prebiotic chemistry of Earth. Titan and other icy bodies, where methane plays significant roles, are especially good targets. In the case of Titan, methane is both in the atmosphere and in liquidospheres that are composed of methane and other hydrocarbons, and these have been studied in simulation experiments. Here, we review the wide range of experimental work in which these various terrestrial and extraterrestrial environments have been modeled, and we examine the possible role of methane in chemical evolution.

  12. Experimental quantum annealing: case study involving the graph isomorphism problem.

    Science.gov (United States)

    Zick, Kenneth M; Shehab, Omar; French, Matthew

    2015-06-08

    Quantum annealing is a proposed combinatorial optimization technique meant to exploit quantum mechanical effects such as tunneling and entanglement. Real-world quantum annealing-based solvers require a combination of annealing and classical pre- and post-processing; at this early stage, little is known about how to partition and optimize the processing. This article presents an experimental case study of quantum annealing and some of the factors involved in real-world solvers, using a 504-qubit D-Wave Two machine and the graph isomorphism problem. To illustrate the role of classical pre-processing, a compact Hamiltonian is presented that enables a reduced Ising model for each problem instance. On random N-vertex graphs, the median number of variables is reduced from N(2) to fewer than N log2 N and solvable graph sizes increase from N = 5 to N = 13. Additionally, error correction via classical post-processing majority voting is evaluated. While the solution times are not competitive with classical approaches to graph isomorphism, the enhanced solver ultimately classified correctly every problem that was mapped to the processor and demonstrated clear advantages over the baseline approach. The results shed some light on the nature of real-world quantum annealing and the associated hybrid classical-quantum solvers.

  13. Low-Scaling Quantum Chemistry Approach to Excited-State Properties via an ab Initio Exciton Model: Application to Excitation Energy Transfer in a Self-Assembled Nanotube.

    Science.gov (United States)

    Morrison, Adrian F; Herbert, John M

    2015-11-05

    We introduce a charge-embedding scheme for an excited-state quantum chemistry method aimed at weakly interacting molecular aggregates. The Hamiltonian matrix for the aggregate is constructed in a basis of direct products of configuration-state functions for the monomers, and diagonalization of this matrix affords excitation energies within ∼0.2 eV of the corresponding supersystem calculation. Both the basis states and the coupling matrix elements can be computed in a distributed way, resulting in an algorithm whose time-to-solution is independent of the number of chromophores, and we report calculations on systems with almost 55 000 basis functions using fewer than 450 processors. In a semiconducting organic nanotube, we find evidence of ultrafast, coherent dynamics followed by energy localization driven by static disorder. Truncation of the model system has a qualitative effect on the energy-transfer dynamics, demonstrating the importance of simulating an extended portion of the nanotube, which is not feasible using traditional quantum chemistry.

  14. Modelling CH+ in the ISM: impact of new quantum depletion rates on evolutionary studies

    CERN Document Server

    Bovino, S; Tacconi, M; Gianturco, F A

    2013-01-01

    We present new, accurate quantum calculations of the reaction rates of methyldyne depleted by hydrogen atoms for temperature ranging from 10 K to 1000 K. Although a wide range of calculations have been presented over the years on the chemistry of CH+, no final assessment for this reaction has been given in the literature. In this study, the negative imaginary potential (NIP) approach, which has been previously shown in other systems to provide accurate results for ionic reactions, was employed to generate quantum reaction cross sections for the depletion path: CH+ + H -> C+ + H2. The relevant rates obtained have been compared with the available experimental data and with various earlier calculations. Our results were found to be in very good agreement with the quantum close-coupling results reported by Warmbier et al. 2011 and also follow the general behaviour found from cold-trap experiment. The new rates have been then included in a sub-network we have chosen from the well-known, extensive UMIST database an...

  15. Iridium Cyclometalated Complexes in Host-Guest Chemistry: A Strategy for Maximizing Quantum Yield in Aqueous Media.

    Science.gov (United States)

    Alrawashdeh, Lubna R; Cronin, Michael P; Woodward, Clifford E; Day, Anthony I; Wallace, Lynne

    2016-07-01

    The weaker emission typically seen for iridium(III) cyclometalated complexes in aqueous medium can be reversed via encapsulation in cucurbit[10]uril (Q[10]). The Q[10] cavity is shown to effectively maximize quantum yields for the complexes, compared to any other medium. This may provide significant advantages for a number of sensor applications. NMR studies show that the complexes are accommodated similarly within the host molecule, even with cationic substituents attached to the ppy ligands, indicating that the hydrophobic effect is the dominant driving force for binding. Cavity-encapsulated 1:1 host-guest species dominate the emission, but 1:2 species are also indicated, which also give some enhancement of intensity. Results demonstrate that the enhancement is due primarily to much lower rates of nonradiative decay but also suggest that the encapsulation can cause a change in character of the emitting state.

  16. A tracer aided study on silicon chemistry in biological systems

    NARCIS (Netherlands)

    Brasser, H.J.

    2009-01-01

    Silicon (Si) is omnipresent in nature, and it is involved in important but diverse roles in a broad range of organisms, including diatoms, higher plants and humans. Some organisms, like the diatoms, need high amounts of silicon, and master silicon chemistry to a high extend using several enzymes. Ot

  17. Experimental and Theoretical Studies of Atmosphereic Inorganic Chlorine Chemistry

    Science.gov (United States)

    Sander, Stanley P.; Friedl, Randall R.

    1993-01-01

    Over the last five years substantial progress has been made in defining the realm of new chlorine chemistry in the polar stratosphere. Application of existing experimental techniques to potentially important chlorine-containing compounds has yielded quantitative kinetic and spectroscopic data as well as qualitative mechanistic insights into the relevant reactions.

  18. A Case Study on German First Year Chemistry Student Teachers' Beliefs about Chemistry Teaching, and Their Comparison with Student Teachers from Other Science Teaching Domains

    Science.gov (United States)

    Markic, Silvija; Eilks, Ingo

    2008-01-01

    This paper gives insights into the beliefs of 85 German first year chemistry student teachers about chemistry teaching and learning at the beginning of their teacher education. The study is based on student teachers' drawings of themselves in a typical classroom situation and four open questions. The approach evaluated: (I) Beliefs about Classroom…

  19. Art, Meet Chemistry; Chemistry, Meet Art: Case Studies, Current Literature, and Instrumental Methods Combined to Create a Hands-On Experience for Nonmajors and Instrumental Analysis Students

    Science.gov (United States)

    Nivens, Delana A.; Padgett, Clifford W.; Chase, Jeffery M.; Verges, Katie J.; Jamieson, Deborah S.

    2010-01-01

    Case studies and current literature are combined with spectroscopic analysis to provide a unique chemistry experience for art history students and to provide a unique inquiry-based laboratory experiment for analytical chemistry students. The XRF analysis method was used to demonstrate to nonscience majors (art history students) a powerful…

  20. Studies of Arctic Middle Atmosphere Chemistry using Infrared Absorption Spectroscopy

    Science.gov (United States)

    Lindenmaier, Rodica

    The objective of this Ph.D. project is to investigate Arctic middle atmosphere chemistry using solar infrared absorption spectroscopy. These measurements were made at the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut, which is operated by the Canadian Network for the Detection of Atmospheric Change (CANDAC). This research is part of the CANDAC/PEARL Arctic Middle Atmosphere Chemistry theme and aims to improve our understanding of the processes controlling the stratospheric ozone budget using measurements of the concentrations of stratospheric constituents. The instrument, a Bruker IFS 125HR Fourier transform infrared (FTIR) spectrometer, has been specifically designed for high-resolution measurements over a broad spectral range and has been used to measure reactive species, source gases, reservoirs, and dynamical tracers at PEARL since August 2006. The first part of this research focuses on the optimization of ozone retrievals, for which 22 microwindows were studied and compared. The spectral region from 1000 to 1005 cm-1 was found to be the most sensitive in both the stratosphere and troposphere, giving the highest number of independent pieces of information and the smallest total error for retrievals at Eureka. Similar studies were performed in coordination with the Network for the Detection of Atmospheric Composition Change for nine other species, with the goal of improving and harmonizing the retrieval parameters among all Infrared Working Group sites. Previous satellite validation exercises have identified the highly variable polar conditions of the spring period to be a challenge. In this work, comparisons between the 125HR and ACE-FTS (Atmospheric Chemistry Experiment-Fourier transform spectrometer) from 2007 to 2010 have been used to develop strict criteria that allow the ground and satellite-based instruments to be confidently compared. After applying these criteria, the differences between the two instruments were generally

  1. Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling

    Directory of Open Access Journals (Sweden)

    Z. Peng

    2015-09-01

    Full Text Available Oxidation flow reactors (OFRs using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D, O(3P, and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to relative humidity (RH and external OH reactivity (OHRext, as both non-OH reactants and OH scale roughly proportional to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D, O(3P, and O3 have relative contributions to VOC consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. Under "pathological OFR conditions" of low RH and/or high OHRext, the importance of non-OH reactants is enhanced because OH is suppressed. Some biogenics can have substantial destructions by O3, and photolysis at non-tropospheric wavelengths (185 and 254 nm may also play a significant role in the degradation of some aromatics under pathological conditions. Working under low O2 with the OFR185 mode allows OH to completely dominate over O3 reactions even for the biogenic species most reactive with O3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in lab

  2. Quantum-chemical studies of quasi-one-dimensional electron systems. 1. Polyenes

    Directory of Open Access Journals (Sweden)

    Yuriy Kruglyak

    2015-05-01

    Full Text Available This review is devoted to the basic problem in quantum theory of quasi-one-dimensional electron systems like polyenes (Part 1 and cumulenes (Part 2 – physical origin of the forbidden zone in these and analogous 1D electron systems due to two possible effects – Peierls instability (bond alternation and Mott instability (electron correlation. Both possible contradiction and coexistence of the Mott and Peierls instabilities are summerized on the basis of the Kiev quantum chemistry team research projects.

  3. Development of a Polarizable Force Field For Proteins via Ab Initio Quantum Chemistry: First Generation Model and Gas Phase Tests

    Science.gov (United States)

    KAMINSKI, GEORGE A.; STERN, HARRY A.; BERNE, B. J.; FRIESNER, RICHARD A.; CAO, YIXIANG X.; MURPHY, ROBERT B.; ZHOU, RUHONG; HALGREN, THOMAS A.

    2014-01-01

    We present results of developing a methodology suitable for producing molecular mechanics force fields with explicit treatment of electrostatic polarization for proteins and other molecular system of biological interest. The technique allows simulation of realistic-size systems. Employing high-level ab initio data as a target for fitting allows us to avoid the problem of the lack of detailed experimental data. Using the fast and reliable quantum mechanical methods supplies robust fitting data for the resulting parameter sets. As a result, gas-phase many-body effects for dipeptides are captured within the average RMSD of 0.22 kcal/mol from their ab initio values, and conformational energies for the di- and tetrapeptides are reproduced within the average RMSD of 0.43 kcal/mol from their quantum mechanical counterparts. The latter is achieved in part because of application of a novel torsional fitting technique recently developed in our group, which has already been used to greatly improve accuracy of the peptide conformational equilibrium prediction with the OPLS-AA force field.1 Finally, we have employed the newly developed first-generation model in computing gas-phase conformations of real proteins, as well as in molecular dynamics studies of the systems. The results show that, although the overall accuracy is no better than what can be achieved with a fixed-charges model, the methodology produces robust results, permits reasonably low computational cost, and avoids other computational problems typical for polarizable force fields. It can be considered as a solid basis for building a more accurate and complete second-generation model. PMID:12395421

  4. Anisotropic mechanoresponse of energetic crystallites: a quantum molecular dynamics study of nano-collision

    Science.gov (United States)

    Li, Ying; Kalia, Rajiv K.; Misawa, Masaaki; Nakano, Aiichiro; Nomura, Ken-Ichi; Shimamura, Kohei; Shimojo, Fuyuki; Vashishta, Priya

    2016-05-01

    At the nanoscale, chemistry can happen quite differently due to mechanical forces selectively breaking the chemical bonds of materials. The interaction between chemistry and mechanical forces can be classified as mechanochemistry. An example of archetypal mechanochemistry occurs at the nanoscale in anisotropic detonating of a broad class of layered energetic molecular crystals bonded by inter-layer van der Waals (vdW) interactions. Here, we introduce an ab initio study of the collision, in which quantum molecular dynamic simulations of binary collisions between energetic vdW crystallites, TATB molecules, reveal atomistic mechanisms of anisotropic shock sensitivity. The highly sensitive lateral collision was found to originate from the twisting and bending to breaking of nitro-groups mediated by strong intra-layer hydrogen bonds. This causes the closing of the electronic energy gap due to an inverse Jahn-Teller effect. On the other hand, the insensitive collisions normal to multilayers are accomplished by more delocalized molecular deformations mediated by inter-layer interactions. Our nano-collision studies provide a much needed atomistic understanding for the rational design of insensitive energetic nanomaterials and the detonation synthesis of novel nanomaterials.At the nanoscale, chemistry can happen quite differently due to mechanical forces selectively breaking the chemical bonds of materials. The interaction between chemistry and mechanical forces can be classified as mechanochemistry. An example of archetypal mechanochemistry occurs at the nanoscale in anisotropic detonating of a broad class of layered energetic molecular crystals bonded by inter-layer van der Waals (vdW) interactions. Here, we introduce an ab initio study of the collision, in which quantum molecular dynamic simulations of binary collisions between energetic vdW crystallites, TATB molecules, reveal atomistic mechanisms of anisotropic shock sensitivity. The highly sensitive lateral collision

  5. 2D Quantum Mechanical Study of Nanoscale MOSFETs

    Science.gov (United States)

    Svizhenko, Alexei; Anantram, M. P.; Govindan, T. R.; Biegel, B.; Kwak, Dochan (Technical Monitor)

    2000-01-01

    With the onset of quantum confinement in the inversion layer in nanoscale MOSFETs, behavior of the resonant level inevitably determines all device characteristics. While most classical device simulators take quantization into account in some simplified manner, the important details of electrostatics are missing. Our work addresses this shortcoming and provides: (a) a framework to quantitatively explore device physics issues such as the source-drain and gate leakage currents, DIBL, and threshold voltage shift due to quantization, and b) a means of benchmarking quantum corrections to semiclassical models (such as density-gradient and quantum-corrected MEDICI). We have developed physical approximations and computer code capable of realistically simulating 2-D nanoscale transistors, using the non-equilibrium Green's function (NEGF) method. This is the most accurate full quantum model yet applied to 2-D device simulation. Open boundary conditions and oxide tunneling are treated on an equal footing. Electrons in the ellipsoids of the conduction band are treated within the anisotropic effective mass approximation. We present the results of our simulations of MIT 25, 50 and 90 nm "well-tempered" MOSFETs and compare them to those of classical and quantum corrected models. The important feature of quantum model is smaller slope of Id-Vg curve and consequently higher threshold voltage. Surprisingly, the self-consistent potential profile shows lower injection barrier in the channel in quantum case. These results are qualitatively consistent with ID Schroedinger-Poisson calculations. The effect of gate length on gate-oxide leakage and subthreshold current has been studied. The shorter gate length device has an order of magnitude smaller current at zero gate bias than the longer gate length device without a significant trade-off in on-current. This should be a device design consideration.

  6. Extending molecular simulation time scales: Parallel in time integrations for high-level quantum chemistry and complex force representations.

    Science.gov (United States)

    Bylaska, Eric J; Weare, Jonathan Q; Weare, John H

    2013-08-21

    distributed computing environment using very slow transmission control protocol/Internet protocol networks. Scripts written in Python that make calls to a precompiled quantum chemistry package (NWChem) are demonstrated to provide an actual speedup of 8.2 for a 2.5 ps AIMD simulation of HCl + 4H2O at the MP2/6-31G* level. Implemented in this way these algorithms can be used for long time high-level AIMD simulations at a modest cost using machines connected by very slow networks such as WiFi, or in different time zones connected by the Internet. The algorithms can also be used with programs that are already parallel. Using these algorithms, we are able to reduce the cost of a MP2/6-311++G(2d,2p) simulation that had reached its maximum possible speedup in the parallelization of the electronic structure calculation from 32 s/time step to 6.9 s/time step.

  7. Extending molecular simulation time scales: Parallel in time integrations for high-level quantum chemistry and complex force representations

    Science.gov (United States)

    Bylaska, Eric J.; Weare, Jonathan Q.; Weare, John H.

    2013-08-01

    environment using very slow transmission control protocol/Internet protocol networks. Scripts written in Python that make calls to a precompiled quantum chemistry package (NWChem) are demonstrated to provide an actual speedup of 8.2 for a 2.5 ps AIMD simulation of HCl + 4H2O at the MP2/6-31G* level. Implemented in this way these algorithms can be used for long time high-level AIMD simulations at a modest cost using machines connected by very slow networks such as WiFi, or in different time zones connected by the Internet. The algorithms can also be used with programs that are already parallel. Using these algorithms, we are able to reduce the cost of a MP2/6-311++G(2d,2p) simulation that had reached its maximum possible speedup in the parallelization of the electronic structure calculation from 32 s/time step to 6.9 s/time step.

  8. Extending molecular simulation time scales: Parallel in time integrations for high-level quantum chemistry and complex force representations

    Energy Technology Data Exchange (ETDEWEB)

    Bylaska, Eric J., E-mail: Eric.Bylaska@pnnl.gov [Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352 (United States); Weare, Jonathan Q., E-mail: weare@uchicago.edu [Department of Mathematics, University of Chicago, Chicago, Illinois 60637 (United States); Weare, John H., E-mail: jweare@ucsd.edu [Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093 (United States)

    2013-08-21

    to 14.3. The parallel in time algorithms can be implemented in a distributed computing environment using very slow transmission control protocol/Internet protocol networks. Scripts written in Python that make calls to a precompiled quantum chemistry package (NWChem) are demonstrated to provide an actual speedup of 8.2 for a 2.5 ps AIMD simulation of HCl + 4H{sub 2}O at the MP2/6-31G* level. Implemented in this way these algorithms can be used for long time high-level AIMD simulations at a modest cost using machines connected by very slow networks such as WiFi, or in different time zones connected by the Internet. The algorithms can also be used with programs that are already parallel. Using these algorithms, we are able to reduce the cost of a MP2/6-311++G(2d,2p) simulation that had reached its maximum possible speedup in the parallelization of the electronic structure calculation from 32 s/time step to 6.9 s/time step.

  9. An approximate approach to quantum mechanical study of biomacromolecules

    Science.gov (United States)

    Chen, Xihua

    This thesis summarizes the author's major work in Prof. John Z.H. Zhang's Threoretical Chemistry research group. In Chapter 1, we present a general description of MFCC (molecular fractionation with conjugated caps) method that has been developed in this group to treat biomacromolecules in a divide-and-conquer fashion. Then we give in detail a computational study of MFCC application to peptide/protein that contains disulfide bonds. Continued on the basis of previous MFCC tests, this study provides another numerical support for the accuracy of the MFCC approach to full quantum mechanical calculation of protein/peptide-small molecule interaction. In Chapter 2, we further develop the MFCC scheme for quantum mechanical computation of DNA-ligand interaction energy. We study three oligonuclear acid interaction systems: dinucleotide dCG/water, trinucleotide dCGT/water and a Watson-Crick paired DNA segment dCGT/dGCA. The MFCC interaction energies are found to be in excellent agreement with the corresponding results obtained from the full system ab initio calculations. This study is an exemplification of the application of the general MFCC approach to biomacromolecules. In Chapter 3, firstly, a MFCC-downhill simplex method is proposed to study binding structures of ligands (atoms, ions, or small molecules) in large molecular complex systems. This method employs the MFCC approach to compute the interaction energy-structure relation of the system and implements the downhill simplex algorithm for structural optimization. Secondly, this method is numerically tested on a system of [KCp(18-crown-6)], as a simplest monatomic case study, to optimize the binding position of the potassium cation in a fixed coordination Cp and 18-crown-6 coordinating sphere. The result of the MFCC-downhill simplex optimization shows good agreement with both the crystal structure and with the full-system downhill simplex optimized structure. The effects of the initial structure of the simplex and of the

  10. A quantum mechanical study of alkylimidazolium halide ionic liquids

    Science.gov (United States)

    Li, Wei; Qi, Chuansong; Rong, Hua; Wu, Xinmin; Gong, Liangfa

    2012-07-01

    Thirty imidazolium (IM) halide compounds were studied using quantum chemical calculations. Geometry optimization and interaction energy calculations were performed using the B3LYP/6-311++G(d,p) method for ions composed of one alkylimidazolium cation and two or three halogen anions. The obtained structures were consistent with experimental results. In addition, a linear correlation between melting points and interaction energies was obtained for the compounds studied, and this relationship was consistent with that obtained for amino acid cation based ionic liquids. Our Letter demonstrates the potential for quantum mechanical calculations to predict the melting points of ionic liquids.

  11. An extensive Study of Teaching / Learning Quantum Mechanics in College

    CERN Document Server

    Akarsu, Bayram

    2010-01-01

    Quantum physics is considered as one of the most remarkable discoveries of contemporary physics grown during previous century and gradually manifested to the scientific world such as inventions of laser, the transistor, the electron microscope, and semiconductor. Teaching of physical science has been stressed in the National Science Education Standards (NSES) from level K-12 as well as many state science standards (Gossard, 2000). The objectives of the current study are to investigate prospective elucidation of the most common learning difficulties, insufficient teaching strategies and other significant instructional or conceptual problems encountered by science and engineering college students at the senior and/or junior level during the instruction of Quantum Physics. Although conceptual issues about learning and teaching of Quantum Physics were addressed in the current study, I mainly focused on the ways the teachers approach teaching it, as well as considerations of how the classroom environments should f...

  12. Chemistry Teachers' Views on Teaching "Climate Change"--An Interview Case Study from Research-Oriented Learning in Teacher Education

    Science.gov (United States)

    Feierabend, Timo; Jokmin, Sebastian; Eilks, Ingo

    2011-01-01

    This paper presents a case study from research-oriented learning in chemistry teacher education. The study evaluates the views of twenty experienced German chemistry teachers about the teaching of climate change in chemistry education. Data was collected using semi-structured interviews about the teachers' experiences and their views about…

  13. Chemistry Teachers' Views on Teaching "Climate Change"--An Interview Case Study from Research-Oriented Learning in Teacher Education

    Science.gov (United States)

    Feierabend, Timo; Jokmin, Sebastian; Eilks, Ingo

    2011-01-01

    This paper presents a case study from research-oriented learning in chemistry teacher education. The study evaluates the views of twenty experienced German chemistry teachers about the teaching of climate change in chemistry education. Data was collected using semi-structured interviews about the teachers' experiences and their views about…

  14. The JMB Applied Chemistry Syllabus--the Place of Case Studies and Industrial Processes

    Science.gov (United States)

    Hallas, G.; Hughes, W. J.

    1974-01-01

    Describes two novel topics in the JMB Applied Chemistry Core Syllabus. These are the social and economic aspects of chemical technology, involving the use of six case studies, and industrial processes. (Author/GS)

  15. Study of band gap and determination of size of PbS quantum dots synthesized by colloidal solution

    Directory of Open Access Journals (Sweden)

    M. S. Ghamsari

    2005-03-01

    Full Text Available   PbS semiconductor non-crystals have been synthesized in order to study the modification of their electronic structures and optical properties in relation to their size. The synthesis has been carried out by using the techniques of colloidal chemistry. Strong quantum confinement behavior has been observed based on the analysis of optical spectra of these particles. The average particle size approximated by x-ray line width and hyperbolic band model calculation. Heterogeneous broadening of optical spectrum is studied finally.

  16. Spectroscopic studies in open quantum systems

    CERN Document Server

    Rotter, I; Pichugin, K N; Seba, P

    2000-01-01

    The spectroscopic properties of an open quantum system are determined by theeigenvalues and eigenfunctions of an effective Hamiltonian H consisting of theHamiltonian H_0 of the corresponding closed system and a non-Hermitiancorrection term W arising from the interaction via the continuum of decaychannels. The eigenvalues E_R of H are complex. They are the poles of theS-matrix and provide both the energies and widths of the states. We illustratethe interplay between Re(H) and Im(H) by means of the different interferencephenomena between two neighboured resonance states. Level repulsion along thereal axis appears if the interaction is caused mainly by Re(H) while abifurcation of the widths appears if the interaction occurs mainly due toIm(H). We then calculate the poles of the S-matrix and the correspondingwavefunctions for a rectangular microwave resonator with a scatter as afunction of the area of the resonator as well as of the degree of opening to aguide. The calculations are performed by using the method o...

  17. Use of pulse radiolysis for the study of the chemistry of aqueous ozone and ozonide solutions

    DEFF Research Database (Denmark)

    Sehested, Knud; Holcman, Jerzy; Bjergbakke, Erling

    1986-01-01

    The chemistry of aqeous ozone, O3, and ozonide, O3−, is of great interest from a technological, environmental and scientific point of view. The literature about their aqueous chemistry is extensive, the reaction mechanisms are still not well understood. The ozonide anion is a free radical...... of a detailed mechanism. We have investigated the reaction mechanisms using pulse radiolysis in combination with a high pressure cell, rapid mixing and numerical simulation of the experiments. This study makes it possible to give a detailed description of the reaction mechanisms in terms of uni- and bimolecular...... reactions and provides kinetic data sufficient for computer simulations of aqueous O3/O3− chemistry....

  18. Nano-design of quantum dot-based photocatalysts for hydrogen generation using advanced surface molecular chemistry

    KAUST Repository

    Yu, Weili

    2015-01-01

    Efficient photocatalytic hydrogen generation in a suspension system requires a sophisticated nano-device that combines a photon absorber with effective redox catalysts. This study demonstrates an innovative molecular linking strategy for fabricating photocatalytic materials that allow effective charge separation of excited carriers, followed by efficient hydrogen evolution. The method for the sequential replacement of ligands with appropriate molecules developed in this study tethers both quantum dots (QDs), as photosensitizers, and metal nanoparticles, as hydrogen evolution catalysts, to TiO2 surfaces in a controlled manner at the nano-level. Combining hydrophobic and hydrophilic interactions on the surface, CdSe-ZnS core-shell QDs and an Au-Pt alloy were attached to TiO2 without overlapping during the synthesis. The resultant nano-photocatalysts achieved substantially high-performance visible-light-driven photocatalysis for hydrogen evolution. All syntheses were conducted at room temperature and in ambient air, providing a promising route for fabricating visible-light-responsive photocatalysts.

  19. Linear spin-wave study of a quantum kagome ice

    Science.gov (United States)

    Owerre, S. A.; Burkov, A. A.; Melko, Roger G.

    2016-04-01

    We present a large-S study of a quantum spin ice Hamiltonian, introduced by Huang et al. [Phys. Rev. Lett. 112, 167203 (2014), 10.1103/PhysRevLett.112.167203], on the kagome lattice. This model involves a competition between the frustrating Ising term of classical kagome ice, a Zeeman magnetic field h , and a nearest-neighbor transverse spin-flip term SixSjx-SiySjy . Recent quantum Monte Carlo (QMC) simulations by Carrasquilla et al. [Nat. Commun. 6, 7421 (2015), 10.1038/ncomms8421], uncovered lobes of a disordered phase for large Ising interaction and h ≠0 —a putative quantum spin liquid phase. Here, we examine the nature of this model using large-S expansion. We show that the ground state properties generally have the same trends with those observed in QMC simulations. In particular, the large-S ground state phase diagram captures the existence of the disordered lobes.

  20. Fiscal 1999 survey report. Part 2. Research study on restraint of carbon dioxide generation by green chemistry; 1999 nendo green chemistry ni yoru CO{sub 2} hassei yokusei ni kakawaru chosa kenkyu. 2

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2000-03-01

    In connection with green chemistry, a concept of bringing paradigm shift to chemical technologies as something that makes reduction in environmental load compatible with economic activities; surveys were made this year on the developments of fine chemicals from renewable resources such as cellulose among the cases of developing chemical substances/products to be called 'green chemicals' reducing environmental load; developments of surfactants produced by certain microorganism, plastic additives with reduced pollutant loads, particularly fire retardants and environmentally benign reactant solvents; concept of green chemistry in the development of chlorofluorocarbon-alternatives; and up-to-date technological level concerning a design method of chemical materials and an estimation method for chemical safety using quantum chemistry calculation. In regard to the chemical materials and products intrinsically containing a certain level of risk, R and D should be reinforced and accelerated in the future on the alternative materials/products reducing their toxicity. In this case, along with the importance of discussing compatibility of technological possibility with economical adaptability, sociological study seems to be necessary in incorporating environmental load reduction into economic evaluation. (NEDO)

  1. Synthesis and Characterization of Quantum Dots: A Case Study Using PbS

    Science.gov (United States)

    Pan, Yi; Li, Yue Ru; Zhao, Yu; Akins, Daniel L.

    2015-01-01

    A research project for senior undergraduates of chemistry has been developed to introduce syntheses of a series of monodispersed semiconductor PbS quantum dots (QDs) and their characterization methodologies. In this paper, we report the preparation of monodispersed semiconductor PbS QDs with sizes smaller than the exciton Bohr radius using a…

  2. Study of quantum spin correlations of relativistic electron pairs - Testing nonlocality of relativistic quantum mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Bodek, K.; Rozpędzik, D.; Zejma, J. [Jagiellonian University, Faculty of Physics, Astronomy and Applied Informatics, Reymonta 4, 30059 Kraków (Poland); Caban, P.; Rembieliński, J.; Włodarczyk, M. [University of Łódź, Faculty of Physics and Applied Informatics, Pomorska 149/153, 90236 Łódź (Poland); Ciborowski, J. [University of Warsaw, Faculty of Physics, Hoza 69, 00681 Warsaw (Poland); Enders, J.; Köhler, A. [Technische Universität Darmstadt, Institut für Kernphysik, Schlossgartenstraße 9, 64289 Darmstadt (Germany); Kozela, A. [Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31342 Kraków (Poland)

    2013-11-07

    The Polish-German project QUEST aims at studying relativistic quantum spin correlations of the Einstein-Rosen-Podolsky-Bohm type, through measurement of the correlation function and the corresponding probabilities for relativistic electron pairs. The results will be compared to theoretical predictions obtained by us within the framework of relativistic quantum mechanics, based on assumptions regarding the form of the relativistic spin operator. Agreement or divergence will be interpreted in the context of non-uniqueness of the relativistic spin operator in quantum mechanics as well as dependence of the correlation function on the choice of observables representing the spin. Pairs of correlated electrons will originate from the Mo/ller scattering of polarized 15 MeV electrons provided by the superconducting Darmstadt electron linear accelerator S-DALINAC, TU Darmstadt, incident on a Be target. Spin projections will be determined using the Mott polarimetry technique. Measurements (starting 2013) are planned for longitudinal and transverse beam polarizations and different orientations of the beam polarization vector w.r.t. the Mo/ller scattering plane. This is the first project to study relativistic spin correlations for particles with mass.

  3. Quantum-enhanced absorption refrigerators

    CERN Document Server

    Correa, Luis A; Alonso, Daniel; Adesso, Gerardo

    2014-01-01

    Thermodynamics is a branch of science blessed by an unparalleled combination of generality of scope and formal simplicity. Based on few natural assumptions together with the four laws, it sets the boundaries between possible and impossible in macroscopic aggregates of matter. This triggered groundbreaking achievements in physics, chemistry and engineering over the last two centuries. Close analogues of those fundamental laws are now being established at the level of individual quantum systems, thus placing limits on the operation of quantum-mechanical devices. Here we study quantum absorption refrigerators, which are driven by heat rather than external work. We establish thermodynamic performance bounds for these machines and investigate their quantum origin. We also show how those bounds may be pushed beyond what is classically achievable, by suitably tailoring the environmental fluctuations via quantum reservoir engineering techniques. Such superefficient quantum-enhanced cooling realises a promising step t...

  4. Study on spectral structure of quantum remote sensing

    Institute of Scientific and Technical Information of China (English)

    BI; Siwen; HAN; Jixia

    2006-01-01

    A study of the use of fine spectral structure in quantum remote sensing, including an expression, begins with a summary of present-day applications of spectrum remote sensing, which is followed by a theoretical discussion of the influence of electronic spin upon hydrogen-like atom energy levels and the calculation of spectral line in the absence of a circumstance field.

  5. Learning with and about Advertising in Chemistry Education with a Lesson Plan on Natural Cosmetics--A Case Study

    Science.gov (United States)

    Belova, Nadja; Eilks, Ingo

    2015-01-01

    This paper describes a case study on the chemistry behind natural cosmetics in five chemistry learning groups (grades 7-11, age range 13-17) in a German comprehensive school. The lesson plan intends to promote critical media literacy in the chemistry classroom and specifically emphasizes learning with and about advertising. The lessons of four…

  6. Learning with and about Advertising in Chemistry Education with a Lesson Plan on Natural Cosmetics--A Case Study

    Science.gov (United States)

    Belova, Nadja; Eilks, Ingo

    2015-01-01

    This paper describes a case study on the chemistry behind natural cosmetics in five chemistry learning groups (grades 7-11, age range 13-17) in a German comprehensive school. The lesson plan intends to promote critical media literacy in the chemistry classroom and specifically emphasizes learning with and about advertising. The lessons of four…

  7. Thermodynamics of small alkali metal halide cluster ions: comparison of classical molecular simulations with experiment and quantum chemistry.

    Science.gov (United States)

    Vlcek, Lukas; Uhlik, Filip; Moucka, Filip; Nezbeda, Ivo; Chialvo, Ariel A

    2015-01-22

    We evaluate the ability of selected classical molecular models to describe the thermodynamic and structural aspects of gas-phase hydration of alkali metal halide ions and the formation of small water clusters. To understand the effect of many-body interactions (polarization) and charge penetration effects on the accuracy of a force field, we perform Monte Carlo simulations with three rigid water models using different functional forms to account for these effects: (i) point charge nonpolarizable SPC/E, (ii) Drude point charge polarizable SWM4-DP, and (iii) Drude Gaussian charge polarizable BK3. Model predictions are compared with experimental Gibbs free energies and enthalpies of ion hydration, and with microscopic structural properties obtained from quantum DFT calculations. We find that all three models provide comparable predictions for pure water clusters and cation hydration but differ significantly in their description of anion hydration. None of the investigated classical force fields can consistently and quantitatively reproduce the experimental gas-phase hydration thermodynamics. The outcome of this study highlights the relation between the functional form that describes the effective intermolecular interactions and the accuracy of the resulting ion hydration properties.

  8. Physical chemistry II essentials

    CERN Document Server

    REA, The Editors of

    1992-01-01

    REA's Essentials provide quick and easy access to critical information in a variety of different fields, ranging from the most basic to the most advanced. As its name implies, these concise, comprehensive study guides summarize the essentials of the field covered. Essentials are helpful when preparing for exams, doing homework and will remain a lasting reference source for students, teachers, and professionals. Physical Chemistry II includes reaction mechanisms, theoretical approaches to chemical kinetics, gravitational work, electrical and magnetic work, surface work, kinetic theory, collisional and transport properties of gases, statistical mechanics, matter and waves, quantum mechanics, and rotations and vibrations of atoms and molecules.

  9. Low temperature synthesis of silicon quantum dots with plasma chemistry control in dual frequency non-thermal plasmas.

    Science.gov (United States)

    Sahu, Bibhuti Bhusan; Yin, Yongyi; Han, Jeon Geon; Shiratani, Masaharu

    2016-06-21

    The advanced materials process by non-thermal plasmas with a high plasma density allows the synthesis of small-to-big sized Si quantum dots by combining low-temperature deposition with superior crystalline quality in the background of an amorphous hydrogenated silicon nitride matrix. Here, we make quantum dot thin films in a reactive mixture of ammonia/silane/hydrogen utilizing dual-frequency capacitively coupled plasmas with high atomic hydrogen and nitrogen radical densities. Systematic data analysis using different film and plasma characterization tools reveals that the quantum dots with different sizes exhibit size dependent film properties, which are sensitively dependent on plasma characteristics. These films exhibit intense photoluminescence in the visible range with violet to orange colors and with narrow to broad widths (∼0.3-0.9 eV). The observed luminescence behavior can come from the quantum confinement effect, quasi-direct band-to-band recombination, and variation of atomic hydrogen and nitrogen radicals in the film growth network. The high luminescence yields in the visible range of the spectrum and size-tunable low-temperature synthesis with plasma and radical control make these quantum dot films good candidates for light emitting applications.

  10. Anisotropic mechanoresponse of energetic crystallites: a quantum molecular dynamics study of nano-collision.

    Science.gov (United States)

    Li, Ying; Kalia, Rajiv K; Misawa, Masaaki; Nakano, Aiichiro; Nomura, Ken-Ichi; Shimamura, Kohei; Shimojo, Fuyuki; Vashishta, Priya

    2016-05-14

    At the nanoscale, chemistry can happen quite differently due to mechanical forces selectively breaking the chemical bonds of materials. The interaction between chemistry and mechanical forces can be classified as mechanochemistry. An example of archetypal mechanochemistry occurs at the nanoscale in anisotropic detonating of a broad class of layered energetic molecular crystals bonded by inter-layer van der Waals (vdW) interactions. Here, we introduce an ab initio study of the collision, in which quantum molecular dynamic simulations of binary collisions between energetic vdW crystallites, TATB molecules, reveal atomistic mechanisms of anisotropic shock sensitivity. The highly sensitive lateral collision was found to originate from the twisting and bending to breaking of nitro-groups mediated by strong intra-layer hydrogen bonds. This causes the closing of the electronic energy gap due to an inverse Jahn-Teller effect. On the other hand, the insensitive collisions normal to multilayers are accomplished by more delocalized molecular deformations mediated by inter-layer interactions. Our nano-collision studies provide a much needed atomistic understanding for the rational design of insensitive energetic nanomaterials and the detonation synthesis of novel nanomaterials.

  11. Relationships of approaches to studying, metacognition, and intellectual development of general chemistry students

    Science.gov (United States)

    Egenti, Henrietta N.

    This study investigated approaches to studying, intellectual developments, and metacognitive skills of general chemistry students enrolled for the spring 2011 semester at a single campus of a multi-campus community college. The three instruments used were the Approaches and Study Skills Inventory for Students (ASSIST), the Learning Environment Preferences (LEP), and the Executive Process Questionnaire (EPQ). The subjects were 138 students enrolled in either general chemistry 1 or 2. The results revealed that the preferred approach to study was the strategic approach. The intellectual development of the students was predominantly Perry's position 2 (dualist) in transition to position 3 (multiplicity). Correlation statistics revealed that deep approach to studying is related to effective employment of metacognitive skills. Students with a deep approach to studying were likely to utilize effective metacognitive skills. Students with a surface approach to studying used no metacognitive skills or ineffective metacognitive skills. Multiple logistic regression analysis was conducted to ascertain which of the three variables, namely approaches to studying, ability to metacognate, or level of intellectual development, was the most salient in predicting the success of general chemistry students. No single variable was found to predict students’ success in general chemistry classes; however, a surface approach to studying predisposes general chemistry students to fail. The implication of this study is that students’ study approaches, intellectual developments, and metacognitive skills are requisite information to enable instructional remediation early in the semester.

  12. Studies of the chemistry of transuranium elements and technetium at the Institute of Physical Chemistry, Russian Academy of Sciences, supported by the US Department of Energy

    Energy Technology Data Exchange (ETDEWEB)

    Peretrukhin, V.F. [Russian Academy of Sciences, Moscow (Russian Federation). Inst. of Physical Chemistry; Delegard, C.H. [Westinghouse Hanford Co., Richland, WA (United States)

    1995-04-01

    Studies at Hanford in the 1980s revealed the potential for actinides to form stable soluble complexes in alkaline media, simulating radioactive tank waste. Pu(IV) hydrous oxide and Pu(VI) solubility increased with hydroxide concentration, ionic strength, and aluminate/carbonate concentrations. Subsequent contacts between US and Russian researchers in 1993 led to a technical literature review of the chemistry of TRU and Tc in alkaline media; this review addresses oxidation states, solubility, speciation, redox reactions, electrochemistry, radiation chemistry, and separations in alkaline media. As an outgrowth, a program of fundamental and applied chemistry studies of TRU and Tc is being conducted at IPC/RAS with US DOE support: solubility, redox reagents, coprecipitation, and radiation chemistry. This overview provides information on the Hanford Site tank waste system, US DOE technological needs, and IPC/RAS developments.

  13. Femtosecond two-photon photoassociation of hot magnesium atoms: A quantum dynamical study using thermal random phase wavefunctions

    Energy Technology Data Exchange (ETDEWEB)

    Amaran, Saieswari; Kosloff, Ronnie [Fritz Haber Research Centre and The Department of Physical Chemistry, Hebrew University, Jerusalem 91904 (Israel); Tomza, Michał; Skomorowski, Wojciech; Pawłowski, Filip; Moszynski, Robert [Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw (Poland); Rybak, Leonid; Levin, Liat; Amitay, Zohar [The Shirlee Jacobs Femtosecond Laser Research Laboratory, Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel); Berglund, J. Martin; Reich, Daniel M.; Koch, Christiane P. [Theoretische Physik, Universität Kassel, Heinrich-Plett-Straße 40, 34132 Kassel (Germany)

    2013-10-28

    Two-photon photoassociation of hot magnesium atoms by femtosecond laser pulses, creating electronically excited magnesium dimer molecules, is studied from first principles, combining ab initio quantum chemistry and molecular quantum dynamics. This theoretical framework allows for rationalizing the generation of molecular rovibrational coherence from thermally hot atoms [L. Rybak, S. Amaran, L. Levin, M. Tomza, R. Moszynski, R. Kosloff, C. P. Koch, and Z. Amitay, Phys. Rev. Lett. 107, 273001 (2011)]. Random phase thermal wavefunctions are employed to model the thermal ensemble of hot colliding atoms. Comparing two different choices of basis functions, random phase wavefunctions built from eigenstates are found to have the fastest convergence for the photoassociation yield. The interaction of the colliding atoms with a femtosecond laser pulse is modeled non-perturbatively to account for strong-field effects.

  14. Determination of equilibrium structures of bromothymol blue revealed by using quantum chemistry with an aid of multivariate analysis of electronic absorption spectra.

    Science.gov (United States)

    Shimada, Toru; Hasegawa, Takeshi

    2017-10-05

    The pH dependent chemical structures of bromothymol blue (BTB), which have long been under controversy, are determined by employing a combined technique of multivariate analysis of electronic absorption spectra and quantum chemistry. Principle component analysis (PCA) of the pH dependent spectra apparently reveals that only two chemical species are adequate to fully account for the color changes, with which the spectral decomposition is readily performed by using augmented alternative least-squares (ALS) regression analysis. The quantity variation by the ALS analysis also reveals the practical acid dissociation constant, pKa'. The determination of pKa' is performed for various ionic strengths, which reveals the thermodynamic acid constant (pKa=7.5) and the number of charge on each chemical species; the yellow form is negatively charged species of -1 and the blue form that of -2. On this chemical information, the quantum chemical calculation is carried out to find that BTB molecules take the pure quinoid form in an acid solution and the quinoid-phenolate form in an alkaline solution. The time-dependent density functional theory (TD-DFT) calculations for the theoretically determined chemical structures account for the peak shift of the electronic spectra. In this manner, the structures of all the chemical species appeared in equilibrium have finally been confirmed. Copyright © 2017 Elsevier B.V. All rights reserved.

  15. Determination of equilibrium structures of bromothymol blue revealed by using quantum chemistry with an aid of multivariate analysis of electronic absorption spectra

    Science.gov (United States)

    Shimada, Toru; Hasegawa, Takeshi

    2017-10-01

    The pH dependent chemical structures of bromothymol blue (BTB), which have long been under controversy, are determined by employing a combined technique of multivariate analysis of electronic absorption spectra and quantum chemistry. Principle component analysis (PCA) of the pH dependent spectra apparently reveals that only two chemical species are adequate to fully account for the color changes, with which the spectral decomposition is readily performed by using augmented alternative least-squares (ALS) regression analysis. The quantity variation by the ALS analysis also reveals the practical acid dissociation constant, pKa‧. The determination of pKa‧ is performed for various ionic strengths, which reveals the thermodynamic acid constant (pKa = 7.5) and the number of charge on each chemical species; the yellow form is negatively charged species of - 1 and the blue form that of - 2. On this chemical information, the quantum chemical calculation is carried out to find that BTB molecules take the pure quinoid form in an acid solution and the quinoid-phenolate form in an alkaline solution. The time-dependent density functional theory (TD-DFT) calculations for the theoretically determined chemical structures account for the peak shift of the electronic spectra. In this manner, the structures of all the chemical species appeared in equilibrium have finally been confirmed.

  16. Stability of gas-phase tartaric acid anions investigated by quantum chemistry, mass spectrometry, and infrared spectroscopy.

    Science.gov (United States)

    Tonner, Ralf; Schwerdtfeger, Peter; May, Amanda L; Steill, Jeffrey D; Berden, Giel; Oomens, Jos; Campagna, Shawn R; Compton, Robert N

    2012-05-17

    In an effort to understand the chemical factors that stabilize dianions, experimental and theoretical studies on the stability of the tartrate dianion were performed. Quantum chemical calculations at the coupled cluster level reveal only a metastable state with a possible decomposition pathway (O(2)C-CH(OH)-CH(OH)-CO(2))(2-) → (O(2)C-CH(OH)-CH(OH))(•-) + CO(2) + e(-) explaining the observed gas-phase instability of this dianion. Further theoretical data were collected for the bare dianion, this molecule complexed to water, sodium, and a proton, in both the meso and l forms as well as for the uncomplexed radical anion and neutral diradical. The calculations suggest that the l-tartrate dianion is more thermodynamically stable than the dianion of the meso stereoisomer and that either dianion can be further stabilized by association with a separate species that can help to balance the charge of the molecular complex. Mass spectrometry was then used to measure the energy needed to initiate collisionally induced dissociation of the racemic tartrate dianion and for the proton and sodium adducts of both the racemic and meso form of this molecule. Infrared action spectra of the dianion stereoisomers complexed with sodium were also acquired to determine the influence of the metal ion on the vibrations of the dianions and validate the computationally predicted structures. These experimental data support the theoretical conclusions and highlight the instability of the bare tartrate dianion. From the experimental work, it could also be concluded that the pathway leading to dissociation is under kinetic control because the sodium adduct of the racemic stereoisomer dissociated at lower collisional energy, although it was calculated to be more stable, and that decomposition proceeded via C-C bond dissociation as computationally predicted. Taken together, these data provide insight into the gas-phase stability of the tartrate dianion and highlight the role of adducts in

  17. Compiling Planning into Quantum Optimization Problems: A Comparative Study

    Science.gov (United States)

    2015-06-07

    become available: quantum annealing. Quantum annealing is one of the most accessible quantum algorithms for a computer sci- ence audience not versed...in quantum computing because of its close ties to classical optimization algorithms such as simulated annealing. While large-scale universal quantum ...devices designed to run only this type of quantum algorithm . Other types of quan- tum algorithms are known that take on quite a different form, and are

  18. Exploring Do-It-Yourself Approaches in Computational Quantum Chemistry: The Pedagogical Benefits of the Classical Boys Algorithm

    Science.gov (United States)

    Orsini, Gabriele

    2015-01-01

    The ever-increasing impact of molecular quantum calculations over chemical sciences implies a strong and urgent need for the elaboration of proper teaching strategies in university curricula. In such perspective, this paper proposes an extensive project for a student-driven, cooperative, from-scratch implementation of a general Hartree-Fock…

  19. A gist of comprehensive review of hadronic chemistry and its applications

    Energy Technology Data Exchange (ETDEWEB)

    Tangde, Vijay M. [Post Graduate Teaching Department of Chemistry, Rashtrasant Tukadoji Maharaj Nagpur University, Amravati Road Campus, NAGPUR - 440 033, India, Email: vijaytn6@gmail.com (India)

    2015-03-10

    20{sup th} century theories of Quantum Mechanics and Quantum Chemistry are exactly valid only when considered to represent the atomic structures. While considering the more general aspects of atomic combinations these theories fail to explain all the related experimental data from first unadulterated axiomatic principles. According to Quantum Chemistry two valence electrons should repel each other and as such there is no mathematical representation of a strong attractive forces between such valence electrons. In view of these and other insufficiencies of Quantum Chemistry, an Italian-American Scientist Professor Ruggero Maria Santilli during his more than five decades of dedicated and sustained research has denounced the fact that quantum chemistry is mostly based on mere nomenclatures. Professor R M Santilli first formulated the iso-, geno- and hyper- mathematics [1, 2, 3, 4] that helped in understanding numerous diversified problems and removing inadequacies in most of the established and celebrated theories of 20th century physics and chemistry. This involves the isotopic, genotopic, etc. lifting of Lie algebra that generated Lie admissible mathematics to properly describe irreversible processes. The studies on Hadronic Mechanics in general and chemistry in particular based on Santilli’s mathematics[3, 4, 5] for the first time has removed the very fundamental limitations of quantum chemistry [2, 6, 7, 8]. In the present discussion, a comprehensive review of Hadronic Chemistry is presented that imparts the completeness to the Quantum Chemistry via an addition of effects at distances of the order of 1 fm (only) which are assumed to be Non-linear, Non-local, Non-potential, Non-hamiltonian and thus Non-unitary, stepwise successes of Hadronic Chemistry and its application in development of a new chemical species called Magnecules.

  20. Some double resonance and multiple quantum NMR studies in solids

    Energy Technology Data Exchange (ETDEWEB)

    Wemmer, D.E.

    1978-08-01

    The first section of this work presents the theory and experimental applications to analysis of molecular motion of chemical shielding lineshapes obtained with high resolution double resonance NMR techniques. Analysis of /sup 13/C powder lineshapes in hexamethylbenzene (HMB) and decamethylferrocene (DMFe) show that these molecules reorient in a jumping manner about the symmetry axis. Analysis of proton chemical shielding lineshapes of residual protons in heavy ice (D/sub 2/O) show that protons are exchanged among the tetrahedral positions of neighboring oxygen atoms, consistent with motion expected from defect migration. The second section describes the application of Fourier Transform Double Quantum NMR to measurement of chemical shielding of deuterium in powder samples. Studies of partially deuterated benzene and ferrocene give equal shielding anisotropies, ..delta..sigma = -6.5 ppM. Theoretical predictions and experimental measurements of dipolar couplings between deuterons using FTDQ NMR are presented. Crystals of BaClO/sub 3/.D/sub 2/O, ..cap alpha..,..beta.. d-2 HMB and ..cap alpha..,..beta..,..gamma.. d-3 HMB were studied, as were powders of d-2 HMB and anisic acid. The third section discusses general multiple quantum spectroscopy in dipolar coupled spin systems. Theoretical description is made for creation and detection of coherences between states without quantum number selection rules ..delta..m = +-1. Descriptions of techniques for partial selectivity of order in preparation and detection of multiple quantum coherences are made. The effects on selectivity and resolution of echo pulses during multiple quantum experiments are discussed. Experimental observation of coherences up to order 6 have been made in a sample of benzene dissolved in a liquid crystal. Experimental verifications of order selection and echo generation have been made.

  1. From Cathode Rays To Alpha Particles To Quantum of Action: A Rational Reconstruction of Structure of the Atom and Its Implications for Chemistry Textbooks.

    Science.gov (United States)

    Niaz, Mansoor

    1998-01-01

    Reports on a study that involves the analysis of chemistry textbooks at the college freshman level to determine the degree to which they address developments in the history and philosophy of science. Twenty-three textbooks were evaluated on eight criteria. Contains 108 references. (DDR)

  2. Quantum chromodynamics studies at LEP2

    Indian Academy of Sciences (India)

    Sunanda Banerjee

    2000-07-01

    Several studies have been made to the hadronic final states in +- collisions at LEP. Studies of the annihilation process at LEP2 have given rise to results on jet rate, event shape, heavy flavour production, inclusive momentum spectra, Bose–Einstein correlation and colour reconnection effects. Event shape studies have given rise to accurate determination of the strong coupling constant s using $\\mathcal{O}(^{2}_{s})$ with resummed leading and next-to-leading log calculation and also with power law corrections. Studies of 2-photon processes have yielded results on cross-section, heavy flavour production, photon structure function and ** scattering.

  3. Gapless modes of fractional quantum Hall edges: a Hamiltonian study

    Science.gov (United States)

    Nguyen, Hoang; Joglekar, Yogesh; Murthy, Ganpathy

    2004-03-01

    We study the collective modes of the fractional quantum Hall edge states using the Hamiltonian formalism [1]. In this theory, the composite fermions are fully interacting; the collective modes are obtained within a conserving approximation which respects the constraints [2]. We present the gapless edge-mode dispersions at 1/3 and 2/5 filling fractions of unreconstructed and reconstructed edges. The dispersions are found to be nonlinear due to the variation of the effective magnetic field on the composite fermions. The implications of our study to the tunneling experiments into the edge of a fractional quantum Hall system [3] are discussed*. 1. R. Shankar and G. Murthy, Phys. Rev. Lett. 79, 4437 (1997). 2. G. Murthy, Phys. Rev. B 64, 195310 (2001). 3. A.M.Chang et. al., Phys. Rev. Lett. 86, 143 (2000). * Work supported by the NSF, Grant number DMR 031176.

  4. Quantum-chemical studies of metal oxides for photoelectrochemical applications

    Science.gov (United States)

    Persson, P.; Bergström, R.; Ojamäe, L.; Lunell, S.

    A review of recent research, as well as new results, are presented on transition metal oxide clusters, surfaces, and crystals. Quantum-chemical calculations of clusters of first row transition metal oxides have been made to evaluate the accuracy of ab initio and density functional calculations. Adsorbates on metal oxide surfaces have been studied with both ab initio and semi-empirical methods, and results are presented for the bonding and electronic interactions of large organic adsorbates, e.g. aromatic molecules, on Ti02 and ZnO. Defects and intercalation, notably of H, Li, and Na in Ti02 have been investigated theoretically. Comparisons with experiments are made throughout to validate the calculations. Finally, the role of quantum-chemical calculations in the study of metal oxide based photoelectrochemical devices, such as dyesensitized solar cells and electrochromic displays. is discussed.

  5. DNA-METAFECTENE PRO complexation: a physical chemistry study.

    Science.gov (United States)

    Alatorre-Meda, Manuel; González-Pérez, Alfredo; Rodríguez, Julio R

    2010-07-21

    Complexes formed between cationic liposomes and DNA (also known as lipoplexes or genosomes) have proven, for years now, to be a suitable option for gene delivery to cells, transfection, however, some aspects regarding the liposome-DNA interaction mechanism and complex stability remain still unclear. This work aims to improve the understanding of the poorly defined mechanisms and structural conformation associated with the interaction of METAFECTENE PRO (MEP), a commercial liposomal transfection reagent, with poly-anion DNA at mass ratios around the mass ratio recommended for transfection (L/D congruent with 700). A physical chemistry characterization was conducted at a pH of 6.5 and at a temperature of 25 degrees C by means of dynamic light scattering (DLS), electrophoretic mobility (zeta-potential), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Five parameters important for transfection were determined for the lipoplexes: (i) the hydrodynamic radius, R(H), (ii) the stability with time, (iii) the mass ratio of at which both moieties start to interact, (L/D)(i), (iv) the overall charge, and (v) the morphology. Results in ensemble point to a "beads on a string" conformation, with the lipoplex formation occurring well below isoneutrality from (L/D)(i) congruent with 600. The lipoplexes were found to be stable within at least seven days presenting an average R(H) of 135 nm.

  6. Theoretical study of quantum confined Stark shift in InAs/GaAs quantum dots

    Institute of Scientific and Technical Information of China (English)

    Guo Ru-Hai; Shi Hong-Yan; Sun Xiu-Dong

    2004-01-01

    The quantum confined Stark effect (QCSE) of the self-assembled InAs/GaAs quantum dots has been investigated theoretically. The ground-state transition energies for quantum dots in the shape of a cube, pyramid or "truncated pyramid" are calculated and analysed. We use a method based on the Green function technique for calculating the strain in quantum dots and an efficient plane-wave envelope-function technique to determine the ground-state electronic structure of them with different shapes. The symmetry of quantum dots is broken by the effect of strain. So the properties of carriers show different behaviours from the traditional quantum device. Based on these results, we also calculate permanent built-in dipole moments and compare them with recent experimental data. Our results demonstrate that the measured Stark effect in self-assembled InAs/GaAs quantum dot structures can be explained by including linear grading.

  7. Do quantum strategies always win? A case study in the entangled quantum penny flip game

    CERN Document Server

    Anand, Namit

    2014-01-01

    In a seminal paper, Meyer\\cite{Meyer} described the advantages of quantum game theory by looking at the classical penny flip game. A player using quantum strategy can win against a classical player almost 100% of the time. Here we make a slight modification of the quantum game in which the two players share an entangled state to begin with. We then analyse two different scenarios one in which the quantum player makes unitary transformations to her qubit while classical player uses a pure strategy of either flipping or not flipping the state of his qubit. In the second scenario we have the quantum player making similar unitary transformations while the classical player makes use of a mixed strategy wherein he either flips or not with some probability "p". We show that in the second scenario 100% win record of a quantum player is drastically reduced and for a particular probability "p" the classical player may even win against the quantum player.

  8. Study and modeling of finite rate chemistry effects in turbulent non-premixed flames

    Science.gov (United States)

    Vervisch, Luc

    1993-01-01

    The development of numerical models that reflect some of the most important features of turbulent reacting flows requires information about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between turbulent and chemical processes is so strong that it is extremely difficult to isolate the role played by one individual physical phenomenon. Direct numerical simulation (hereafter DNS) allows us to study in detail the turbulence-chemistry interaction in some restricted but completely defined situations. Globally, non-premixed flames are controlled by two limiting regimes: the fast chemistry case, where the turbulent flame can be pictured as a random distribution of local chemical equilibrium problems; and the slow chemistry case, where the chemistry integrates in time the turbulent fluctuations. The Damkoehler number, ratio of a mechanical time scale to chemical time scale, is used to distinguish between these regimes. Today most of the industrial computer codes are able to perform predictions in the hypothesis of local equilibrium chemistry using a presumed shape for the probability density function (pdt) of the conserved scalar. However, the finite rate chemistry situation is of great interest because industrial burners usually generate regimes in which, at some points, the flame is undergoing local extinction or at least non-equilibrium situations. Moreover, this variety of situations strongly influences the production of pollutants. To quantify finite rate chemistry effect, the interaction between a non-premixed flame and a free decaying turbulence is studied using DNS. The attention is focused on the dynamic of extinction, and an attempt is made to quantify the effect of the reaction on the small scale mixing process. The unequal diffusivity effect is also addressed. Finally, a simple turbulent combustion model based on the DNS observations and tractable in real flow configurations is proposed.

  9. Quantum dot density studies for quantum dot intermediate band solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Thomassen, Sedsel Fretheim; Zhou, Dayong; Vitelli, Stefano; Mayani, Maryam Gholami; Fimland, Bjoern-Ove; Reenaas, Turid Worren

    2010-07-01

    Quantum dots (QDs) have been an active area of research for many years and have been implemented in several applications, such as lasers and detectors. During the last years, some attempts have been made to increase the absorption and efficiency of solar cells by inserting QDs into the intrinsic region of pin solar cells. So far, these attempts have been successful in increasing the absorption, but not the cell efficiency. There are probably several reasons for this lack of efficiency increase, but we believe that one important reason is the low density of the implemented QDs. In this work, samples of single layer InAs QDs on n-GaAs(001) substrates have been grown by molecular beam epitaxy (MBE) and we have performed a systematic study of how deposition parameters affect the QD density. The aim is to achieve densities > 1011 cm-2. The nominal substrate temperature (360 - 500 deg. C), the InAs growth rate (0.085 - 1 ML/s) and thickness (2.0 - 2.8 ML) have been varied in a systematic way for two different deposition methods of InAs, i.e. continuous deposition or deposition with interruptions. In addition, we have for the continuous growth samples also varied the As-flux (0.5 - 6 centre dot10-6 torr). Scanning electron microscopy (SEM) has been the main characterization method to determine quantum dot sizes and densities, and atomic force microscopy (AFM) has been used for evaluation of the quantum dot heights. We find that the QD density increases with reduced growth temperature and that it is higher for samples grown continuously than for samples grown with growth interruptions. The homogeneity is also strongly affected by temperature, InAs deposition method and the As-flux. We have observed QD densities as high as 2.5 centre dot1011 cm-2 for the samples grown at the lowest growth temperatures. (Author)

  10. Numerical studies of entangled PPT states in composite quantum systems

    CERN Document Server

    Leinaas, Jon Magne; Sollid, Per Oyvind

    2010-01-01

    We report here on the results of numerical searches for PPT states with specified ranks for density matrices and their partial transpose. The study includes several bipartite quantum systems of low dimensions. For a series of ranks extremal PPT states are found. The results are listed in tables and charted in diagrams. Comparison of the results for systems of different dimensions reveal several regularities. We discuss lower and upper bounds on the ranks of extremal PPT states.

  11. Lifetime statistics of quantum chaos studied by a multiscale analysis

    KAUST Repository

    Di Falco, A.

    2012-04-30

    In a series of pump and probe experiments, we study the lifetime statistics of a quantum chaotic resonator when the number of open channels is greater than one. Our design embeds a stadium billiard into a two dimensional photonic crystal realized on a silicon-on-insulator substrate. We calculate resonances through a multiscale procedure that combines energy landscape analysis and wavelet transforms. Experimental data is found to follow the universal predictions arising from random matrix theory with an excellent level of agreement.

  12. Quantum Monte Carlo Study of Random Antiferromagnetic Heisenberg Chain

    OpenAIRE

    Todo, Synge; Kato, Kiyoshi; Takayama, Hajime

    1998-01-01

    Effects of randomness on the spin-1/2 and 1 antiferromagnetic Heisenberg chains are studied using the quantum Monte Carlo method with the continuous-time loop algorithm. We precisely calculated the uniform susceptibility, string order parameter, spatial and temporal correlation length, and the dynamical exponent, and obtained a phase diagram. The generalization of the continuous-time loop algorithm for the systems with higher-S spins is also presented.

  13. Comparative study of quantum anharmonic potentials

    Energy Technology Data Exchange (ETDEWEB)

    Amore, Paolo [Facultad de Ciencias, Universidad de Colima, Bernal Diaz del Castillo 340, Colima (Mexico)]. E-mail: paolo@ucol.mx; Aranda, Alfredo [Facultad de Ciencias, Universidad de Colima, Bernal Diaz del Castillo 340, Colima (Mexico); De Pace, Arturo [Istituto Nazionale di Fisica Nucleare, Sezione di Torino, via P. Giuria 1, I-10125 Torino (Italy); Lopez, Jorge A. [Physics Department, University of Texas at El Paso, El Paso, TX (United States)

    2004-09-06

    We perform a study of various anharmonic potentials using a recently developed method. We calculate both the wave functions and the energy eigenvalues for the ground and first excited states of the quartic, sextic and octic potentials with high precision, comparing the results with other techniques available in the literature.

  14. Relationships of Approaches to Studying, Metacognition, and Intellectual Development of General Chemistry Students

    Science.gov (United States)

    Egenti, Henrietta N.

    2012-01-01

    This study investigated approaches to studying, intellectual developments, and metacognitive skills of general chemistry students enrolled for the spring 2011 semester at a single campus of a multi-campus community college. The three instruments used were the Approaches and Study Skills Inventory for Students (ASSIST), the Learning Environment…

  15. Relationships of Approaches to Studying, Metacognition, and Intellectual Development of General Chemistry Students

    Science.gov (United States)

    Egenti, Henrietta N.

    2012-01-01

    This study investigated approaches to studying, intellectual developments, and metacognitive skills of general chemistry students enrolled for the spring 2011 semester at a single campus of a multi-campus community college. The three instruments used were the Approaches and Study Skills Inventory for Students (ASSIST), the Learning Environment…

  16. Content-Related Interactions and Methods of Reasoning within Self-Initiated Organic Chemistry Study Groups

    Science.gov (United States)

    Christian, Karen Jeanne

    2011-01-01

    Students often use study groups to prepare for class or exams; yet to date, we know very little about how these groups actually function. This study looked at the ways in which undergraduate organic chemistry students prepared for exams through self-initiated study groups. We sought to characterize the methods of social regulation, levels of…

  17. Quantum simulations with ultracold atoms in optical lattices.

    Science.gov (United States)

    Gross, Christian; Bloch, Immanuel

    2017-09-08

    Quantum simulation, a subdiscipline of quantum computation, can provide valuable insight into difficult quantum problems in physics or chemistry. Ultracold atoms in optical lattices represent an ideal platform for simulations of quantum many-body problems. Within this setting, quantum gas microscopes enable single atom observation and manipulation in large samples. Ultracold atom-based quantum simulators have already been used to probe quantum magnetism, to realize and detect topological quantum matter, and to study quantum systems with controlled long-range interactions. Experiments on many-body systems out of equilibrium have also provided results in regimes unavailable to the most advanced supercomputers. We review recent experimental progress in this field and comment on future directions. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  18. New frontiers for quantum gases of polar molecules

    Science.gov (United States)

    Moses, Steven A.; Covey, Jacob P.; Miecnikowski, Matthew T.; Jin, Deborah S.; Ye, Jun

    2017-01-01

    Compared to atoms, molecules possess additional degrees of freedom that can be exploited in fundamental tests, ultracold chemistry, and engineering new quantum phases in many-body systems. Here, we review the recent progress in creating and manipulating ultracold bialkali molecules to study quantum gases of polar molecules.

  19. Indirect Controllability of Quantum Systems; A Study of Two Interacting Quantum Bits

    CERN Document Server

    D'Alessandro, Domenico

    2012-01-01

    A quantum mechanical system S is indirectly controlled when the control affects an ancillary system A and the evolution of S is modified through the interaction with A only. A study of indirect controllability gives a description of the set of states that can be obtained for S with this scheme. In this paper, we study the indirect controllability of quantum systems in the finite dimensional case. After discussing the relevant definitions, we give a general necessary condition for controllability in Lie algebraic terms. We present a detailed treatment of the case where both systems, S and A, are two-dimensional (qubits). In particular, we characterize the dynamical Lie algebra associated with S+A, extending previous results, and prove that complete controllability of S+A and an appropriate notion of indirect controllability are equivalent properties for this system. We also prove several further indirect controllability properties for the system of two qubits, and illustrate the role of the Lie algebraic analy...

  20. Studying Quantum Phase-Based Electronic Devices

    Science.gov (United States)

    1990-08-15

    variety of different III-V material configurations, (4) and treat transient transport in silicon and germanium heterostructures. It is capable of studying...nonuniform field distribution may prevent the appearance of NDR . TRANSPORT IN ULTRA-SUBMICRON DEVICES The entire discussion of transport has been predicated...differential resistance. Indeed, the calculations .ugpt that it is the significantly reduced velocity at resonance that is resjponsible for NDR . The low

  1. The quantum gamble

    CERN Document Server

    Boeyens, Jan C A

    2016-01-01

    This volume, written by a highly cited author, presents the history of quantum theory together with open questions and remaining problems in terms of the plausibility of quantum chemistry and physics. It also provides insights into the theory of matter-wave mechanics. The content is aimed at students and lecturers in chemistry, physics and the philosophy of science.

  2. Quantum Blobs

    OpenAIRE

    Gosson, Maurice A. de

    2012-01-01

    Quantum blobs are the smallest phase space units of phase space compatible with the uncertainty principle of quantum mechanics and having the symplectic group as group of symmetries. Quantum blobs are in a bijective correspondence with the squeezed coherent states from standard quantum mechanics, of which they are a phase space picture. This allows us to propose a substitute for phase space in quantum mechanics. We study the relationship between quantum blobs with a certain class of level set...

  3. Quantum chemistry and relativity: exploring the physical and chemical properties of the complexes of heavy elements; Chimie quantique et relativite. Exploration des proprietes physiques et chimiques des complexes d'atomes lourds

    Energy Technology Data Exchange (ETDEWEB)

    Vallet, V. [Munich Univ., Institute for Theoretical Chemistry, Technical (Germany)

    2003-01-01

    Molecular and nano-molecular systems containing rare earth and actinides elements have extraordinary chemical and physical properties. Computer simulations using quantum chemistry methods can play an important role in many investigative procedures and provide help in understanding the microscopic nature of the interactions governing these macroscopic properties. The recent theoretical efforts have been devoted to the development of accurate and efficient methods that take into account all important interactions influencing the electronic structures, such as electron correlation and relativity. In particular, we illustrate the importance of relativity on chemical and spectroscopic properties. We will then focus on the modelling aspects of solution chemistry. (author)

  4. A Study of Faculty Approaches to Teaching Undergraduate Physical Chemistry Courses

    Science.gov (United States)

    Mack, Michael Ryan

    Chemistry education researchers have not adequately studied teaching and learning experiences at all levels in the undergraduate chemistry curriculum leaving gaps in discipline-based STEM education communities understanding about how the upper- division curricula works (National Research Council, 2012b; Towns, 2013). This study explored faculty approaches to teaching in upper-division physical chemistry course settings using an interview-based methodology. Two conceptualizations of approaches to teaching emerged from a phenomenographic analysis of interview transcripts: (1) faculty beliefs about the purposes for teaching physical chemistry and (2) their conceptions of their role as an instructor in these course settings. Faculty who reported beliefs predominantly centered on helping students develop conceptual knowledge and problem-solving skills in physical chemistry often worked with didactic models of teaching, which emphasized the transfer of expert knowledge to students. When faculty expressed beliefs that were more inclusive of conceptual, epistemic, and social learning goals in science education they often described more student-centered models of teaching and learning, which put more responsibilities on them to facilitate students' interactive engagement with the material and peers during regularly scheduled class time. Knowledge of faculty thinking, as evinced in a rich description of their accounts of their experience, provides researchers and professional developers with useful information about the potential opportunities or barriers that exist for helping faculty align their beliefs and goals for teaching with research-based instructional strategies.

  5. Rigorous ab initio quantum embedding for quantum chemistry using Green's function theory: screened interaction, non-local self-energy relaxation, orbital basis, and chemical accuracy

    CERN Document Server

    Lan, Tran Nguyen; Zgid, Dominika

    2016-01-01

    We present a detailed discussion of self-energy embedding theory (SEET) which is a quantum embedding scheme allowing us to describe a chosen subsystem very accurately while keeping the description of the environment at a lower cost. We apply SEET to molecular examples where commonly our chosen subsystem is made out of a set of strongly correlated orbitals while the weakly correlated orbitals constitute an environment. Such a self-energy separation is very general and to make this procedure applicable to multiple systems a detailed and practical procedure for the evaluation of the system and environment self-energy is necessary. We list all the intricacies for one of the possible procedures while focusing our discussion on many practical implementation aspects such as the choice of best orbital basis, impurity solver, and many steps necessary to reach chemical accuracy. Finally, on a set of carefully chosen molecular examples, we demonstrate that SEET which is a controlled, systematically improvable Green's fu...

  6. Conceptual versus Algorithmic Learning in High School Chemistry: The Case of Basic Quantum Chemical Concepts--Part 2. Students' Common Errors, Misconceptions and Difficulties in Understanding

    Science.gov (United States)

    Papaphotis, Georgios; Tsaparlis, Georgios

    2008-01-01

    Part 2 of the findings are presented of a quantitative study (n = 125) on basic quantum chemical concepts taught at twelfth grade (age 17-18 years) in Greece. A paper-and-pencil test of fourteen questions was used that were of two kinds: five questions that tested recall of knowledge or application of algorithmic procedures (type-A questions);…

  7. Aplicação da química quântica computacional no estudo de processos químicos envolvidos em espectrometria de massas Application of computational quantum chemistry to chemical processes involved in mass spectrometry

    Directory of Open Access Journals (Sweden)

    Ricardo Vessecchi

    2008-01-01

    Full Text Available The field of application of mass spectrometry (MS has increased considerably due to the development of ionization techniques. Other factors that have stimulated the use of MS are the tandem mass spectrometry (MS/MS and sequential mass spectrometry (MSn techniques. However, the interpretation of the MS/MS and MSn data may lead to speculative conclusions. Thus, various quantum chemical methods have been applied for obtaining high quality thermochemical data in gas phase. In this review, we show some applications of computational quantum chemistry to understand the formation and fragmentation of gaseous ions of organic compounds in a MS analysis.

  8. Textbook-Bundled Metacognitive Tools: A Study of LearnSmart's Efficacy in General Chemistry

    Science.gov (United States)

    Thadani, Vandana; Bouvier-Brown, Nicole C.

    2016-01-01

    College textbook publishers increasingly bundle sophisticated technology-based study tools with their texts. These tools appear promising, but empirical work on their efficacy is needed. We examined whether LearnSmart, a study tool bundled with McGraw-Hill's textbook "Chemistry" (Chang & Goldsby, 2013), improved learning in an…

  9. Case studies on sugar production from underutilized woody biomass using sulfite chemistry

    Science.gov (United States)

    J.Y. Zhu; M. Subhosh Chandra; Roland Gleisner; William Gilles; Johnway Gao; Gevan Marrs; Dwight Anderson; John Sessions

    2015-01-01

    We examined two case studies to demonstrate the advantages of sulfite chemistry for pretreating underutilized woody biomass to produce sugars through enzymatic saccharification. In the first case study, we evaluated knot rejects from a magnesium-basedsulfite mill for direct enzymatic sugar production.We found that the sulfite mill rejects are an excellent feedstock for...

  10. A SWOT Analysis of Male and Female Students' Performance in Chemistry: A Comparative Study

    Science.gov (United States)

    Ezeudu, Florence O.; Chiaha, Gertrude-Theresa Uzoamaka; Anazor, Lynda Chioma; Eze, Justina Uzoamaka; Omeke, Faith Chinwe

    2015-01-01

    The purpose of this study was to do a SWOT analysis and compare performances of male and female students in chemistry. Four research questions and four null hypotheses guided the study. Two boys', two girls' and two coeducational schools involving 1319 males and 1831 females, were selected by a stratified, deliberate sampling technique. A…

  11. Textbook-Bundled Metacognitive Tools: A Study of LearnSmart's Efficacy in General Chemistry

    Science.gov (United States)

    Thadani, Vandana; Bouvier-Brown, Nicole C.

    2016-01-01

    College textbook publishers increasingly bundle sophisticated technology-based study tools with their texts. These tools appear promising, but empirical work on their efficacy is needed. We examined whether LearnSmart, a study tool bundled with McGraw-Hill's textbook "Chemistry" (Chang & Goldsby, 2013), improved learning in an…

  12. Far-infrared study of tracers of oxygen chemistry in diffuse clouds

    CERN Document Server

    Wiesemeyer, H; Heyminck, S; Hübers, H W; Menten, K M; Neufeld, D A; Richter, H; Simon, R; Stutzki, J; Winkel, B; Wyrowski, F

    2016-01-01

    Context. The chemistry of the diffuse interstellar medium rests upon three pillars: exothermic ion-neutral reactions (" cold chemistry "), endothermic neutral-neutral reactions with significant activation barriers (" warm chemistry "), and reactions on the surfaces of dust grains. While warm chemistry becomes important in the shocks associated with turbulent dissipation regions, the main path for the formation of interstellar OH and H2O is that of cold chemistry. Aims. The aim of this study is to observationally confirm the association of atomic oxygen with both atomic and molecular gas phases, and to understand the measured abundances of OH and OH + as a function of the available reservoir of H2. Methods. We obtained absorption spectra of the ground states of OH, OH+ and OI with high-velocity resolution, with GREAT on-board SOFIA, and with the THz receiver at the APEX. We analyzed them along with ancillary spectra of HF and CH from HIFI. To deconvolve them from the hyperfine structure and to separate the ble...

  13. Accelerating resolution-of-the-identity second-order Møller-Plesset quantum chemistry calculations with graphical processing units.

    Science.gov (United States)

    Vogt, Leslie; Olivares-Amaya, Roberto; Kermes, Sean; Shao, Yihan; Amador-Bedolla, Carlos; Aspuru-Guzik, Alan

    2008-03-13

    The modification of a general purpose code for quantum mechanical calculations of molecular properties (Q-Chem) to use a graphical processing unit (GPU) is reported. A 4.3x speedup of the resolution-of-the-identity second-order Møller-Plesset perturbation theory (RI-MP2) execution time is observed in single point energy calculations of linear alkanes. The code modification is accomplished using the compute unified basic linear algebra subprograms (CUBLAS) library for an NVIDIA Quadro FX 5600 graphics card. Furthermore, speedups of other matrix algebra based electronic structure calculations are anticipated as a result of using a similar approach.

  14. Quantum physics for beginners

    CERN Document Server

    Ficek, Zbigniew

    2016-01-01

    The textbook introduces students to the main ideas of quantum physics and the basic mathematical methods and techniques used in the fields of advanced quantum physics, atomic physics, laser physics, nanotechnology, quantum chemistry, and theoretical mathematics. The textbook explains how microscopic objects (particles) behave in unusual ways, giving rise to what's called quantum effects. It contains a wide range of tutorial problems from simple confidence-builders to fairly challenging exercises that provide adequate understanding of the basic concepts of quantum physics.

  15. Study of quantum correlation swapping with relative entropy methods

    Science.gov (United States)

    Xie, Chuanmei; Liu, Yimin; Chen, Jianlan; Zhang, Zhanjun

    2016-02-01

    To generate long-distance shared quantum correlations (QCs) for information processing in future quantum networks, recently we proposed the concept of QC repeater and its kernel technique named QC swapping. Besides, we extensively studied the QC swapping between two simple QC resources (i.e., a pair of Werner states) with four different methods to quantify QCs (Xie et al. in Quantum Inf Process 14:653-679, 2015). In this paper, we continue to treat the same issue by employing other three different methods associated with relative entropies, i.e., the MPSVW method (Modi et al. in Phys Rev Lett 104:080501, 2010), the Zhang method (arXiv:1011.4333 [quant-ph]) and the RS method (Rulli and Sarandy in Phys Rev A 84:042109, 2011). We first derive analytic expressions of all QCs which occur during the swapping process and then reveal their properties about monotonicity and threshold. Importantly, we find that a long-distance shared QC can be generated from two short-distance ones via QC swapping indeed. In addition, we simply compare our present results with our previous ones.

  16. Kinetics and Product Channels in Combustion Chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Hershberger, John F. [North Dakota State Univ., Fargo, ND (United States)

    2017-02-28

    We report study of the chemical kinetics and/or photochemistry of several chemical reactions of potential interest in understanding the gas phase combustion chemistry of nitrogen-containing molecules. Studies completed during the final grant period include determination of quantum yields of the photolysis of HCNO, fulminic acid, a kinetics and product channel study of the reaction of CN radicals with methyl bromide, and study of the products of the reaction of hydroxymethyl radical with nitric oxide.

  17. Chemistry in plumes of high-flying aircraft with H2 combustion engines: a modelling study

    Directory of Open Access Journals (Sweden)

    G. Weibring

    Full Text Available Recent discussions on high-speed civil transport (HSCT systems have renewed the interest in the chemistry of supersonic-aircraft plumes. The engines of these aircraft emit large concentrations of radicals like O, H, OH, and NO. In order to study the effect of these species on the composition of the atmosphere, the detailed chemistry of an expanding and cooling plume is examined for different expansion models.

    For a representative flight at 26 km the computed trace gas concentrations do not differ significantly for different models of the expansion behaviour. However, it is shown that the distributions predicted by all these models differ significantly from those adopted in conventional meso-scale and global models in which the plume chemistry is not treated in detail. This applies in particular to the reservoir species HONO and H2O2.

  18. Cluster Chemistry

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    @@ Cansisting of eight scientists from the State Key Laboratory of Physical Chemistry of Solid Surfaces and Xiamen University, this creative research group is devoted to the research of cluster chemistry and creation of nanomaterials.After three-year hard work, the group scored a series of encouraging progresses in synthesis of clusters with special structures, including novel fullerenes, fullerene-like metal cluster compounds as well as other related nanomaterials, and their properties study.

  19. Quantum Chemical Study on Reaction of Acetaldehyde with Hydroxyl Radical

    Institute of Scientific and Technical Information of China (English)

    LI,Ming(李明); ZHANG,Jin-Sheng(张金生); SHEN,Wei(申伟); MENG,Qing-Xi(孟庆喜)

    2004-01-01

    The reaction of acetaldehyde with hydroxyl radical was studied by means of quantum chemical methods. The geometries for all the stationary points on the potential energy surfaces were optimized fully, respectively, at the G3MP2, G3, and MP2/6-311++G(d,p) levels. Single-point energies of all the species were calculated at the QCISD/6-311 + +G(d,p) level. The mechanism of the reaction studied was confirmed. The predicted product is acetyl radical that is in agreement with the experiment.

  20. Toxicological studies of semiconductor quantum dots on immune cells.

    Energy Technology Data Exchange (ETDEWEB)

    Ricken, James Bryce; Rios, Lynette; Poschet, Jens Fredrich; Bachand, Marlene; Bachand, George David; Greene, Adrienne Celeste; Carroll-Portillo, Amanda

    2008-11-01

    Nanoengineered materials hold a vast promise of enabling revolutionary technologies, but also pose an emerging and potentially serious threat to human and environmental health. While there is increasing knowledge concerning the risks posed by engineered nanomaterials, significant inconsistencies exist within the current data based on the high degree of variability in the materials (e.g., synthesis method, coatings, etc) and biological test systems (e.g., cell lines, whole organism, etc). In this project, we evaluated the uptake and response of two immune cell lines (RAW macrophage and RBL mast cells) to nanocrystal quantum dots (Qdots) with different sizes and surface chemistries, and at different concentrations. The basic experimental design followed a 2 x 2 x 3 factorial model: two Qdot sizes (Qdot 520 and 620), two surface chemistries (amine 'NH{sub 2}' and carboxylic acid 'COOH'), and three concentrations (0, 1 nM, and 1 {micro}M). Based on this design, the following Qdots from Evident Technologies were used for all experiments: Qdot 520-COOH, Qdot 520-NH{sub 2}, Qdot 620-COOH, and Qdot 620-NH{sub 2}. Fluorescence and confocal imaging demonstrated that Qdot 620-COOH and Qdot 620-NH{sub 2} nanoparticles had a greater level of internalization and cell membrane association in RAW and RBL cells, respectively. From these data, a two-way interaction between Qdot size and concentration was observed in relation to the level of cellular uptake in RAW cells, and association with RBL cell membranes. Toxicity of both RBL and RAW cells was also significantly dependent on the interaction of Qdot size and concentration; the 1 {micro}M concentrations of the larger, Qdot 620 nanoparticles induced a greater toxic effect on both cell lines. The RBL data also demonstrate that Qdot exposure can induce significant toxicity independent of cellular uptake. A significant increase in TNF-{alpha} and decrease in IL-10 release was observed in RAW cells, and suggested

  1. Intramolecular tautomerisation and the conformational variability of some classical mutagens – cytosine derivatives: quantum chemical study

    OpenAIRE

    Hovorun D. M.; Brovarets’ O. O.

    2011-01-01

    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 for...

  2. Designing a Study Abroad Course in Chemistry: Information from Three Different Courses to Europe

    Science.gov (United States)

    Marine, Susan Sonchik

    2013-01-01

    Guidelines for planning a study abroad course in chemistry start with defining the course objectives and outcomes. These, in turn, guide the choice of course content and format, location, length of travel, activities, and assessment. Budgetary issues include transportation, lodging, admission fees, activities, docents and guides (including audio…

  3. A Study of First-Year Chemistry Students' Understanding of Solution Concentration at the Tertiary Level

    Science.gov (United States)

    de Berg, Kevin

    2012-01-01

    This paper reports on students' understanding of sugar concentration in aqueous solutions presented in two different modes: a visual submicroscopic mode for particles and a verbal mode referring to macroscopic amounts of sugar. One hundred and forty-five tertiary college students studying some form of first-year chemistry participated in the…

  4. Retention of Differential and Integral Calculus: A Case Study of a University Student in Physical Chemistry

    Science.gov (United States)

    Jukic Matic, Ljerka; Dahl, Bettina

    2014-01-01

    This paper reports a study on retention of differential and integral calculus concepts of a second-year student of physical chemistry at a Danish university. The focus was on what knowledge the student retained 14 months after the course and on what effect beliefs about mathematics had on the retention. We argue that if a student can quickly…

  5. Can They Succeed? Exploring At-Risk Students' Study Habits in College General Chemistry

    Science.gov (United States)

    Ye, Li; Shuniak, Constantine; Oueini, Razanne; Robert, Jenay; Lewis, Scott

    2016-01-01

    A well-established literature base identifies a portion of students enrolled in post-secondary General Chemistry as at-risk of failing the course based on incoming metrics. Learning about the experiences and factors that lead to this higher failure rate is essential toward improving retention in this course. This study examines the relationship…

  6. Retention of Differential and Integral Calculus: A Case Study of a University Student in Physical Chemistry

    Science.gov (United States)

    Jukic Matic, Ljerka; Dahl, Bettina

    2014-01-01

    This paper reports a study on retention of differential and integral calculus concepts of a second-year student of physical chemistry at a Danish university. The focus was on what knowledge the student retained 14 months after the course and on what effect beliefs about mathematics had on the retention. We argue that if a student can quickly…

  7. Preservice Teachers' Epistemological Beliefs in Physics, Chemistry, and Biology: A Mixed Study

    Science.gov (United States)

    Topcu, Mustafa Sami

    2013-01-01

    The purposes of the study were to assess preservice teachers' domain-specific epistemological beliefs and to investigate whether preservice teachers distinguish disciplinary differences (physics, chemistry, and biology) in domain-specific epistemological beliefs. Mixed-method research design guided the present research. The researcher explored…

  8. Seeing Chemistry through the Eyes of the Blind: A Case Study Examining Multiple Gas Law Representations

    Science.gov (United States)

    Harshman, Jordan; Bretz, Stacey Lowery; Yezierski, Ellen

    2013-01-01

    Adequately accommodating students who are blind or low-vision (BLV) in the sciences has been a focus of recent inquiry, but much of the research to date has addressed broad accommodations rather than devising and testing specific teaching strategies that respond to the unique challenges of BLV students learning chemistry. This case study seeks to…

  9. Exploratory Factor Analysis Study for the Scale of High School Students' Attitudes towards Chemistry

    Science.gov (United States)

    Demircioglu, Gökhan; Aslan, Aysegül; Yadigaroglu, Mustafa

    2014-01-01

    It is important to develop students' positive attitudes chemistry lessons in school because research has suggested that attitudes are linked with academic achievement. Therefore, how to evaluate the attitudes is an important topic in education. The purpose of this study was to develop a Likert-type scale that could measure high school students'…

  10. Identifying Students' Misconceptions about Nuclear Chemistry: A Study of Turkish High School Students

    Science.gov (United States)

    Nakiboglu, Canan; Tekin, Berna Bulbul

    2006-01-01

    This study represents the first attempt to elucidate and detail the types of misconceptions high school students hold relating to basic concepts and topics of nuclear chemistry. A diagnostic multiple-choice test was administered to 157 tenth-grade students (15-16 years old) and the data were analyzed. The results show that high school students…

  11. Structure activity study on the quinone/quinone methide chemistry of flavonoids

    NARCIS (Netherlands)

    Awad, H.M.; Boersma, M.G.; Boeren, S.; Bladeren, van P.J.; Vervoort, J.; Rietjens, I.M.C.M.

    2001-01-01

    A structure-activity study on the quinone/quinone methide chemistry of a series of 3',4'-dihydroxyflavonoids was performed. Using the glutathione trapping method followed by HPLC, 1H NMR, MALDI-TOF, and LC/MS analysis to identify the glutathionyl adducts, the chemical behavior of the

  12. Structure activity study on the quinone/quinone methide chemistry of flavonoids

    NARCIS (Netherlands)

    Awad, H.M.; Boersma, M.G.; Boeren, S.; Bladeren, van P.J.; Vervoort, J.; Rietjens, I.M.C.M.

    2001-01-01

    A structure-activity study on the quinone/quinone methide chemistry of a series of 3',4'-dihydroxyflavonoids was performed. Using the glutathione trapping method followed by HPLC, 1H NMR, MALDI-TOF, and LC/MS analysis to identify the glutathionyl adducts, the chemical behavior of the quinones/quinon

  13. Can They Succeed? Exploring At-Risk Students' Study Habits in College General Chemistry

    Science.gov (United States)

    Ye, Li; Shuniak, Constantine; Oueini, Razanne; Robert, Jenay; Lewis, Scott

    2016-01-01

    A well-established literature base identifies a portion of students enrolled in post-secondary General Chemistry as at-risk of failing the course based on incoming metrics. Learning about the experiences and factors that lead to this higher failure rate is essential toward improving retention in this course. This study examines the relationship…

  14. On the atmospheric chemistry of NO2 - O3 systems; a laboratory study.

    NARCIS (Netherlands)

    Verhees, P.W.C.

    1986-01-01

    In this dissertation a laboratory study dealing with the atmospheric chemistry of NO 2 -O 3 systems is described. Knowledge of this system is relevant for a better understanding of a number of air pollution problems, particularly th

  15. Study of Heterogeneouse Processes Related to the Chemistry of Tropospheric Oxidants and Aerosols

    Energy Technology Data Exchange (ETDEWEB)

    Davidovits, Paul; Worsnop, D R; Jayne, J T; Colb, C E

    2013-02-13

    The objective of the studies was to elucidate the heterogeneous chemistry of tropospheric aerosols. Experiments were designed to measure both specifically needed parameters, and to obtain systematic data required to build a fundamental understanding of the nature of gas-surface physical and chemical interactions

  16. Surface chemistry of arenethiolate-capped PbS quantum dots and application as colloidally stable photovoltaic ink

    Energy Technology Data Exchange (ETDEWEB)

    Giansante, Carlo, E-mail: carlo.giansante@iit.it [Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, Via Barsanti 1, 73010 Arnesano, LE (Italy); NNL-CNR Istituto di Nanoscienze, Via per Arnesano, 73100 Lecce (Italy); Carbone, Luigi [IPCF-CNR UOS di Pisa, Via G. Moruzzi 1, 56124 Pisa (Italy); Giannini, Cinzia; Altamura, Davide [IC-CNR Istituto di Cristallografia, Via Amendola 122/O, 70126 Bari (Italy); Ameer, Zoobia [Dipartimento di Matematica e Fisica ‘E. De Giorgi’, Università del Salento, Via per Arnesano, 73100 Lecce (Italy); Maruccio, Giuseppe [Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, Via Barsanti 1, 73010 Arnesano, LE (Italy); NNL-CNR Istituto di Nanoscienze, Via per Arnesano, 73100 Lecce (Italy); Dipartimento di Matematica e Fisica ‘E. De Giorgi’, Università del Salento, Via per Arnesano, 73100 Lecce (Italy); Loiudice, Anna [Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, Via Barsanti 1, 73010 Arnesano, LE (Italy); Belviso, Maria R. [NNL-CNR Istituto di Nanoscienze, Via per Arnesano, 73100 Lecce (Italy); Cozzoli, P. Davide [NNL-CNR Istituto di Nanoscienze, Via per Arnesano, 73100 Lecce (Italy); Dipartimento di Matematica e Fisica ‘E. De Giorgi’, Università del Salento, Via per Arnesano, 73100 Lecce (Italy); Rizzo, Aurora [Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, Via Barsanti 1, 73010 Arnesano, LE (Italy); NNL-CNR Istituto di Nanoscienze, Via per Arnesano, 73100 Lecce (Italy); and others

    2014-06-02

    Suitable post-synthesis surface modification of lead-chalcogenide quantum dots (QDs) is crucial to enable their integration in photovoltaic devices. We have developed a solution-phase ligand exchange strategy that exploits arenethiolate anions to replace the pristine oleate ligands on PbS QDs, while preserving the long-term colloidal stability of QDs and allowing their solution-based processability into photoconductive thin-films. Complete QD surface modification is demonstrated by IR spectroscopy analysis, whereas UV–Vis–NIR Absorption Spectroscopy provides quantitative evaluation of stoichiometry and thermodynamic stability of the resulting system. Arenethiolate ligands permit to reduce the inter-particle distance in PbS QD solids, leading to a drastic improvement of the photoinduced charge transport properties. Therefore, smooth dense-packed thin-films of arenethiolate-capped PbS QDs obtained via a single solution-processing step are integrated in heterojunction solar cells: such devices generate remarkable photocurrent densities (14 mA cm{sup −2}) and overall efficiencies (1.85%), which are outstanding for a single PbS QD layer. Solution-phase surface modification of QDs thus represents an effective intermediate step towards low-cost processing for all-inorganic and hybrid organic/inorganic QD-based photovoltaics. - Highlights: • We developed a solution-phase ligand exchange strategy on PbS quantum dots (QDs). • We evaluated stoichiometry and thermodynamic stability of the resulting system. • Arenethiolate ligands preserve the long-term colloidal stability of PbS QDs. • Arenethiolate ligands allow QD solution-casting into photoconductive thin-films. • Photovoltaic devices based on a single PbS QD layer show outstanding performances.

  17. Extremal quantum correlations: Experimental study with two-qubit states

    Energy Technology Data Exchange (ETDEWEB)

    Chiuri, A.; Mataloni, P. [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Istituto Nazionale di Ottica (INO-CNR), L.go E. Fermi 6, I-50125 Firenze (Italy); Vallone, G. [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Via Panisperna 89/A, Compendio del Viminale, I-00184 Roma (Italy); Paternostro, M. [Centre for Theoretical Atomic, Molecular, and Optical Physics, School of Mathematics and Physics, Queen' s University, Belfast BT7 1NN (United Kingdom)

    2011-08-15

    We explore experimentally the space of two-qubit quantum-correlated mixed states, including frontier states as defined by the use of quantum discord and von Neumann entropy. Our experimental setup is flexible enough to allow for high-quality generation of a vast variety of states. We address quantitatively the relation between quantum discord and a recently suggested alternative measure of quantum correlations.

  18. Analytical studies of Spectrum Broadcast Structures in Quantum Brownian Motion

    OpenAIRE

    2016-01-01

    Spectrum Broadcast Structures are a new and fresh concept in the quantum-to-classical transition, introduced recently in the context of decoherence and the appearance of objective features in quantum mechanics. These are specific quantum state structures, responsible for an apparent objectivity of a decohered state of a system. Recently they have been shown to appear in the well known Quantum Brownian Motion model, however the final analysis relied on numerics. Here, after a presentation of t...

  19. Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl- attack on CH3Cl

    Science.gov (United States)

    Kuechler, Erich R.; York, Darrin M.

    2014-02-01

    The nucleophilic attack of a chloride ion on methyl chloride is an important prototype SN2 reaction in organic chemistry that is known to be sensitive to the effects of the surrounding solvent. Herein, we develop a highly accurate Specific Reaction Parameter (SRP) model based on the Austin Model 1 Hamiltonian for chlorine to study the effects of solvation into an aqueous environment on the reaction mechanism. To accomplish this task, we apply high-level quantum mechanical calculations to study the reaction in the gas phase and combined quantum mechanical/molecular mechanical simulations with TIP3P and TIP4P-ew water models and the resulting free energy profiles are compared with those determined from simulations using other fast semi-empirical quantum models. Both gas phase and solution results with the SRP model agree very well with experiment and provide insight into the specific role of solvent on the reaction coordinate. Overall, the newly parameterized SRP Hamiltonian is able to reproduce both the gas phase and solution phase barriers, suggesting it is an accurate and robust model for simulations in the aqueous phase at greatly reduced computational cost relative to comparably accurate ab initio and density functional models.

  20. Simulation Study on Quantum Capacitances of Graphene Nanoribbon VLSI Interconnects

    Science.gov (United States)

    Dutta, Arin; Rahman, Silvia; Nandy, Turja; Mahmood, Zahid Hasan

    2016-03-01

    In this paper, study on the capacitive effects of Graphene nanoribbon (GNR) in VLSI interconnect has been studied as a function of GNR width, Fermi function and gate voltage. The quantum capacitance of GNR has been simulated in terms of Fermi function for three different values of insulator thickness — 1.5nm, 2nm and 2.5nm. After that, quantum capacitance is studied in both degenerate and nondegenerate region with respect to Fermi function and gate voltage of range 1-5V. Then, the total capacitance of GNR is studied as a function of gate voltage of -2-5V range at degenerate and nondegenerate regions, where width of GNR is considered 4nm. Finally, the total capacitance of GNR is studied in both regions with varying GNR width, considering fixed gate voltage of 3V. After analyzing these simulations, it has been found that GNR in degenerate region shows nearly steady capacitance under a certain applied gate voltage.