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

PubMed

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

2017-07-21

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

Quantum-chemical Calculations in the Study of Antitumour Compounds

NASA Astrophysics Data System (ADS)

Luzhkov, V. B.; Bogdanov, G. N.

1986-01-01

The results of quantum-chemical calculations on antitumour preparations concerning the mechanism of their action at the electronic and molecular levels and structure-activity correlations are discussed in this review. Preparations whose action involves alkylating and free-radial mechanisms, complex-forming agents, and antimetabolites are considered. Modern quantum-chemical methods for calculations on biologically active substances are described. The bibliography includes 106 references.

Quantum chemical investigations of AlN-doped C60 for use as a nano-biosensor in detection of mispairing between DNA bases.

PubMed

Siddiqui, Shamoon Ahmad; Bouarissa, Nadir; Rasheed, Tabish; Al-Hajry, A

2014-12-01

Quantum chemical calculations were carried out to study the electronic structure and stability of adenine-thymine and the rare tautomer of adenine-thymine base pairs along with their Cu 2+ complexes and their interactions with AlN-modified fullerene (C58AlN) using Density Functional Theory (B3LYP method). Since, these two forms of base pairs and their Cu 2+ complexes have almost similar electronic structures, their chemical differentiation is an extremely difficult task. In this investigation, we have observed that AlN-doped C 60 could be used as a potentially viable nanoscale sensor to detect these two base pairs as well as their Cu2+ complexes.

Recent Trends in Quantum Chemical Modeling of Enzymatic Reactions.

PubMed

Himo, Fahmi

2017-05-24

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

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

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

Polynomial-time quantum algorithm for the simulation of chemical dynamics

PubMed Central

Kassal, Ivan; Jordan, Stephen P.; Love, Peter J.; Mohseni, Masoud; Aspuru-Guzik, Alán

2008-01-01

The computational cost of exact methods for quantum simulation using classical computers grows exponentially with system size. As a consequence, these techniques can be applied only to small systems. By contrast, we demonstrate that quantum computers could exactly simulate chemical reactions in polynomial time. Our algorithm uses the split-operator approach and explicitly simulates all electron-nuclear and interelectronic interactions in quadratic time. Surprisingly, this treatment is not only more accurate than the Born–Oppenheimer approximation but faster and more efficient as well, for all reactions with more than about four atoms. This is the case even though the entire electronic wave function is propagated on a grid with appropriately short time steps. Although the preparation and measurement of arbitrary states on a quantum computer is inefficient, here we demonstrate how to prepare states of chemical interest efficiently. We also show how to efficiently obtain chemically relevant observables, such as state-to-state transition probabilities and thermal reaction rates. Quantum computers using these techniques could outperform current classical computers with 100 qubits. PMID:19033207

Ab initio Quantum Chemical and Experimental Reaction Kinetics Studies in the Combustion of Bipropellants

DTIC Science & Technology

2017-03-24

NUMBER (Include area code) 24 March 2017 Briefing Charts 01 March 2017 - 31 March 2017 Ab initio Quantum Chemical and Experimental Reaction Kinetics...Laboratory AFRL/RQRS 1 Ara Road Edwards AFB, CA 93524 *Email: ghanshyam.vaghjiani@us.af.mil Ab initio Quantum Chemical and Experimental Reaction ...Clearance 17161 Zador et al., Prog. Energ. Combust. Sci., 37 371 (2011) Why Quantum Chemical Reaction Kinetics Studies? DISTRIBUTION A: Approved for

Quantum chemical approach to estimating the thermodynamics of metabolic reactions.

PubMed

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

2014-11-12

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

Quantum Chemical Approach to Estimating the Thermodynamics of Metabolic Reactions

PubMed Central

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

2014-01-01

Thermodynamics plays an increasingly important role in modeling and engineering metabolism. We present the first nonempirical computational method for estimating standard Gibbs reaction energies of metabolic reactions based on quantum chemistry, which can help fill in the gaps in the existing thermodynamic data. When applied to a test set of reactions from core metabolism, the quantum chemical approach is comparable in accuracy to group contribution methods for isomerization and group transfer reactions and for reactions not including multiply charged anions. The errors in standard Gibbs reaction energy estimates are correlated with the charges of the participating molecules. The quantum chemical approach is amenable to systematic improvements and holds potential for providing thermodynamic data for all of metabolism. PMID:25387603

Investigations of quantum heuristics for optimization

NASA Astrophysics Data System (ADS)

Rieffel, Eleanor; Hadfield, Stuart; Jiang, Zhang; Mandra, Salvatore; Venturelli, Davide; Wang, Zhihui

We explore the design of quantum heuristics for optimization, focusing on the quantum approximate optimization algorithm, a metaheuristic developed by Farhi, Goldstone, and Gutmann. We develop specific instantiations of the of quantum approximate optimization algorithm for a variety of challenging combinatorial optimization problems. Through theoretical analyses and numeric investigations of select problems, we provide insight into parameter setting and Hamiltonian design for quantum approximate optimization algorithms and related quantum heuristics, and into their implementation on hardware realizable in the near term.

Chemical application of diffusion quantum Monte Carlo

NASA Technical Reports Server (NTRS)

Reynolds, P. J.; Lester, W. A., Jr.

1984-01-01

The diffusion quantum Monte Carlo (QMC) method gives a stochastic solution to the Schroedinger equation. This approach is receiving increasing attention in chemical applications as a result of its high accuracy. However, reducing statistical uncertainty remains a priority because chemical effects are often obtained as small differences of large numbers. As an example, the single-triplet splitting of the energy of the methylene molecule CH sub 2 is given. The QMC algorithm was implemented on the CYBER 205, first as a direct transcription of the algorithm running on the VAX 11/780, and second by explicitly writing vector code for all loops longer than a crossover length C. The speed of the codes relative to one another as a function of C, and relative to the VAX, are discussed. The computational time dependence obtained versus the number of basis functions is discussed and this is compared with that obtained from traditional quantum chemistry codes and that obtained from traditional computer architectures.

Synthesis, vibrational and quantum chemical investigations of hydrogen bonded complex betaine dihydrogen selenite

NASA Astrophysics Data System (ADS)

Arjunan, V.; Marchewka, Mariusz K.; Kalaivani, M.

2012-10-01

The molecular complex of betaine with selenious acid namely, betaine dihydrogen selenite (C5H13NO5Se, BDHSe) was synthesised by the reaction of betaine and SeO2 in a 1:1:1 solution of isopropanol, methanol and water. Crystals were grown from this solution by cooling to 253 K for few days. The complex was formed without accompanying proton transfer from selenious acid molecule to betaine. The complete vibrational assignments and analysis of BDHSe have been performed by FTIR, FT-Raman and far-infrared spectral studies. More support on the experimental findings was added from the quantum chemical studies performed with DFT (B3LYP) method using 6-311++G∗∗, 6-31G∗∗, cc-pVDZ and 3-21G basis sets. The structural parameters, energies, thermodynamic parameters and the NBO charges of BDHSe were determined by the DFT method. The 1H and 13C isotropic chemical shifts (δ ppm) of BDHSe with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. SHG experiment was carried out using Kurtz-Perry powder technique. The efficiency of second harmonic generation for BDHSe was estimated relatively to KDP: deff = 0.97 deff (KDP).

DFT simulation, quantum chemical electronic structure, spectroscopic and structure-activity investigations of 4-acetylpyridine

NASA Astrophysics Data System (ADS)

Atilgan, A.; Yurdakul, Ş.; Erdogdu, Y.; Güllüoğlu, M. T.

2018-06-01

The spectroscopic (UV-Vis and infrared), structural and some electronic property observations of the 4-acetylpyridine (4-AP) were reported, which are investigated by using some spectral methods and DFT calculations. FT-IR spectra were obtained for 4-AP at room temperature in the region 4000 cm-1- 400 cm-1. In the DFT calculations, the B3LYP functional with 6-311G++G(d,p) basis set was applied to carry out the quantum mechanical calculations. The Fourier Transform Infrared (FT-IR) and FT-Raman spectra were interpreted by using of normal coordinate analysis based on scaled quantum mechanical force field. The present work expands our understanding of the both the vibrational and structural properties as well as some electronic properties of the 4-AP by means of the theoretical and experimental methods.

From Einstein-Podolsky-Rosen paradox to quantum nonlocality: experimental investigation of quantum correlations

NASA Astrophysics Data System (ADS)

Xu, Jin-Shi; Li, Chuan-Feng; Guo, Guang-Can

2016-11-01

In 1935, Einstein, Podolsky and Rosen published their influential paper proposing a now famous paradox (the EPR paradox) that threw doubt on the completeness of quantum mechanics. Two fundamental concepts: entanglement and steering, were given in the response to the EPR paper by Schrodinger, which both reflect the nonlocal nature of quantum mechanics. In 1964, John Bell obtained an experimentally testable inequality, in which its violation contradicts the prediction of local hidden variable models and agrees with that of quantum mechanics. Since then, great efforts have been made to experimentally investigate the nonlocal feature of quantum mechanics and many distinguished quantum properties were observed. In this work, along with the discussion of the development of quantum nonlocality, we would focus on our recent experimental efforts in investigating quantum correlations and their applications with optical systems, including the study of entanglement-assisted entropic uncertainty principle, Einstein-Podolsky-Rosen steering and the dynamics of quantum correlations.

Ammonolysis of ketene as a potential source of acetamide in the troposphere: a quantum chemical investigation.

PubMed

Sarkar, Saptarshi; Mallick, Subhasish; Kumar, Pradeep; Bandyopadhyay, Biman

2018-05-16

Quantum chemical calculations at the CCSD(T)/CBS//MP2/aug-cc-pVTZ levels of theory have been carried out to investigate a potential new source of acetamide in Earth's atmosphere through the ammonolysis of the simplest ketene. It was found that the reaction can occur via the addition of ammonia at either the C[double bond, length as m-dash]C or C[double bond, length as m-dash]O bond of ketene. The potential energy surface as well as calculated rate coefficients indicate that under tropospheric conditions, ammonolysis would occur almost exclusively via ammonia addition at the C[double bond, length as m-dash]O bond with negligible contribution from addition at the C[double bond, length as m-dash]C bond. The reaction of ketene with water has also been investigated in order to compare between hydrolysis and ammonolysis, as the former is known to be responsible for the formation of acetic acid. The rate coefficient for the formation of acetamide was found to be ∼106 to 109 times higher than that for the formation of acetic acid from the same ketene source in the troposphere. By means of the relative rate of ammonolysis with respect to hydrolysis, it was shown that acetamide formation would dominate over acetic acid formation at various altitudes in the troposphere.

Chemical accuracy from quantum Monte Carlo for the benzene dimer.

PubMed

Azadi, Sam; Cohen, R E

2015-09-14

We report an accurate study of interactions between benzene molecules using variational quantum Monte Carlo (VMC) and diffusion quantum Monte Carlo (DMC) methods. We compare these results with density functional theory using different van der Waals functionals. In our quantum Monte Carlo (QMC) calculations, we use accurate correlated trial wave functions including three-body Jastrow factors and backflow transformations. We consider two benzene molecules in the parallel displaced geometry, and find that by highly optimizing the wave function and introducing more dynamical correlation into the wave function, we compute the weak chemical binding energy between aromatic rings accurately. We find optimal VMC and DMC binding energies of -2.3(4) and -2.7(3) kcal/mol, respectively. The best estimate of the coupled-cluster theory through perturbative triplets/complete basis set limit is -2.65(2) kcal/mol [Miliordos et al., J. Phys. Chem. A 118, 7568 (2014)]. Our results indicate that QMC methods give chemical accuracy for weakly bound van der Waals molecular interactions, comparable to results from the best quantum chemistry methods.

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

NASA Astrophysics Data System (ADS)

Vlaisavljevich, Bess

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

X-ray diffraction, vibrational and quantum chemical investigations of 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid

NASA Astrophysics Data System (ADS)

Arjunan, V.; Marchewka, Mariusz K.; Pietraszko, A.; Kalaivani, M.

2012-11-01

The structural investigations of the molecular complex of 2-methyl-4-nitroaniline with trichloroacetic acid, namely 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid (C11H10Cl6N2O6) have been performed by means of single crystal and powder X-ray diffraction method. The complex was formed with accompanying proton transfer from trichloroacetic acid molecule to 2-methyl-4-nitroaniline. The studied crystal is built up of singly protonated 2-methyl-4-nitroanilinium cations, trichloroacetate anions and neutral trichloroacetic acid molecules. The crystals are monoclinic, space group P21/c, with a = 14.947 Å, b = 6.432 Å, c = 19.609 Å and Z = 4. The vibrational assignments and analysis of 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid have also been performed by FTIR, FT-Raman and far-infrared spectral studies. More support on the experimental findings were added from the quantum chemical studies performed with DFT (B3LYP) method using 6-31G**, cc-pVDZ, 6-31G and 6-31++G basis sets. The structural parameters, energies, thermodynamic parameters and the NBO charges of 2M4NATCA were also determined by the DFT methods.

Spectroscopic, quantum chemical calculation and molecular docking of dipfluzine

NASA Astrophysics Data System (ADS)

Srivastava, Karnica; Srivastava, Anubha; Tandon, Poonam; Sinha, Kirti; Wang, Jing

2016-12-01

Molecular structure and vibrational analysis of dipfluzine (C27H29FN2O) were presented using FT-IR and FT-Raman spectroscopy and quantum chemical calculations. The theoretical ground state geometry and electronic structure of dipfluzine are optimized by the DFT/B3LYP/6-311++G (d,p) method and compared with those of the crystal data. The 1D potential energy scan was performed by varying the dihedral angle using B3LYP functional at 6-31G(d,p) level of theory and thus the most stable conformer of the compound were determined. Molecular electrostatic potential surface (MEPS), frontier orbital analysis and electronic reactivity descriptor were used to predict the chemical reactivity of molecule. Energies of intra- and inter-molecular hydrogen bonds in molecule and their electronic aspects were investigated by natural bond orbital (NBO). To find out the anti-apoptotic activity of the title compound molecular docking studies have been performed against protein Fas.

Investigation of germanium quantum-well light sources.

PubMed

Fei, Edward T; Chen, Xiaochi; Zang, Kai; Huo, Yijie; Shambat, Gary; Miller, Gerald; Liu, Xi; Dutt, Raj; Kamins, Theodore I; Vuckovic, Jelena; Harris, James S

2015-08-24

In this paper, we report a broad investigation of the optical properties of germanium (Ge) quantum-well devices. Our simulations show a significant increase of carrier density in the Ge quantum wells. Photoluminescence (PL) measurements show the enhanced direct-bandgap radiative recombination rates due to the carrier density increase in the Ge quantum wells. Electroluminescence (EL) measurements show the temperature-dependent properties of our Ge quantum-well devices, which are in good agreement with our theoretical models. We also demonstrate the PL measurements of Ge quantum-well microdisks using tapered-fiber collection method and quantify the optical loss of the Ge quantum-well structure from the measured PL spectra for the first time.

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

PubMed

Zhang, Hai-Mei; Chen, Shi-Lu

2015-06-09

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

X-ray diffraction, vibrational and quantum chemical investigations of 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid.

PubMed

Arjunan, V; Marchewka, Mariusz K; Pietraszko, A; Kalaivani, M

2012-11-01

The structural investigations of the molecular complex of 2-methyl-4-nitroaniline with trichloroacetic acid, namely 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid (C(11)H(10)Cl(6)N(2)O(6)) have been performed by means of single crystal and powder X-ray diffraction method. The complex was formed with accompanying proton transfer from trichloroacetic acid molecule to 2-methyl-4-nitroaniline. The studied crystal is built up of singly protonated 2-methyl-4-nitroanilinium cations, trichloroacetate anions and neutral trichloroacetic acid molecules. The crystals are monoclinic, space group P2(1)/c, with a=14.947Å, b=6.432Å, c=19.609Å and Z=4. The vibrational assignments and analysis of 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid have also been performed by FTIR, FT-Raman and far-infrared spectral studies. More support on the experimental findings were added from the quantum chemical studies performed with DFT (B3LYP) method using 6-31G, cc-pVDZ, 6-31G and 6-31++G basis sets. The structural parameters, energies, thermodynamic parameters and the NBO charges of 2M4NATCA were also determined by the DFT methods. Copyright © 2012 Elsevier B.V. All rights reserved.

An efficient matrix product operator representation of the quantum chemical Hamiltonian

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keller, Sebastian, E-mail: sebastian.keller@phys.chem.ethz.ch; Reiher, Markus, E-mail: markus.reiher@phys.chem.ethz.ch; Dolfi, Michele, E-mail: dolfim@phys.ethz.ch

We describe how to efficiently construct the quantum chemical Hamiltonian operator in matrix product form. We present its implementation as a density matrix renormalization group (DMRG) algorithm for quantum chemical applications. Existing implementations of DMRG for quantum chemistry are based on the traditional formulation of the method, which was developed from the point of view of Hilbert space decimation and attained higher performance compared to straightforward implementations of matrix product based DMRG. The latter variationally optimizes a class of ansatz states known as matrix product states, where operators are correspondingly represented as matrix product operators (MPOs). The MPO construction schememore » presented here eliminates the previous performance disadvantages while retaining the additional flexibility provided by a matrix product approach, for example, the specification of expectation values becomes an input parameter. In this way, MPOs for different symmetries — abelian and non-abelian — and different relativistic and non-relativistic models may be solved by an otherwise unmodified program.« less

Intrinsic Atomic Orbitals: An Unbiased Bridge between Quantum Theory and Chemical Concepts.

PubMed

Knizia, Gerald

2013-11-12

Modern quantum chemistry can make quantitative predictions on an immense array of chemical systems. However, the interpretation of those predictions is often complicated by the complex wave function expansions used. Here we show that an exceptionally simple algebraic construction allows for defining atomic core and valence orbitals, polarized by the molecular environment, which can exactly represent self-consistent field wave functions. This construction provides an unbiased and direct connection between quantum chemistry and empirical chemical concepts, and can be used, for example, to calculate the nature of bonding in molecules, in chemical terms, from first principles. In particular, we find consistency with electronegativities (χ), C 1s core-level shifts, resonance substituent parameters (σR), Lewis structures, and oxidation states of transition-metal complexes.

A quantum informational approach for dissecting chemical reactions

NASA Astrophysics Data System (ADS)

Duperrouzel, Corinne; Tecmer, Paweł; Boguslawski, Katharina; Barcza, Gergely; Legeza, Örs; Ayers, Paul W.

2015-02-01

We present a conceptionally different approach to dissect bond-formation processes in metal-driven catalysis using concepts from quantum information theory. Our method uses the entanglement and correlation among molecular orbitals to analyze changes in electronic structure that accompany chemical processes. As a proof-of-principle example, the evolution of nickel-ethene bond-formation is dissected, which allows us to monitor the interplay of back-bonding and π-donation along the reaction coordinate. Furthermore, the reaction pathway of nickel-ethene complexation is analyzed using quantum chemistry methods, revealing the presence of a transition state. Our study supports the crucial role of metal-to-ligand back-donation in the bond-forming process of nickel-ethene.

Incorporation of Mn2+ into CdSe quantum dots by chemical bath co-deposition method for photovoltaic enhancement of quantum dot-sensitized solar cells

NASA Astrophysics Data System (ADS)

Zhang, Chenguang; Liu, Shaowen; Liu, Xingwei; Deng, Fei; Xiong, Yan; Tsai, Fang-Chang

2018-03-01

A photoelectric conversion efficiency (PCE) of 4.9% was obtained under 100 mW cm-2 illumination by quantum-dot-sensitized solar cells (QDSSCs) using a CdS/Mn : CdSe sensitizer. CdS quantum dots (QDs) were deposited on a TiO2 mesoporous oxide film by successive ionic layer absorption and reaction. Mn2+ doping into CdSe QDs is an innovative and simple method-chemical bath co-deposition, that is, mixing the Mn ion source with CdSe precursor solution for Mn : CdSe QD deposition. Compared with the CdS/CdSe sensitizer without Mn2+ incorporation, the PCE was increased from 3.4% to 4.9%. The effects of Mn2+ doping on the chemical, physical and photovoltaic properties of the QDSSCs were investigated by energy dispersive spectrometry, absorption spectroscopy, photocurrent density-voltage characteristics and electrochemical impedance spectroscopy. Mn-doped CdSe QDs in QDSSCs can obtain superior light absorption, faster electron transport and slower charge recombination than CdSe QDs.

Quantum chemical parameters in QSAR: what do I use when?

USGS Publications Warehouse

Hickey, James P.; Ostrander, Gary K.

1996-01-01

This chapter provides a brief overview of the numerous quantum chemical parameters that have been/are currently being used in quantitative structure activity relationships (QSAR), along with a representative bibliography. The parameters will be grouped according to their mechanistic interpretations, and representative biological and physical chemical applications will be mentioned. Parmater computation methods and the appropriate software are highlighted, as are sources for software.

Combined friction force microscopy and quantum chemical investigation of the tribotronic response at the propylammonium nitrate-graphite interface.

PubMed

Li, H; Atkin, R; Page, A J

2015-06-28

The energetic origins of the variation in friction with potential at the propylammonium nitrate-graphite interface are revealed using friction force microscopy (FFM) in combination with quantum chemical simulations. For boundary layer lubrication, as the FFM tip slides energy is dissipated via (1) boundary layer ions and (2) expulsion of near-surface ion layers from the space between the surface and advancing tip. Simulations reveal how changing the surface potential changes the ion composition of the boundary and near surface layer, which controls energy dissipation through both pathways, and thus the friction.

DFT simulation, quantum chemical electronic structure, spectroscopic and structure-activity investigations of 2-benzothiazole acetonitrile.

PubMed

Arjunan, V; Thillai Govindaraja, S; Jose, Sujin P; Mohan, S

2014-07-15

The Fourier transform infrared and FT-Raman spectra of 2-benzothiazole acetonitrile (BTAN) have been recorded in the range 4000-450 and 4000-100 cm(-1) respectively. The conformational analysis of the compound has been carried out to obtain the stable geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compound are carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The experimental vibrational frequencies are compared with the wavenumbers derived theoretically by B3LYP gradient calculations employing the standard 6-31G(**), high level 6-311++G(**) and cc-pVTZ basis sets. The structural parameters, thermodynamic properties and vibrational frequencies of the normal modes obtained from the B3LYP methods are in good agreement with the experimental data. The (1)H (400 MHz; CDCl3) and (13)C (100 MHz;CDCl3) nuclear magnetic resonance (NMR) spectra are also recorded. The electronic properties, the energies of the highest occupied and lowest unoccupied molecular orbitals are measured by DFT approach. The kinetic stability of the molecule has been determined from the frontier molecular orbital energy gap. The charges of the atoms and the structure-chemical reactivity relations of the compound are determined by its chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods. The non-linear optical properties of the compound have been discussed by measuring the polarisability and hyperpolarisability tensors. Copyright © 2014 Elsevier B.V. All rights reserved.

Intramolecular hydrogen bonding in myricetin and myricitrin. Quantum chemical calculations and vibrational spectroscopy

NASA Astrophysics Data System (ADS)

Vojta, Danijela; Dominković, Katarina; Miljanić, Snežana; Spanget-Larsen, Jens

2017-03-01

The molecular structures of myricetin (3,3‧,4‧,5,5‧,7-hexahydroxyflavone; MCE) and myricitrin (myricetin 3-O-rhamnoside; MCI) are investigated by quantum chemical calculations (B3LYP/6-311G**). Two preferred molecular rotamers of MCI are predicted, corresponding to different conformations of the O-rhamnoside subunit. The rotamers are characterized by different hydrogen bonded cross-links between the hydroxy groups of the rhamnoside substituent and the parent MCE moiety. The predicted OH stretching frequencies are compared with vibrational spectra of MCE and MCI recorded for the sake of this investigation (IR and Raman). In addition, a reassignment of the Cdbnd O stretching bands is suggested.

Characterization of heterocyclic rings through quantum chemical topology.

PubMed

Griffiths, Mark Z; Popelier, Paul L A

2013-07-22

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

Quantum chemical investigation on photodegradation mechanisms of sulfamethoxypyridazine with dissolved inorganic matter and hydroxyl radical.

PubMed

Shah, Shaheen; Hao, Ce

2017-07-01

Sulfamethoxypyridazine (SMP) is one of the commonly used sulfonamide antibiotics (SAs). SAs are mainly studied to undergo triplet-sensitized photodegradation in water under natural sunlight with other coexisting aquatic environmental organic pollutants. In this work, SMP was selected as a representative of SAs. We studied the mechanisms of triplet-sensitized photodegradation of SMP and the influence of selected dissolved inorganic matter, i.e., anions (Br - , Cl - , and NO 3 - ) and cations ions (Ca 2+ , Mg 2+ , and Zn 2+ ) on SMP photodegradation mechanism by quantum chemical methods. In addition, the degradation mechanisms of SMP by hydroxyl radical (OH) were also investigated. The creation of SO 2 extrusion product was accessed with two different energy pathways (pathway-1 and pathway-2) by following two steps (step-I and step-II) in the triplet-sensitized photodegradation of SMP. Due to low activation energy, the pathway-1 was considered as the main pathway to obtain SO 2 extrusion product. Step-II of pathway-1 was measured to be the rate-limiting step (RLS) of SMP photodegradation mechanism and the effect of the selected anions and cations was estimated for this step. All selected anions and cations promoted photodegradation of SMP by dropping the activation energy of pathway-1. The estimated low activation energies of different degradation pathways of SMP with OH radical indicate that OH radical is a very powerful oxidizing agent for SMP degradation via attack through benzene derivative and pyridazine derivative ring. Copyright © 2016. Published by Elsevier B.V.

Quantum Dots Investigated for Solar Cells

NASA Technical Reports Server (NTRS)

Bailey, Sheila G.; Castro, Stephanie L.; Raffaelle, Ryne P.; Hepp, Aloysius F.

2001-01-01

The NASA Glenn Research Center has been investigating the synthesis of quantum dots of CdSe and CuInS2 for use in intermediate-bandgap solar cells. Using quantum dots in a solar cell to create an intermediate band will allow the harvesting of a much larger portion of the available solar spectrum. Theoretical studies predict a potential efficiency of 63.2 percent, which is approximately a factor of 2 better than any state-of-the-art devices available today. This technology is also applicable to thin-film devices--where it offers a potential four-fold increase in power-to-weight ratio over the state of the art. Intermediate-bandgap solar cells require that quantum dots be sandwiched in an intrinsic region between the photovoltaic solar cell's ordinary p- and n-type regions (see the preceding figure). The quantum dots form the intermediate band of discrete states that allow sub-bandgap energies to be absorbed. However, when the current is extracted, it is limited by the bandgap, not the individual photon energies. The energy states of the quantum dot can be controlled by controlling the size of the dot. Ironically, the ground-state energy levels are inversely proportional to the size of the quantum dots. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Ba Wendi et al., in the early 1990's. The most studied quantum dots prepared by this method have been of CdSe. To produce these dots, researchers inject a syringe of the desired organometallic precursors into heated triocytlphosphine oxide (TOPO) that has been vigorously stirred under an inert atmosphere (see the following figure). The solution immediately begins to change from colorless to yellow, then orange and red/brown, as the quantum dots increase in size. When the desired size is reached, the heat is removed from the flask. Quantum dots of different sizes can be identified by placing them under a "black light" and observing the various color differences in

Prediction of contaminant persistence in aqueous phase: a quantum chemical approach.

PubMed

Blotevogel, Jens; Mayeno, Arthur N; Sale, Tom C; Borch, Thomas

2011-03-15

At contaminated field sites where active remediation measures are not feasible, monitored natural attenuation is sometimes the only alternative for surface water or groundwater decontamination. However, due to slow degradation rates of some contaminants under natural conditions, attenuation processes and their performance assessment can take several years to decades to complete. Here, we apply quantum chemical calculations to predict contaminant persistence in the aqueous phase. For the test compound hexamethylphosphoramide (HMPA), P-N bond hydrolysis is the only thermodynamically favorable reaction that may lead to its degradation under reducing conditions. Through calculation of aqueous Gibbs free energies of activation for all potential reaction mechanisms, it is predicted that HMPA hydrolyzes via an acid-catalyzed mechanism at pH < 8.2, and an uncatalyzed mechanism at pH 8.2-8.5. The estimated half-lives of thousands to hundreds of thousands of years over the groundwater-typical pH range of 6.0 to 8.5 indicate that HMPA will be persistent in the absence of suitable oxidants. At pH 0, where the hydrolysis reaction is rapid enough to enable measurement, the experimentally determined rate constant and half-life are in excellent agreement with the predicted values. Since the quantum chemical methodology described herein can be applied to virtually any contaminant or reaction of interest, it is especially valuable for the prediction of persistence when slow reaction rates impede experimental investigations and appropriate QSARs are unavailable.

Quantum Degeneracy in Atomic Point Contacts Revealed by Chemical Force and Conductance

NASA Astrophysics Data System (ADS)

Sugimoto, Yoshiaki; Ondráček, Martin; Abe, Masayuki; Pou, Pablo; Morita, Seizo; Perez, Ruben; Flores, Fernando; Jelínek, Pavel

2013-09-01

Quantum degeneracy is an important concept in quantum mechanics with large implications to many processes in condensed matter. Here, we show the consequences of electron energy level degeneracy on the conductance and the chemical force between two bodies at the atomic scale. We propose a novel way in which a scanning probe microscope can detect the presence of degenerate states in atomic-sized contacts even at room temperature. The tunneling conductance G and chemical binding force F between two bodies both tend to decay exponentially with distance in a certain distance range, usually maintaining direct proportionality G∝F. However, we show that a square relation G∝F2 arises as a consequence of quantum degeneracy between the interacting frontier states of the scanning tip and a surface atom. We demonstrate this phenomenon on the Si(111)-(7×7) surface reconstruction where the Si adatom possesses a strongly localized dangling-bond state at the Fermi level.

Incorporation of Mn2+ into CdSe quantum dots by chemical bath co-deposition method for photovoltaic enhancement of quantum dot-sensitized solar cells.

PubMed

Zhang, Chenguang; Liu, Shaowen; Liu, Xingwei; Deng, Fei; Xiong, Yan; Tsai, Fang-Chang

2018-03-01

A photoelectric conversion efficiency (PCE) of 4.9% was obtained under 100 mW cm -2 illumination by quantum-dot-sensitized solar cells (QDSSCs) using a CdS/Mn : CdSe sensitizer. CdS quantum dots (QDs) were deposited on a TiO 2 mesoporous oxide film by successive ionic layer absorption and reaction. Mn 2+ doping into CdSe QDs is an innovative and simple method-chemical bath co-deposition, that is, mixing the Mn ion source with CdSe precursor solution for Mn : CdSe QD deposition. Compared with the CdS/CdSe sensitizer without Mn 2+ incorporation, the PCE was increased from 3.4% to 4.9%. The effects of Mn 2+ doping on the chemical, physical and photovoltaic properties of the QDSSCs were investigated by energy dispersive spectrometry, absorption spectroscopy, photocurrent density-voltage characteristics and electrochemical impedance spectroscopy. Mn-doped CdSe QDs in QDSSCs can obtain superior light absorption, faster electron transport and slower charge recombination than CdSe QDs.

Incorporation of Mn2+ into CdSe quantum dots by chemical bath co-deposition method for photovoltaic enhancement of quantum dot-sensitized solar cells

PubMed Central

Zhang, Chenguang; Liu, Shaowen; Liu, Xingwei; Deng, Fei

2018-01-01

A photoelectric conversion efficiency (PCE) of 4.9% was obtained under 100 mW cm−2 illumination by quantum-dot-sensitized solar cells (QDSSCs) using a CdS/Mn : CdSe sensitizer. CdS quantum dots (QDs) were deposited on a TiO2 mesoporous oxide film by successive ionic layer absorption and reaction. Mn2+ doping into CdSe QDs is an innovative and simple method—chemical bath co-deposition, that is, mixing the Mn ion source with CdSe precursor solution for Mn : CdSe QD deposition. Compared with the CdS/CdSe sensitizer without Mn2+ incorporation, the PCE was increased from 3.4% to 4.9%. The effects of Mn2+ doping on the chemical, physical and photovoltaic properties of the QDSSCs were investigated by energy dispersive spectrometry, absorption spectroscopy, photocurrent density–voltage characteristics and electrochemical impedance spectroscopy. Mn-doped CdSe QDs in QDSSCs can obtain superior light absorption, faster electron transport and slower charge recombination than CdSe QDs. PMID:29657776

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

PubMed

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

2018-06-13

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

Chemically Triggered Formation of Two-Dimensional Epitaxial Quantum Dot Superlattices.

PubMed

Walravens, Willem; De Roo, Jonathan; Drijvers, Emile; Ten Brinck, Stephanie; Solano, Eduardo; Dendooven, Jolien; Detavernier, Christophe; Infante, Ivan; Hens, Zeger

2016-07-26

Two dimensional superlattices of epitaxially connected quantum dots enable size-quantization effects to be combined with high charge carrier mobilities, an essential prerequisite for highly performing QD devices based on charge transport. Here, we demonstrate that surface active additives known to restore nanocrystal stoichiometry can trigger the formation of epitaxial superlattices of PbSe and PbS quantum dots. More specifically, we show that both chalcogen-adding (sodium sulfide) and lead oleate displacing (amines) additives induce small area epitaxial superlattices of PbSe quantum dots. In the latter case, the amine basicity is a sensitive handle to tune the superlattice symmetry, with strong and weak bases yielding pseudohexagonal or quasi-square lattices, respectively. Through density functional theory calculations and in situ titrations monitored by nuclear magnetic resonance spectroscopy, we link this observation to the concomitantly different coordination enthalpy and ligand displacement potency of the amine. Next to that, an initial ∼10% reduction of the initial ligand density prior to monolayer formation and addition of a mild, lead oleate displacing chemical trigger such as aniline proved key to induce square superlattices with long-range, square micrometer order; an effect that is the more pronounced the larger the quantum dots. Because the approach applies to PbS quantum dots as well, we conclude that it offers a reproducible and rational method for the formation of highly ordered epitaxial quantum dot superlattices.

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

PubMed

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

2009-01-21

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

Experimental and theoretical quantum chemical investigations of 8-hydroxy-5-nitroquinoline.

PubMed

Arjunan, V; Balamourougane, P S; Kalaivani, M; Raj, Arushma; Mohan, S

2012-10-01

The FT-IR and FT-Raman spectra of 8-hydroxy-5-nitroquinoline have been recorded in the regions 4000-400 and 4000-100 cm(-1), respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The normal coordinate analysis was carried out to confirm the precision of the assignments. The structure of the compound was optimised and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G(**), 6-311++G(**) and cc-pVDZ basis sets. The vibrational frequencies were calculated in all these methods and were compared with the experimental frequencies which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. (1)H and (13)C NMR spectra were recorded and (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-Visible spectrum of the compound was recorded and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The influences of the nitro and hydroxy groups on the skeletal modes and on the proton chemical shifts have been investigated. Copyright © 2012 Elsevier B.V. All rights reserved.

Quantum Monte Carlo tunneling from quantum chemistry to quantum annealing

NASA Astrophysics Data System (ADS)

Mazzola, Guglielmo; Smelyanskiy, Vadim N.; Troyer, Matthias

2017-10-01

Quantum tunneling is ubiquitous across different fields, from quantum chemical reactions and magnetic materials to quantum simulators and quantum computers. While simulating the real-time quantum dynamics of tunneling is infeasible for high-dimensional systems, quantum tunneling also shows up in quantum Monte Carlo (QMC) simulations, which aim to simulate quantum statistics with resources growing only polynomially with the system size. Here we extend the recent results obtained for quantum spin models [Phys. Rev. Lett. 117, 180402 (2016), 10.1103/PhysRevLett.117.180402], and we study continuous-variable models for proton transfer reactions. We demonstrate that QMC simulations efficiently recover the scaling of ground-state tunneling rates due to the existence of an instanton path, which always connects the reactant state with the product. We discuss the implications of our results in the context of quantum chemical reactions and quantum annealing, where quantum tunneling is expected to be a valuable resource for solving combinatorial optimization problems.

Non-Markovian Investigation of an Autonomous Quantum Heat Engine

NASA Astrophysics Data System (ADS)

Goyal, Ketan

A systematic study of a quantum heat engine is presented in this thesis. In particular, we study heat conduction through a two-two level composite system, which is then connected to a photon cavity to extract work, forming an autonomous quantum heat engine. The question as to what extent quantum effects such as quantum coherence and correlations impact thermodynamic properties of such a system is addressed. The investigated heat engine has been previously studied using the popular Born-Markovian quantum master equation under weak internal coupling approximation. However, we show that the used approach is quite limited in addressing such problems as it is incapable of correctly accounting for the quantum effects. By using a non-Markovian approach involving hierarchical equations of motion, we show that quantum coherence and correlations between system and environments play a significant role in energy transfer processes of heat conduction and work.

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

NASA Astrophysics Data System (ADS)

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

2015-10-01

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

Quantum Chemically Estimated Abraham Solute Parameters Using Multiple Solvent-Water Partition Coefficients and Molecular Polarizability.

PubMed

Liang, Yuzhen; Xiong, Ruichang; Sandler, Stanley I; Di Toro, Dominic M

2017-09-05

Polyparameter Linear Free Energy Relationships (pp-LFERs), also called Linear Solvation Energy Relationships (LSERs), are used to predict many environmentally significant properties of chemicals. A method is presented for computing the necessary chemical parameters, the Abraham parameters (AP), used by many pp-LFERs. It employs quantum chemical calculations and uses only the chemical's molecular structure. The method computes the Abraham E parameter using density functional theory computed molecular polarizability and the Clausius-Mossotti equation relating the index refraction to the molecular polarizability, estimates the Abraham V as the COSMO calculated molecular volume, and computes the remaining AP S, A, and B jointly with a multiple linear regression using sixty-five solvent-water partition coefficients computed using the quantum mechanical COSMO-SAC solvation model. These solute parameters, referred to as Quantum Chemically estimated Abraham Parameters (QCAP), are further adjusted by fitting to experimentally based APs using QCAP parameters as the independent variables so that they are compatible with existing Abraham pp-LFERs. QCAP and adjusted QCAP for 1827 neutral chemicals are included. For 24 solvent-water systems including octanol-water, predicted log solvent-water partition coefficients using adjusted QCAP have the smallest root-mean-square errors (RMSEs, 0.314-0.602) compared to predictions made using APs estimated using the molecular fragment based method ABSOLV (0.45-0.716). For munition and munition-like compounds, adjusted QCAP has much lower RMSE (0.860) than does ABSOLV (4.45) which essentially fails for these compounds.

Quantum chemical modeling of new derivatives of (E,E)-azomethines: Synthesis, spectroscopic (FT-IR, UV/Vis, polarization) and thermophysical investigations

NASA Astrophysics Data System (ADS)

Shahab, Siyamak; Sheikhi, Masoome; Filippovich, Liudmila; Anatol'evich, Dikusar Evgenij; Yahyaei, Hooriye

2017-06-01

In the present work, the molecular structures of three new azomethine dyes: N-benzylidene-4-((E)-phenyldiazenyl)aniline (PAZB-1), 2-methoxy-4-(((4-((E)- phenyldiazenyl)phenyl)imino)methyl)phenol (PAZB-2) and 2-methoxy-5-((E)-((4-((E)- phenyldiazenyl)phenyl)imino)methyl)phenol (PAZB-8) have been predicted and investigated using Density Functional Theory (DFT) in dimethylformamide (DMF). The geometries of the azomethine dyes were optimized by PBE0/6-31 + G* level of theory. The electronic spectra of these azomethine dyes in a DMF solution was carried out by TDPBE0/6-31 + G* method. After quantum-chemical calculations three new azomethine dyes for optoelectronic applications were synthesized. FT-IR spectra of the title compounds are recorded and discussed. The computed absorption spectral data of the azomethine dyes are in good agreement with the experimental data, thus allowing an assignment of the UV/Vis spectra. On the basis of polyvinyl alcohol (PVA) and the new synthesized azomethine dyes polarizing films for Visible region of spectrum were developed. The main optical parameters of polarizing PVA-films (Transmittance, Polarization Efficiency and Dichroic Ratio) have been measured and discussed. Anisotropy of thermal conductivity of the PVA-films has been studied.

Double quantum coherence ESR spectroscopy and quantum chemical calculations on a BDPA biradical.

PubMed

Haeri, Haleh Hashemi; Spindler, Philipp; Plackmeyer, Jörn; Prisner, Thomas

2016-10-26

Carbon-centered radicals are interesting alternatives to otherwise commonly used nitroxide spin labels for dipolar spectroscopy techniques because of their narrow ESR linewidth. Herein, we present a novel BDPA biradical, where two BDPA (α,α,γ,γ-bisdiphenylene-β-phenylallyl) radicals are covalently tethered by a saturated biphenyl acetylene linker. The inter-spin distance between the two spin carrier fragments was measured using double quantum coherence (DQC) ESR methodology. The DQC experiment revealed a mean distance of only 1.8 nm between the two unpaired electron spins. This distance is shorter than the predictions based on a simple modelling of the biradical geometry with the electron spins located at the central carbon atoms. Therefore, DFT (density functional theory) calculations were performed to obtain a picture of the spin delocalization, which may give rise to a modified dipolar interaction tensor, and to find those conformations that correspond best to the experimentally observed inter-spin distance. Quantum chemical calculations showed that the attachment of the biphenyl acetylene linker at the second position of the fluorenyl ring of BDPA did not affect the spin population or geometry of the BDPA radical. Therefore, spin delocalization and geometry optimization of each BDPA moiety could be performed on the monomeric unit alone. The allylic dihedral angle θ 1 between the fluorenyl rings in the monomer subunit was determined to be 30° or 150° using quantum chemical calculations. The proton hyperfine coupling constant calculated from both energy minima was in very good agreement with literature values. Based on the optimal monomer geometries and spin density distributions, the dipolar coupling interaction between both BDPA units could be calculated for several dimer geometries. It was shown that the rotation of the BDPA units around the linker axis (θ 2 ) does not significantly influence the dipolar coupling strength when compared to the allylic

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

NASA Astrophysics Data System (ADS)

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

1997-01-01

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

Cluster Quantum Chemical Study of the Grignard Reagent Formation

NASA Astrophysics Data System (ADS)

Tulub, A. V.; Porsev, V. V.

The main stages of the Grignard reagent formation are described in a framework of quantum chemical cluster model. We have established two kinds of the adsorption of CH3Hal on Mgn clusters, one of which leads to radical formation and the second is responsible for radical free dissociate adsorption. The charge redistribution in cluster CH3MgnHal result to the strong electrostatic interaction with ether and Grignard reagent formation without any activation barrier.

Lighting up micromotors with quantum dots for smart chemical sensing.

PubMed

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

2015-09-25

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

A new chalcone structure of (E)-1-(4-Bromophenyl)-3-(napthalen-2-yl)prop-2-en-1-one: Synthesis, structural characterizations, quantum chemical investigations and biological evaluations.

PubMed

Thanigaimani, Kaliyaperumal; Arshad, Suhana; Khalib, Nuridayanti Che; Razak, Ibrahim Abdul; Arunagiri, C; Subashini, A; Sulaiman, Shaida Fariza; Hashim, Nurul Shafiqah; Ooi, Kheng Leong

2015-01-01

The structure of (E)-1-(4-Bromophenyl)-3-(napthalen-2-yl)prop-2-en-1-one (C19H13BrO) crystallized in the triclinic system of P-1 space group. The unit cell dimensions are: a=5.8944 (9)Å, b=7.8190 (12)Å, c=16.320 (2)Å, α=102.4364 (19)°, β=95.943 (2)°, γ=96.274 (2)° and Z=2. The physical properties of this compound was determined by the spectroscopic methods (FTIR and (1)H and (13)C NMR). Quantum chemical investigations have been employed to investigate the structural and spectral properties. The molecular structure, vibrational assignments, (1)H and (13)C NMR chemical shift values, non-linear optical (NLO) effect, HOMO-LUMO analysis and natural bonding orbital (NBO) analysis were calculated using HF and DFT/B3LYP methods with 6-311++G(d,p) basis set in the ground state. The results show that the theoretical calculation of the geometrical parameters, vibrational frequencies and chemical shifts are comparable with the experimental data. The crystal structure is influenced and stabilized by weak C-H⋯π interactions connecting the molecules into infinite supramolecular one dimensional ladder-like arrangement. Additionally, this compound is evaluated for their antibacterial activities against gram positive and gram negative strains using a micro dilution procedure and shows activities against a panel of microorganisms. Copyright © 2015 Elsevier B.V. All rights reserved.

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

PubMed

Sevastik, Robin; Himo, Fahmi

2007-12-01

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

Spectroscopic and chemical reactivity analysis of D-Myo-Inositol using quantum chemical approach and its experimental verification

NASA Astrophysics Data System (ADS)

Mishra, Devendra P.; Srivastava, Anchal; Shukla, R. K.

2017-07-01

This paper describes the spectroscopic (^1H and ^{13}C NMR, FT-IR and UV-Visible), chemical, nonlinear optical and thermodynamic properties of D-Myo-Inositol using quantum chemical technique and its experimental verification. The structural parameters of the compound are determined from the optimized geometry by B3LYP method with 6 {-}311{+}{+}G(d,p) basis set. It was found that the optimized parameters thus obtained are almost in agreement with the experimental ones. A detailed interpretation of the infrared spectra of D-Myo-Inositol is also reported in the present work. After optimization, the proton and carbon NMR chemical shifts of the studied compound are calculated using GIAO and 6 {-}311{+}{+}G(d,p) basis set. The search of organic materials with improved charge transfer properties requires precise quantum chemical calculations of space-charge density distribution, state and transition dipole moments and HOMO-LUMO states. The nature of the transitions in the observed UV-Visible spectrum of the compound has been studied by the time-dependent density functional theory (TD-DFT). The global reactivity descriptors like chemical potential, electronegativity, hardness, softness and electrophilicity index, have been calculated using DFT. The thermodynamic calculation related to the title compound was also performed at B3LYP/ 6 {-}311{+}{+}G(d,p) level of theory. The standard statistical thermodynamic functions like heat capacity at constant pressure, entropy and enthalpy change were obtained from the theoretical harmonic frequencies of the optimized molecule. It is observed that the values of heat capacity, entropy and enthalpy increase with increase in temperature from 100 to 1000 K, which is attributed to the enhancement of molecular vibration with the increase in temperature.

Rhorix: An interface between quantum chemical topology and the 3D graphics program blender

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mills, Matthew J. L.; Sale, Kenneth L.; Simmons, Blake A.

Journal of Computational Chemistry Published by Wiley Periodicals, Inc. Chemical research is assisted by the creation of visual representations that map concepts (such as atoms and bonds) to 3D objects. These concepts are rooted in chemical theory that predates routine solution of the Schrödinger equation for systems of interesting size. The method of Quantum Chemical Topology (QCT) provides an alternative, parameter-free means to understand chemical phenomena directly from quantum mechanical principles. Representation of the topological elements of QCT has lagged behind the best tools available. Here, we describe a general abstraction (and corresponding file format) that permits the definition ofmore » mappings between topological objects and their 3D representations. Possible mappings are discussed and a canonical example is suggested, which has been implemented as a Python “Add-On” named Rhorix for the state-of-the-art 3D modeling program Blender. This allows chemists to use modern drawing tools and artists to access QCT data in a familiar context. Finally, a number of examples are discussed..« less

Rhorix: An interface between quantum chemical topology and the 3D graphics program blender

PubMed Central

Sale, Kenneth L.; Simmons, Blake A.; Popelier, Paul L. A.

2017-01-01

Chemical research is assisted by the creation of visual representations that map concepts (such as atoms and bonds) to 3D objects. These concepts are rooted in chemical theory that predates routine solution of the Schrödinger equation for systems of interesting size. The method of Quantum Chemical Topology (QCT) provides an alternative, parameter‐free means to understand chemical phenomena directly from quantum mechanical principles. Representation of the topological elements of QCT has lagged behind the best tools available. Here, we describe a general abstraction (and corresponding file format) that permits the definition of mappings between topological objects and their 3D representations. Possible mappings are discussed and a canonical example is suggested, which has been implemented as a Python “Add‐On” named Rhorix for the state‐of‐the‐art 3D modeling program Blender. This allows chemists to use modern drawing tools and artists to access QCT data in a familiar context. A number of examples are discussed. © 2017 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc. PMID:28857244

Rhorix: An interface between quantum chemical topology and the 3D graphics program blender

DOE PAGES

Mills, Matthew J. L.; Sale, Kenneth L.; Simmons, Blake A.; ...

2017-08-31

Journal of Computational Chemistry Published by Wiley Periodicals, Inc. Chemical research is assisted by the creation of visual representations that map concepts (such as atoms and bonds) to 3D objects. These concepts are rooted in chemical theory that predates routine solution of the Schrödinger equation for systems of interesting size. The method of Quantum Chemical Topology (QCT) provides an alternative, parameter-free means to understand chemical phenomena directly from quantum mechanical principles. Representation of the topological elements of QCT has lagged behind the best tools available. Here, we describe a general abstraction (and corresponding file format) that permits the definition ofmore » mappings between topological objects and their 3D representations. Possible mappings are discussed and a canonical example is suggested, which has been implemented as a Python “Add-On” named Rhorix for the state-of-the-art 3D modeling program Blender. This allows chemists to use modern drawing tools and artists to access QCT data in a familiar context. Finally, a number of examples are discussed..« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Rongchun; Mroue, Kamal H.; Ramamoorthy, Ayyalusamy, E-mail: ramamoor@umich.edu

2015-10-14

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yiteng; Kais, Sabre; Berman, Gennady Petrovich

2015-02-02

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

Quantum Chemical Molecular Dynamics Simulations of 1,3-Dichloropropene Combustion.

PubMed

Ahubelem, Nwakamma; Shah, Kalpit; Moghtaderi, Behdad; Page, Alister J

2015-09-03

Oxidative decomposition of 1,3-dichloropropene was investigated using quantum chemical molecular dynamics (QM/MD) at 1500 and 3000 K. Thermal oxidation of 1,3-dichloropropene was initiated by (1) abstraction of allylic H/Cl by O2 and (2) intra-annular C-Cl bond scission and elimination of allylic Cl. A kinetic analysis shows that (2) is the more dominant initiation pathway, in agreement with QM/MD results. These QM/MD simulations reveal new routes to the formation of major products (H2O, CO, HCl, CO2), which are propagated primarily by the chloroperoxy (ClO2), OH, and 1,3-dichloropropene derived radicals. In particular, intra-annular C-C/C-H bond dissociation reactions of intermediate aldehydes/ketones are shown to play a dominant role in the formation of CO and CO2. Our simulations demonstrate that both combustion temperature and radical concentration can influence the product yield, however not the combustion mechanism.

Chemical reaction CO+OH • → CO 2+H • autocatalyzed by carbon dioxide: Quantum chemical study of the potential energy surfaces

DOE PAGES

Masunov, Artem E.; Wait, Elizabeth; Vasu, Subith S.

2016-06-28

The supercritical carbon dioxide medium, used to increase efficiency in oxy combustion fossil energy technology, may drastically alter both rates and mechanisms of chemical reactions. Here we investigate potential energy surface of the second most important combustion reaction with quantum chemistry methods. Two types of effects are reported: formation of the covalent intermediates and formation of van der Waals complexes by spectator CO 2 molecule. While spectator molecule alter the activation barrier only slightly, the covalent bonding opens a new reaction pathway. The mechanism includes sequential covalent binding of CO 2 to OH radical and CO molecule, hydrogen transfer frommore » oxygen to carbon atoms, and CH bond dissociation. This reduces the activation barrier by 11 kcal/mol at the rate-determining step and is expected to accelerate the reaction rate. The finding of predicted catalytic effect is expected to play an important role not only in combustion but also in a broad array of chemical processes taking place in supercritical CO 2 medium. Furthermore, tt may open a new venue for controlling reaction rates for chemical manufacturing.« less

Structural, vibrational, electronic investigations and quantum chemical studies of 2-amino-4-methoxybenzothiazole.

PubMed

Arjunan, V; Raj, Arushma; Santhanam, R; Marchewka, M K; Mohan, S

2013-02-01

Extensive vibrational investigations of 2-amino-4-methoxybenzothiazole have been carried out with FTIR and FT-Raman spectral techniques. The electronic structure of the molecule has been analysed by UV-Visible and NMR spectroscopies. The DFT studies were carried out with B3LYP and HF methods utilising 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets to determine the structural, thermodynamical, vibrational, electronic characteristics of the compound and also to understand the electronic and steric influence of the methoxy amino groups on the skeletal frequencies. The mixing of the fundamental modes was determined with the help of total energy distribution (TED). The energies of the frontier molecular orbitals have also been determined. The kinetic and thermodynamic stability and chemical hardness of the molecule have been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. (1)H and (13)C NMR chemical shifts and the electronic transitions of the molecule are also discussed. Copyright © 2012 Elsevier B.V. All rights reserved.

Structural, vibrational, electronic investigations and quantum chemical studies of 2-amino-4-methoxybenzothiazole

NASA Astrophysics Data System (ADS)

Arjunan, V.; Raj, Arushma; Santhanam, R.; Marchewka, M. K.; Mohan, S.

2013-02-01

Extensive vibrational investigations of 2-amino-4-methoxybenzothiazole have been carried out with FTIR and FT-Raman spectral techniques. The electronic structure of the molecule has been analysed by UV-Visible and NMR spectroscopies. The DFT studies were carried out with B3LYP and HF methods utilising 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets to determine the structural, thermodynamical, vibrational, electronic characteristics of the compound and also to understand the electronic and steric influence of the methoxy amino groups on the skeletal frequencies. The mixing of the fundamental modes was determined with the help of total energy distribution (TED). The energies of the frontier molecular orbitals have also been determined. The kinetic and thermodynamic stability and chemical hardness of the molecule have been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. 1H and 13C NMR chemical shifts and the electronic transitions of the molecule are also discussed.

Quantum Chemical Mass Spectrometry: Verification and Extension of the Mobile Proton Model for Histidine

NASA Astrophysics Data System (ADS)

Cautereels, Julie; Blockhuys, Frank

2017-06-01

The quantum chemical mass spectrometry for materials science (QCMS2) method is used to verify the proposed mechanism for proton transfer - the Mobile Proton Model (MPM) - by histidine for ten XHS tripeptides, based on quantum chemical calculations at the DFT/B3LYP/6-311+G* level of theory. The fragmentations of the different intermediate structures in the MPM mechanism are studied within the QCMS2 framework, and the energetics of the proposed mechanism itself and those of the fragmentations of the intermediate structures are compared, leading to the computational confirmation of the MPM. In addition, the calculations suggest that the mechanism should be extended from considering only the formation of five-membered ring intermediates to include larger-ring intermediates. [Figure not available: see fulltext.

Radiation and quantum chemical studies of chalcone derivatives.

PubMed

Gaikwad, P; Priyadarsini, K I; Naumov, S; Rao, B S M

2010-08-05

The reactions of oxidizing radicals ((*)OH, Br(2)(*-), and SO(4)(*-)) with -OH-, -CH(3)-, or -NH(2)-substituted indole chalcones and hydroxy benzenoid chalcones were studied by radiation and quantum chemical methods. The (*)OH radical was found to react by addition at diffusion-controlled rates (k = 1.1-1.7 x 10(10) dm(3) mol(-1) s(-1)), but Br(2)(*-) radical reacted by 2 orders of magnitude lower. Quantum chemical calculations at the B3LYP/6-31+G(d,p) level of theory have shown that the (C2-OH)(*), (C11-OH)(*), and (C10-OH)(*) adducts of the indole chalcones and the (C7-OH)(*) and (C8-OH)(*) adducts of the hydroxy benzenoid chalcones are more stable with DeltaH = -39 to -28 kcal mol(-1) and DeltaG = -32 to -19 kcal mol(-1). This suggests that (*)OH addition to the alpha,beta-unsaturated bond is a major reaction channel in both types of chalcones and is barrierless. The stability and lack of dehydration of the (*)OH adducts arise from two factors: strong frontier orbital interaction due to the low energy gap between interacting orbitals and the negligible Coulombic repulsion due to small absolute values of Mulliken charges. The transient absorption spectrum measured in the (*)OH radical reaction with all the indole chalcone derivatives exhibited a maximum at 390 nm, which is in excellent agreement with the computed value (394 nm). The formation of three phenolic products under steady-state radiolysis is in line with the three stable (*)OH adducts predicted by theory. Independent of the substituent, identical spectra (lambda(max) = 330-360 and approximately 580 nm) were obtained on one-electron oxidation of the three indole chalcones. MO calculations predict the deprotonation from the -NH group is more efficient than from the substituent due to the larger electron density on the N1 atom forming the chalcone indolyl radical. Its reduction potential was determined to be 0.56 V from the ABTS(*-)/ABTS(2-) couple. In benzenoid chalcones, the (*)OH adduct spectrum is

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

PubMed

Bratholm, Lars A; Jensen, Jan H

2017-03-01

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

Adsorption, Thermodynamic and Quantum Chemical Studies of 1-hexyl-3-methylimidazolium Based Ionic Liquids as Corrosion Inhibitors for Mild Steel in HCl

PubMed Central

Mashuga, Motsie E.; Olasunkanmi, Lukman O.; Adekunle, Abolanle S.; Yesudass, Sasikumar; Kabanda, Mwadham M.; Ebenso, Eno E.

2015-01-01

The inhibition of mild steel corrosion in 1 M HCl solution by some ionic liquids (ILs) namely, 1-hexyl-3-methylimidazolium trifluoromethanesulfonate [HMIM][TfO], 1-hexyl-3-methylimidazolium tetrafluoroborate [HMIM][BF4], 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF6], and 1-hexyl-3-methylimidazolium iodide [HMIM][I] was investigated using electrochemical measurements, spectroscopic analyses and quantum chemical calculations. All the ILs showed appreciably high inhibition efficiency. At 303 K, the results of electrochemical measurements indicated that the studied ILs are mixed-type inhibitors. The adsorption studies showed that all the four ILs adsorb spontaneously on steel surface with [HMIM][TfO], [HMIM][BF4] and [HMIM][I] obeying Langmuir adsorption isotherm, while [HMIM][PF6] conformed better with Temkin adsorption isotherm. Spectroscopic analyses suggested the formation of Fe/ILs complexes. Some quantum chemical parameters were calculated to corroborate experimental results.

Investigations of quantum pendulum dynamics in a spin-1 BEC

NASA Astrophysics Data System (ADS)

Hoang, Thai; Gerving, Corey; Land, Ben; Anquez, Martin; Hamley, Chris; Chapman, Michael

2013-05-01

We investigate the quantum spin dynamics of a spin-1 BEC initialized to an unstable critical point of the dynamical phase space. The subsequent evolution of the collective states of the system is analogous to an inverted simple pendulum in the quantum limit and yields non-classical states with quantum correlations. For short evolution times in the low depletion limit, we observe squeezed states and for longer times beyond the low depletion limit we observe highly non-Gaussian distributions. C.D. Hamley, C.S. Gerving, T.M. Hoang, E.M. Bookjans, and M.S. Chapman, ``Spin-Nematic Squeezed Vacuum in a Quantum Gas,'' Nature Physics 8, 305-308 (2012).

Quantum chemical study of a derivative of 3-substituted dithiocarbamic flavanone

NASA Astrophysics Data System (ADS)

Gosav, Steluta; Paduraru, Nicoleta; Maftei, Dan; Birsa, Mihail Lucian; Praisler, Mirela

2017-02-01

The aim of this work is to characterize a quite novel 3-dithiocarbamic flavonoid by vibrational spectroscopy in conjunction with Density Functional Theory (DFT) calculations. Quantum mechanics calculations of energies, geometries and vibrational wavenumbers in the ground state were carried out by using hybrid functional B3LYP with 6-311G(d,p) as basis set. The results indicate a remarkable agreement between the calculated molecular geometries, as well as vibrational frequencies, and the corresponding experimental data. In addition, a complete assignment of all the absorption bands present in the vibrational spectrum has been performed. In order to assess its chemical potential, quantum molecular descriptors characterizing the interactions between the 3-dithiocarbamic flavonoid and its biological receptors have been computed. The frontier molecular orbitals and the HOMO-LUMO energy gap have been used in order to explain the way in which the new molecule can interact with other species and to characterize its molecular chemical stability/reactivity. The molecular electrostatic potential (MEP) map, computed in order to identify the sites of the studied flavonoid that are most likely to interact with electrophilic and nucleophilic species, is discussed.

Observation of the Quantum Anomalous Hall Insulator to Anderson Insulator Quantum Phase Transition and its Scaling Behavior.

PubMed

Chang, Cui-Zu; Zhao, Weiwei; Li, Jian; Jain, J K; Liu, Chaoxing; Moodera, Jagadeesh S; Chan, Moses H W

2016-09-16

Fundamental insight into the nature of the quantum phase transition from a superconductor to an insulator in two dimensions, or from one plateau to the next or to an insulator in the quantum Hall effect, has been revealed through the study of its scaling behavior. Here, we report on the experimental observation of a quantum phase transition from a quantum-anomalous-Hall insulator to an Anderson insulator in a magnetic topological insulator by tuning the chemical potential. Our experiment demonstrates the existence of scaling behavior from which we extract the critical exponent for this quantum phase transition. We expect that our work will motivate much further investigation of many properties of quantum phase transition in this new context.

QSTR of the toxicity of some organophosphorus compounds by using the quantum chemical and topological descriptors.

PubMed

Senior, Samir A; Madbouly, Magdy D; El massry, Abdel-Moneim

2011-09-01

Quantum chemical and topological descriptors of some organophosphorus compounds (OP) were correlated with their toxicity LD(50) as a dermal. The quantum chemical parameters were obtained using B3LYP/LANL2DZdp-ECP optimization. Using linear regression analysis, equations were derived to calculate the theoretical LD(50) of the studied compounds. The inclusion of quantum parameters, having both charge indices and topological indices, affects the toxicity of the studied compounds resulting in high correlation coefficient factors for the obtained equations. Two of the new four firstly supposed descriptors give higher correlation coefficients namely the Heteroatom Corrected Extended Connectivity Randic index ((1)X(HCEC)) and the Density Randic index ((1)X(Den)). The obtained linear equations were applied to predict the toxicity of some related structures. It was found that the sulfur atoms in these compounds must be replaced by oxygen atoms to achieve improved toxicity. Copyright © 2011 Elsevier Ltd. All rights reserved.

Surface emitting ring quantum cascade lasers for chemical sensing

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

Simulating chemistry using quantum computers.

PubMed

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.

On the bathochromic shift of the absorption by astaxanthin in crustacyanin: a quantum chemical study

NASA Astrophysics Data System (ADS)

Durbeej, Bo; Eriksson, Leif A.

2003-06-01

The structural origin of the bathochromic shift assumed by the electronic absorption spectrum of protein-bound astaxanthin, the carotenoid that upon binding to crustacyanin is responsible for the blue colouration of lobster shell, is investigated by means of quantum chemical methods. The calculations suggest that the bathochromic shift is largely due to one of the astaxanthin C4 keto groups being hydrogen-bonded to a histidine residue of the surrounding protein, and that the effect of this histidine is directly dependent on its protonation state. Out of the different methodologies (CIS, TD-DFT, and ZINDO/S) employed to calculate wavelengths of maximum absorption, the best agreement with experimental data is obtained using the semiempirical ZINDO/S method.

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

NASA Astrophysics Data System (ADS)

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

2010-05-01

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

Quantum chemical approaches to [NiFe] hydrogenase.

PubMed

Vaissier, Valerie; Van Voorhis, Troy

2017-05-09

The mechanism by which [NiFe] hydrogenase catalyses the oxidation of molecular hydrogen is a significant yet challenging topic in bioinorganic chemistry. With far-reaching applications in renewable energy and carbon mitigation, significant effort has been invested in the study of these complexes. In particular, computational approaches offer a unique perspective on how this enzyme functions at an electronic and atomistic level. In this article, we discuss state-of-the art quantum chemical methods and how they have helped deepen our comprehension of [NiFe] hydrogenase. We outline the key strategies that can be used to compute the (i) geometry, (ii) electronic structure, (iii) thermodynamics and (iv) kinetic properties associated with the enzymatic activity of [NiFe] hydrogenase and other bioinorganic complexes. © 2017 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society.

Chemical bonding in TiSb(2) and VSb(2): a quantum chemical and experimental study.

PubMed

Armbrüster, Marc; Schnelle, Walter; Schwarz, Ulrich; Grin, Yuri

2007-08-06

The chemical bonding in the isostructural intermetallic compounds TiSb2 and VSb2, crystallizing in the CuAl2 type, was investigated by means of quantum chemical calculations, particularly the electron localization function (ELF), as well as by Raman spectroscopy, Hall effect and conductivity measurements on oriented single crystals, and high-pressure X-ray powder diffraction. The homogeneity ranges of the compounds were determined by powder X-ray diffraction, WDXS, and DSC measurements. TiSb2 exhibits no significant homogeneity range, while VSb2 shows a small homogeneity range of approximately 0.3 at. %. According to the ELF calculations, the Sb atoms form dumbbells via a two-center two-electron bond, while the T atoms (T = Ti, V) build up chains along the crystallographic c-axis. Both building units are connected by covalent T-Sb-T three-center bonds, thus forming a three-dimensional network. The strength of the bonds involving Sb was determined by fitting a force constant model to the vibrational mode frequencies observed by polarized Raman measurements on oriented single crystals. The resulting bond order of the Sb2 dumbbells is 1, while the strength of the three-center bonds resembles a bond order of 1.5. The weak pressure dependence of the c/a ratio confirms the slightly different bonding picture in TiSb2 compared to that in CuAl2. Electrical transport measurements show the presence of free charge carriers, as well as a metal-like temperature dependence of the electrical resistivity.

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

ERIC Educational Resources Information Center

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

2015-01-01

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

Quantum chemical study on the stability of honeybee queen pheromone against atmospheric factors.

PubMed

Shi, Rongwei; Liu, Fanglin

2016-06-01

The managed honeybee, Apis mellifera, has been experienced a puzzling event, termed as colony collapse disorder (CCD), in which worker bees abruptly disappear from their hives. Potential factors include parasites, pesticides, malnutrition, and environmental stresses. However, so far, no definitive relationship has been established between specific causal factors and CCD events. Here we theoretically test whether atmospheric environment could disturb the chemical communication between the queen and their workers in a colony. A quantum chemistry method has been used to investigate for the stability of the component of A. mellifera queen mandibular pheromone (QMP), (E)-9-keto-2-decenoic acid (9-ODA), against atmospheric water and free radicals. The results show that 9-ODA is less likely to react with water due to the high barrier heights (~36.5 kcal · mol(-1)) and very low reaction rates. However, it can easily react with triplet oxygen and hydroxyl radicals because of low or negative energy barriers. Thus, the atmospheric free radicals may disturb the chemical communication between the queen and their daughters in a colony. Our pilot study provides new insight for the cause of CCD, which has been reported throughout the world.

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

NASA Astrophysics Data System (ADS)

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

2008-06-01

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

High Color-Purity Green, Orange, and Red Light-Emitting Didoes Based on Chemically Functionalized Graphene Quantum Dots

NASA Astrophysics Data System (ADS)

Kwon, Woosung; Kim, Young-Hoon; Kim, Ji-Hee; Lee, Taehyung; Do, Sungan; Park, Yoonsang; Jeong, Mun Seok; Lee, Tae-Woo; Rhee, Shi-Woo

2016-04-01

Chemically derived graphene quantum dots (GQDs) to date have showed very broad emission linewidth due to many kinds of chemical bondings with different energy levels, which significantly degrades the color purity and color tunability. Here, we show that use of aniline derivatives to chemically functionalize GQDs generates new extrinsic energy levels that lead to photoluminescence of very narrow linewidths. We use transient absorption and time-resolved photoluminescence spectroscopies to study the electronic structures and related electronic transitions of our GQDs, which reveals that their underlying carrier dynamics is strongly related to the chemical properties of aniline derivatives. Using these functionalized GQDs as lumophores, we fabricate light-emitting didoes (LEDs) that exhibit green, orange, and red electroluminescence that has high color purity. The maximum current efficiency of 3.47 cd A-1 and external quantum efficiency of 1.28% are recorded with our LEDs; these are the highest values ever reported for LEDs based on carbon-nanoparticle phosphors. This functionalization of GQDs with aniline derivatives represents a new method to fabricate LEDs that produce natural color.

Experimental and Quantum-Chemical Study of Electronically Excited States of Protolytic Isovanillin Species

NASA Astrophysics Data System (ADS)

Vusovich, O. V.; Tchaikovskaya, O. N.; Sokolova, I. V.; Vasil'eva, N. Yu.

2014-05-01

Methods of electronic spectroscopy and quantum chemistry are used to compare protolytic vanillin and isovanillin species. Three protolytic species: anion, cation, and neutral are distinguished in the ground state of the examined molecules. Vanillin and isovanillin in the ground state in water possess identical spectral characteristics: line positions and intensities in the absorption spectra coincide. Minima of the electrostatic potential demonstrate that the deepest isomer minimum is observed on the carbonyl oxygen atom. However, investigations of the fluorescence spectra show that the radiative properties of isomers differ. An analysis of results of quantum-chemical calculations demonstrate that the long-wavelength ππ* transition in the vanillin absorption spectra is formed due to electron charge transfer from the phenol part of the molecule to oxygen atoms of the methoxy and carbonyl groups, and in the isovanillin absorption spectra, it is formed only on the oxygen atom of the methoxy group. The presence of hydroxyl and carbonyl groups in the structure of the examined molecules leads to the fact that isovanillin in the ground S0 state, the same as vanillin, possesses acidic properties, whereas in the excited S1 state, they possess basic properties. A comparison of the рKа values of aqueous solutions demonstrates that vanillin possesses stronger acidic and basic properties in comparison with isovanillin.

Investigation of the quantum efficiency of optical heterodyne detectors

NASA Technical Reports Server (NTRS)

Batchman, T. E.

1984-01-01

The frequency response and quantum efficiency of optical photodetectors for heterodyne receivers is investigated. The measurements utilized two spectral lines from the output of two lasers as input to the photodetectors. These lines are easily measurable in power and frequency and hence serve as known inputs. By measuring the output current of the photodetector the quantum efficiency is determined as a function of frequency separation between the two input signals. An investigation of the theoretical basis and accuracy of this type of measurement relative to similar measurements utilizing risetime is undertaken. A theoretical study of the heterodyne process in photodetectors based on semiconductor physics is included so that higher bandwidth detectors may be designed. All measurements are made on commercially available detectors and manufacturers' specifications for normal photodetector operation are compared to the measured heterodyne characteristics.

Some Phthalocyanine and Naphthalocyanine Derivatives as Corrosion Inhibitors for Aluminium in Acidic Medium: Experimental, Quantum Chemical Calculations, QSAR Studies and Synergistic Effect of Iodide Ions.

PubMed

Dibetsoe, Masego; Olasunkanmi, Lukman O; Fayemi, Omolola E; Yesudass, Sasikumar; Ramaganthan, Baskar; Bahadur, Indra; Adekunle, Abolanle S; Kabanda, Mwadham M; Ebenso, Eno E

2015-08-28

The effects of seven macrocyclic compounds comprising four phthalocyanines (Pcs) namely 1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (Pc1), 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (Pc2), 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (Pc3) and 29H,31H-phthalocyanine (Pc4), and three naphthalocyanines namely 5,9,14,18,23,27,32,36-octabutoxy-2,3-naphthalocyanine (nPc1), 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (nPc2) and 2,3-naphthalocyanine (nP3) were investigated on the corrosion of aluminium (Al) in 1 M HCl using a gravimetric method, potentiodynamic polarization technique, quantum chemical calculations and quantitative structure activity relationship (QSAR). Synergistic effects of KI on the corrosion inhibition properties of the compounds were also investigated. All the studied compounds showed appreciable inhibition efficiencies, which decrease with increasing temperature from 30 °C to 70 °C. At each concentration of the inhibitor, addition of 0.1% KI increased the inhibition efficiency compared to the absence of KI indicating the occurrence of synergistic interactions between the studied molecules and I(-) ions. From the potentiodynamic polarization studies, the studied Pcs and nPcs are mixed type corrosion inhibitors both without and with addition of KI. The adsorption of the studied molecules on Al surface obeys the Langmuir adsorption isotherm, while the thermodynamic and kinetic parameters revealed that the adsorption of the studied compounds on Al surface is spontaneous and involves competitive physisorption and chemisorption mechanisms. The experimental results revealed the aggregated interactions between the inhibitor molecules and the results further indicated that the peripheral groups on the compounds affect these interactions. The calculated quantum chemical parameters and the QSAR results revealed the possibility of strong interactions between the studied inhibitors and metal surface. QSAR analysis on the

Towards quantum chemistry on a quantum computer.

PubMed

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.

Chemical and explosive detections using photo-acoustic effect and quantum cascade lasers

NASA Astrophysics Data System (ADS)

Choa, Fow-Sen

2013-12-01

Photoacoustic (PA) effect is a sensitive spectroscopic technique for chemical sensing. In recent years, with the development of quantum cascade lasers (QCLs), significant progress has been achieved for PA sensing applications. Using high-power, tunable mid-IR QCLs as laser sources, PA chemical sensor systems have demonstrated parts-pertrillion- level detection sensitivity. Many of these high sensitivity measurements were demonstrated locally in PA cells. Recently, we have demonstrated standoff PA detection of isopropanol vapor for more than 41 feet distance using a quantum cascade laser and a microphone with acoustic reflectors. We also further demonstrated solid phase TNT detections at a standoff distance of 8 feet. To further calibrate the detection sensitivity, we use nerve gas simulants that were generated and calibrated by a commercial vapor generator. Standoff detection of gas samples with calibrated concentration of 2.3 ppm was achieved at a detection distance of more than 2 feet. An extended detection distance up to 14 feet was observed for a higher gas concentration of 13.9 ppm. For field operations, array of microphones and microphone-reflector pairs can be utilized to achieve noise rejection and signal enhancement. We have experimentally demonstrated that the signal and noise spectra of the 4 microphone/4 reflector system with a combined SNR of 12.48 dB. For the 16-microphone and one reflector case, an SNR of 17.82 was achieved. These successful chemical sensing demonstrations will likely create new demands for widely tunable QCLs with ultralow threshold (for local fire-alarm size detection systems) and high-power (for standoff detection systems) performances.

Computer simulations of local anesthetic mechanisms: Quantum chemical investigation of procaine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Jeremy C; Bondar, A.N.; Suhai, Sandor

2007-02-01

A description at the atomic level of detail of the interaction between local anesthetics, lipid membranes and membrane proteins, is essential for understanding the mechanism of local anesthesia. The importance of performing computer simulations to decipher the mechanism of local anesthesia is discussed here in the context of the current status of understanding of the local anesthetics action. As a first step towards accurate simulations of the interaction between local anesthetics, proteins, lipid and water molecules, here we use quantum mechanical methods to assess the charge distribution and structural properties of procaine in the presence and in the absence ofmore » water molecules. The calculations indicate that, in the absence of hydrogen-bonding water molecules, protonated procaine strongly prefers a compact structure enabled by intramolecular hydrogen bonding. In the presence of water molecules the torsional energy pro?le of procaine is modified, and hydrogen bonding to water molecules is favored relative to intra-molecular hydrogen bonding.« less

Toward the realization of a compact chemical sensor platform using quantum cascade lasers

NASA Astrophysics Data System (ADS)

Holthoff, Ellen L.; Marcus, Logan S.; Pellegrino, Paul M.

2015-05-01

The Army is investigating several spectroscopic techniques (e.g., infrared spectroscopy) that could allow for an adaptable sensor platform. Traditionally, chemical sensing platforms have been hampered by the opposing concerns of increasing sensor capability while maintaining a minimal package size. Current sensors, although reasonably sized, are geared to more classical chemical threats, and the ability to expand their capabilities to a broader range of emerging threats is uncertain. Recently, photoacoustic spectroscopy, employed in a sensor format, has shown enormous potential to address these ever-changing threats, while maintaining a compact sensor design. In order to realize the advantage of photoacoustic sensor miniaturization, light sources of comparable size are required. Recent research has employed quantum cascade lasers (QCLs) in combination with MEMS-scale photoacoustic cell designs. The continuous tuning capability of QCLs over a broad wavelength range in the mid-infrared spectral region greatly expands the number of compounds that can be identified. Results have demonstrated that utilizing a tunable QCL with a MEMS-scale photoacoustic cell produces favorable detection limits (ppb levels) for chemical targets (e.g., dimethyl methyl phosphonate (DMMP), vinyl acetate, 1,4-dioxane). Although our chemical sensing research has benefitted from the broad tuning capabilities of QCLs, the limitations of these sources must be considered. Current commercially available tunable systems are still expensive and obviously geared more toward laboratory operation, not fielding. Although the laser element itself is quite small, the packaging, power supply, and controller remain logistical burdens. Additionally, operational features such as continuous wave (CW) modulation and laser output powers while maintaining wide tunability are not yet ideal for a variety of sensing applications. In this paper, we will discuss our continuing evaluation of QCL technology as it matures

Experimental investigation of practical unforgeable quantum money

NASA Astrophysics Data System (ADS)

Bozzio, Mathieu; Orieux, Adeline; Trigo Vidarte, Luis; Zaquine, Isabelle; Kerenidis, Iordanis; Diamanti, Eleni

2018-01-01

Wiesner's unforgeable quantum money scheme is widely celebrated as the first quantum information application. Based on the no-cloning property of quantum mechanics, this scheme allows for the creation of credit cards used in authenticated transactions offering security guarantees impossible to achieve by classical means. However, despite its central role in quantum cryptography, its experimental implementation has remained elusive because of the lack of quantum memories and of practical verification techniques. Here, we experimentally implement a quantum money protocol relying on classical verification that rigorously satisfies the security condition for unforgeability. Our system exploits polarization encoding of weak coherent states of light and operates under conditions that ensure compatibility with state-of-the-art quantum memories. We derive working regimes for our system using a security analysis taking into account all practical imperfections. Our results constitute a major step towards a real-world realization of this milestone protocol.

Biomimetic, Mild Chemical Synthesis of CdTe-GSH Quantum Dots with Improved Biocompatibility

PubMed Central

Pérez-Donoso, José M.; Monrás, Juan P.; Bravo, Denisse; Aguirre, Adam; Quest, Andrew F.; Osorio-Román, Igor O.; Aroca, Ricardo F.; Chasteen, Thomas G.; Vásquez, Claudio C.

2012-01-01

Multiple applications of nanotechnology, especially those involving highly fluorescent nanoparticles (NPs) or quantum dots (QDs) have stimulated the research to develop simple, rapid and environmentally friendly protocols for synthesizing NPs exhibiting novel properties and increased biocompatibility. In this study, a simple protocol for the chemical synthesis of glutathione (GSH)-capped CdTe QDs (CdTe-GSH) resembling conditions found in biological systems is described. Using only CdCl2, K2TeO3 and GSH, highly fluorescent QDs were obtained under pH, temperature, buffer and oxygen conditions that allow microorganisms growth. These CdTe-GSH NPs displayed similar size, chemical composition, absorbance and fluorescence spectra and quantum yields as QDs synthesized using more complicated and expensive methods. CdTe QDs were not freely incorporated into eukaryotic cells thus favoring their biocompatibility and potential applications in biomedicine. In addition, NPs entry was facilitated by lipofectamine, resulting in intracellular fluorescence and a slight increase in cell death by necrosis. Toxicity of the as prepared CdTe QDs was lower than that observed with QDs produced by other chemical methods, probably as consequence of decreased levels of Cd+2 and higher amounts of GSH. We present here the simplest, fast and economical method for CdTe QDs synthesis described to date. Also, this biomimetic protocol favors NPs biocompatibility and helps to establish the basis for the development of new, “greener” methods to synthesize cadmium-containing QDs. PMID:22292028

Studies of quantum dots in the quantum Hall regime

NASA Astrophysics Data System (ADS)

Goldmann, Eyal

We present two studies of quantum dots in the quantum Hall regime. In the first study, presented in Chapter 3, we investigate the edge reconstruction phenomenon believed to occur when the quantum dot filling fraction is n≲1 . Our approach involves the examination of large dots (≤40 electrons) using a partial diagonalization technique in which the occupancies of the deep interior orbitals are frozen. To interpret the results of this calculation, we evaluate the overlap between the diagonalized ground state and a set of trial wavefunctions which we call projected necklace (PN) states. A PN state is simply the angular momentum projection of a maximum density droplet surrounded by a ring of localized electrons. Our calculations reveal that PN states have up to 99% overlap with the diagonalized ground states, and are lower in energy than the states identified in Chamon and Wen's study of the edge reconstruction. In the second study, presented in Chapter 4, we investigate quantum dots in the fractional quantum Hall regime using a Hartree formulation of composite fermion theory. We find that under appropriate conditions, the chemical potential of the dots oscillates periodically with B due to the transfer of composite fermions between quasi-Landau bands. This effect is analogous the addition spectrum oscillations which occur in quantum dots in the integer quantum Hall regime. Period f0 oscillations are found in sharply confined dots with filling factors nu = 2/5 and nu = 2/3. Period 3 f0 oscillations are found in a parabolically confined nu = 2/5 dot. More generally, we argue that the oscillation period of dots with band pinning should vary continuously with B, whereas the period of dots without band pinning is f0 .

Exploiting Locality in Quantum Computation for Quantum Chemistry.

PubMed

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.

Investigation of temperature-dependent photoluminescence in multi-quantum wells.

PubMed

Fang, Yutao; Wang, Lu; Sun, Qingling; Lu, Taiping; Deng, Zhen; Ma, Ziguang; Jiang, Yang; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Chen, Hong

2015-07-31

Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells.

FTIR, FT-Raman, FT-NMR, UV-visible and quantum chemical investigations of 2-amino-4-methylbenzothiazole.

PubMed

Arjunan, V; Sakiladevi, S; Rani, T; Mythili, C V; Mohan, S

2012-03-01

The FT-IR (4000-400 cm(-1)) and FT-Raman (4000-100 cm(-1)) spectral measurements and complete assignments of the observed spectra of 2-amino-4-methylbenzothiazole (2A4MBT) have been proposed. Ab initio and DFT calculations have been performed and the structural parameters of the compound were determined from the optimised geometry with 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets and giving energies, harmonic vibrational frequencies, depolarisation ratios, IR intensities and Raman activities. (1)H and (13)C NMR spectra were recorded and (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-visible spectrum of the compound was also recorded and the electronic properties, such as HOMO, LUMO and band gap energies were measured by time-dependent DFT (TD-DFT) approach. The geometric parameters, energies, harmonic vibrational frequencies, IR intensities, Raman activities chemical shifts and absorption wavelengths were compared with the available experimental data of the molecule. The influences of methyl and amino groups on the skeletal modes and on the proton chemical shifts have been investigated. Copyright © 2011 Elsevier B.V. All rights reserved.

Quantum Dot and Polymer Composite Cross-Reactive Array for Chemical Vapor Detection.

PubMed

Bright, Collin J; Nallon, Eric C; Polcha, Michael P; Schnee, Vincent P

2015-12-15

A cross-reactive chemical sensing array was made from CdSe Quantum Dots (QDs) and five different organic polymers by inkjet printing to create segmented fluorescent composite regions on quartz substrates. The sensor array was challenged with exposures from two sets of analytes, including one set of 14 different functionalized benzenes and one set of 14 compounds related to security concerns, including the explosives trinitrotoluene (TNT) and ammonium nitrate. The array was broadly responsive to analytes with different chemical functionalities due to the multiple sensing mechanisms that altered the QDs' fluorescence. The sensor array displayed excellent discrimination between members within both sets. Classification accuracy of more than 93% was achieved, including the complete discrimination of very similar dinitrobenzene isomers and three halogenated, substituted benzene compounds. The simple fabrication, broad responsivity, and high discrimination capacity of this type of cross-reactive array are ideal qualities for the development of sensors with excellent sensitivity to chemical and explosive threats while maintaining low false alarm rates.

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

NASA Astrophysics Data System (ADS)

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

2014-05-01

The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Assary, R. S.; Curtiss, L. A.; MSD)

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

Chemical potentials and thermodynamic characteristics of ideal Bose- and Fermi-gases in the region of quantum degeneracy

NASA Astrophysics Data System (ADS)

Sotnikov, A. G.; Sereda, K. V.; Slyusarenko, Yu. V.

2017-01-01

Calculations of chemical potentials for ideal monatomic gases with Bose-Einstein and Fermi-Dirac statistics as functions of temperature, across the temperature region that is typical for the collective quantum degeneracy effect, are presented. Numerical calculations are performed without any additional approximations, and explicit dependences of the chemical potentials on temperature are constructed at a fixed density of gas particles. Approximate polynomial dependences of chemical potentials on temperature are obtained that allow for the results to be used in further studies without re-applying the involved numerical methods. The ease of using the obtained representations is demonstrated on examples of deformation of distribution for a population of energy states at low temperatures, and on the impact of quantum statistics (exchange interaction) on the equations of state for ideal gases and some of the thermodynamic properties thereof. The results of this study essentially unify two opposite limiting cases in an intermediate region that are used to describe the equilibrium states of ideal gases, which are well known from university courses on statistical physics, thus adding value from an educational point of view.

Quantum cascade transmitters for ultrasensitive chemical agent and explosives detection

NASA Astrophysics Data System (ADS)

Schultz, John F.; Taubman, Matthew S.; Harper, Warren W.; Williams, Richard M.; Myers, Tanya L.; Cannon, Bret D.; Sheen, David M.; Anheier, Norman C., Jr.; Allen, Paul J.; Sundaram, S. K.; Johnson, Bradley R.; Aker, Pamela M.; Wu, Ming C.; Lau, Erwin K.

2003-07-01

The small size, high power, promise of access to any wavelength between 3.5 and 16 microns, substantial tuning range about a chosen center wavelength, and general robustness of quantum cascade (QC) lasers provide opportunities for new approaches to ultra-sensitive chemical detection and other applications in the mid-wave infrared. PNNL is developing novel remote and sampling chemical sensing systems based on QC lasers, using QC lasers loaned by Lucent Technologies. In recent months laboratory cavity-enhanced sensing experiments have achieved absorption sensitivities of 8.5 x 10-11 cm-1 Hz-1/2, and the PNNL team has begun monostatic and bi-static frequency modulated, differential absorption lidar (FM DIAL) experiments at ranges of up to 2.5 kilometers. In related work, PNNL and UCLA are developing miniature QC laser transmitters with the multiplexed tunable wavelengths, frequency and amplitude stability, modulation characteristics, and power levels needed for chemical sensing and other applications. Current miniaturization concepts envision coupling QC oscillators, QC amplifiers, frequency references, and detectors with miniature waveguides and waveguide-based modulators, isolators, and other devices formed from chalcogenide or other types of glass. Significant progress has been made on QC laser stabilization and amplification, and on development and characterization of high-purity chalcogenide glasses, waveguide writing techniques, and waveguide metrology.

Quantum Chemical and Docking Insights into Bioavailability Enhancement of Curcumin by Piperine in Pepper.

PubMed

Patil, Vaishali M; Das, Sukanya; Balasubramanian, Krishnan

2016-05-26

We combine quantum chemical and molecular docking techniques to provide new insights into how piperine molecule in various forms of pepper enhances bioavailability of a number of drugs including curcumin in turmeric for which it increases its bioavailability by a 20-fold. We have carried out docking studies of quantum chemically optimized piperine structure binding to curcumin, CYP3A4 in cytochrome P450, p-Glycoprotein and UDP-glucuronosyltransferase (UGT), the enzyme responsible for glucuronosylation, which increases the solubility of curcumin. All of these studies establish that piperine binds to multiple sites on the enzymes and also intercalates with curcumin forming a hydrogen bonded complex with curcumin. The conjugated network of double bonds and the presence of multiple charge centers of piperine offer optimal binding sites for piperine to bind to enzymes such as UDP-GDH, UGT, and CYP3A4. Piperine competes for curcumin's intermolecular hydrogen bonding and its stacking propensity by hydrogen bonding with enolic proton of curcumin. This facilitates its metabolic transport, thereby increasing its bioavailability both through intercalation into curcumin layers through intermolecular hydrogen bonding, and by inhibiting enzymes that cause glucuronosylation of curcumin.

Error Sensitivity to Environmental Noise in Quantum Circuits for Chemical State Preparation.

PubMed

Sawaya, Nicolas P D; Smelyanskiy, Mikhail; McClean, Jarrod R; Aspuru-Guzik, Alán

2016-07-12

Calculating molecular energies is likely to be one of the first useful applications to achieve quantum supremacy, performing faster on a quantum than a classical computer. However, if future quantum devices are to produce accurate calculations, errors due to environmental noise and algorithmic approximations need to be characterized and reduced. In this study, we use the high performance qHiPSTER software to investigate the effects of environmental noise on the preparation of quantum chemistry states. We simulated 18 16-qubit quantum circuits under environmental noise, each corresponding to a unitary coupled cluster state preparation of a different molecule or molecular configuration. Additionally, we analyze the nature of simple gate errors in noise-free circuits of up to 40 qubits. We find that, in most cases, the Jordan-Wigner (JW) encoding produces smaller errors under a noisy environment as compared to the Bravyi-Kitaev (BK) encoding. For the JW encoding, pure dephasing noise is shown to produce substantially smaller errors than pure relaxation noise of the same magnitude. We report error trends in both molecular energy and electron particle number within a unitary coupled cluster state preparation scheme, against changes in nuclear charge, bond length, number of electrons, noise types, and noise magnitude. These trends may prove to be useful in making algorithmic and hardware-related choices for quantum simulation of molecular energies.

Quantum mechanical model for the anticarcinogenic effect of extremely-low-frequency electromagnetic fields on early chemical hepatocarcinogenesis

NASA Astrophysics Data System (ADS)

Godina-Nava, Juan José; Torres-Vega, Gabino; López-Riquelme, Germán Octavio; López-Sandoval, Eduardo; Samana, Arturo Rodolfo; García Velasco, Fermín; Hernández-Aguilar, Claudia; Domínguez-Pacheco, Arturo

2017-02-01

Using the conventional Haberkorn approach, it is evaluated the recombination of the radical pair (RP) singlet spin state to study theoretically the cytoprotective effect of an extremely-low-frequency electromagnetic field (ELF-EMF) on early stages of hepatic cancer chemically induced in rats. The proposal is that ELF-EMF modulates the interconversion rate of singlet and triplet spin states of the RP populations modifying the products from the metabolization of carcinogens. Previously, we found that the daily treatment with ELF-EMF 120 Hz inhibited the number and area of preneoplastic lesions in chemical carcinogenesis. The singlet spin population is evaluated diagonalizing the spin density matrix through the Lanczos method in a radical pair mechanism (RPM). Using four values of the interchange energy, we have studied the variations over the singlet population. The low magnetic field effect as a test of the influence over the enzymatic chemical reaction is evaluated calculating the quantum yield. Through a bootstrap technique the range is found for the singlet decay rate for the process. Applying the quantum measurements concept, we addressed the impact toward hepatic cells. The result contributes to improving our understanding of the chemical carcinogenesis process affected by charged particles that damage the DNA.

Quantum chemical study of the inhibition of the corrosion of mild steel in H2SO4 by some antibiotics.

PubMed

Eddy, Nnabuk O; Ibok, Udo J; Ebenso, Eno E; El Nemr, Ahmed; El Ashry, El Sayed H

2009-09-01

The inhibition efficiency of some antibiotics against mild steel corrosion was studied using weight loss and quantum chemical techniques. Values of inhibition efficiency obtained from weight loss measurements correlated strongly with theoretical values obtained through semi empirical calculations. High correlation coefficients were also obtained between inhibition efficiency of the antibiotics and some quantum chemical parameters, including frontier orbital (E (HOMO) and E (LUMO)), dipole moment, log P, TNC and LSER parameters (critical volume and dipolar-polarisability factor), which indicated that these parameters affect the inhibition efficiency of the compounds. It was also found that quantitative structure activity relation can be used to adequately predict the inhibition effectiveness of these compounds.

FTIR, FT-Raman, FT-NMR and quantum chemical investigations of 3-acetylcoumarin

NASA Astrophysics Data System (ADS)

Arjunan, V.; Sakiladevi, S.; Marchewka, M. K.; Mohan, S.

2013-05-01

3-Acetylcoumarin (3AC) was synthesised by a Knoevenagel reaction. Conformational analysis using the B3LYP method was also carried out to determine the most stable conformation of the compound. FTIR and FT-Raman spectra of 3AC have been recorded in the range 4000-400 and 4000-100 cm-1, respectively. 1H and 13C NMR spectra have also been recorded. The complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the experimental FTIR and FT-Raman data and quantum mechanical studies. The experimental vibrational frequencies were compared with the wavenumbers obtained theoretically from the DFT-B3LYP/B3PW91 gradient calculations employing the standard 6-31G**, high level 6-311++G** and cc-pVTZ basis sets for optimised geometry of the compound. The frontier molecular orbital energies of the compound are determined by DFT method.

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

PubMed

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

2011-05-10

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

Ferrocene-based diradicals of imino nitroxide, nitronyl nitroxide and verdazyl, and their cations are possible SMM: A quantum chemical study

NASA Astrophysics Data System (ADS)

Pal, Arun K.; Datta, Sambhu N.

2017-05-01

Six diradicals designed from imino nitroxide, verdazyl and nitronyl nitroxide monoradicals coupled via the ferrocene moiety and six corresponding triradical cations are quantum chemically investigated. The transoid conformation is employed for considerations of general stability. All biradicals are found as very weakly and antiferromagnetically coupled. This agrees with experiment. The cations have strong antiferromagnetic spin-coupling. The charge and spin population distributions, spin alternation pattern, and the disjoint nature of SOMOs can be used to explain the nature and extent of magnetic interaction. Calculated EPR characteristics identify the neutral species as well as their cations as possible single molecule magnets.

Graphene-based quantum Hall resistance standards grown by chemical vapor deposition on silicon carbide

NASA Astrophysics Data System (ADS)

Ribeiro-Palau, Rebeca; Lafont, Fabien; Kazazis, Dimitris; Michon, Adrien; Couturaud, Olivier; Consejo, Christophe; Jouault, Benoit; Poirier, Wilfrid; Schopfer, Felicien

2015-03-01

Replace GaAs-based quantum Hall resistance standards (GaAs-QHRS) by a more convenient one, based on graphene (Gr-QHRS), is an ongoing goal in metrology. The new Gr-QHRS are expected to work in less demanding experimental conditions than GaAs ones. It will open the way to a broad dissemination of quantum standards, potentially towards industrial end-users, and it will support the implementation of a new International System of Units based on fixed fundamental constants. Here, we present accurate quantum Hall resistance measurements in large graphene Hall bars, grown by the hybrid scalable technique of propane/hydrogen chemical vapor deposition (CVD) on silicon carbide (SiC). This new Gr-QHRS shows a relative accuracy of 1 ×10-9 of the Hall resistance under the lowest magnetic field ever achieved in graphene. These experimental conditions surpass those of the most wildely used GaAs-QHRS. These results confirm the promises of graphene for resistance metrology applications and emphasizes the quality of the graphene produced by the CVD on SiC for applications as demanding as the resistance metrology.

Combined EXAFS Spectroscopic and Quantum Chemical Study on the Complex Formation of Am(III) with Formate.

PubMed

Fröhlich, Daniel R; Kremleva, Alena; Rossberg, André; Skerencak-Frech, Andrej; Koke, Carsten; Krüger, Sven; Rösch, Notker; Panak, Petra J

2017-06-19

The complexation of Am(III) with formate in aqueous solution is studied as a function of the pH value using a combination of extended X-ray absorption fine structure (EXAFS) spectroscopy, iterative transformation factor analysis (ITFA), and quantum chemical calculations. The Am L III -edge EXAFS spectra are analyzed to determine the molecular structure (coordination numbers; Am-O and Am-C distances) of the formed Am(III)-formate species and to track the shift of the Am(III) speciation with increasing pH. The experimental data are compared to predictions from density functional calculations. The results indicate that formate binds to Am(III) in a monodentate fashion, in agreement with crystal structures of lanthanide formates. Furthermore, the investigations are complemented by thermodynamic speciation calculations to verify further the results obtained.

Structure, vibrations and quantum chemical investigations of hydrogen bonded complex of bis(1-hydroxy-2-methylpropan-2-aminium)selenate

NASA Astrophysics Data System (ADS)

Thirunarayanan, S.; Arjunan, V.; Marchewka, M. K.; Mohan, S.

2017-04-01

The hydrogen bonded molecular complex bis(1-hydroxy-2-methylpropan-2-aminium)selenate (C8H24N2O6Se) has been prepared by the reaction of 2-amino-2-methyl propanol and selenic acid. The X-ray diffraction analysis revealed that the intermolecular proton transfer from selenic acid (SeO4H2) to 2-amino-2-methylpropanol results in the formation of bis(1-hydroxy-2-methylpropan-2-aminium)selenate (HMPAS) salt and the fragments are connected through H-bonding and ion pairing. The N-H⋯O and O-H⋯O interactions between 2-amino-2-methylpropanol and selenic acid determine the supramolecular arrangement in three-dimensional space. The salt crystallises in the space group P121/n1 of monoclinic system. The complete vibrational assignments of HMPAS have been performed by FTIR and FT-Raman spectroscopy. The experimental data are correlated with the structural properties namely the energy, thermodynamic parameters, atomic charges, hybridization concepts and vibrational frequencies determined by quantum chemical studies performed with B3LYP method using 6-311++G*, 6-31+G* and 6-31G** basis sets.

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

PubMed

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

2017-10-06

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

FTIR, FT-Raman, FT-NMR and quantum chemical investigations of 3-acetylcoumarin.

PubMed

Arjunan, V; Sakiladevi, S; Marchewka, M K; Mohan, S

2013-05-15

3-Acetylcoumarin (3AC) was synthesised by a Knoevenagel reaction. Conformational analysis using the B3LYP method was also carried out to determine the most stable conformation of the compound. FTIR and FT-Raman spectra of 3AC have been recorded in the range 4000-400 and 4000-100 cm(-1), respectively. (1)H and (13)C NMR spectra have also been recorded. The complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the experimental FTIR and FT-Raman data and quantum mechanical studies. The experimental vibrational frequencies were compared with the wavenumbers obtained theoretically from the DFT-B3LYP/B3PW91 gradient calculations employing the standard 6-31G(**), high level 6-311++G(**) and cc-pVTZ basis sets for optimised geometry of the compound. The frontier molecular orbital energies of the compound are determined by DFT method. Copyright © 2013 Elsevier B.V. All rights reserved.

Development of multicomponent hybrid density functional theory with polarizable continuum model for the analysis of nuclear quantum effect and solvent effect on NMR chemical shift.

PubMed

Kanematsu, Yusuke; Tachikawa, Masanori

2014-04-28

We have developed the multicomponent hybrid density functional theory [MC_(HF+DFT)] method with polarizable continuum model (PCM) for the analysis of molecular properties including both nuclear quantum effect and solvent effect. The chemical shifts and H/D isotope shifts of the picolinic acid N-oxide (PANO) molecule in chloroform and acetonitrile solvents are applied by B3LYP electron exchange-correlation functional for our MC_(HF+DFT) method with PCM (MC_B3LYP/PCM). Our MC_B3LYP/PCM results for PANO are in reasonable agreement with the corresponding experimental chemical shifts and isotope shifts. We further investigated the applicability of our method for acetylacetone in several solvents.

Experimental and quantum-chemical studies on the three-particle fragmentation of neutral triatomic hydrogen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galster, Ulrich; Baumgartner, Frank; Mueller, Ulrich

2005-12-15

Dissociation of well-defined H{sub 3} Rydberg states into three ground state hydrogen atoms reveals characteristic correlation patterns in the center-of-mass motion of the three fragments. We present an extensive experimental dataset of momentum correlation maps for all lower Rydberg states of H{sub 3} and D{sub 3}. In particular the states with principal quantum number n=2 feature simple correlation patterns with regular occurence of mutual affinities. Energetically higher-lying states typically show more complex patterns which are unique for each state. Quantum-chemical calculations on adiabatic potential energy surfaces of H{sub 3} Rydberg states are presented to illuminate the likely origin of thesemore » differences. We discuss the likely dissociation mechanisms and paths which are responsible for the observed continuum correlation.« less

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

Graphene quantum dots as enhanced plant growth regulators: effects on coriander and garlic plants.

PubMed

Chakravarty, Disha; Erande, Manisha B; Late, Dattatray J

2015-10-01

We report investigations on the use of graphene quantum dots for growth enhancement in coriander (Coriandrum sativam L.) and garlic (Allium sativum) plants. The as-received seeds of coriander and garlic were treated with 0.2 mg mL(-1) of graphene quantum dots for 3 h before planting. Graphene quantum dots enhanced the growth rate in coriander and garlic plants, including leaves, roots, shoots, flowers and fruits, when the seeds were treated with graphene quantum dots. Our investigations open up the opportunity to use graphene quantum dots as plant growth regulators that can be used in a variety of other food plants for high yield. © 2015 Society of Chemical Industry.

Quantum chemical determination of young?s modulus of lignin. Calculations on ß-O-4' model compound

Treesearch

Thomas Elder

2007-01-01

The calculation of Young?s modulus of lignin has been examined by subjecting a dimeric model compound to strain, coupled with the determination of energy and stress. The computational results, derived from quantum chemical calculations, are in agreement with available experimental results. Changes in geometry indicate that modifications in dihedral angles occur in...

Investigations of the polarization behavior of quantum cascade lasers by Stokes parameters.

PubMed

Janassek, Patrick; Hartmann, Sébastien; Molitor, Andreas; Michel, Florian; Elsäßer, Wolfgang

2016-01-15

We experimentally investigate the full polarization behavior of mid-infrared emitting quantum cascade lasers (QCLs) in terms of measuring the complete Stokes parameters, instead of only projecting them on a linear polarization basis. We demonstrate that besides the pre-dominant linear TM polarization of the emitted light as governed by the selection rules of the intersubband transition, small non-TM contributions, e.g., circularly polarized light, are present reflecting the birefringent behavior of the semiconductor quantum well waveguide. Surprisingly unique is the persistence of these polarization properties well below laser threshold. These investigations give further insight into understanding, manipulating, and exploiting the polarization properties of QCLs, both from a laser point of view and with respect toward applications.

The furan microsolvation blind challenge for quantum chemical methods: First steps

NASA Astrophysics Data System (ADS)

Gottschalk, Hannes C.; Poblotzki, Anja; Suhm, Martin A.; Al-Mogren, Muneerah M.; Antony, Jens; Auer, Alexander A.; Baptista, Leonardo; Benoit, David M.; Bistoni, Giovanni; Bohle, Fabian; Dahmani, Rahma; Firaha, Dzmitry; Grimme, Stefan; Hansen, Andreas; Harding, Michael E.; Hochlaf, Majdi; Holzer, Christof; Jansen, Georg; Klopper, Wim; Kopp, Wassja A.; Kröger, Leif C.; Leonhard, Kai; Mouhib, Halima; Neese, Frank; Pereira, Max N.; Ulusoy, Inga S.; Wuttke, Axel; Mata, Ricardo A.

2018-01-01

Herein we present the results of a blind challenge to quantum chemical methods in the calculation of dimerization preferences in the low temperature gas phase. The target of study was the first step of the microsolvation of furan, 2-methylfuran and 2,5-dimethylfuran with methanol. The dimers were investigated through IR spectroscopy of a supersonic jet expansion. From the measured bands, it was possible to identify a persistent hydrogen bonding OH-O motif in the predominant species. From the presence of another band, which can be attributed to an OH-π interaction, we were able to assert that the energy gap between the two types of dimers should be less than or close to 1 kJ/mol across the series. These values served as a first evaluation ruler for the 12 entries featured in the challenge. A tentative stricter evaluation of the challenge results is also carried out, combining theoretical and experimental results in order to define a smaller error bar. The process was carried out in a double-blind fashion, with both theory and experimental groups unaware of the results on the other side, with the exception of the 2,5-dimethylfuran system which was featured in an earlier publication.

New generation of docking programs: Supercomputer validation of force fields and quantum-chemical methods for docking.

PubMed

Sulimov, Alexey V; Kutov, Danil C; Katkova, Ekaterina V; Ilin, Ivan S; Sulimov, Vladimir B

2017-11-01

Discovery of new inhibitors of the protein associated with a given disease is the initial and most important stage of the whole process of the rational development of new pharmaceutical substances. New inhibitors block the active site of the target protein and the disease is cured. Computer-aided molecular modeling can considerably increase effectiveness of new inhibitors development. Reliable predictions of the target protein inhibition by a small molecule, ligand, is defined by the accuracy of docking programs. Such programs position a ligand in the target protein and estimate the protein-ligand binding energy. Positioning accuracy of modern docking programs is satisfactory. However, the accuracy of binding energy calculations is too low to predict good inhibitors. For effective application of docking programs to new inhibitors development the accuracy of binding energy calculations should be higher than 1kcal/mol. Reasons of limited accuracy of modern docking programs are discussed. One of the most important aspects limiting this accuracy is imperfection of protein-ligand energy calculations. Results of supercomputer validation of several force fields and quantum-chemical methods for docking are presented. The validation was performed by quasi-docking as follows. First, the low energy minima spectra of 16 protein-ligand complexes were found by exhaustive minima search in the MMFF94 force field. Second, energies of the lowest 8192 minima are recalculated with CHARMM force field and PM6-D3H4X and PM7 quantum-chemical methods for each complex. The analysis of minima energies reveals the docking positioning accuracies of the PM7 and PM6-D3H4X quantum-chemical methods and the CHARMM force field are close to one another and they are better than the positioning accuracy of the MMFF94 force field. Copyright © 2017 Elsevier Inc. All rights reserved.

Conformational, structural, vibrational and quantum chemical analysis on 4-aminobenzohydrazide and 4-hydroxybenzohydrazide--a comparative study.

PubMed

Arjunan, V; Jayaprakash, A; Carthigayan, K; Periandy, S; Mohan, S

2013-05-01

Experimental and theoretical quantum chemical studies were carried out on 4-hydroxybenzohydrazide (4HBH) and 4-aminobenzohydrazide (4ABH) using FTIR and FT-Raman spectral data. The structural characteristics and vibrational spectroscopic analysis were carried performed by quantum chemical methods with the hybrid exchange-correlation functional B3LYP using 6-31G(**), 6-311++G(**) and aug-cc-pVDZ basis sets. The most stable conformer of the title compounds have been determined from the analysis of potential energy surface. The stable molecular geometries, electronic and thermodynamic parameters, IR intensities, harmonic vibrational frequencies, depolarisation ratio and Raman intensities have been computed. Molecular electrostatic potential and frontier molecular orbitals were constructed to understand the electronic properties. The potential energy distributions (PEDs) were calculated to explain the mixing of fundamental modes. The theoretical geometrical parameters and the fundamental frequencies were compared with the experimental. The interactions of hydroxy and amino group substitutions on the characteristic vibrations of the ring and hydrazide group have been analysed. Copyright © 2013 Elsevier B.V. All rights reserved.

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

PubMed

Siegbahn, Per E M; Himo, Fahmi

2009-06-01

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

Quantum chemistry simulation on quantum computers: theories and experiments.

PubMed

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.

Composition and conductance distributions of single GeSi quantum rings studied by conductive atomic force microscopy combined with selective chemical etching.

PubMed

Lv, Y; Cui, J; Jiang, Z M; Yang, X J

2013-02-15

Atomic force microscopy imaging combined with selective chemical etching is employed to quantitatively investigate three-dimensional (3D) composition distributions of single GeSi quantum rings (QRs). In addition, the 3D quantitative composition distributions and the corresponding conductance distributions are simultaneously obtained on the same single GeSi QRs by conductive atomic force microscopy combined with selective chemical etching, allowing us to investigate the correlations between the conductance and composition distributions of single QRs. The results show that the QRs' central holes have higher Ge content, but exhibit lower conductance, indicating that the QRs' conductance distribution is not consistent with their composition distribution. By comparing the topography, composition and conductance profiles of the same single QRs before and after different etching processes, it is found that the conductance distributions of GeSi QRs do not vary with the change of composition distribution. Instead, the QRs' conductance distributions are found to be consistent with their topographic shapes, which can be supposed to be due to the shape determined electronic structures.

"Chemical-Free" Foods: An Investigation of Student's Definitions of a Chemical

NASA Astrophysics Data System (ADS)

Nicoll, Gayle

1997-04-01

There appear to exist at least two definitions of what a chemical is, a popular society definition and a scientific one. This study investigated the pervasiveness of these views among students enrolled in a freshman level college general chemistry course. It was found that only 30 percent of the students in second semester held a scientific definition of a chemical, while another 30 percent held a popular definition. The remaining 40 percent held views intermediate between these. A correlation may exist between the amount of television students watched as they grew up and the type of views they hold about chemicals.

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

PubMed

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

2008-01-01

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

Chemical Investigations of the Castor Bean Plant Ricinus communis

DTIC Science & Technology

2012-12-01

of the castor bean plant Ricinus communis. A major focus of this grant was to understand the chemical composition of the seeds, and to ascertain if...UNCLASSIFIED Chemical Investigations of the Castor Bean Plant Ricinus communis Simon P. B. Ovenden, Christina K. Bagas, David J...investigation of several forensic aspects of the castor bean plant Ricinus communis. A major focus of this grant was to understand the chemical

Protein Structure Validation and Refinement Using Amide Proton Chemical Shifts Derived from Quantum Mechanics

PubMed Central

Christensen, Anders S.; Linnet, Troels E.; Borg, Mikael; Boomsma, Wouter; Lindorff-Larsen, Kresten; Hamelryck, Thomas; Jensen, Jan H.

2013-01-01

We present the ProCS method for the rapid and accurate prediction of protein backbone amide proton chemical shifts - sensitive probes of the geometry of key hydrogen bonds that determine protein structure. ProCS is parameterized against quantum mechanical (QM) calculations and reproduces high level QM results obtained for a small protein with an RMSD of 0.25 ppm (r = 0.94). ProCS is interfaced with the PHAISTOS protein simulation program and is used to infer statistical protein ensembles that reflect experimentally measured amide proton chemical shift values. Such chemical shift-based structural refinements, starting from high-resolution X-ray structures of Protein G, ubiquitin, and SMN Tudor Domain, result in average chemical shifts, hydrogen bond geometries, and trans-hydrogen bond (h3 JNC') spin-spin coupling constants that are in excellent agreement with experiment. We show that the structural sensitivity of the QM-based amide proton chemical shift predictions is needed to obtain this agreement. The ProCS method thus offers a powerful new tool for refining the structures of hydrogen bonding networks to high accuracy with many potential applications such as protein flexibility in ligand binding. PMID:24391900

The quantum dynamics of electronically nonadiabatic chemical reactions

NASA Technical Reports Server (NTRS)

Truhlar, Donald G.

1993-01-01

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

QSAR, DFT and quantum chemical studies on the inhibition potentials of some carbozones for the corrosion of mild steel in HCl.

PubMed

Eddy, Nnabuk O; Ita, Benedict I

2011-02-01

Experimental aspects of the inhibition of the corrosion of mild steel in HCl solutions by some carbozones were studied using gravimetric, thermometric and gasometric methods, while a theoretical study was carried out using density functional theory, a quantitative structure-activity relation, and quantum chemical principles. The results obtained indicated that the studied carbozones are good adsorption inhibitors for the corrosion of mild steel in HCl. The inhibition efficiencies of the studied carbozones were found to increase with increasing concentration of the respective inhibitor. A strong correlation was found between the average inhibition efficiency and some quantum chemical parameters, and also between the experimental and theoretical inhibition efficiencies (obtained from the quantitative structure-activity relation).

Chemical Shifts of the Carbohydrate Binding Domain of Galectin-3 from Magic Angle Spinning NMR and Hybrid Quantum Mechanics/Molecular Mechanics Calculations.

PubMed

Kraus, Jodi; Gupta, Rupal; Yehl, Jenna; Lu, Manman; Case, David A; Gronenborn, Angela M; Akke, Mikael; Polenova, Tatyana

2018-03-22

Magic angle spinning NMR spectroscopy is uniquely suited to probe the structure and dynamics of insoluble proteins and protein assemblies at atomic resolution, with NMR chemical shifts containing rich information about biomolecular structure. Access to this information, however, is problematic, since accurate quantum mechanical calculation of chemical shifts in proteins remains challenging, particularly for 15 N H . Here we report on isotropic chemical shift predictions for the carbohydrate recognition domain of microcrystalline galectin-3, obtained from using hybrid quantum mechanics/molecular mechanics (QM/MM) calculations, implemented using an automated fragmentation approach, and using very high resolution (0.86 Å lactose-bound and 1.25 Å apo form) X-ray crystal structures. The resolution of the X-ray crystal structure used as an input into the AF-NMR program did not affect the accuracy of the chemical shift calculations to any significant extent. Excellent agreement between experimental and computed shifts is obtained for 13 C α , while larger scatter is observed for 15 N H chemical shifts, which are influenced to a greater extent by electrostatic interactions, hydrogen bonding, and solvation.

Admittance Investigation of MIS Structures with HgTe-Based Single Quantum Wells.

PubMed

Izhnin, Ihor I; Nesmelov, Sergey N; Dzyadukh, Stanislav M; Voitsekhovskii, Alexander V; Gorn, Dmitry I; Dvoretsky, Sergey A; Mikhailov, Nikolaj N

2016-12-01

This work presents results of the investigation of admittance of metal-insulator-semiconductor structure based on Hg1 - x Cd x Te grown by molecular beam epitaxy. The structure contains a single quantum well Hg0.35Cd0.65Te/HgTe/Hg0.35Cd0.65Te with thickness of 5.6 nm in the sub-surface layer of the semiconductor. Both the conductance-voltage and capacitance-voltage characteristics show strong oscillations when the metal-insulator-semiconductor (MIS) structure with a single quantum well based on HgTe is biased into the strong inversion mode. Also, oscillations on the voltage dependencies of differential resistance of the space charge region were observed. These oscillations were related to the recharging of quantum levels in HgTe.

Spectroscopic (vibrational, NMR and UV-vis.) and quantum chemical investigations on 4-hexyloxy-3-methoxybenzaldehyde.

PubMed

Abbas, Ashgar; Gökce, Halil; Bahçeli, Semiha

2016-01-05

In this study, the 4-hexyloxy-3-methoxybenzaldehyde compound as one of the derivatives of vanillin which is a well known flavoring agent, C14H20O3, has been investigated by experimentally and extensively utilizing density functional theory (DFT) at the B3LYP/6-311++G(d,p) level. In this context, the optimized geometry, vibrational frequencies, (1)H and (13)C NMR chemical shifts, UV-vis. (in gas phase and in methanol solvent) spectra, HOMO-LUMO analysis, molecular electrostatic potential (MEP), thermodynamic parameters and atomic charges of 4-hexyloxy-3-methoxybenzaldehyde have been calculated. In addition, theoretically predicted IR, Raman and UV-vis. (in gas phase and in methanol solvent) spectra of the mentioned molecule have been constructed. The results calculated were compared with the experimental data. Copyright © 2015 Elsevier B.V. All rights reserved.

Epitaxial Zn quantum dots coherently grown on Si(1 1 1): growth mechanism, nonlinear optical and chemical states analyses

NASA Astrophysics Data System (ADS)

Huang, Bo-Jia; Kao, Li-Chi; Brahma, Sanjaya; Jeng, Yu-En; Chiu, Shang-Jui; Ku, Ching-Shun; Lo, Kuang-Yao

2017-05-01

Oxide- and defect-free metal/semiconductor interface is important to improve Ohmic contact for the suppression of electron scattering and the avoidance of an extrinsic surface state in estimating the barrier of the Schottky contact at the nanodevice interface. This study reports the growth mechanism of Zn quantum dots coherently grown on Si(1 1 1) and the physical phenomena of the crystalline, nonlinear optics, and the chemical states of Zn quantum dots. Epitaxial Zn quantum dots were coherently formed on a non-oxide Si(1 1 1) surface through the liquid- to solid-phase transformation as a result of pattern matching between the Zn(0 0 2) and Si(1 1 1) surfaces. The growth mechanism of constrained Zn quantum dots grown through strategic magnetron radio frequency sputtering is complex. Some factors, such as substrate temperature, hydrogen gas flow, and negative DC bias, influence the configuration of epitaxial Zn quantum dots. In particular, hydrogen gas plays an important role in reducing the ZnO+ and native oxide that is bombarded by accelerated ions, thereby enhancing the Zn ion surface diffusion. The reduction reaction can be inspected by distinguishing the chemical states of ZnO/Zn quantum dots from natural oxidation or the states of Zn 3d through the analysis of x-ray absorption near the edge structure spectrum. The complex growth mechanism can be systematically understood by analyzing a noncancelled anisotropic 3 m dipole from reflective second harmonic generation and inspecting the evolution between the Zn(0 0 2) and Zn(1 1 1) peaks of the collective ZnO/Zn quantum dots in synchrotron XRD.

Use of external cavity quantum cascade laser compliance voltage in real-time trace gas sensing of multiple chemicals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phillips, Mark C.; Taubman, Matthew S.; Kriesel, Jason M.

2015-02-08

We describe a prototype trace gas sensor designed for real-time detection of multiple chemicals. The sensor uses an external cavity quantum cascade laser (ECQCL) swept over its tuning range of 940-1075 cm-1 (9.30-10.7 µm) at a 10 Hz repetition rate.

Investigation of the spinfoam path integral with quantum cuboid intertwiners

NASA Astrophysics Data System (ADS)

Bahr, Benjamin; Steinhaus, Sebastian

2016-05-01

In this work, we investigate the 4d path integral for Euclidean quantum gravity on a hypercubic lattice, as given by the spinfoam model by Engle, Pereira, Rovelli, Livine, Freidel and Krasnov. To tackle the problem, we restrict to a set of quantum geometries that reflects the large amount of lattice symmetries. In particular, the sum over intertwiners is restricted to quantum cuboids, i.e. coherent intertwiners which describe a cuboidal geometry in the large-j limit. Using asymptotic expressions for the vertex amplitude, we find several interesting properties of the state sum. First of all, the value of coupling constants in the amplitude functions determines whether geometric or nongeometric configurations dominate the path integral. Secondly, there is a critical value of the coupling constant α , which separates two phases. In both phases, the diffeomorphism symmetry appears to be broken. In one, the dominant contribution comes from highly irregular, in the other from highly regular configurations, both describing flat Euclidean space with small quantum fluctuations around them, viewed in different coordinate systems. On the critical point diffeomorphism symmetry is nearly restored, however. Thirdly, we use the state sum to compute the physical norm of kinematical states, i.e. their norm in the physical Hilbert space. We find that states which describe boundary geometry with high torsion have an exponentially suppressed physical norm. We argue that this allows one to exclude them from the state sum in calculations.

Quantum chemical characterization of zwitterionic structures: Supramolecular complexes for modifying the wettability of oil-water-limestone system.

PubMed

Lopez-Chavez, Ernesto; Garcia-Quiroz, Alberto; Gonzalez-Garcia, Gerardo; Orozco-Duran, Gabriela E; Zamudio-Rivera, Luis S; Martinez-Magadan, José M; Buenrostro-Gonzalez, Eduardo; Hernandez-Altamirano, Raul

2014-06-01

In this work, we present a quantum chemical study pertaining to some supramolecular complexes acting as wettability modifiers of oil-water-limestone system. The complexes studied are derived from zwitterionic liquids of the types N'-alkyl-bis, N-alquenil, N-cycloalkyl, N-amyl-bis-beta amino acid or salts acting as sparkling agents. We studied two molecules of zwitterionic liquids (ZL10 and ZL13), HOMO and LUMO levels, and the energy gap between them, were calculated, as well as the electron affinity (EA) and ionization potential (IP), chemical potential, chemical hardness, chemical electrophilicity index and selectivity descriptors such Fukui indices. In this work, electrochemical comparison was realized with cocamidopropyl betaine (CPB), which is a structure zwitterionic liquid type, nowadays widely applied in enhanced recovery processes. Copyright © 2014 Elsevier Inc. All rights reserved.

Thermal Quantum Correlations in Photosynthetic Light-Harvesting Complexes

NASA Astrophysics Data System (ADS)

Mahdian, M.; Kouhestani, H.

2015-08-01

Photosynthesis is one of the ancient biological processes, playing crucial role converting solar energy to cellular usable currency. Environmental factors and external perturbations has forced nature to choose systems with the highest efficiency and performance. Recent theoretical and experimental studies have proved the presence of quantum properties in biological systems. Energy transfer systems like Fenna-Matthews-Olson (FMO) complex shows quantum entanglement between sites of Bacteriophylla molecules in protein environment and presence of decoherence. Complex biological systems implement more truthful mechanisms beside chemical-quantum correlations to assure system's efficiency. In this study we investigate thermal quantum correlations in FMO protein of the photosynthetic apparatus of green sulfur bacteria by quantum discord measure. The results confirmed existence of remarkable quantum correlations of of BChla pigments in room temperature. This results approve involvement of quantum correlation mechanisms for information storage and retention in living organisms that could be useful for further evolutionary studies. Inspired idea of this study is potentially interesting to practice by the same procedure in genetic data transfer mechanisms.

High-School Students' Conceptual Difficulties and Attempts at Conceptual Change: The Case of Basic Quantum Chemical Concepts

ERIC Educational Resources Information Center

Tsaparlis, Georgios; Papaphotis, Georgios

2009-01-01

This study tested for deep understanding and critical thinking about basic quantum chemical concepts taught at 12th grade (age 17-18). Our aim was to achieve conceptual change in students. A quantitative study was conducted first (n = 125), and following this 23 selected students took part in semi-structured interviews either individually or in…

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

ERIC Educational Resources Information Center

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

2012-01-01

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

Chemical potential and compressibility of quantum Hall bilayer excitons,.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skinner, Brian

2016-02-25

I consider a system of two parallel quantum Hall layers with total filling factor 0 or 1. When the distance between the layers is small enough, electrons and holes in opposite layers can form inter-layer excitons, which have a finite effective mass and interact via a dipole-dipole potential. I present results for the chemical potential u of the resulting bosonic system as a function of the exciton concentration n and the interlayer separation d. I show that both u and the interlayer capacitance have an unusual nonmonotonic dependence on d, owing to the interplay between an increasing dipole moment andmore » an increasing effective mass with increasing d. Finally, I discuss the transition between the superfluid and Wigner crystal phases, which is shown to occur at d x n-1/10. Results are derived first via simple intuitive arguments, and then verified with more careful analytic derivations and numeric calculations.« less

Computational investigations of trans-platinum(II) oxime complexes used as anticancer drug

NASA Astrophysics Data System (ADS)

Sayin, Koray; Karakaş, Duran

2018-01-01

Some platinum oxime complexes are optimized at HF/CEP-31G level which has been reported as the best level for these type complexes in the gas phase. IR spectrum is calculated and the new scale factor is derived. NMR spectrum is calculated at the same level of theory and examined in detail. Quantum chemical parameters which have been mainly used are investigated and their formulas are given in detail. Additionally, selected quantum chemical parameters of studied complexes are calculated. New theoretical IC50% formulas are derived and biological activity rankings of mentioned complexes are investigated.

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

PubMed

Mezey, Paul G

2015-05-28

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

Demonstration of a rapidly-swept external cavity quantum cascade laser for rapid and sensitive quantification of chemical mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brumfield, Brian E.; Taubman, Matthew S.; Phillips, Mark C.

2016-02-13

A rapidly-swept external cavity quantum cascade laser (ECQCL) system for fast open-path quantification of multiple chemicals and mixtures is presented. The ECQCL system is swept over its entire tuning range (>100 cm-1) at frequencies up to 200 Hz. At 200 Hz the wavelength tuning rate and spectral resolution are 2x104 cm-1/sec and < 0.2 cm-1, respectively. The capability of the current system to quantify changes in chemical concentrations on millesecond timescales is demonstrated at atmospheric pressure using an open-path multi-pass cell. The detection limits for chemicals ranged from ppb to ppm levels depending on the absorption cross-section.

[Mass spectrometric and quantum chemical study of dimeric associates of nucleosides].

PubMed

Sukhodub, L F; Aksenov, S A; Boldeskul, A I

1995-01-01

Deoxyribonucleosides H-bonded pairs were investigated using fast atom bombardment mass spectrometry and MNDO/H quantum chemistry method. It was shown that "rare" (enol or imin) forms of the nitrogen bases could form pairs with energy comparable with "canonical" base pair energy. It was shown that pair stability rows, which are measured using different experimental techniques, were in conformity each with other.

Rotational Spectrum, Conformational Composition, Intramolecular Hydrogen Bonding, and Quantum Chemical Calculations of Mercaptoacetonitrile (HSCH2C≡N), a Compound of Potential Astrochemical Interest.

PubMed

Møllendal, Harald; Samdal, Svein; Guillemin, Jean-Claude

2016-03-31

The microwave spectra of mercaptoacetonitrile (HSCH2C≡N) and one deuterated species (DSCH2C≡N) were investigated in the 7.5-124 GHz spectral interval. The spectra of two conformers denoted SC and AP were assigned. The H-S-C-C chain of atoms is synclinal in SC and anti-periplanar in AP. The ground state of SC is split into two substates separated by a comparatively small energy difference resulting in closely spaced transitions with equal intensities. Several transitions of the parent species of SC deviate from Watson's Hamiltonian. Only slight improvements were obtained using a Hamiltonian that takes coupling between the two substates into account. Deviations from Watson's Hamiltonian were also observed for the parent species of AP. However, the spectrum of the deuterated species, which was investigated only for the SC conformer, fits satisfactorily to Watson's Hamiltonian. Relative intensity measurements found SC to be lower in energy than AP by 3.8(3) kJ/mol. The strength of the intramolecular hydrogen bond between the thiol and cyano groups was estimated to be ∼2.1 kJ/mol. The microwave work was augmented by quantum chemical calculations at CCSD and MP2 levels using basis sets of minimum triple-ζ quality. Mercaptoacetonitrile has astrochemical interest, and the spectra presented herein should be useful for a potential identification of this compound in the interstellar medium. Three different ways of generating mercaptoacetonitrile from compounds already found in the interstellar medium were explored by quantum chemical calculations.

The Nature of the Chemical Bond--1990.

ERIC Educational Resources Information Center

Ogilvie, J. F.

1990-01-01

Three aspects of quantum mechanics in modern chemistry are stressed: the fundamental structure of quantum mechanics as a basis of chemical applications, the relationship of quantum mechanics to atomic and molecular structure, and the consequent implications for chemical education. A list of 64 references is included. (CW)

Investigating High School Students' Understanding of Chemical Equilibrium Concepts

ERIC Educational Resources Information Center

Karpudewan, Mageswary; Treagust, David F.; Mocerino, Mauro; Won, Mihye; Chandrasegaran, A. L.

2015-01-01

This study investigated the year 12 students' (N = 56) understanding of chemical equilibrium concepts after instruction using two conceptual tests, the "Chemical Equilibrium Conceptual Test 1" ("CECT-1") consisting of nine two-tier multiple-choice items and the "Chemical Equilibrium Conceptual Test 2"…

Quantum chemical investigation of the primary thermal pyrolysis reactions of the sodium carboxylate group in a brown coal model.

PubMed

Li, Jian; Zhang, Baisheng; Zhang, Zhiqiang; Yan, Kefeng; Kang, Lixun

2014-12-01

The primary pyrolysis mechanisms of the sodium carboxylate group in sodium benzoate-used as a model compound of brown coal-were studied by performing quantum chemical computations using B3LYP and the CBS method. Various possible reaction pathways involving reactions such as unimolecular and bimolecular decarboxylation and decarbonylation, crosslinking, and radical attack in the brown coal matrix were explored. Without the participation of reactive radicals, unimolecular decarboxylation to release CO2 was calculated to be the most energetically favorable primary reaction pathway at the B3LYP/6-311+G (d, p) level of theory, and was also found to be more energetically favorable than decarboxylation of an carboxylic acid group. When CBS-QBS results were included, crosslinking between the sodium carboxylate group and the carboxylic acid and the decarboxylation of the sodium carboxylate group (catalyzed by the phenolic hydroxyl group) were found to be possible; this pathway competes with unimolecular decarboxylation of the sodium carboxylate group. Provided that H and CH3 radicals are present in the brown coal matrix and can access the sodium carboxylate group, accelerated pyrolysis of the sodium carboxylate group becomes feasible, leading to the release of an Na atom or an NaCO2 radical at the B3LYP/6-311+G (d, p) or CBS-QB3 level of theory, respectively.

The measurement problem in quantum mechanics: A phenomenological investigation

NASA Astrophysics Data System (ADS)

Hunter, Joel Brooks

2008-10-01

This dissertation is a phenomenological investigation of the measurement problem in quantum mechanics. The primary subject matter for description and analysis is scientific instruments and their use in experiments which elicit the measurement problem. A methodological critique is mounted against the ontological commitments taken for granted in the canonical interpretations of quantum theory and the scientific activity of measurement as the necessary interface between theoretical interest and perceptual results. I argue that an aesthetic dimension of reality functions as aproto-scientific establishment of sense-making that constantly operates to set integratively all other cognitively neat determinations, including scientifically rendered objects that are intrinsically non-visualizable. The way in which data "key in" to the original and originative register of the sensible in observation is clarified by examining prostheses, measuring apparatuses and instruments that are sense-conveying and -integrative with the human sensorium. Experiments, technology and instrumentation are examined in order to understand how knowing and that which is known is bonded by praxis-aisthesis. Quantum measurement is a praxic-dynamie activity and homologically structured and structur ing functional engagement in terms of instantiation, quantifiability, and spatiotemporal differentiation. The distinctions between a beauty-aesthetic and praxis-aisthesis are delineated. It is argued that a beauty-aesthetic is a construal of the economic dimension of scientific objects and work, and is not the primary manner in which the aesthetic dimension is disclosed. The economic dimension of abstractions reduces to an austere aesthetic of calculative economy. Nature itself, however, is not stingy; it is intrinsically capacious, extravagant, full of surprise, nuance, ambiguity and allusiveness. The capaciousness of Nature and the way in which we are integratively set within Nature in a materiality

Investigation of structural, morphological and opto-electronic properties of CdS quantum dot thin film

NASA Astrophysics Data System (ADS)

Ibrahim Mohammed S., M.; Gubari, Ghamdan M. M.; Huse, Nanasaheb P.; Dive, Avinash S.; Sharma, Ramphal

2018-05-01

We have successfully deposited CdS quantum dot thin film on the glass substrate by simple and economic chemical bath deposition method at ˜50 ˚C. The X-ray diffraction study confirms the formation of CdS when compared with standard JCPDS data with average crystallite size ˜3 nm. The morphology of the film was studied by FE-SEM, which suggests the homogeneous and uniform deposition of the CdS material over the entire glass substrate with a porous structure. From UV absorption spectra we observed that the sample exhibited a band edge near ˜400 nm with a slight deviation with the presence of excitonic peak for the sample. The presence of excitonic peak may be attributed to the formation of quantum dots. The calculated band gap energy of CdS quantum dot thin film was found to be ˜3.136 eV. The thin film further characterized to study electrical parameters and the sample show a drastic increase in current after light illumination.

Remote Chemical Sensing Using Quantum Cascade Lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harper, Warren W.; Schultz, John F.

2003-01-30

Spectroscopic chemical sensing research at Pacific Northwest National Laboratory (PNNL) is focused on developing advanced sensors for detecting the production of nuclear, chemical, or biological weapons; use of chemical weapons; or the presence of explosives, firearms, narcotics, or other contraband of significance to homeland security in airports, cargo terminals, public buildings, or other sensitive locations. For most of these missions, the signature chemicals are expected to occur in very low concentrations, and in mixture with ambient air or airborne waste streams that contain large numbers of other species that may interfere with spectroscopic detection, or be mistaken for signatures ofmore » illicit activity. PNNL’s emphasis is therefore on developing remote and sampling sensors with extreme sensitivity, and resistance to interferents, or selectivity. PNNL’s research activities include: 1. Identification of signature chemicals and quantification of their spectral characteristics, 2. Identification and development of laser and other technologies that enable breakthroughs in sensitivity and selectivity, 3. Development of promising sensing techniques through experimentation and modeling the physical phenomenology and practical engineering limitations affecting their performance, and 4. Development and testing of data collection methods and analysis algorithms. Close coordination of all aspects of the research is important to ensure that all parts are focused on productive avenues of investigation. Close coordination of experimental development and numerical modeling is particularly important because the theoretical component provides understanding and predictive capability, while the experiments validate calculations and ensure that all phenomena and engineering limitations are considered.« less

Chemical processing of three-dimensional graphene networks on transparent conducting electrodes for depleted-heterojunction quantum dot solar cells.

PubMed

Tavakoli, Mohammad Mahdi; Simchi, Abdolreza; Fan, Zhiyong; Aashuri, Hossein

2016-01-07

We present a novel chemical procedure to prepare three-dimensional graphene networks (3DGNs) as a transparent conductive film to enhance the photovoltaic performance of PbS quantum-dot (QD) solar cells. It is shown that 3DGN electrodes enhance electron extraction, yielding a 30% improvement in performance compared with the conventional device.

A new look into the quantum chemical and spectroscopic investigations of 5-chloro-1-methyl-4-nitroimidazole.

PubMed

Arjunan, V; Raj, Arushma; Anitha, R; Mohan, S

2014-05-05

Optimised geometrical structural parameters, harmonic vibrational frequencies, natural bonding orbital analysis and frontier molecular orbitals are determined by B3LYP and B3PW91 methods. The exact geometry of 5-chloro-1-methyl-4-nitroimidazole is determined through conformational analysis. The experimentally observed infrared and Raman bands have been assigned and analysed. The (13)C and (1)H NMR chemical shifts of the compound are investigated. The total electron density and molecular electrostatic potentials are determined. The electrostatic potential (electron+nuclei) distribution, molecular shape, size and dipole moments of the molecule have been displayed. The energies of the frontier molecular orbitals and LUMO-HOMO energy gap are measured. The possible electronic transitions of the molecule are studied by TD-DFT method along with the UV-Visible spectrum. The structure-activity relationship of the compound is also investigated by conceptual DFT methods. Copyright © 2014 Elsevier B.V. All rights reserved.

Investigating Quantum Modulation States

DTIC Science & Technology

2016-03-01

Coherent state quantum data encryption is highly interoperable with current classical optical infrastructure in both fiber and free space optical networks...hub’s field of regard has a transmit/receive module that are endpoints of the Lyot filter stage tree within the hub’s backend electro-optics control... mobile airborne and space-borne networking. Just like any laser communication technology, QC links are affected by several sources of distortions

Experimentally investigate ionospheric depletion chemicals in artificially created ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Yu; Cao Jinxiang; Wang Jian

2012-09-15

A new approach for investigating ionosphere chemical depletion in the laboratory is introduced. Air glow discharge plasma closely resembling the ionosphere in both composition and chemical reactions is used as the artificially created ionosphere. The ionospheric depletion experiment is accomplished by releasing chemicals such as SF{sub 6}, CCl{sub 2}F{sub 2}, and CO{sub 2} into the model discharge. The evolution of the electron density is investigated by varying the plasma pressure and input power. It is found that the negative ion (SF{sub 6}{sup -}, CCl{sub 2}F{sub 2}{sup -}) intermediary species provide larger reduction of the electron density than the positive ionmore » (CO{sub 2}{sup +}) intermediary species. The negative ion intermediary species are also more efficient in producing ionospheric holes because of their fast reaction rates. Airglow enhancement attributed to SF{sub 6} and CO{sub 2} releases agrees well with the published data. Compared to the traditional methods, the new scheme is simpler to use, both in the release of chemicals and in the electron density measurements. It is therefore more efficient for investigating the release of chemicals in the ionosphere.« less

Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

PubMed

Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

2016-05-17

Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in

Quantum correlations in multipartite quantum systems

NASA Astrophysics Data System (ADS)

Jafarizadeh, M. A.; Heshmati, A.; Karimi, N.; Yahyavi, M.

2018-03-01

Quantum entanglement is the most famous type of quantum correlation between elements of a quantum system that has a basic role in quantum communication protocols like quantum cryptography, teleportation and Bell inequality detection. However, it has already been shown that various applications in quantum information theory do not require entanglement. Quantum discord as a new kind of quantum correlations beyond entanglement, is the most popular candidate for general quantum correlations. In this paper, first we find the entanglement witness in a particular multipartite quantum system which consists of a N-partite system in 2 n -dimensional space. Then we give an exact analytical formula for the quantum discord of this system. At the end of the paper, we investigate the additivity relation of the quantum correlation and show that this relation is satisfied for a N-partite system with 2 n -dimensional space.

Advances in Quantum Mechanochemistry: Electronic Structure Methods and Force Analysis.

PubMed

Stauch, Tim; Dreuw, Andreas

2016-11-23

In quantum mechanochemistry, quantum chemical methods are used to describe molecules under the influence of an external force. The calculation of geometries, energies, transition states, reaction rates, and spectroscopic properties of molecules on the force-modified potential energy surfaces is the key to gain an in-depth understanding of mechanochemical processes at the molecular level. In this review, we present recent advances in the field of quantum mechanochemistry and introduce the quantum chemical methods used to calculate the properties of molecules under an external force. We place special emphasis on quantum chemical force analysis tools, which can be used to identify the mechanochemically relevant degrees of freedom in a deformed molecule, and spotlight selected applications of quantum mechanochemical methods to point out their synergistic relationship with experiments.

Investigation of electronic structure of tri- and tetranuclear molybdenum clusters by X-ray photoelectron and emission spectroscopies and quantum chemical methods

NASA Astrophysics Data System (ADS)

Kryuchkova, Natalya A.; Syrokvashin, Mikhail M.; Gushchin, Artem L.; Korotaev, Evgeniy V.; Kalinkin, Alexander V.; Laricheva, Yuliya A.; Sokolov, Maxim N.

2018-02-01

Charge state studies of compounds [Mo3S4(tu)8(H2O)]Cl4·4H2O (1), [Mo3S4Cl3(dbbpy)3]Cl·5H2O (2), [Mo3S4(CuCl)Cl3(dbbpy)3][CuCl2] (3), containing {Mo3S4}4+ and {Mo3CuS4}5+ cluster cores bearing terminal thiourea (tu) or 4,4‧-di-tert-butyl-2,2‧-bipyridine (dbbpy) ligands, have been performed by X-ray photoelectron and X-ray emission spectroscopies combined with quantum chemical calculations. The best agreement between theory and experiments has been obtained using the B3LYP method. According to the experimental and calculated data, the Mo atoms are in the oxidation state 4+ for all compounds. The energies and shapes of the Cu2p lines indicate formal oxidation states of Cu as 1+. The coordination of Cu(I) to the cluster {Mo3S4} in 3 does not lead to significant changes in the charge state of the molybdenum atoms and the {Mo3S4} unit can be considered as a tridentate metallothia crown ether.

Rapid prediction of chemical metabolism by human UDP-glucuronosyltransferase isoforms using quantum chemical descriptors derived with the electronegativity equalization method.

PubMed

Sorich, Michael J; McKinnon, Ross A; Miners, John O; Winkler, David A; Smith, Paul A

2004-10-07

This study aimed to evaluate in silico models based on quantum chemical (QC) descriptors derived using the electronegativity equalization method (EEM) and to assess the use of QC properties to predict chemical metabolism by human UDP-glucuronosyltransferase (UGT) isoforms. Various EEM-derived QC molecular descriptors were calculated for known UGT substrates and nonsubstrates. Classification models were developed using support vector machine and partial least squares discriminant analysis. In general, the most predictive models were generated with the support vector machine. Combining QC and 2D descriptors (from previous work) using a consensus approach resulted in a statistically significant improvement in predictivity (to 84%) over both the QC and 2D models and the other methods of combining the descriptors. EEM-derived QC descriptors were shown to be both highly predictive and computationally efficient. It is likely that EEM-derived QC properties will be generally useful for predicting ADMET and physicochemical properties during drug discovery.

Quantum chemical study of the mechanism of action of vitamin K epoxide reductase (VKOR)

NASA Astrophysics Data System (ADS)

Deerfield, David, II; Davis, Charles H.; Wymore, Troy; Stafford, Darrel W.; Pedersen, Lee G.

Possible model, but simplistic, mechanisms for the action of vitamin K epoxide reductase (VKOR) are investigated with quantum mechanical methods (B3LYP/6-311G**). The geometries of proposed model intermediates in the mechanisms are energy optimized. Finally, the energetics of the proposed (pseudo-enzymatic) pathways are compared. We find that the several pathways are all energetically feasible. These results will be useful for designing quantum mechanical/molecular mechanical method (QM/MM) studies of the enzymatic pathway once three-dimensional structural data are determined and available for VKOR.

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

PubMed

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

2018-04-10

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

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

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

NASA Astrophysics Data System (ADS)

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

2015-11-01

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

Overview of Stabilizing Ligands for Biocompatible Quantum Dot Nanocrystals

PubMed Central

Zhang, Yanjie; Clapp, Aaron

2011-01-01

Luminescent colloidal quantum dots (QDs) possess numerous advantages as fluorophores in biological applications. However, a principal challenge is how to retain the desirable optical properties of quantum dots in aqueous media while maintaining biocompatibility. Because QD photophysical properties are directly related to surface states, it is critical to control the surface chemistry that renders QDs biocompatible while maintaining electronic passivation. For more than a decade, investigators have used diverse strategies for altering the QD surface. This review summarizes the most successful approaches for preparing biocompatible QDs using various chemical ligands. PMID:22247651

An experimental and quantum chemical study of removal of utmostly quantified heavy metals in wastewater using coconut husk: A novel approach to mechanism.

PubMed

Malik, Reena; Dahiya, Shefali; Lata, Suman

2017-05-01

The present study explores the uptake capacity of low cost agricultural waste i.e.Unmodified Coconut (Cocos nucifera L.) Husk for the removal of heavy metal (Pb 2+ , Cu 2+ , Ni 2+ and Zn 2+ ) ions from industrial wastewater. The effect of various operational parameters such as adsorbent dose, high initial metal concentration (100mg/L-500mg/L), pH, temperature and agitation time on the removal of these ions has been investigated using batch experiments. The results showed that maximum uptake through adsorption occurred at 443.0mg/g (88.6%) for Cu, for Ni with 404.5mg/g (80.9%), 362.2mg/g (72.4%) for Pb 2+ and 338.0mg/g (67.6%) for Zn 2+ ion simultaneously. The adsorption capacity was found to be sensitive to the amount of adsorbent, heavy metal ion concentration, pH, temperature and contact time. The experimental statistics have been correlated and interpreted by a new proposed mechanism based upon quantum chemical study of the adsorbent. The theoretical study using quantum has provided the rich electron donation sites of Coconut Husk and hence proposed mechanism of removal. The various adsorption isotherms (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich and Flory-Huggins), SEM study and physico-chemical properties of the ions suit well to the observed data. Copyright © 2017 Elsevier B.V. All rights reserved.

Experimental investigation of measurement-induced disturbance and time symmetry in quantum physics

NASA Astrophysics Data System (ADS)

Curic, D.; Richardson, M. C.; Thekkadath, G. S.; Flórez, J.; Giner, L.; Lundeen, J. S.

2018-04-01

Unlike regular time evolution governed by the Schrödinger equation, standard quantum measurement appears to violate time-reversal symmetry. Measurement creates random disturbances (e.g., collapse) that prevent back-tracing the quantum state of the system. The effect of these disturbances is explicit in the results of subsequent measurements. In this way, the joint result of sequences of measurements depends on the order in time in which those measurements are performed. One might expect that if the disturbance could be eliminated this time-ordering dependence would vanish. Following a recent theoretical proposal [Bednorz, Franke, and Belzig, New J. Phys. 15, 023043 (2013), 10.1088/1367-2630/15/2/023043], we experimentally investigate this dependence for a kind of measurement that creates an arbitrarily small disturbance: weak measurement. We perform various sequences of a set of polarization weak measurements on photons. We experimentally demonstrate that, although the weak measurements are minimally disturbing, their time ordering affects the outcome of the measurement sequence for quantum systems.

Prediction of Radical Scavenging Activities of Anthocyanins Applying Adaptive Neuro-Fuzzy Inference System (ANFIS) with Quantum Chemical Descriptors

PubMed Central

Jhin, Changho; Hwang, Keum Taek

2014-01-01

Radical scavenging activity of anthocyanins is well known, but only a few studies have been conducted by quantum chemical approach. The adaptive neuro-fuzzy inference system (ANFIS) is an effective technique for solving problems with uncertainty. The purpose of this study was to construct and evaluate quantitative structure-activity relationship (QSAR) models for predicting radical scavenging activities of anthocyanins with good prediction efficiency. ANFIS-applied QSAR models were developed by using quantum chemical descriptors of anthocyanins calculated by semi-empirical PM6 and PM7 methods. Electron affinity (A) and electronegativity (χ) of flavylium cation, and ionization potential (I) of quinoidal base were significantly correlated with radical scavenging activities of anthocyanins. These descriptors were used as independent variables for QSAR models. ANFIS models with two triangular-shaped input fuzzy functions for each independent variable were constructed and optimized by 100 learning epochs. The constructed models using descriptors calculated by both PM6 and PM7 had good prediction efficiency with Q-square of 0.82 and 0.86, respectively. PMID:25153627

A DMFT+CTQMC Investigation of Strange Metallicity in Local Quantum Critical Scenario

NASA Astrophysics Data System (ADS)

Acharya, Swagata; Laad, M. S.; Taraphder, A.

2016-10-01

“Strange” metallicity is now a pseudonym for a novel metallic state exhibiting anomalous infra-red (branch-cut) continuum features in one- and two-particle responses. Here, we employ dynamical mean-field theory (DMFT) using low-temperature continuous-time- quantum Monte-Carlo (CTQMC) solver for an extended periodic Anderson model (EPAM) model to investigate unusual magnetic fluctuations in the strange metal. We show how extinction of Landau quasiparticles in the orbital selective Mott phase (OSMP) leads to (i) qualitative explication of strange transport features and (ii) anomalous quantum critical magnetic fluctuations due to critical liquid-like features in dynamical spin fluctuations, in excellent accord with data in some f-electron systems.

Adsorption and Corrosion Inhibition Studies of Some Selected Dyes as Corrosion Inhibitors for Mild Steel in Acidic Medium: Gravimetric, Electrochemical, Quantum Chemical Studies and Synergistic Effect with Iodide Ions.

PubMed

Peme, Thabo; Olasunkanmi, Lukman O; Bahadur, Indra; Adekunle, Abolanle S; Kabanda, Mwadham M; Ebenso, Eno E

2015-09-02

The corrosion inhibition properties of some organic dyes, namely Sunset Yellow (SS), Amaranth (AM), Allura Red (AR), Tartrazine (TZ) and Fast Green (FG), for mild steel corrosion in 0.5 M HCl solution, were investigated using gravimetric, potentiodynamic polarization techniques and quantum chemical calculations. The results showed that the studied dyes are good corrosion inhibitors with enhanced inhibition efficiencies. The inhibition efficiency of all the studied dyes increases with increase in concentration, and decreases with increase in temperature. The results showed that the inhibition efficiency of the dyes increases in the presence of KI due to synergistic interactions of the dye molecules with iodide (I(-)) ions. Potentiodynamic polarization results revealed that the studied dyes are mixed-type inhibitors both in the absence and presence of KI. The adsorption of the studied dyes on mild steel surface, with and without KI, obeys the Langmuir adsorption isotherm and involves physical adsorption mechanism. Quantum chemical calculations revealed that the most likely sites in the dye molecules for interactions with mild steel are the S, O, and N heteroatoms.

Investigation of Quantum Dot Lasers

DTIC Science & Technology

2004-08-09

Accomplishments: • Introduction Since the first demonstration of room-temperature operation of self-assembled quantum-dot (QD) lasers about a...regions (JGaAs), wetting layer (JWL), and Auger recombination in the dots ( JAug ). for the present 1.3µm dots, the temperature invariant measured

Studies on the Conformational Landscape of Tert-Butyl Acetate Using Microwave Spectroscopy and Quantum Chemical Calculations

NASA Astrophysics Data System (ADS)

Zhao, YueYue; Mouhib, Halima; Li, Guohua; Stahl, Wolfgang; Kleiner, Isabelle

2014-06-01

The tert-Butyl acetate molecule was studied using a combination of quantum chemical calculations and molecular beam Fourier transform microwave spectroscopy in the 9 to 14 GHz range. Due to its rather rigid frame, the molecule possesses only two different conformers: one of Cs and one of C1 symmetry. According to ab initio calculations, the Cs conformer is 46 kJ/mol lower in energy and is the one observed in the supersonic jet. We report on the structure and dynamics of the most abundant conformer of tert-butyl acetate, with accurate rotational and centrifugal distortion constants. Additionally, the barrier to internal rotation of the acetyl methyl group was determined. Splittings due to the internal rotation of the methyl group of up to 1.3 GHz were observed in the spectrum. Using the programs XIAM and BELGI-Cs, we determine the barrier height to be about 113 cm-1 and compare the molecular parameters obtained from these two codes. Additionally, the experimental rotational constants were used to validate numerous quantum chemical calculations. This study is part of a larger project which aims at determining the lowest energy conformers of organic esters and ketones which are of interest for flavor or perfume synthetic applications Project partly supported by the PHC PROCOPE 25059YB.

Portable open-path chemical sensor using a quantum cascade laser

NASA Astrophysics Data System (ADS)

Corrigan, Paul; Lwin, Maung; Huntley, Reuven; Chhabra, Amandeep; Moshary, Fred; Gross, Barry; Ahmed, Samir

2009-05-01

Remote sensing of enemy installations or their movements by trace gas detection is a critical but challenging military objective. Open path measurements over ranges of a few meters to many kilometers with sensitivity in the parts per million or billion regime are crucial in anticipating the presence of a threat. Previous approaches to detect ground level chemical plumes, explosive constituents, or combustion have relied on low-resolution, short range Fourier transform infrared spectrometer (FTIR), or low-sensitivity near-infrared differential optical absorption spectroscopy (DOAS). As mid-infrared quantum cascade laser (QCL) sources have improved in cost and performance, systems based on QCL's that can be tailored to monitor multiple chemical species in real time are becoming a viable alternative. We present the design of a portable, high-resolution, multi-kilometer open path trace gas sensor based on QCL technology. Using a tunable (1045-1047cm-1) QCL, a modeled atmosphere and link-budget analysis with commercial component specifications, we show that with this approach, accuracy in parts per billion ozone or ammonia can be obtained in seconds at path lengths up to 10 km. We have assembled an open-path QCL sensor based on this theoretical approach at City College of New York, and we present preliminary results demonstrating the potential of QCLs in open-path sensing applications.

Investigation of trypsin-CdSe quantum dot interactions via spectroscopic methods and effects on enzymatic activity.

PubMed

Kaur, Gurvir; Tripathi, S K

2015-01-05

The paper presents the interactions between trypsin and water soluble cadmium selenide (CdSe) quantum dots investigated by spectrophotometric methods. CdSe quantum dots have strong ability to quench the intrinsic fluorescence of trypsin by a static quenching mechanism. The quenching has been studied at three different temperatures where the results revealed that electrostatic interactions exist between CdSe quantum dots and trypsin and are responsible to stabilize the complex. The Scatchard plot from quenching revealed 1 binding site for quantum dots by trypsin, the same has been confirmed by making isothermal titrations of quantum dots against trypsin. The distance between donor and acceptor for trypsin-CdSe quantum dot complexes is calculated to be 2.8 nm by energy transfer mechanisms. The intrinsic fluorescence of CdSe quantum dots has also been enhanced by the trypsin, and is linear for concentration of trypsin ranging 1-80 μl. All the observations evidence the formation of trypsin-CdSe quantum dot conjugates, where trypsin retains the enzymatic activity which in turn is temperature and pH dependent. Copyright © 2014 Elsevier B.V. All rights reserved.

POSSIBLE NATURE OF THE RADIATION-INDUCED SIGNAL IN NAILS: HIGH-FIELD EPR, CONFIRMING CHEMICAL SYNTHESIS, AND QUANTUM CHEMICAL CALCULATIONS

PubMed Central

Tipikin, Dmitriy S.; Swarts, Steven G.; Sidabras, Jason W.; Trompier, François; Swartz, Harold M.

2016-01-01

Exposure of finger- and toe-nails to ionizing radiation generates an Electron Paramagnetic Resonance (EPR) signal whose intensity is dose dependent and stable at room temperature for several days. The dependency of the radiation-induced signal (RIS) on the received dose may be used as the basis for retrospective dosimetry of an individual's fortuitous exposure to ionizing radiation. Two radiation-induced signals, a quasi-stable (RIS2) and stable signal (RIS5), have been identified in nails irradiated up to a dose of 50 Gy. Using X-band EPR, both RIS signals exhibit a singlet line shape with a line width around 1.0 mT and an apparent g-value of 2.0044. In this work, we seek information on the exact chemical nature of the radiation-induced free radicals underlying the signal. This knowledge may provide insights into the reason for the discrepancy in the stabilities of the two RIS signals and help develop strategies for stabilizing the radicals in nails or devising methods for restoring the radicals after decay. In this work an analysis of high field (94 GHz and 240 GHz) EPR spectra of the RIS using quantum chemical calculations, the oxidation–reduction properties and the pH dependence of the signal intensities are used to show that spectroscopic and chemical properties of the RIS are consistent with a semiquinone-type radical underlying the RIS. It has been suggested that semiquinone radicals formed on trace amounts of melanin in nails are the basis for the RIS signals. However, based on the quantum chemical calculations and chemical properties of the RIS, it is likely that the radicals underlying this signal are generated from the radiolysis of L-3,4-dihydroxyphenylalanine (DOPA) amino acids in the keratin proteins. These DOPA amino acids are likely formed from the exogenous oxidation of tyrosine in keratin by the oxygen from the air prior to irradiation. We show that these DOPA amino acids can work as radical traps, capturing the highly reactive and unstable

Spectroscopic investigation of alloyed quantum dot-based FRET to cresyl violet dye.

PubMed

Kotresh, M G; Adarsh, K S; Shivkumar, M A; Mulimani, B G; Savadatti, M I; Inamdar, S R

2016-05-01

Quantum dots (QDs), bright luminescent semiconductor nanoparticles, have found numerous applications ranging from optoelectronics to bioimaging. Here, we present a systematic investigation of fluorescence resonance energy transfer (FRET) from hydrophilic ternary alloyed quantum dots (CdSeS/ZnS) to cresyl violet dye with a view to explore the effect of composition of QD donors on FRET efficiency. Fluorescence emission of QD is controlled by varying the composition of QD without altering the particle size. The results show that quantum yield of the QDs increases with increase in the emission wavelength. The FRET parameters such as spectral overlap J(λ), Förster distance R0, intermolecular distance (r), rate of energy transfer k(T)(r), and transfer efficiency (E) are determined by employing both steady-state and time-resolved fluorescence spectroscopy. Additionally, dynamic quenching is noticed to occur in the present FRET system. Stern-Volmer (K(D)) and bimolecular quenching constants (k(q)) are determined from the Stern-Volmer plot. It is observed that the transfer efficiency follows a linear dependence on the spectral overlap and the quantum yield of the donor as predicted by the Förster theory upon changing the composition of the QD. Copyright © 2015 John Wiley & Sons, Ltd.

Conformational, structural, vibrational, electronic and quantum chemical investigations of cis-2-methoxycinnamic acid

NASA Astrophysics Data System (ADS)

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

2015-01-01

The Fourier transform infrared (FTIR) and FT-Raman spectra of cis-2-methoxycinnamic acid have been measured in the range 4000-400 and 4000-100 cm-1, respectively. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman data. The geometry was optimised without any symmetry constrains using the DFT/B3LYP method utilising 6-311++G∗∗ and cc-pVTZ basis sets. The thermodynamic stability and chemical reactivity descriptors of the molecule have been determined. The exact environment of C and H of the molecule has been analysed by NMR spectroscopies through 1H and 13C NMR chemical shifts of the molecule. The energies of the frontier molecular orbitals have also been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. The vibrational frequencies which were determined experimentally are compared with those obtained theoretically from density functional theory (DFT) gradient calculations employing the B3LYP/6-311++G∗∗ and cc-pVTZ methods.

Wavy carbon: A new series of carbon structures explored by quantum chemical calculations

NASA Astrophysics Data System (ADS)

Ohno, Koichi; Satoh, Hiroko; Iwamoto, Takeaki; Tokoyama, Hiroaki; Yamakado, Hideo

2015-10-01

A new carbon family adopting wavy structures has been found by quantum chemical calculations. The key motif of this family is a condensed four-membered ring. Periodically wavy-carbon sheets (wavy-Cn sheets, n = 2, 6, and 8) as well as wavy-C36 tube were found to be very similar to the previously reported prism-Cn carbon tubes (n = 5, 6, and 8) in several respects, including the relative energies per one carbon atom with respect to graphene, CC bond lengths, and CCC bond angles. Because of very high relative energies with respect to graphene (206-253 kJ mol-1), the wavy-carbons may behave as energy reserving materials.

Carotenoid radical cation formation in LH2 of purple bacteria: a quantum chemical study.

PubMed

Wormit, Michael; Dreuw, Andreas

2006-11-30

In LH2 complexes of Rhodobacter sphaeroides the formation of a carotenoid radical cation has recently been observed upon photoexcitation of the carotenoid S2 state. To shed more light onto the yet unknown molecular mechanism leading to carotenoid radical formation in LH2, the interactions between carotenoid and bacteriochlorophyll in LH2 are investigated by means of quantum chemical calculations for three different carotenoids--neurosporene, spheroidene, and spheroidenone--using time-dependent density functional theory. Crossings of the calculated potential energy curve of the electron transfer state with the bacteriochlorophyll Qx state and the carotenoid S1 and S2 states occur along an intermolecular distance coordinate for neurosporene and spheroidene, but for spheroidenone no crossing of the electron transfer state with the carotenoid S1 state could be found. By comparison with recent experiments where no formation of a spheroidenone radical cation has been observed, a molecular mechanism for carotenoid radical cation formation is proposed in which it is formed via a vibrationally excited carotenoid S1 or S*state. Arguments are given why the formation of the carotenoid radical cation does not proceed via the Qx, S2, or higher excited electron transfer states.

Chemical and quantum simulation of electron transfer through a polypeptide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ungar, L.W.; Voth, G.A.; Newton, M.D.

1999-08-26

Quantum rate theory, molecular dynamics simulations, and semiempirical electronic structure calculations are used to fully investigate electron transfer mediated by a solvated polypeptide for the first time. Using a stationary-phase approximation, the nonadiabatic electron-transfer rate constant is calculated from the nuclear free energies and the electronic coupling between the initial and final states. The former are obtained from quantum path integral and classical molecular dynamics simulations; the latter are calculated using semiempirical electronic structure calculations and the generalized Mulliken-Hush method. Importantly, no parameters are fit to kinetic data. The simulated system consists of a solvated four-proline polypeptide with a tris(bipyridine)rutheniummore » donor group and an oxypentamminecobalt acceptor group. From the simulation data entropy and energy contributions to the free energies are distinguished. Quantum suppression of the barrier, including important solvent contributions, is demonstrated. Although free energy profiles along the reaction coordinate are nearly parabolic, pronounced departures from harmonic behavior are found for the separate energy and entropy functions. Harmonic models of the system are compared to simulation results in order to quantify anharmonic effects. Electronic structure calculations show that electronic coupling elements vary considerably with system conformation, even when the effective donor-acceptor separation remains roughly constant. The calculations indicate that electron transfer in a significant range of conformations linking the polypeptide to the acceptor may contribute to the overall rate constant. After correction for limitations of the solvent model, the simulations and calculations agree well with the experimental activation energy and Arrhenius prefactor.« less

Toward prethreshold gate-based quantum simulation of chemical dynamics: using potential energy surfaces to simulate few-channel molecular collisions

DOE PAGES

Sornborger, Andrew Tyler; Stancil, Phillip; Geller, Michael R.

2018-03-22

Here, one of the most promising applications of an error-corrected universal quantum computer is the efficient simulation of complex quantum systems such as large molecular systems. In this application, one is interested in both the electronic structure such as the ground state energy and dynamical properties such as the scattering cross section and chemical reaction rates. However, most theoretical work and experimental demonstrations have focused on the quantum computation of energies and energy surfaces. In this work, we attempt to make the prethreshold (not error-corrected) quantum simulation of dynamical properties practical as well. We show that the use of precomputedmore » potential energy surfaces and couplings enables the gate-based simulation of few-channel but otherwise realistic molecular collisions. Our approach is based on the widely used Born–Oppenheimer approximation for the structure problem coupled with a semiclassical method for the dynamics. In the latter the electrons are treated quantum mechanically but the nuclei are classical, which restricts the collisions to high energy or temperature (typically above ≈10 eV). By using operator splitting techniques optimized for the resulting time-dependent Hamiltonian simulation problem, we give several physically realistic collision examples, with 3–8 channels and circuit depths < 1000.« less

Toward prethreshold gate-based quantum simulation of chemical dynamics: using potential energy surfaces to simulate few-channel molecular collisions

NASA Astrophysics Data System (ADS)

Sornborger, Andrew T.; Stancil, Phillip; Geller, Michael R.

2018-05-01

One of the most promising applications of an error-corrected universal quantum computer is the efficient simulation of complex quantum systems such as large molecular systems. In this application, one is interested in both the electronic structure such as the ground state energy and dynamical properties such as the scattering cross section and chemical reaction rates. However, most theoretical work and experimental demonstrations have focused on the quantum computation of energies and energy surfaces. In this work, we attempt to make the prethreshold (not error-corrected) quantum simulation of dynamical properties practical as well. We show that the use of precomputed potential energy surfaces and couplings enables the gate-based simulation of few-channel but otherwise realistic molecular collisions. Our approach is based on the widely used Born-Oppenheimer approximation for the structure problem coupled with a semiclassical method for the dynamics. In the latter the electrons are treated quantum mechanically but the nuclei are classical, which restricts the collisions to high energy or temperature (typically above ≈ 10 eV). By using operator splitting techniques optimized for the resulting time-dependent Hamiltonian simulation problem, we give several physically realistic collision examples, with 3-8 channels and circuit depths < 1000.

Toward prethreshold gate-based quantum simulation of chemical dynamics: using potential energy surfaces to simulate few-channel molecular collisions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sornborger, Andrew Tyler; Stancil, Phillip; Geller, Michael R.

Here, one of the most promising applications of an error-corrected universal quantum computer is the efficient simulation of complex quantum systems such as large molecular systems. In this application, one is interested in both the electronic structure such as the ground state energy and dynamical properties such as the scattering cross section and chemical reaction rates. However, most theoretical work and experimental demonstrations have focused on the quantum computation of energies and energy surfaces. In this work, we attempt to make the prethreshold (not error-corrected) quantum simulation of dynamical properties practical as well. We show that the use of precomputedmore » potential energy surfaces and couplings enables the gate-based simulation of few-channel but otherwise realistic molecular collisions. Our approach is based on the widely used Born–Oppenheimer approximation for the structure problem coupled with a semiclassical method for the dynamics. In the latter the electrons are treated quantum mechanically but the nuclei are classical, which restricts the collisions to high energy or temperature (typically above ≈10 eV). By using operator splitting techniques optimized for the resulting time-dependent Hamiltonian simulation problem, we give several physically realistic collision examples, with 3–8 channels and circuit depths < 1000.« less

Quantum Hall resistance standards from graphene grown by chemical vapour deposition on silicon carbide

NASA Astrophysics Data System (ADS)

Lafont, F.; Ribeiro-Palau, R.; Kazazis, D.; Michon, A.; Couturaud, O.; Consejo, C.; Chassagne, T.; Zielinski, M.; Portail, M.; Jouault, B.; Schopfer, F.; Poirier, W.

2015-04-01

Replacing GaAs by graphene to realize more practical quantum Hall resistance standards (QHRS), accurate to within 10-9 in relative value, but operating at lower magnetic fields than 10 T, is an ongoing goal in metrology. To date, the required accuracy has been reported, only few times, in graphene grown on SiC by Si sublimation, under higher magnetic fields. Here, we report on a graphene device grown by chemical vapour deposition on SiC, which demonstrates such accuracies of the Hall resistance from 10 T up to 19 T at 1.4 K. This is explained by a quantum Hall effect with low dissipation, resulting from strongly localized bulk states at the magnetic length scale, over a wide magnetic field range. Our results show that graphene-based QHRS can replace their GaAs counterparts by operating in as-convenient cryomagnetic conditions, but over an extended magnetic field range. They rely on a promising hybrid and scalable growth method and a fabrication process achieving low-electron-density devices.

Quantum Hall resistance standards from graphene grown by chemical vapour deposition on silicon carbide

PubMed Central

Lafont, F.; Ribeiro-Palau, R.; Kazazis, D.; Michon, A.; Couturaud, O.; Consejo, C.; Chassagne, T.; Zielinski, M.; Portail, M.; Jouault, B.; Schopfer, F.; Poirier, W.

2015-01-01

Replacing GaAs by graphene to realize more practical quantum Hall resistance standards (QHRS), accurate to within 10−9 in relative value, but operating at lower magnetic fields than 10 T, is an ongoing goal in metrology. To date, the required accuracy has been reported, only few times, in graphene grown on SiC by Si sublimation, under higher magnetic fields. Here, we report on a graphene device grown by chemical vapour deposition on SiC, which demonstrates such accuracies of the Hall resistance from 10 T up to 19 T at 1.4 K. This is explained by a quantum Hall effect with low dissipation, resulting from strongly localized bulk states at the magnetic length scale, over a wide magnetic field range. Our results show that graphene-based QHRS can replace their GaAs counterparts by operating in as-convenient cryomagnetic conditions, but over an extended magnetic field range. They rely on a promising hybrid and scalable growth method and a fabrication process achieving low-electron-density devices. PMID:25891533

Investigations in quantum games using EPR-type set-ups

NASA Astrophysics Data System (ADS)

Iqbal, Azhar

2006-04-01

Research in quantum games has flourished during recent years. However, it seems that opinion remains divided about their true quantum character and content. For example, one argument says that quantum games are nothing but 'disguised' classical games and that to quantize a game is equivalent to replacing the original game by a different classical game. The present thesis contributes towards the ongoing debate about quantum nature of quantum games by developing two approaches addressing the related issues. Both approaches take Einstein-Podolsky-Rosen (EPR)-type experiments as the underlying physical set-ups to play two-player quantum games. In the first approach, the players' strategies are unit vectors in their respective planes, with the knowledge of coordinate axes being shared between them. Players perform measurements in an EPR-type setting and their payoffs are defined as functions of the correlations, i.e. without reference to classical or quantum mechanics. Classical bimatrix games are reproduced if the input states are classical and perfectly anti-correlated, as for a classical correlation game. However, for a quantum correlation game, with an entangled singlet state as input, qualitatively different solutions are obtained. The second approach uses the result that when the predictions of a Local Hidden Variable (LHV) model are made to violate the Bell inequalities the result is that some probability measures assume negative values. With the requirement that classical games result when the predictions of a LHV model do not violate the Bell inequalities, our analysis looks at the impact which the emergence of negative probabilities has on the solutions of two-player games which are physically implemented using the EPR-type experiments.

Experimental investigations of quantum confined silicon nanoparticle light emitting devices

NASA Astrophysics Data System (ADS)

Ligman, Rebekah Kristine

2007-12-01

As the demands on our world's energy resources continue to grow, alternative high efficiency materials such as quantum confined silicon nanoparticles (Si nps) are desirable for their potential low cost application in white light illumination, in optical displays, and in on-chip optical interconnects. Many fabrication and passivation techniques exist that produce Si nps with high photogenerated quantum yield. However, high electrically generated Si np quantum efficiency has eluded our society. Predominantly due to the lack of a stable surface passivation and a device fabrication technique that preserves the Si np optical properties. To amend these deficiencies, the passivation of nonthermal plasma fabricated Si nps with a surface oxide grown under UV exposure was first investigated. Control over the surface oxidized Si np (Si/SiO2) passivation growth was demonstrated and the optical stability of Si/SiO2 nps was suitable for demonstrating Si np electroluminescence (EL). Two approaches for constructing hybrid organic light emitting diode (OLED) devices around nonthermal plasma fabricated Si nps were then investigated. Multilayer devices, composed of a nonthermal plasma fabricated Si np layer embedded within an OLED, were first studied. However, no EL from Si nps was obtained using the multilayer device architecture due to poor control over the Si np film thickness. Single layer polymer(Si/SiO2) hybrid devices, composed of nps randomly dispersed within an extrinsic conductive polymer, were then studied and EL from Si/SiO2 nps was obtained. The hybrid device optical and electrical response was enhanced over the control devices, possibly due to morphology changes induced by the Si/SiO2 nps. The energy transfer (ET) processes in single layer polymer(Si/SiO 2) hybrid devices were then investigated by imposing known spatial separations between the intrinsic conductive polymers and Si/SiO2 nps. No measurable Si/SiO2 np emission was observed from the intrinsic hybrid devices

Algorithms Bridging Quantum Computation and Chemistry

NASA Astrophysics Data System (ADS)

McClean, Jarrod Ryan

The design of new materials and chemicals derived entirely from computation has long been a goal of computational chemistry, and the governing equation whose solution would permit this dream is known. Unfortunately, the exact solution to this equation has been far too expensive and clever approximations fail in critical situations. Quantum computers offer a novel solution to this problem. In this work, we develop not only new algorithms to use quantum computers to study hard problems in chemistry, but also explore how such algorithms can help us to better understand and improve our traditional approaches. In particular, we first introduce a new method, the variational quantum eigensolver, which is designed to maximally utilize the quantum resources available in a device to solve chemical problems. We apply this method in a real quantum photonic device in the lab to study the dissociation of the helium hydride (HeH+) molecule. We also enhance this methodology with architecture specific optimizations on ion trap computers and show how linear-scaling techniques from traditional quantum chemistry can be used to improve the outlook of similar algorithms on quantum computers. We then show how studying quantum algorithms such as these can be used to understand and enhance the development of classical algorithms. In particular we use a tool from adiabatic quantum computation, Feynman's Clock, to develop a new discrete time variational principle and further establish a connection between real-time quantum dynamics and ground state eigenvalue problems. We use these tools to develop two novel parallel-in-time quantum algorithms that outperform competitive algorithms as well as offer new insights into the connection between the fermion sign problem of ground states and the dynamical sign problem of quantum dynamics. Finally we use insights gained in the study of quantum circuits to explore a general notion of sparsity in many-body quantum systems. In particular we use

Quantum chemical study of the mechanism of reaction between NH (X 3sigma-) and H2, H2O, and CO2 under combustion conditions.

PubMed

Mackie, John C; Bacskay, George B

2005-12-29

Reactions of ground-state NH (3sigma-) radicals with H2, H2O, and CO2 have been investigated quantum chemically, whereby the stationary points of the appropriate reaction potential energy surfaces, that is, reactants, products, intermediates, and transition states, have been identified at the G3//B3LYP level of theory. Reaction between NH and H2 takes place via a simple abstraction transition state, and the rate coefficient for this reaction as derived from the quantum chemical calculations, k(NH + H2) = (1.1 x 10(14)) exp(-20.9 kcal mol(-1)/RT) cm3 mol(-1) s(-1) between 1000 and 2000 K, is found to be in good agreement with experiment. For reaction between triplet NH and H2O, no stable intermediates were located on the triplet reaction surface although several stable species were found on the singlet surface. No intersystem crossing seam between triplet NH + H2O and singlet HNO + H2 (the products of lowest energy) was found; hence there is no evidence to support the existence of a low-energy pathway to these products. A rate coefficient of k(NH + H2O) = (6.1 x 10(13)) exp(-32.8 kcal mol(-1)/RT) cm3 mol(-1) s(-1) between 1000 and 2000 K for the reaction NH (3sigma-) + H2O --> NH2 (2B) + OH (2pi) was derived from the quantum chemical results. The reverse rate coefficient, calculated via the equilibrium constant, is in agreement with values used in modeling the thermal de-NO(x) process. For the reaction between triplet NH and CO2, several stable intermediates on both triplet and singlet reaction surfaces were located. Although a pathway from triplet NH + CO2 to singlet HNO + CO involving intersystem crossing in an HN-CO2 adduct was discovered, no pathway of sufficiently low activation energy was discovered to compare with that found in an earlier experiment [Rohrig, M.; Wagner, H. G. Proc. Combust. Inst. 1994, 25, 993.].

A general intermolecular force field based on tight-binding quantum chemical calculations

NASA Astrophysics Data System (ADS)

Grimme, Stefan; Bannwarth, Christoph; Caldeweyher, Eike; Pisarek, Jana; Hansen, Andreas

2017-10-01

A black-box type procedure is presented for the generation of a molecule-specific, intermolecular potential energy function. The method uses quantum chemical (QC) information from our recently published extended tight-binding semi-empirical scheme (GFN-xTB) and can treat non-covalently bound complexes and aggregates with almost arbitrary chemical structure. The necessary QC information consists of the equilibrium structure, Mulliken atomic charges, charge centers of localized molecular orbitals, and also of frontier orbitals and orbital energies. The molecular pair potential includes model density dependent Pauli repulsion, penetration, as well as point charge electrostatics, the newly developed D4 dispersion energy model, Drude oscillators for polarization, and a charge-transfer term. Only one element-specific and about 20 global empirical parameters are needed to cover systems with nuclear charges up to radon (Z = 86). The method is tested for standard small molecule interaction energy benchmark sets where it provides accurate intermolecular energies and equilibrium distances. Examples for structures with a few hundred atoms including charged systems demonstrate the versatility of the approach. The method is implemented in a stand-alone computer code which enables rigid-body, global minimum energy searches for molecular aggregation or alignment.

Chemically differentiating ascorbate-mediated dissolution of quantum dots in cell culture media

NASA Astrophysics Data System (ADS)

Su, Cheng-Kuan; Sun, Yuh-Chang

2013-02-01

To investigate the dynamic dissolution of quantum dots (QDs) in cell culture media, in this study we constructed an online automatic analytical system comprising a sequential in-tube solid phase extraction (SPE) device and an inductively coupled plasma (ICP) mass spectrometer. By means of selectively extracting QDs and cadmium ions (Cd2+) onto the interior surface of the polytetrafluoroethylene (PTFE) tube, this novel SPE device could be used to determine the degree of QD dissolution through a simple adjustment of sample acidity. To the best of our knowledge, this study is the first to exploit PTFE tubing as a selective SPE adsorbent for the online chemical differentiation of QDs and Cd2+ ions with the goal of monitoring the phenomenon of QD dissolution in complicated biological matrices. We confirmed the analytical reliability of this system through comparison of the measured Cd-to-QD ratios to the expected values. When analyzing QDs and Cd2+ ions at picomolar levels, a temporal resolution of 8 min was required to load sufficient amounts of the analytes to meet the sensitivity requirements of the ICP mass spectrometer. To demonstrate the practicability of this developed method, we measured the dynamic variations in the Cd-to-QD705 ratio in the presence of ascorbate as a physiological stimulant to generate reactive oxygen species in cell culture media and trigger the dissolution of QDs; our results suggest that the ascorbate-induced QD dissolution was dependent on the time, treatment concentration, and nature of the biomolecule.To investigate the dynamic dissolution of quantum dots (QDs) in cell culture media, in this study we constructed an online automatic analytical system comprising a sequential in-tube solid phase extraction (SPE) device and an inductively coupled plasma (ICP) mass spectrometer. By means of selectively extracting QDs and cadmium ions (Cd2+) onto the interior surface of the polytetrafluoroethylene (PTFE) tube, this novel SPE device could be

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

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phillips, Mark C.; Brumfield, Brian E.

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

Time-Resolved Quantum Cascade Laser Absorption Spectroscopy of Pulsed Plasma Assisted Chemical Vapor Deposition Processes Containing BCl3

NASA Astrophysics Data System (ADS)

Lang, Norbert; Hempel, Frank; Strämke, Siegfried; Röpcke, Jürgen

2011-08-01

In situ measurements are reported giving insight into the plasma chemical conversion of the precursor BCl3 in industrial applications of boriding plasmas. For the online monitoring of its ground state concentration, quantum cascade laser absorption spectroscopy (QCLAS) in the mid-infrared spectral range was applied in a plasma assisted chemical vapor deposition (PACVD) reactor. A compact quantum cascade laser measurement and control system (Q-MACS) was developed to allow a flexible and completely dust-sealed optical coupling to the reactor chamber of an industrial plasma surface modification system. The process under the study was a pulsed DC plasma with periodically injected BCl3 at 200 Pa. A synchronization of the Q-MACS with the process control unit enabled an insight into individual process cycles with a sensitivity of 10-6 cm-1·Hz-1/2. Different fragmentation rates of the precursor were found during an individual process cycle. The detected BCl3 concentrations were in the order of 1014 molecules·cm-3. The reported results of in situ monitoring with QCLAS demonstrate the potential for effective optimization procedures in industrial PACVD processes.

Quantum entanglement properties of geometrical and topological quantum gates

NASA Astrophysics Data System (ADS)

Sezer, Hasan Cavit; Duy, Hoang Ngoc; Heydari, Hoshang

2011-03-01

In this paper we will investigate the action of holonomic and topological quantum gates on different classes of four qubit states. In particular, we review the construction of holonomic quantum gate based on geometric phase and topological quantum gate based on braid group. Then, we investigate the entanglement properties of three different classes of four-qubit states based on geometric invariants. The result shows that entanglement properties of the two most generic classes of four-qubit states can be controlled by holonomic and topological quantum gate..

From quantum coherence to quantum correlations

NASA Astrophysics Data System (ADS)

Sun, Yuan; Mao, Yuanyuan; Luo, Shunlong

2017-06-01

In quantum mechanics, quantum coherence of a state relative to a quantum measurement can be identified with the quantumness that has to be destroyed by the measurement. In particular, quantum coherence of a bipartite state relative to a local quantum measurement encodes quantum correlations in the state. If one takes minimization with respect to the local measurements, then one is led to quantifiers which capture quantum correlations from the perspective of coherence. In this vein, quantum discord, which quantifies the minimal correlations that have to be destroyed by quantum measurements, can be identified as the minimal coherence, with the coherence measured by the relative entropy of coherence. To advocate and formulate this idea in a general context, we first review coherence relative to Lüders measurements which extends the notion of coherence relative to von Neumann measurements (or equivalently, orthonomal bases), and highlight the observation that quantum discord arises as minimal coherence through two prototypical examples. Then, we introduce some novel measures of quantum correlations in terms of coherence, illustrate them through examples, investigate their fundamental properties and implications, and indicate their applications to quantum metrology.

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

PubMed

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

2013-06-01

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

Noncovalent Interactions and Internal Dynamics in Pyridine-Ammonia: A Combined Quantum-Chemical and Microwave Spectroscopy Study.

PubMed

Spada, Lorenzo; Tasinato, Nicola; Vazart, Fanny; Barone, Vincenzo; Caminati, Walther; Puzzarini, Cristina

2017-04-06

The 1:1 complex of ammonia with pyridine is characterized by using state-of-the-art quantum-chemical computations combined with pulsed-jet Fourier-transform microwave spectroscopy. The computed potential energy landscape indicates the formation of a stable σ-type complex, which is confirmed experimentally: analysis of the rotational spectrum shows the presence of only one 1:1 pyridine-ammonia adduct. Each rotational transition is split into several components owing to the internal rotation of NH 3 around its C 3 axis and to the hyperfine structure of both 14 N quadrupolar nuclei, thus providing unequivocal proof that the two molecules form a σ-type complex involving both a N-H⋅⋅⋅N and a C-H⋅⋅⋅N hydrogen bond. The dissociation energy (BSSE- and ZPE-corrected) is estimated to be 11.5 kJ mol -1 . This work represents the first application of an accurate yet efficient computational scheme, designed for the investigation of small biomolecules, to a molecular cluster. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spectral characterization of guanine C4-OH adduct: a radiation and quantum chemical study.

PubMed

Phadatare, Suvarna D; Sharma, Kiran Kumar K; Rao, B S M; Naumov, S; Sharma, Geeta K

2011-11-24

The reaction of hydroxyl radical ((•)OH) with guanine was investigated under restricted pH condition (pH 4.6) using pulse radiolysis technique. The time-resolved optical transient absorption spectra showed two peaks centered at 300 and 330 nm at 4 μs after the pulse which exhibited different reactivity toward molecular oxygen (O(2)). The peak at 300 nm was found to be relatively more stable than the peak at 330 nm. The peak corresponding to 330 nm decayed within 20 μs having a first order rate constant 4-7 × 10(4) s(-1) and was pH dependent. On longer time scale, the species decayed by a bimolecular process. The presence of O(2) did not affect its decay rate constant. The (•)OH reacts with guanine at pH 4.6 with a diffusion-controlled second order rate constant of ≥1 × 10(10) mol(-1) dm(3) s(-1). The reaction of Br(2)(•-), O(2)(•-), and 2-hydroxy-2-propyl radical with guanine was also investigated to differentiate among the one-electron oxidized, one-electron reduced species of guanine and the guanine-OH adducts formed in the reaction of (•)OH at pH 4.6. On the basis of the spectral characteristics and reactivity toward O(2), two guanine-OH adduct species were identified (i) the C4-OH adduct species absorbing at 330 nm which has not been reported so far and (ii) the C8-OH adduct species absorbing at 300 nm in agreement with the known literature absorption features. Quantum chemical calculations using BHandHLYP with 6-31+G(d,p) basis set and excited state calculations using TDDFT for all possible transients complement the assignment of the observed spectral peak at 330 nm to the C4-OH adduct of guanine. Furthermore, steady state radiolysis revealed the formation of 8-hydroxy-guanine whose precursor is known to be the C8-OH adduct species. © 2011 American Chemical Society

Molecular mechanism of NDMA formation from N,N-dimethylsulfamide during ozonation: quantum chemical insights into a bromide-catalyzed pathway.

PubMed

Trogolo, Daniela; Mishra, Brijesh Kumar; Heeb, Michèle B; von Gunten, Urs; Arey, J Samuel

2015-04-07

During ozonation of drinking water, the fungicide metabolite N,N-dimethylsulfamide (DMS) can be transformed into a highly toxic product, N-nitrosodimethylamine (NDMA). We used quantum chemical computations and stopped-flow experiments to evaluate a chemical mechanism proposed previously to describe this transformation. Stopped-flow experiments indicate a pK(a) = 10.4 for DMS. Experiments show that hypobromous acid (HOBr), generated by ozone oxidation of naturally occurring bromide, brominates the deprotonated DMS(-) anion with a near-diffusion controlled rate constant (7.1 ± 0.6 × 10(8) M(-1) s(-1)), forming Br-DMS(-) anion. According to quantum chemical calculations, Br-DMS has a pK(a) ∼ 9.0 and thus remains partially deprotonated at neutral pH. The anionic Br-DMS(-) bromamine can react with ozone with a high rate constant (10(5 ± 2.5) M(-1) s(-1)), forming the reaction intermediate (BrNO)(SO2)N(CH3)2(-). This intermediate resembles a loosely bound complex between an electrophilic nitrosyl bromide (BrNO) molecule and an electron-rich dimethylaminosulfinate ((SO2)N(CH3)2(-)) fragment, based on inspection of computed natural charges and geometric parameters. This fragile complex undergoes immediate (10(10 ± 2.5) s(-1)) reaction by two branches: an exothermic channel that produces NDMA, and an entropy-driven channel giving non-NDMA products. Computational results bring new insights into the electronic nature, chemical equilibria, and kinetics of the elementary reactions of this pathway, enabled by computed energies of structures that are not possible to access experimentally.

Chemically functionalized ZnS quantum dots as new optical nanosensor of herbicides

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

Microscopic origin of the fast blue-green luminescence of chemically synthesized non-oxidized silicon quantum dots.

PubMed

Dohnalová, Kateřina; Fučíková, Anna; Umesh, Chinnaswamy P; Humpolíčková, Jana; Paulusse, Jos M J; Valenta, Jan; Zuilhof, Han; Hof, Martin; Gregorkiewicz, Tom

2012-10-22

The microscopic origin of the bright nanosecond blue-green photoluminescence (PL), frequently reported for synthesized organically terminated Si quantum dots (Si-QDs), has not been fully resolved, hampering potential applications of this interesting material. Here a comprehensive study of the PL from alkyl-terminated Si-QDs of 2-3 nm size, prepared by wet chemical synthesis is reported. Results obtained on the ensemble and those from the single nano-object level are compared, and they provide conclusive evidence that efficient and tunable emission arises due to radiative recombination of electron-hole pairs confined in the Si-QDs. This understanding paves the way towards applications of chemical synthesis for the development of Si-QDs with tunable sizes and bandgaps. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigations of the Quantum Correlation in Two-Qubit Heisenberg XYZ Model with Decoherence

NASA Astrophysics Data System (ADS)

Guo-Hui, Yang

2017-03-01

Quantum correlation dynamics in an anisotropic Heisenberg XYZ model under decoherence is investigated with the use of concurrence C and quantum discord (QD). With the Werner state as the initial state, we discuss the influence of mixture degree r on the dynamics. There are some difference between the time evolution behaviors of these two correlation measures with different value of r. For 0 ≤ r ≤ 1/3, there exists quantum discord but no entanglement; For 1/3< r<1, there is a "entanglement sudden death and birth" phenomenon in the concurrence but not in the QD; For r=1, there is one interesting thing that the concurrence decays from 1 to a minimum value close to 0 but the QD vanish. In addition, we have investigated the influence of different parameters on the two correlation measures. It has been found that, the concurrence and QD both exhibit osillatory behaviors with the time evolution, which is independent on the magnetic field B and the coupling coefficient J z . However, the Dzyaloshinskii-Moriya interaction (D) and coupling coefficient J have strong influence on concurrence and QD. With the increasing of the D or J, the frequency of the oscillation getting larger. When time is fixed, with the increasing of D or J, the concurrence and QD change periodically.

Experimental quantum forgery of quantum optical money

NASA Astrophysics Data System (ADS)

Bartkiewicz, Karol; Černoch, Antonín; Chimczak, Grzegorz; Lemr, Karel; Miranowicz, Adam; Nori, Franco

2017-03-01

Unknown quantum information cannot be perfectly copied (cloned). This statement is the bedrock of quantum technologies and quantum cryptography, including the seminal scheme of Wiesner's quantum money, which was the first quantum-cryptographic proposal. Surprisingly, to our knowledge, quantum money has not been tested experimentally yet. Here, we experimentally revisit the Wiesner idea, assuming a banknote to be an image encoded in the polarization states of single photons. We demonstrate that it is possible to use quantum states to prepare a banknote that cannot be ideally copied without making the owner aware of only unauthorized actions. We provide the security conditions for quantum money by investigating the physically-achievable limits on the fidelity of 1-to-2 copying of arbitrary sequences of qubits. These results can be applied as a security measure in quantum digital right management.

Quantum junction solar cells.

PubMed

Tang, Jiang; Liu, Huan; Zhitomirsky, David; Hoogland, Sjoerd; Wang, Xihua; Furukawa, Melissa; Levina, Larissa; Sargent, Edward H

2012-09-12

Colloidal quantum dot solids combine convenient solution-processing with quantum size effect tuning, offering avenues to high-efficiency multijunction cells based on a single materials synthesis and processing platform. The highest-performing colloidal quantum dot rectifying devices reported to date have relied on a junction between a quantum-tuned absorber and a bulk material (e.g., TiO(2)); however, quantum tuning of the absorber then requires complete redesign of the bulk acceptor, compromising the benefits of facile quantum tuning. Here we report rectifying junctions constructed entirely using inherently band-aligned quantum-tuned materials. Realizing these quantum junction diodes relied upon the creation of an n-type quantum dot solid having a clean bandgap. We combine stable, chemically compatible, high-performance n-type and p-type materials to create the first quantum junction solar cells. We present a family of photovoltaic devices having widely tuned bandgaps of 0.6-1.6 eV that excel where conventional quantum-to-bulk devices fail to perform. Devices having optimal single-junction bandgaps exhibit certified AM1.5 solar power conversion efficiencies of 5.4%. Control over doping in quantum solids, and the successful integration of these materials to form stable quantum junctions, offers a powerful new degree of freedom to colloidal quantum dot optoelectronics.

The molecular structure of 4-methylpyridine-N-oxide: Gas-phase electron diffraction and quantum chemical calculations

NASA Astrophysics Data System (ADS)

Belova, Natalya V.; Girichev, Georgiy V.; Kotova, Vitaliya E.; Korolkova, Kseniya A.; Trang, Nguyen Hoang

2018-03-01

The molecular structure of 4-methylpiridine-N-oxide, 4-MePyO, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both, quantum chemistry and GED analyses resulted in CS molecular symmetry with the planar pyridine ring. Obtained molecular parameters confirm the hyperconjugation in the pyridine ring and the sp2 hybridization concept of the nitrogen and carbon atoms in the ring. The experimental geometric parameters are in a good agreement with the parameters for non-substituted N-oxide and reproduced very closely by DFT calculations. The presence of the electron-donating CH3 substituent in 4-MePyO leads to a decrease of the ipso-angle and to an increase of r(N→O) in comparison with the non-substituted PyO. Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme. The nature of the semipolar N→O bond is discussed.

Quantum demultiplexer of quantum parameter-estimation information in quantum networks

NASA Astrophysics Data System (ADS)

Xie, Yanqing; Huang, Yumeng; Wu, Yinzhong; Hao, Xiang

2018-05-01

The quantum demultiplexer is constructed by a series of unitary operators and multipartite entangled states. It is used to realize information broadcasting from an input node to multiple output nodes in quantum networks. The scheme of quantum network communication with respect to phase estimation is put forward through the demultiplexer subjected to amplitude damping noises. The generalized partial measurements can be applied to protect the transferring efficiency from environmental noises in the protocol. It is found out that there are some optimal coherent states which can be prepared to enhance the transmission of phase estimation. The dynamics of state fidelity and quantum Fisher information are investigated to evaluate the feasibility of the network communication. While the state fidelity deteriorates rapidly, the quantum Fisher information can be enhanced to a maximum value and then decreases slowly. The memory effect of the environment induces the oscillations of fidelity and quantum Fisher information. The adjustment of the strength of partial measurements is helpful to increase quantum Fisher information.

The IINS/quantum chemical studies of 17α- and 21-hydroxy-derivatives of progesterone

NASA Astrophysics Data System (ADS)

Szyczewski, A.; Hołderna-Natkaniec, K.; Natkaniec, I.

2003-05-01

The inelastic incoherent neutron scattering and quantum chemical studies have been performed on 17 and 21 hydroxy progesterone and the assignment of internal modes have been proposed in the range up to 700 cm -1. The lattice branch of PDS reveals modes which could be attributed to torsions of rings A and D (cyclohexane and cyclopentane) of the pregnane skeleton. An assignment of the torsional vibrations of methyl groups in the range 150-300 cm -1 and the deformation and out-of plane vibrations of CCOH groups has been proposed. An analysis of the effect of hydrogen bonds on PDS spectra has been performed.

Long distance quantum communication with quantum Reed-Solomon codes

NASA Astrophysics Data System (ADS)

Muralidharan, Sreraman; Zou, Chang-Ling; Li, Linshu; Jiang, Liang; Jianggroup Team

We study the construction of quantum Reed Solomon codes from classical Reed Solomon codes and show that they achieve the capacity of quantum erasure channel for multi-level quantum systems. We extend the application of quantum Reed Solomon codes to long distance quantum communication, investigate the local resource overhead needed for the functioning of one-way quantum repeaters with these codes, and numerically identify the parameter regime where these codes perform better than the known quantum polynomial codes and quantum parity codes . Finally, we discuss the implementation of these codes into time-bin photonic states of qubits and qudits respectively, and optimize the performance for one-way quantum repeaters.

One-way quantum repeaters with quantum Reed-Solomon codes

NASA Astrophysics Data System (ADS)

Muralidharan, Sreraman; Zou, Chang-Ling; Li, Linshu; Jiang, Liang

2018-05-01

We show that quantum Reed-Solomon codes constructed from classical Reed-Solomon codes can approach the capacity on the quantum erasure channel of d -level systems for large dimension d . We study the performance of one-way quantum repeaters with these codes and obtain a significant improvement in key generation rate compared to previously investigated encoding schemes with quantum parity codes and quantum polynomial codes. We also compare the three generations of quantum repeaters using quantum Reed-Solomon codes and identify parameter regimes where each generation performs the best.

Hybrid quantum processors: molecular ensembles as quantum memory for solid state circuits.

PubMed

Rabl, P; DeMille, D; Doyle, J M; Lukin, M D; Schoelkopf, R J; Zoller, P

2006-07-21

We investigate a hybrid quantum circuit where ensembles of cold polar molecules serve as long-lived quantum memories and optical interfaces for solid state quantum processors. The quantum memory realized by collective spin states (ensemble qubit) is coupled to a high-Q stripline cavity via microwave Raman processes. We show that, for convenient trap-surface distances of a few microm, strong coupling between the cavity and ensemble qubit can be achieved. We discuss basic quantum information protocols, including a swap from the cavity photon bus to the molecular quantum memory, and a deterministic two qubit gate. Finally, we investigate coherence properties of molecular ensemble quantum bits.

Quantum Metropolis sampling.

PubMed

Temme, K; Osborne, T J; Vollbrecht, K G; Poulin, D; Verstraete, F

2011-03-03

The original motivation to build a quantum computer came from Feynman, who imagined a machine capable of simulating generic quantum mechanical systems--a task that is believed to be intractable for classical computers. Such a machine could have far-reaching applications in the simulation of many-body quantum physics in condensed-matter, chemical and high-energy systems. Part of Feynman's challenge was met by Lloyd, who showed how to approximately decompose the time evolution operator of interacting quantum particles into a short sequence of elementary gates, suitable for operation on a quantum computer. However, this left open the problem of how to simulate the equilibrium and static properties of quantum systems. This requires the preparation of ground and Gibbs states on a quantum computer. For classical systems, this problem is solved by the ubiquitous Metropolis algorithm, a method that has basically acquired a monopoly on the simulation of interacting particles. Here we demonstrate how to implement a quantum version of the Metropolis algorithm. This algorithm permits sampling directly from the eigenstates of the Hamiltonian, and thus evades the sign problem present in classical simulations. A small-scale implementation of this algorithm should be achievable with today's technology.

Quantum optics. Gravity meets quantum physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Bernhard W.

2015-02-27

Albert Einstein’s general theory of relativity is a classical formulation but a quantum mechanical description of gravitational forces is needed, not only to investigate the coupling of classical and quantum systems but simply to give a more complete description of our physical surroundings. In this issue of Nature Photonics, Wen-Te Liao and Sven Ahrens reveal a link between quantum and gravitational physics. They propose that in the quantum-optical effect of superradiance, the world line of electromagnetic radiation is changed by the presence of a gravitational field.

Quantitative structure-activation barrier relationship modeling for Diels-Alder ligations utilizing quantum chemical structural descriptors.

PubMed

Nandi, Sisir; Monesi, Alessandro; Drgan, Viktor; Merzel, Franci; Novič, Marjana

2013-10-30

In the present study, we show the correlation of quantum chemical structural descriptors with the activation barriers of the Diels-Alder ligations. A set of 72 non-catalysed Diels-Alder reactions were subjected to quantitative structure-activation barrier relationship (QSABR) under the framework of theoretical quantum chemical descriptors calculated solely from the structures of diene and dienophile reactants. Experimental activation barrier data were obtained from literature. Descriptors were computed using Hartree-Fock theory using 6-31G(d) basis set as implemented in Gaussian 09 software. Variable selection and model development were carried out by stepwise multiple linear regression methodology. Predictive performance of the quantitative structure-activation barrier relationship (QSABR) model was assessed by training and test set concept and by calculating leave-one-out cross-validated Q2 and predictive R2 values. The QSABR model can explain and predict 86.5% and 80% of the variances, respectively, in the activation energy barrier training data. Alternatively, a neural network model based on back propagation of errors was developed to assess the nonlinearity of the sought correlations between theoretical descriptors and experimental reaction barriers. A reasonable predictability for the activation barrier of the test set reactions was obtained, which enabled an exploration and interpretation of the significant variables responsible for Diels-Alder interaction between dienes and dienophiles. Thus, studies in the direction of QSABR modelling that provide efficient and fast prediction of activation barriers of the Diels-Alder reactions turn out to be a meaningful alternative to transition state theory based computation.

Investigation of non-stationary self-focusing of intense laser pulse in cold quantum plasma using ramp density profile

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habibi, M.; Ghamari, F.

2012-11-15

The authors have investigated the non-stationary self-focusing of Gaussian laser pulse in cold quantum plasma. In case of high dense plasma, the nonlinearity in the dielectric constant is mainly due to relativistic high intense interactions and quantum effects. In this paper, we have introduced a ramp density profile for plasma and presented graphically the behavior of spot size oscillations of pulse at rear and front portions of the pulse. It is observed that the ramp density profile and quantum effects play a vital role in stronger and better focusing at the rear of the pulse than at the front inmore » cold quantum plasmas.« less

Quantum interpolation for high-resolution sensing.

PubMed

Ajoy, Ashok; Liu, Yi-Xiang; Saha, Kasturi; Marseglia, Luca; Jaskula, Jean-Christophe; Bissbort, Ulf; Cappellaro, Paola

2017-02-28

Recent advances in engineering and control of nanoscale quantum sensors have opened new paradigms in precision metrology. Unfortunately, hardware restrictions often limit the sensor performance. In nanoscale magnetic resonance probes, for instance, finite sampling times greatly limit the achievable sensitivity and spectral resolution. Here we introduce a technique for coherent quantum interpolation that can overcome these problems. Using a quantum sensor associated with the nitrogen vacancy center in diamond, we experimentally demonstrate that quantum interpolation can achieve spectroscopy of classical magnetic fields and individual quantum spins with orders of magnitude finer frequency resolution than conventionally possible. Not only is quantum interpolation an enabling technique to extract structural and chemical information from single biomolecules, but it can be directly applied to other quantum systems for superresolution quantum spectroscopy.

Maxwell’s demon in the quantum-Zeno regime and beyond

NASA Astrophysics Data System (ADS)

Engelhardt, G.; Schaller, G.

2018-02-01

The long-standing paradigm of Maxwell’s demon is till nowadays a frequently investigated issue, which still provides interesting insights into basic physical questions. Considering a single-electron transistor, where we implement a Maxwell demon by a piecewise-constant feedback protocol, we investigate quantum implications of the Maxwell demon. To this end, we harness a dynamical coarse-graining method, which provides a convenient and accurate description of the system dynamics even for high measurement rates. In doing so, we are able to investigate the Maxwell demon in a quantum-Zeno regime leading to transport blockade. We argue that there is a measurement rate providing an optimal performance. Moreover, we find that besides building up a chemical gradient, there can be also a regime where the feedback loop additionally extracts energy, which results from the energy non-conserving character of the projective measurement.

Comperative investigations of non chemical weed management methods in Hungary.

PubMed

Pali, Orsolya; Reisinger, Peter; Pomsar, Peter

2007-01-01

Organic farming has an increasing tendency in Hungary because of growing consumers' demands according to organic products not only in inland but also in the countries of the European Union. Developments of weed control methods in organically cropped field plants have become conspicuous next to developing chemical weed management methods of convencionally cropped cultural plants. The aim of our investigations was to make comperative investigations of non chemical weed control methods in wide rowed plants.

Standoff detection of explosives and chemical agents using broadly tuned external-cavity quantum cascade lasers (EC-QCLs)

NASA Astrophysics Data System (ADS)

Takeuchi, Eric B.; Rayner, Timothy; Weida, Miles; Crivello, Salvatore; Day, Timothy

2007-10-01

Civilian soft targets such as transportation systems are being targeted by terrorists using IEDs and suicide bombers. Having the capability to remotely detect explosives, precursors and other chemicals would enable these assets to be protected with minimal interruption of the flow of commerce. Mid-IR laser technology offers the potential to detect explosives and other chemicals in real-time and from a safe standoff distance. While many of these agents possess "fingerprint" signatures in the mid-IR (i.e. in the 3-20 micron regime), their effective interrogation by a practical, field-deployable system has been limited by size, complexity, reliability and cost constraints of the base laser technology. Daylight Solutions has addressed these shortcomings by developing compact, portable, broadly tunable mid-IR laser sources based upon external-cavity quantum cascade technology. This technology is now being applied by Daylight in system level architectures for standoff and remote detection of explosives, precursors and chemical agents. Several of these architectures and predicted levels of performance will be presented.

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

ERIC Educational Resources Information Center

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…

Quantum chemical approach for condensed-phase thermochemistry (V): Development of rigid-body type harmonic solvation model

NASA Astrophysics Data System (ADS)

Tarumi, Moto; Nakai, Hiromi

2018-05-01

This letter proposes an approximate treatment of the harmonic solvation model (HSM) assuming the solute to be a rigid body (RB-HSM). The HSM method can appropriately estimate the Gibbs free energy for condensed phases even where an ideal gas model used by standard quantum chemical programs fails. The RB-HSM method eliminates calculations for intra-molecular vibrations in order to reduce the computational costs. Numerical assessments indicated that the RB-HSM method can evaluate entropies and internal energies with the same accuracy as the HSM method but with lower calculation costs.

Chemical, physical and tribological investigation of polymercaptanized soybean oil

USDA-ARS?s Scientific Manuscript database

Polymercaptanized soybean oil (PMSO) was investigated for its chemical, physical and tribological properties relative to soybean oil (SO) and also as a potential multi-functional lubricant additive in high oleic sunflower oil (HOSuO). Analytical investigations showed that PMSO is obtained by convers...

Investigating Pharmacological Similarity by Charting Chemical Space.

PubMed

Buonfiglio, Rosa; Engkvist, Ola; Várkonyi, Péter; Henz, Astrid; Vikeved, Elisabet; Backlund, Anders; Kogej, Thierry

2015-11-23

In this study, biologically relevant areas of the chemical space were analyzed using ChemGPS-NP. This application enables comparing groups of ligands within a multidimensional space based on principle components derived from physicochemical descriptors. Also, 3D visualization of the ChemGPS-NP global map can be used to conveniently evaluate bioactive compound similarity and visually distinguish between different types or groups of compounds. To further establish ChemGPS-NP as a method to accurately represent the chemical space, a comparison with structure-based fingerprint has been performed. Interesting complementarities between the two descriptions of molecules were observed. It has been shown that the accuracy of describing molecules with physicochemical descriptors like in ChemGPS-NP is similar to the accuracy of structural fingerprints in retrieving bioactive molecules. Lastly, pharmacological similarity of structurally diverse compounds has been investigated in ChemGPS-NP space. These results further strengthen the case of using ChemGPS-NP as a tool to explore and visualize chemical space.

Mechanism of Microwave-Assisted Pyrolysis of Glucose to Furfural Revealed by Isotopic Tracer and Quantum Chemical Calculations.

PubMed

Bao, Liwei; Shi, Lei; Luo, Hu; Kong, Lingzhao; Li, Shenggang; Wei, Wei; Sun, Yuhan

2017-08-10

Glucose labeled with 13 C or 18 O was used to investigate the mechanism of its conversion into furfural by microwaveassisted pyrolysis. The isotopic content and location in furfural were determined from GC-MS and 13 C NMR spectroscopic measurements and data analysis. The results suggest that the carbon skeleton in furfural is mainly derived from C1 to C5 of glucose, whereas the C of the aldehyde group and the O of the furan ring in furfural primarily originate from C1 and O5 of glucose, respectively. For the first time, the source of O in the furan ring of furfural was elucidated directly by experiment, providing results that are consistent with predictions from recent quantum chemical calculations. Moreover, further theoretical calculations indicate substantially lower energy barriers than previous predictions by considering the potential catalytic effect of formic acid, which is one of the pyrolysis products. The catalytic role of formic acid is further confirmed by experimental evidence. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Non-Covalent Interactions and Internal Dynamics in Pyridine-Ammonia a Combined Quantum-Chemical and Microwave Spectroscopy Study

NASA Astrophysics Data System (ADS)

Spada, Lorenzo; Tasinato, Nicola; Vazart, Fanny; Barone, Vincenzo; Caminati, Walther; Puzzarini, Cristina

2017-06-01

The 1:1 complex of ammonia with pyridine has been characterized by using state-of-the-art quantum-chemical computations combined with pulsed-jet Fourier-Transform microwave spectroscopy. The computed potential energy landscape pointed out the formation of a stable σ-type complex, which has been confirmed experimentally: the analysis of the rotational spectrum showed the presence of only one 1:1 pyridine - ammonia adduct. Each rotational transition is split into several components due to the internal rotation of NH_3 around its C_3 axis and to the hyperfine structure of both ^{14}N quadrupolar nuclei, thus providing the unequivocal proof that the two molecules form a σ-type complex involving both a N-H\\cdotsN and a C-H\\cdotsN hydrogen bond. The dissociation energy (BSSE and ZPE corrected) has been estimated to be 11.5 kJ\\cdotmol^{-1}. This work represents the first application of an accurate, yet efficient computational scheme, designed for the investigation of small biomolecules, to a molecular cluster.

Structural Investigation of Cesium Lead Halide Perovskites for High-Efficiency Quantum Dot Light-Emitting Diodes.

PubMed

Le, Quyet Van; Kim, Jong Beom; Kim, Soo Young; Lee, Byeongdu; Lee, Dong Ryeol

2017-09-07

We have investigated the effect of reaction temperature of hot-injection method on the structural properties of CsPbX 3 (X: Br, I, Cl) perovskite nanocrystals (NCs) using small- and wide-angle X-ray scattering. It is confirmed that the size of the NCs decreased as the reaction temperature decreased, resulting in stronger quantum confinement. The cubic-phase perovskite NCs formed despite the fact that the reaction temperatures increased from 140 to 180 °C; however, monodispersive NC cubes that are required for densely packing self-assembly film were formed only at lower temperatures. From the X-ray scattering measurements, the spin-coated film from more monodispersive perovskite nanocubes synthesized at lower temperatures resulted in more preferred orientation. This dense-packing perovskite film with preferred orientation yielded efficient light-emitting diode (LED) performance. Thus the dense-packing structure of NC assemblies formed after spin-coating should be considered for high-efficient LEDs based on perovskite quantum dots in addition to quantum confinement effect of the quantum dots.

The Effect of Phonons in RbCl Quantum Pseudodot Qubits

NASA Astrophysics Data System (ADS)

Sun, Yong; Ding, Zhao-Hua; Xiao, Jing-Lin

2016-07-01

By employing the Pekar variational method, the eigenenergies and eigenfunctions of the ground and first-excited states are obtained in a strong electron-longitudinal optical (LO) phonon coupling RbCl quantum pseudodot (QPD). A single qubit can be realized in this two-level quantum system. The electron probability density (EPD) oscillates in the RbCl QPD with a certain period. The investigated results show that the EPD rises with raising the chemical potential of the two-dimensional electron gas and the zero point of the pseudoharmonic potential, whereas it decays with increasing the polaron radius. However, the oscillating period (OP) possesses precisely the opposite characteristics. Through the results and analysis above, we find three ways to adjust the EPD and the OP via changing the chemical potential of the two-dimensional electron gas, the zero point of the pseudoharmonic potential, and the polaron radius.

Quantum interpolation for high-resolution sensing

PubMed Central

Ajoy, Ashok; Liu, Yi-Xiang; Saha, Kasturi; Marseglia, Luca; Jaskula, Jean-Christophe; Bissbort, Ulf; Cappellaro, Paola

2017-01-01

Recent advances in engineering and control of nanoscale quantum sensors have opened new paradigms in precision metrology. Unfortunately, hardware restrictions often limit the sensor performance. In nanoscale magnetic resonance probes, for instance, finite sampling times greatly limit the achievable sensitivity and spectral resolution. Here we introduce a technique for coherent quantum interpolation that can overcome these problems. Using a quantum sensor associated with the nitrogen vacancy center in diamond, we experimentally demonstrate that quantum interpolation can achieve spectroscopy of classical magnetic fields and individual quantum spins with orders of magnitude finer frequency resolution than conventionally possible. Not only is quantum interpolation an enabling technique to extract structural and chemical information from single biomolecules, but it can be directly applied to other quantum systems for superresolution quantum spectroscopy. PMID:28196889

Multiscale investigation of chemical interference in proteins

NASA Astrophysics Data System (ADS)

Samiotakis, Antonios; Homouz, Dirar; Cheung, Margaret S.

2010-05-01

We developed a multiscale approach (MultiSCAAL) that integrates the potential of mean force obtained from all-atomistic molecular dynamics simulations with a knowledge-based energy function for coarse-grained molecular simulations in better exploring the energy landscape of a small protein under chemical interference such as chemical denaturation. An excessive amount of water molecules in all-atomistic molecular dynamics simulations often negatively impacts the sampling efficiency of some advanced sampling techniques such as the replica exchange method and it makes the investigation of chemical interferences on protein dynamics difficult. Thus, there is a need to develop an effective strategy that focuses on sampling structural changes in protein conformations rather than solvent molecule fluctuations. In this work, we address this issue by devising a multiscale simulation scheme (MultiSCAAL) that bridges the gap between all-atomistic molecular dynamics simulation and coarse-grained molecular simulation. The two key features of this scheme are the Boltzmann inversion and a protein atomistic reconstruction method we previously developed (SCAAL). Using MultiSCAAL, we were able to enhance the sampling efficiency of proteins solvated by explicit water molecules. Our method has been tested on the folding energy landscape of a small protein Trp-cage with explicit solvent under 8M urea using both the all-atomistic replica exchange molecular dynamics and MultiSCAAL. We compared computational analyses on ensemble conformations of Trp-cage with its available experimental NOE distances. The analysis demonstrated that conformations explored by MultiSCAAL better agree with the ones probed in the experiments because it can effectively capture the changes in side-chain orientations that can flip out of the hydrophobic pocket in the presence of urea and water molecules. In this regard, MultiSCAAL is a promising and effective sampling scheme for investigating chemical interference

Quantum probability ranking principle for ligand-based virtual screening.

PubMed

Al-Dabbagh, Mohammed Mumtaz; Salim, Naomie; Himmat, Mubarak; Ahmed, Ali; Saeed, Faisal

2017-04-01

Chemical libraries contain thousands of compounds that need screening, which increases the need for computational methods that can rank or prioritize compounds. The tools of virtual screening are widely exploited to enhance the cost effectiveness of lead drug discovery programs by ranking chemical compounds databases in decreasing probability of biological activity based upon probability ranking principle (PRP). In this paper, we developed a novel ranking approach for molecular compounds inspired by quantum mechanics, called quantum probability ranking principle (QPRP). The QPRP ranking criteria would make an attempt to draw an analogy between the physical experiment and molecular structure ranking process for 2D fingerprints in ligand based virtual screening (LBVS). The development of QPRP criteria in LBVS has employed the concepts of quantum at three different levels, firstly at representation level, this model makes an effort to develop a new framework of molecular representation by connecting the molecular compounds with mathematical quantum space. Secondly, estimate the similarity between chemical libraries and references based on quantum-based similarity searching method. Finally, rank the molecules using QPRP approach. Simulated virtual screening experiments with MDL drug data report (MDDR) data sets showed that QPRP outperformed the classical ranking principle (PRP) for molecular chemical compounds.

Quantum probability ranking principle for ligand-based virtual screening

NASA Astrophysics Data System (ADS)

Al-Dabbagh, Mohammed Mumtaz; Salim, Naomie; Himmat, Mubarak; Ahmed, Ali; Saeed, Faisal

2017-04-01

Chemical libraries contain thousands of compounds that need screening, which increases the need for computational methods that can rank or prioritize compounds. The tools of virtual screening are widely exploited to enhance the cost effectiveness of lead drug discovery programs by ranking chemical compounds databases in decreasing probability of biological activity based upon probability ranking principle (PRP). In this paper, we developed a novel ranking approach for molecular compounds inspired by quantum mechanics, called quantum probability ranking principle (QPRP). The QPRP ranking criteria would make an attempt to draw an analogy between the physical experiment and molecular structure ranking process for 2D fingerprints in ligand based virtual screening (LBVS). The development of QPRP criteria in LBVS has employed the concepts of quantum at three different levels, firstly at representation level, this model makes an effort to develop a new framework of molecular representation by connecting the molecular compounds with mathematical quantum space. Secondly, estimate the similarity between chemical libraries and references based on quantum-based similarity searching method. Finally, rank the molecules using QPRP approach. Simulated virtual screening experiments with MDL drug data report (MDDR) data sets showed that QPRP outperformed the classical ranking principle (PRP) for molecular chemical compounds.

Isolation, characterization, spectroscopic properties and quantum chemical computations of an important phytoalexin resveratrol as antioxidant component from Vitis labrusca L. and their chemical compositions

NASA Astrophysics Data System (ADS)

Güder, Aytaç; Korkmaz, Halil; Gökce, Halil; Alpaslan, Yelda Bingöl; Alpaslan, Gökhan

2014-12-01

In this study, isolation and characterization of trans-resveratrol (RES) as an antioxidant compound were carried out from VLE, VLG and VLS. Furthermore, antioxidant activities were evaluated by using six different methods. Finally, total phenolic, flavonoid, ascorbic acid, anthocyanin, lycopene, β-carotene and vitamin E contents were carried out. In addition, the FT-IR, 13C and 1H NMR chemical shifts and UV-vis. spectra of trans-resveratrol were experimentally recorded. Quantum chemical computations such as the molecular geometry, vibrational frequencies, UV-vis. spectroscopic parameters, HOMOs-LUMOs energies, molecular electrostatic potential (MEP), natural bond orbitals (NBO) and nonlinear optics (NLO) properties of title molecule have been calculated by using DFT/B3PW91 method with 6-311++G(d,p) basis set in ground state for the first time. The obtained results show that the calculated spectroscopic data are in a good agreement with experimental data.

Investigating and improving student understanding of quantum mechanical observables and their corresponding operators in Dirac notation

NASA Astrophysics Data System (ADS)

Marshman, Emily; Singh, Chandralekha

2018-01-01

In quantum mechanics, for every physical observable, there is a corresponding Hermitian operator. According to the most common interpretation of quantum mechanics, measurement of an observable collapses the quantum state into one of the possible eigenstates of the operator and the corresponding eigenvalue is measured. Since Dirac notation is an elegant notation that is commonly used in upper-level quantum mechanics, it is important that students learn to express quantum operators corresponding to observables in Dirac notation in order to apply the quantum formalism effectively in diverse situations. Here we focus on an investigation that suggests that, even though Dirac notation is used extensively, many advanced undergraduate and PhD students in physics have difficulty expressing the identity operator and other Hermitian operators corresponding to physical observables in Dirac notation. We first describe the difficulties students have with expressing the identity operator and a generic Hermitian operator corresponding to an observable in Dirac notation. We then discuss how the difficulties found via written surveys and individual interviews were used as a guide in the development of a quantum interactive learning tutorial (QuILT) to help students develop a good grasp of these concepts. The QuILT strives to help students become proficient in expressing the identity operator and a generic Hermitian operator corresponding to an observable in Dirac notation. We also discuss the effectiveness of the QuILT based on in-class evaluations.

Quantum neuromorphic hardware for quantum artificial intelligence

NASA Astrophysics Data System (ADS)

Prati, Enrico

2017-08-01

The development of machine learning methods based on deep learning boosted the field of artificial intelligence towards unprecedented achievements and application in several fields. Such prominent results were made in parallel with the first successful demonstrations of fault tolerant hardware for quantum information processing. To which extent deep learning can take advantage of the existence of a hardware based on qubits behaving as a universal quantum computer is an open question under investigation. Here I review the convergence between the two fields towards implementation of advanced quantum algorithms, including quantum deep learning.

Chemical nature and structure of organic coating of quantum dots is crucial for their application in imaging diagnostics

PubMed Central

Bakalova, Rumiana; Zhelev, Zhivko; Kokuryo, Daisuke; Spasov, Lubomir; Aoki, Ichio; Saga, Tsuneo

2011-01-01

enhancement of their size. In concentrations <2.5 nmol/kg bodyweight, these quantum dots did not affect the main physiological variables. It was possible to visualize capillaries, which makes this quantum dot probe appropriate for investigation of mediators of vasoconstriction, vasodilatation, and brain circulation in intact animals in vivo. The multimodal silica-shelled quantum dots allowed visualization of tumor tissue in an early stage of its development, using magnetic resonance imaging. Conclusion: The present study shows that the type and structure of organic/bioorganic shells of quantum dots determine their biocompatibility and are crucial for their application in imaging in vivo, due to the effects of the shell on the following properties: colloidal stability, solubility in physiological fluids, influence of the basic physiological parameters, and cytotoxicity. PMID:21980235

3D Double-Quantum/Double-Quantum Exchange Spectroscopy of Protons under 100 kHz Magic Angle Spinning.

PubMed

Zhang, Rongchun; Duong, Nghia Tuan; Nishiyama, Yusuke; Ramamoorthy, Ayyalusamy

2017-06-22

Solid-state 1 H NMR spectroscopy has attracted much attention in the recent years due to the remarkable spectral resolution improvement by ultrafast magic-angle-spinning (MAS) as well as due to the sensitivity enhancement rendered by proton detection. Although these developments have enabled the investigation of a variety of challenging chemical and biological solids, the proton spectral resolution is still poor for many rigid solid systems owing to the presence of conformational heterogeneity and the unsuppressed residual proton-proton dipolar couplings even with the use of the highest currently feasible sample spinning speed of ∼130 kHz. Although a further increase in the spinning speed of the sample could be beneficial to some extent, there is a need for alternate approaches to enhance the spectral resolution. Herein, by fully utilizing the benefits of double-quantum (DQ) coherences, we propose a single radio frequency channel proton-based 3D pulse sequence that correlates double-quantum (DQ), DQ, and single-quantum (SQ) chemical shifts of protons. In addition to the two-spin homonuclear proximity information, the proposed 3D DQ/DQ/SQ experiment also enables the extraction of three-spin and four-spin proximities, which could be beneficial for revealing the dipolar coupled proton network in the solid state. Besides, the 2D DQ/DQ spectrum sliced at different isotropic SQ chemical shift values of the 3D DQ/DQ/SQ spectrum will also facilitate the identification of DQ correlation peaks and improve the spectral resolution, as it only provides the local homonuclear correlation information associated with the specific protons selected by the SQ chemical shift frequency. The 3D pulse sequence and its efficiency are demonstrated experimentally on small molecular compounds in the solid state. We expect that this approach would create avenues for further developments by suitably combining the benefits of partial deuteration of samples, selective excitation

Quantum chemistry in environmental pesticide risk assessment.

PubMed

Villaverde, Juan J; López-Goti, Carmen; Alcamí, Manuel; Lamsabhi, Al Mokhtar; Alonso-Prados, José L; Sandín-España, Pilar

2017-11-01

The scientific community and regulatory bodies worldwide, currently promote the development of non-experimental tests that produce reliable data for pesticide risk assessment. The use of standard quantum chemistry methods could allow the development of tools to perform a first screening of compounds to be considered for the experimental studies, improving the risk assessment. This fact results in a better distribution of resources and in better planning, allowing a more exhaustive study of the pesticides and their metabolic products. The current paper explores the potential of quantum chemistry in modelling toxicity and environmental behaviour of pesticides and their by-products by using electronic descriptors obtained computationally. Quantum chemistry has potential to estimate the physico-chemical properties of pesticides, including certain chemical reaction mechanisms and their degradation pathways, allowing modelling of the environmental behaviour of both pesticides and their by-products. In this sense, theoretical methods can contribute to performing a more focused risk assessment of pesticides used in the market, and may lead to higher quality and safer agricultural products. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

Low temperature regulated growth of PbS quantum dots by wet chemical method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Hitanshu, E-mail: hitanshuminhas@gmail.com; Barman, P. B.; Singh, Ragini Raj

2015-08-28

Narrow size distribution with regulated synthesis of lead sulfide (PbS) quantum dots (QDs) was achieved through wet chemical method. Different concentrations of 2-mercaptoethanol (capping agent) were used for tailoring the QDs size. Transmission electron microscopy and X-ray diffraction studies revealed that the QDs have mean diameters between 6 to 15 nm. The optical absorption spectra were compared to the predictions of a theoretical model for the electronic structure. The theory agrees well with experiment for QDs larger than 7 nm, but for smaller dots there is some deviation from the theoretical predictions. Consequently, the produced particles are having monodispersity, good water solubility,more » stability and may be good arguments to be biologically compatible due to the use of 2-mercaptoethanol.« less

The quantum chemical study of the electronic states of S2Cl and its monovalent ions.

PubMed

Czernek, Jiří; Zivný, Oldřich

2012-09-01

High-level quantum chemical techniques have been utilized to accurately describe the geometrical parameters, vibrational frequencies and dissociation pathways of the X (2)A″, 1 (2)A', 2 (2)A', 2 (2)A″ states of S(2)Cl; X (1)A', 1 (3)A″, 1 (1)A″, 1 (3)A' states of S(2)Cl(+); X (1)A', 1 (3)A', (1)A″ states of S(2)Cl(-), and the corresponding excitation energies have been obtained from the energies extrapolated to their complete basis set limits. It has been established that the 2 (2)A' and 2 (2)A″ terms of S(2)Cl exhibit a strong multi-reference character, while all the remaining excited states are dominated by the single replacements from the reference determinants. The enthalpies of the decomposition reactions have been obtained to aid in the investigations into the photolysis of S(2)Cl(2) and related systems. The value of the ionization potential of S(2)Cl has been found within the error bars of the experiment, and a reliable estimate of its electron affinity, EA (0) = -2.352 eV, has been proposed.

New cardioprotective agent flokalin and its supramolecular complexes with target amino acids: An integrated mass-spectrometry and quantum-chemical study

NASA Astrophysics Data System (ADS)

Pashynska, Vlada; Stepanian, Stepan; Gömöry, Ágnes; Vékey, Károly; Adamowicz, Ludwik

2017-10-01

This study is devoted to examining the molecular structure and molecular mechanisms of action of the recently developed cardioprotective agent flokalin (Fl), a fluorine containing analogue of pinacidil, which is known as an activator of ATP sensitive potassium membrane channels. A combined experimental and computational investigation of flokalin and its biologically relevant supramolecular complexes with selected amino acids involved in KATP-channels proteins is performed by electrospray ionization mass spectrometry (ESI MS) and by B3LYP/aug-cc-pVDZ quantum-mechanical calculations. First Fl solution is probed by ESI MS and a characteristic mass spectrum of the agent is obtained. Next the intermolecular interactions of Fl with the potentially targeted aminoacids (AA), Lys and Thr, are experimentally investigated. The spectra of the model Fl:AA systems (in 1:1 M ratio) contain information on the ions characteristic to the individual components of the mixtures; though the most interesting spectral results from the biophysical view point are related to the ions of stable molecular clusters formed by flokalin with AA. The peaks of such ions are quite prominent in the spectrum for the Fl:Lys system and less prominent for Fl:Thr. The equilibrium geometries and the corresponding interaction energies of the noncovalent supramolecular complexes registered in the mass spectra are determined in the quantum chemical calculations. The formation of the stable noncovalent complexes of Fl with Lyz and Thr revealed by the ESI MS probing and by the theoretical modelling testify to a possibility of interaction of flokalin with the KATP-channel domains enriched with the two amino acids in biological systems.

Molecular dispersion spectroscopy for chemical sensing using chirped mid-infrared quantum cascade laser.

PubMed

Wysocki, Gerard; Weidmann, Damien

2010-12-06

A spectroscopic method of molecular detection based on dispersion measurements using a frequency-chirped laser source is presented. An infrared quantum cascade laser emitting around 1912 cm(-1) is used as a tunable spectroscopic source to measure dispersion that occurs in the vicinity of molecular ro-vibrational transitions. The sample under study is a mixture of nitric oxide in dry nitrogen. Two experimental configurations based on a coherent detection scheme are investigated and discussed. The theoretical models, which describe the observed spectral signals, are developed and verified experimentally. The method is particularly relevant to optical sensing based on mid-infrared quantum cascade lasers as the high chirp rates available with those sources can significantly enhance the magnitude of the measured dispersion signals. The method relies on heterodyne beatnote frequency measurements and shows high immunity to variations in the optical power received by the photodetector.

INVESTIGATION OF POSSIBLE USES OF CFC/HALON CHEMICALS

EPA Science Inventory

The report documents an investigation of the possibility of alternate uses for surplus chlorofluorocarbon (CFC)/halon chemicals as they are replaced in their traditional service roles. hese uses may be beneficial new products or substances that are nonhazardous to the environment...

Quantum chemical calculations and experimental investigations on 2-aminobenzoic acid-cyclodiphosph(V)azane derivative and its homo-binuclear Cu(II) complex

NASA Astrophysics Data System (ADS)

El-Gogary, Tarek M.; Alaghaz, Abdel-Nasser M. A.; Ammar, Reda A. A.

2012-03-01

A novel 2-aminobenzoic acid-cyclodiphosph(V)azane ligand H4L and its homo-binuclear Cu(II) complex of the type [Cu2L(H2O)2].2.5 H2O in which L is 1,3-di(-o-pyridyl)-2,4-(dioxo)-2',4'-bis-(2-iminobenzoic acid) cyclodiphosph(V)azane, were synthesized and characterized by different physical techniques. Infrared spectra of the complex indicate deprotonation and coordination of the imine NH and carboxyl COOH groups. It also confirms that nitrogen atom of the pyridine ring contribute to the complexation. Electronic spectra and magnetic susceptibility measurements reveal square-planar geometry for the Cu(II) complex. The elemental analyses and thermogravimetric results have justified the [Cu2L(H2O)2]·2.5H2O composition of the complex. Quantum chemical calculations were utilized to explore the electronic structure and stability of the H4L as well as the binuclear Cu(II) complex. Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of H4L and its binuclear Cu(II) complex. Different tautomers and geometrical isomers of the ligand were optimized at the ab initio DFT level. Simulated IR frequencies were scaled and compared with that experimentally measured. TD-DFT method was used to compute the UV-VIS spectra which show good agreement with measured electronic spectra.

A quantum–quantum Metropolis algorithm

PubMed Central

Yung, Man-Hong; Aspuru-Guzik, Alán

2012-01-01

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. PMID:22215584

Viability of pyrite pulled metabolism in the ‘iron-sulfur world’ theory: Quantum chemical assessment

NASA Astrophysics Data System (ADS)

Michalkova, Andrea; Kholod, Yana; Kosenkov, Dmytro; Gorb, Leonid; Leszczynski, Jerzy

2011-04-01

The viability of pyrite-pulled metabolism in the 'iron-sulfur world' theory was assessed using a simple model of iron-nickel sulfide (Fe-Ni-S) surface and data obtained from quantum chemical calculations. We have investigated how the individual reactions in the carbon fixation cycle (carboxylic acids formation) on an Fe-Ni-S surface could have operated to produce carboxylic acids from carbon oxide and water. The proposed model cycle reveals how the individual reactions might have functioned and provides the thermodynamics of each step of the proposed pathway. The feasibility of individual reactions, as well the whole cycle was considered. The reaction of acetic acid production from CH 3SH and CO on an Fe-Ni sulfide surface was revealed to be endergonic with a few partial steps having positive Gibbs free energy. On the other hand, the pyrite formation was found to be slightly exergonic. The significance of the catalytic activity of transition metal sulfides in generation of acetic acid was shown. The Gibbs free energy values indicate that the acetic acid synthesis is unfavorable to proceed on the studied Fe-Ni-S model under simulated conditions. The importance of these results in terms of a primordial chemistry on iron-nickel sulfide surfaces is discussed.

Computing quantum hashing in the model of quantum branching programs

NASA Astrophysics Data System (ADS)

Ablayev, Farid; Ablayev, Marat; Vasiliev, Alexander

2018-02-01

We investigate the branching program complexity of quantum hashing. We consider a quantum hash function that maps elements of a finite field into quantum states. We require that this function is preimage-resistant and collision-resistant. We consider two complexity measures for Quantum Branching Programs (QBP): a number of qubits and a number of compu-tational steps. We show that the quantum hash function can be computed efficiently. Moreover, we prove that such QBP construction is optimal. That is, we prove lower bounds that match the constructed quantum hash function computation.

Anti-oxidant behavior of functionalized chalcone-a combined quantum chemical and crystallographic structural investigation

NASA Astrophysics Data System (ADS)

Mathew, Bijo; Adeniyi, Adebayo A.; Joy, Monu; Mathew, Githa Elizabeth; Singh-Pillay, Ashona; Sudarsanakumar, C.; Soliman, Mahmoud E. S.; Suresh, Jerad

2017-10-01

Compound (2E)-3-(methoxyphenyl)-1-(4-methylphenyl) prop-2-en-1-one (Ch) was synthesized by the Claisen-Schmidt condensation reaction between para-methylacetophenone and para-methoxybenzaldehyde under basic condition. The structure of the molecule was elucidated using X-ray diffraction. Compound (Ch) demonstrated higher antioxidant activities in the DPPH test and H2O2 assay (IC50 = 12.23 ± 0.53 and 15.62 ± 0.98) than with the standard ascorbic acid (IC50 = 17.32 ± 0.44 and 19.07 ± 0.35). An evaluation of the atomic and molecular properties of ascorbic acid and Ch were computed based on their antioxidant activities. The molecular properties give insight into possible reasons for the enhanced antioxidant properties of Ch compared to ascorbic acid. The atomic properties provide further insight into chemical changes of the atoms of the compounds. Such changes include electronic shifting of the compounds electrophilic and/or nucleophilic states which highlight chemical moieties which characterize the antioxidant activity but do not directly relate to a variation in their antioxidant activities. The results obtained reflect oxygen atoms having significant nucleophilic interactions of each of the compounds. This was characterized by higher Fukui indices, isotropic and anisotropic hyperfine and orbital coupling stability energy.

The role of NH3 and hydrocarbon mixtures in GaN pseudo-halide CVD: a quantum chemical study.

PubMed

Gadzhiev, Oleg B; Sennikov, Peter G; Petrov, Alexander I; Kachel, Krzysztof; Golka, Sebastian; Gogova, Daniela; Siche, Dietmar

2014-11-01

The prospects of a control for a novel gallium nitride pseudo-halide vapor phase epitaxy (PHVPE) with HCN were thoroughly analyzed for hydrocarbons-NH3-Ga gas phase on the basis of quantum chemical investigation with DFT (B3LYP, B3LYP with D3 empirical correction on dispersion interaction) and ab-initio (CASSCF, coupled clusters, and multireference configuration interaction including MRCI+Q) methods. The computational screening of reactions for different hydrocarbons (CH4, C2H6, C3H8, C2H4, and C2H2) as readily available carbon precursors for HCN formation, potential chemical transport agents, and for controlled carbon doping of deposited GaN was carried out with the B3LYP method in conjunction with basis sets up to aug-cc-pVTZ. The gas phase intermediates for the reactions in the Ga-hydrocarbon systems were predicted at different theory levels. The located π-complexes Ga…C2H2 and Ga…C2H4 were studied to determine a probable catalytic activity in reactions with NH3. A limited influence of the carbon-containing atmosphere was exhibited for the carbon doping of GaN crystal in the conventional GaN chemical vapor deposition (CVD) process with hydrocarbons injected in the gas phase. Our results provide a basis for experimental studies of GaN crystal growth with C2H4 and C2H2 as auxiliary carbon reagents for the Ga-NH3 and Ga-C-NH3 CVD systems and prerequisites for reactor design to enhance and control the PHVPE process through the HCN synthesis.

Investigation of Photoluminescence and Photocurrent in InGaAsP/InP Strained Multiple Quantum Well Heterostructures

NASA Technical Reports Server (NTRS)

Raisky, O. Y.; Wang, W. B.; Alfano, R. R.; Reynolds, C. L., Jr.; Swaminathan, V.

1997-01-01

Multiple quantum well InGaAsP/InP p-i-n laser heterostructures with different barrier thicknesses have been investigated using photoluminescence (PL) and photocurrent (PC) measurements. The observed PL spectrum and peak positions are in good agreement with those obtained from transfer matrix calculations. Comparing the measured quantum well PC with calculated carrier escape rates, the photocurrent changes are found to be governed by the temperature dependence of the electron escape time.

Toward structural dynamics: protein motions viewed by chemical shift modulations and direct detection of C'N multiple-quantum relaxation.

PubMed

Mori, Mirko; Kateb, Fatiha; Bodenhausen, Geoffrey; Piccioli, Mario; Abergel, Daniel

2010-03-17

Multiple quantum relaxation in proteins reveals unexpected relationships between correlated or anti-correlated conformational backbone dynamics in alpha-helices or beta-sheets. The contributions of conformational exchange to the relaxation rates of C'N coherences (i.e., double- and zero-quantum coherences involving backbone carbonyl (13)C' and neighboring amide (15)N nuclei) depend on the kinetics of slow exchange processes, as well as on the populations of the conformations and chemical shift differences of (13)C' and (15)N nuclei. The relaxation rates of C'N coherences, which reflect concerted fluctuations due to slow chemical shift modulations (CSMs), were determined by direct (13)C detection in diamagnetic and paramagnetic proteins. In well-folded proteins such as lanthanide-substituted calbindin (CaLnCb), copper,zinc superoxide dismutase (Cu,Zn SOD), and matrix metalloproteinase (MMP12), slow conformational exchange occurs along the entire backbone. Our observations demonstrate that relaxation rates of C'N coherences arising from slow backbone dynamics have positive signs (characteristic of correlated fluctuations) in beta-sheets and negative signs (characteristic of anti-correlated fluctuations) in alpha-helices. This extends the prospects of structure-dynamics relationships to slow time scales that are relevant for protein function and enzymatic activity.

Quantum chemical calculations of Cr2O3/SnO2 using density functional theory method

NASA Astrophysics Data System (ADS)

Jawaher, K. Rackesh; Indirajith, R.; Krishnan, S.; Robert, R.; Das, S. Jerome

2018-03-01

Quantum chemical calculations have been employed to study the molecular effects produced by Cr2O3/SnO2 optimised structure. The theoretical parameters of the transparent conducting metal oxides were calculated using DFT / B3LYP / LANL2DZ method. The optimised bond parameters such as bond lengths, bond angles and dihedral angles were calculated using the same theory. The non-linear optical property of the title compound was calculated using first-order hyperpolarisability calculation. The calculated HOMO-LUMO analysis explains the charge transfer interaction between the molecule. In addition, MEP and Mulliken atomic charges were also calculated and analysed.

Best practices in incident investigation in the chemical process industries with examples from the industry sector and specifically from Nova Chemicals.

PubMed

Morrison, Lisa M

2004-07-26

This paper will summarize best practices in incident investigation in the chemical process industries and will provide examples from both the industry sector and specifically from NOVA Chemicals. As a sponsor of the Center for Chemical Process Safety (CCPS), an industry technology alliance of the American Institute of Chemical Engineers, NOVA Chemicals participates in a number of working groups to help develop best practices and tools for the chemical process and associated industries in order to advance chemical process safety. A recent project was to develop an update on guidelines for investigating chemical process incidents. A successful incident investigation management system must ensure that all incidents and near misses are reported, that root causes are identified, that recommendations from incident investigations identify appropriate preventive measures, and that these recommendations are resolved in a timely manner. The key elements of an effective management system for incident investigation will be described. Accepted definitions of such terms as near miss, incident, and root cause will be reviewed. An explanation of the types of incident classification systems in use, along with expected levels of follow-up, will be provided. There are several incident investigation methodologies in use today by members of the CCPS; most of these methodologies incorporate the use of several tools. These tools include: timelines, sequence diagrams, causal factor identification, brainstorming, checklists, pre-defined trees, and team-defined logic trees. Developing appropriate recommendations and then ensuring their resolution is the key to prevention of similar events from recurring, along with the sharing of lessons learned from incidents. There are several sources of information on previous incidents and lessons learned available to companies. In addition, many companies in the chemical process industries use their own internal databases to track recommendations from

Isolation, characterization, spectroscopic properties and quantum chemical computations of an important phytoalexin resveratrol as antioxidant component from Vitis labrusca L. and their chemical compositions.

PubMed

Güder, Aytaç; Korkmaz, Halil; Gökce, Halil; Alpaslan, Yelda Bingöl; Alpaslan, Gökhan

2014-12-10

In this study, isolation and characterization of trans-resveratrol (RES) as an antioxidant compound were carried out from VLE, VLG and VLS. Furthermore, antioxidant activities were evaluated by using six different methods. Finally, total phenolic, flavonoid, ascorbic acid, anthocyanin, lycopene, β-carotene and vitamin E contents were carried out. In addition, the FT-IR, (13)C and (1)H NMR chemical shifts and UV-vis. spectra of trans-resveratrol were experimentally recorded. Quantum chemical computations such as the molecular geometry, vibrational frequencies, UV-vis. spectroscopic parameters, HOMOs-LUMOs energies, molecular electrostatic potential (MEP), natural bond orbitals (NBO) and nonlinear optics (NLO) properties of title molecule have been calculated by using DFT/B3PW91 method with 6-311++G(d,p) basis set in ground state for the first time. The obtained results show that the calculated spectroscopic data are in a good agreement with experimental data. Copyright © 2014 Elsevier B.V. All rights reserved.

Notification: Efficiency of the Chemical Safety Board (CSB) Investigation Process

EPA Pesticide Factsheets

October 17, 2012. The EPA OIG plans to begin fieldwork with a modified objective from our May 15, 2012, preliminary research objective on the U.S. Chemical Safety and Hazard Investigation Board’s (CSB’s) investigation process.

Playing distributed two-party quantum games on quantum networks

NASA Astrophysics Data System (ADS)

Liu, Bo-Yang; Dai, Hong-Yi; Zhang, Ming

2017-12-01

This paper investigates quantum games between two remote players on quantum networks. We propose two schemes for distributed remote quantum games: the client-server scheme based on states transmission between nodes of the network and the peer-to-peer scheme devised upon remote quantum operations. Following these schemes, we construct two designs of the distributed prisoners' dilemma game on quantum entangling networks, where concrete methods are employed for teleportation and nonlocal two-qubits unitary gates, respectively. It seems to us that the requirement for playing distributed quantum games on networks is still an open problem. We explore this problem by comparing and characterizing the two schemes from the viewpoints of network structures, quantum and classical operations, experimental realization and simplification.

Chemically modulated graphene quantum dot for tuning the photoluminescence as novel sensory probe

NASA Astrophysics Data System (ADS)

Hwang, Eunhee; Hwang, Hee Min; Shin, Yonghun; Yoon, Yeoheung; Lee, Hanleem; Yang, Junghee; Bak, Sora; Lee, Hyoyoung

2016-12-01

A band gap tuning of environmental-friendly graphene quantum dot (GQD) becomes a keen interest for novel applications such as photoluminescence (PL) sensor. Here, for tuning the band gap of GQD, a hexafluorohydroxypropanyl benzene (HFHPB) group acted as a receptor of a chemical warfare agent was chemically attached on the GQD via the diazonium coupling reaction of HFHPB diazonium salt, providing new HFHPB-GQD material. With a help of the electron withdrawing HFHPB group, the energy band gap of the HFHPB-GQD was widened and its PL decay life time decreased. As designed, after addition of dimethyl methyl phosphonate (DMMP), the PL intensity of HFHPB-GQD sensor sharply increased up to approximately 200% through a hydrogen bond with DMMP. The fast response and short recovery time was proven by quartz crystal microbalance (QCM) analysis. This HFHPB-GQD sensor shows highly sensitive to DMMP in comparison with GQD sensor without HFHPB and graphene. In addition, the HFHPB-GQD sensor showed high selectivity only to the phosphonate functional group among many other analytes and also stable enough for real device applications. Thus, the tuning of the band gap of the photoluminescent GQDs may open up new promising strategies for the molecular detection of target substrates.

Chemically modulated graphene quantum dot for tuning the photoluminescence as novel sensory probe

PubMed Central

Hwang, Eunhee; Hwang, Hee Min; Shin, Yonghun; Yoon, Yeoheung; Lee, Hanleem; Yang, Junghee; Bak, Sora; Lee, Hyoyoung

2016-01-01

A band gap tuning of environmental-friendly graphene quantum dot (GQD) becomes a keen interest for novel applications such as photoluminescence (PL) sensor. Here, for tuning the band gap of GQD, a hexafluorohydroxypropanyl benzene (HFHPB) group acted as a receptor of a chemical warfare agent was chemically attached on the GQD via the diazonium coupling reaction of HFHPB diazonium salt, providing new HFHPB-GQD material. With a help of the electron withdrawing HFHPB group, the energy band gap of the HFHPB-GQD was widened and its PL decay life time decreased. As designed, after addition of dimethyl methyl phosphonate (DMMP), the PL intensity of HFHPB-GQD sensor sharply increased up to approximately 200% through a hydrogen bond with DMMP. The fast response and short recovery time was proven by quartz crystal microbalance (QCM) analysis. This HFHPB-GQD sensor shows highly sensitive to DMMP in comparison with GQD sensor without HFHPB and graphene. In addition, the HFHPB-GQD sensor showed high selectivity only to the phosphonate functional group among many other analytes and also stable enough for real device applications. Thus, the tuning of the band gap of the photoluminescent GQDs may open up new promising strategies for the molecular detection of target substrates. PMID:27991584

Size-Dependent Optoelectronic Properties and Controlled Doping of Semiconductor Quantum Dots

NASA Astrophysics Data System (ADS)

Engel, Jesse Hart

Given a rapidly developing world, the need exists for inexpensive renewable energy alternatives to help avoid drastic climate change. Photovoltaics have the potential to fill the energy needs of the future, but significant cost decreases are necessary for widespread adoption. Semiconductor nanocrystals, also known as quantum dots, are a nascent technology with long term potential to enable inexpensive and high efficiency photovoltaics. When deposited as a film, quantum dots form unique nanocomposites whose electronic and optical properties can be broadly tuned through manipulation of their individual constituents. The contents of this thesis explore methods to understand and optimize the optoelectronic properties of PbSe quantum dot films for use in photovoltaic applications. Systematic optimization of photovoltaic performance is demonstrated as a function of nanocrystal size, establishing the potential for utilizing extreme quantum confinement to improve device energetics and alignment. Detailed investigations of the mechanisms of electrical transport are performed, revealing that electronic coupling in quantum dot films is significantly less than often assumed based on optical shifts. A method is proposed to employ extended regions of built-in electrical field, through controlled doping, to sidestep issues of poor transport. To this end, treatments with chemical redox agents are found to effect profound and reversible doping within nanocrystal films, sufficient to enable their use as chemical sensors, but lacking the precision required for optoelectronic applications. Finally, a novel doping method employing "redox buffers" is presented to enact precise, stable, and reversible charge-transfer doping in porous semiconductor films. An example of oxidatively doping PbSe quantum dot thin films is presented, and the future potential for redox buffers in photovoltaic applications is examined.

Theoretical investigations of quantum correlations in NMR multiple-pulse spin-locking experiments

NASA Astrophysics Data System (ADS)

Gerasev, S. A.; Fedorova, A. V.; Fel'dman, E. B.; Kuznetsova, E. I.

2018-04-01

Quantum correlations are investigated theoretically in a two-spin system with the dipole-dipole interactions in the NMR multiple-pulse spin-locking experiments. We consider two schemes of the multiple-pulse spin-locking. The first scheme consists of π /2-pulses only and the delays between the pulses can differ. The second scheme contains φ-pulses (0<φ <π ) and has equal delays between them. We calculate entanglement for both schemes for an initial separable state. We show that entanglement is absent for the first scheme at equal delays between π /2-pulses at arbitrary temperatures. Entanglement emerges after several periods of the pulse sequence in the second scheme at φ =π /4 at milliKelvin temperatures. The necessary number of the periods increases with increasing temperature. We demonstrate the dependence of entanglement on the number of the periods of the multiple-pulse sequence. Quantum discord is obtained for the first scheme of the multiple-pulse spin-locking experiment at different temperatures.

The quantum phase-transitions of water

NASA Astrophysics Data System (ADS)

Fillaux, François

2017-08-01

It is shown that hexagonal ices and steam are macroscopically quantum condensates, with continuous spacetime-translation symmetry, whereas liquid water is a quantum fluid with broken time-translation symmetry. Fusion and vaporization are quantum phase-transitions. The heat capacities, the latent heats, the phase-transition temperatures, the critical temperature, the molar volume expansion of ice relative to water, as well as neutron scattering data and dielectric measurements are explained. The phase-transition mechanisms along with the key role of quantum interferences and that of Hartley-Shannon's entropy are enlightened. The notions of chemical bond and force-field are questioned.

Quantum amplification and quantum optical tapping with squeezed states and correlated quantum states

NASA Technical Reports Server (NTRS)

Ou, Z. Y.; Pereira, S. F.; Kimble, H. J.

1994-01-01

Quantum fluctuations in a nondegenerate optical parametric amplifier (NOPA) are investigated experimentally with a squeezed state coupled into the internal idler mode of the NOPA. Reductions of the inherent quantum noise of the amplifier are observed with a minimum noise level 0.7 dB below the usual noise level of the amplifier with its idler mode in a vacuum state. With two correlated quantum fields as the amplifier's inputs and proper adjustment of the gain of the amplifier, it is shown that the amplifier's intrinsic quantum noise can be completely suppressed so that noise-free amplification is achieved. It is also shown that the NOPA, when coupled to either a squeezed state or a nonclassically correlated state, can realize quantum tapping of optical information.

Elucidating reaction mechanisms on quantum computers.

PubMed

Reiher, Markus; Wiebe, Nathan; Svore, Krysta M; Wecker, Dave; Troyer, Matthias

2017-07-18

With rapid recent advances in quantum technology, we are close to the threshold of quantum devices whose computational powers can exceed those of classical supercomputers. Here, we show that a quantum computer can be used to elucidate reaction mechanisms in complex chemical systems, using the open problem of biological nitrogen fixation in nitrogenase as an example. We discuss how quantum computers can augment classical computer simulations used to probe these reaction mechanisms, to significantly increase their accuracy and enable hitherto intractable simulations. Our resource estimates show that, even when taking into account the substantial overhead of quantum error correction, and the need to compile into discrete gate sets, the necessary computations can be performed in reasonable time on small quantum computers. Our results demonstrate that quantum computers will be able to tackle important problems in chemistry without requiring exorbitant resources.

Elucidating reaction mechanisms on quantum computers

PubMed Central

Reiher, Markus; Wiebe, Nathan; Svore, Krysta M.; Wecker, Dave; Troyer, Matthias

2017-01-01

With rapid recent advances in quantum technology, we are close to the threshold of quantum devices whose computational powers can exceed those of classical supercomputers. Here, we show that a quantum computer can be used to elucidate reaction mechanisms in complex chemical systems, using the open problem of biological nitrogen fixation in nitrogenase as an example. We discuss how quantum computers can augment classical computer simulations used to probe these reaction mechanisms, to significantly increase their accuracy and enable hitherto intractable simulations. Our resource estimates show that, even when taking into account the substantial overhead of quantum error correction, and the need to compile into discrete gate sets, the necessary computations can be performed in reasonable time on small quantum computers. Our results demonstrate that quantum computers will be able to tackle important problems in chemistry without requiring exorbitant resources. PMID:28674011

Elucidating reaction mechanisms on quantum computers

NASA Astrophysics Data System (ADS)

Reiher, Markus; Wiebe, Nathan; Svore, Krysta M.; Wecker, Dave; Troyer, Matthias

2017-07-01

With rapid recent advances in quantum technology, we are close to the threshold of quantum devices whose computational powers can exceed those of classical supercomputers. Here, we show that a quantum computer can be used to elucidate reaction mechanisms in complex chemical systems, using the open problem of biological nitrogen fixation in nitrogenase as an example. We discuss how quantum computers can augment classical computer simulations used to probe these reaction mechanisms, to significantly increase their accuracy and enable hitherto intractable simulations. Our resource estimates show that, even when taking into account the substantial overhead of quantum error correction, and the need to compile into discrete gate sets, the necessary computations can be performed in reasonable time on small quantum computers. Our results demonstrate that quantum computers will be able to tackle important problems in chemistry without requiring exorbitant resources.

Elucidating Reaction Mechanisms on Quantum Computers

NASA Astrophysics Data System (ADS)

Wiebe, Nathan; Reiher, Markus; Svore, Krysta; Wecker, Dave; Troyer, Matthias

We show how a quantum computer can be employed to elucidate reaction mechanisms in complex chemical systems, using the open problem of biological nitrogen fixation in nitrogenase as an example. We discuss how quantum computers can augment classical-computer simulations for such problems, to significantly increase their accuracy and enable hitherto intractable simulations. Detailed resource estimates show that, even when taking into account the substantial overhead of quantum error correction, and the need to compile into discrete gate sets, the necessary computations can be performed in reasonable time on small quantum computers. This demonstrates that quantum computers will realistically be able to tackle important problems in chemistry that are both scientifically and economically significant.

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

PubMed

Wu, Xin; Koslowski, Axel; Thiel, Walter

2012-07-10

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

Ab initio quantum chemical calculation of electron transfer matrix elements for large molecules

NASA Astrophysics Data System (ADS)

Zhang, Linda Yu; Friesner, Richard A.; Murphy, Robert B.

1997-07-01

Using a diabatic state formalism and pseudospectral numerical methods, we have developed an efficient ab initio quantum chemical approach to the calculation of electron transfer matrix elements for large molecules. The theory is developed at the Hartree-Fock level and validated by comparison with results in the literature for small systems. As an example of the power of the method, we calculate the electronic coupling between two bacteriochlorophyll molecules in various intermolecular geometries. Only a single self-consistent field (SCF) calculation on each of the monomers is needed to generate coupling matrix elements for all of the molecular pairs. The largest calculations performed, utilizing 1778 basis functions, required ˜14 h on an IBM 390 workstation. This is considerably less cpu time than would be necessitated with a supermolecule adiabatic state calculation and a conventional electronic structure code.

Quantum speed limits in open system dynamics.

PubMed

del Campo, A; Egusquiza, I L; Plenio, M B; Huelga, S F

2013-02-01

Bounds to the speed of evolution of a quantum system are of fundamental interest in quantum metrology, quantum chemical dynamics, and quantum computation. We derive a time-energy uncertainty relation for open quantum systems undergoing a general, completely positive, and trace preserving evolution which provides a bound to the quantum speed limit. When the evolution is of the Lindblad form, the bound is analogous to the Mandelstam-Tamm relation which applies in the unitary case, with the role of the Hamiltonian being played by the adjoint of the generator of the dynamical semigroup. The utility of the new bound is exemplified in different scenarios, ranging from the estimation of the passage time to the determination of precision limits for quantum metrology in the presence of dephasing noise.

Silicon Oxysulfide, OSiS: Rotational Spectrum, Quantum-Chemical Calculations, and Equilibrium Structure.

PubMed

Thorwirth, Sven; Mück, Leonie Anna; Gauss, Jürgen; Tamassia, Filippo; Lattanzi, Valerio; McCarthy, Michael C

2011-06-02

Silicon oxysulfide, OSiS, and seven of its minor isotopic species have been characterized for the first time in the gas phase at high spectral resolution by means of Fourier transform microwave spectroscopy. The equilibrium structure of OSiS has been determined from the experimental data using calculated vibration-rotation interaction constants. The structural parameters (rO-Si = 1.5064 Å and rSi-S = 1.9133 Å) are in very good agreement with values from high-level quantum chemical calculations using coupled-cluster techniques together with sophisticated additivity and extrapolation schemes. The bond distances in OSiS are very short in comparison with those in SiO and SiS. This unexpected finding is explained by the partial charges calculated for OSiS via a natural population analysis. The results suggest that electrostatic effects rather than multiple bonding are the key factors in determining bonding in this triatomic molecule. The data presented provide the spectroscopic information needed for radio astronomical searches for OSiS.

“Quantumness” versus “classicality” of quantum states and quantum protocols

NASA Astrophysics Data System (ADS)

Brodutch, Aharon; Groisman, Berry; Kenigsberg, Dan; Mor, Tal

Entanglement is one of the pillars of quantum mechanics and quantum information processing, and as a result, the quantumness of nonentangled states has typically been overlooked and unrecognized until the last decade. We give a robust definition for the classicality versus quantumness of a single multipartite quantum state, a set of states, and a protocol using quantum states. We show a variety of nonentangled (separable) states that exhibit interesting quantum properties, and we explore the “zoo” of separable states; several interesting subclasses are defined based on the diagonalizing bases of the states, and their nonclassical behavior is investigated.

Fabrication and characterization of silicon quantum dots in Si-rich silicon carbide films.

PubMed

Chang, Geng-Rong; Ma, Fei; Ma, Dayan; Xu, Kewei

2011-12-01

Amorphous Si-rich silicon carbide films were prepared by magnetron co-sputtering and subsequently annealed at 900-1100 degrees C. After annealing at 1100 degrees C, this configuration of silicon quantum dots embedded in amorphous silicon carbide formed. X-ray photoelectron spectroscopy was used to study the chemical modulation of the films. The formation and orientation of silicon quantum dots were characterized by glancing angle X-ray diffraction, which shows that the ratio of silicon and carbon significantly influences the species of quantum dots. High-resolution transmission electron microscopy investigations directly demonstrated that the formation of silicon quantum dots is heavily dependent on the annealing temperatures and the ratio of silicon and carbide. Only the temperature of about 1100 degrees C is enough for the formation of high-density and small-size silicon quantum dots due to phase separation and thermal crystallization. Deconvolution of the first order Raman spectra shows the existence of a lower frequency peak in the range 500-505 cm(-1) corresponding to silicon quantum dots with different atom ratio of silicon and carbon.

Quantum Discord Preservation for Two Quantum-Correlated Qubits in Two Independent Reserviors

NASA Astrophysics Data System (ADS)

Xu, Lan

2018-03-01

We investigate the dynamics of quantum discord using an exactly solvable model where two qubits coupled to independent thermal environments. The quantum discord is employed as a non-classical correlation quantifier. By studying the quantum discord of a class of initial states, we find discord remains preserve for a finite time. The effects of the temperature, initial-state parameter, system-reservoir coupling constant and temperature difference parameter of the two independent reserviors are also investigated. We discover that the quantum nature loses faster in high temperature, however, one can extend the time of quantum nature by choosing smaller system-reservoir coupling constant, larger certain initial-state parameter and larger temperature difference parameter.

The Interplay of Quantum Confinement and Hydrogenation in Amorphous Silicon Quantum Dots.

PubMed

Askari, Sadegh; Svrcek, Vladmir; Maguire, Paul; Mariotti, Davide

2015-12-22

Hydrogenation in amorphous silicon quantum dots (QDs) has a dramatic impact on the corresponding optical properties and band energy structure, leading to a quantum-confined composite material with unique characteristics. The synthesis of a-Si:H QDs is demonstrated with an atmospheric-pressure plasma process, which allows for accurate control of a highly chemically reactive non-equilibrium environment with temperatures well below the crystallization temperature of Si QDs. © 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stable black phosphorus quantum dots for alkali PH sensor

NASA Astrophysics Data System (ADS)

Guo, Weilan; Song, Haizeng; Yan, Shancheng

2018-01-01

Black phosphorus, as a new two-dimensional material has been widely used in sensors, photovoltaic devices, etc. However, thin layered black phosphorus chemically degrades rapidly under ambient and aqueous conditions, which hinders the application of it in the chemical sensors. In this work, stable black phosphorus quantum dots (BPQDs) in solution are successfully synthesized by functionalization with 4-nitrobenzene-diazonium (4-NBD). The stable BPQDs are investigated by TEM, AFM, Raman, and UV-absorption. As a potential application, the stable BPQDs are used as sensors in alkali solution, which exhibit outstanding performance. Our work paves the way towards a new application with BPQDs in solution.

Some new reaction pathways for the formation of cytosine in interstellar space - A quantum chemical study

NASA Astrophysics Data System (ADS)

Gupta, V. P.; Tandon, Poonam; Mishra, Priti

2013-03-01

The detection of nucleic acid bases in carbonaceous meteorites suggests that their formation and survival is possible outside of the Earth. Small N-heterocycles, including pyrimidine, purines and nucleobases, have been extensively sought in the interstellar medium. It has been suggested theoretically that reactions between some interstellar molecules may lead to the formation of cytosine, uracil and thymine though these processes involve significantly high potential barriers. We attempted therefore to use quantum chemical techniques to explore if cytosine can possibly form in the interstellar space by radical-radical and radical-molecule interaction schemes, both in the gas phase and in the grains, through barrier-less or low barrier pathways. Results of DFT calculations for the formation of cytosine starting from some of the simple molecules and radicals detected in the interstellar space are being reported. Global and local descriptors such as molecular hardness, softness and electrophilicity, and condensed Fukui functions and local philicity indices were used to understand the mechanistic aspects of chemical reaction. The presence and nature of weak bonds in the molecules and transition states formed during the reaction process have been ascertained using Bader's quantum theory of atoms in molecules (QTAIMs). Two exothermic reaction pathways starting from propynylidyne (CCCH) and cyanoacetylene (HCCCN), respectively, have been identified. While the first reaction path is found to be totally exothermic, it involves a barrier of 12.5 kcal/mol in the gas phase against the lowest value of about 32 kcal/mol reported in the literature. The second path is both exothermic and barrier-less. The later has, therefore, a greater probability of occurrence in the cold interstellar clouds (10-50 K).

Improving Students' Understanding of Quantum Measurement. I. Investigation of Difficulties

ERIC Educational Resources Information Center

Zhu, Guangtian; Singh, Chandralekha

2012-01-01

We describe the difficulties that advanced undergraduate and graduate students have with quantum measurement within the standard interpretation of quantum mechanics. We explore the possible origins of these difficulties by analyzing student responses to questions from both surveys and interviews. Results from this research are applied to develop…

Characterization and intramolecular bonding patterns of busulfan: Experimental and quantum chemical approach

NASA Astrophysics Data System (ADS)

Karthick, T.; Tandon, Poonam; Singh, Swapnil; Agarwal, Parag; Srivastava, Anubha

2017-02-01

The investigations of structural conformers, molecular interactions and vibrational characterization of pharmaceutical drug are helpful to understand their behaviour. In the present work, the 2D potential energy surface (PES) scan has been performed on the dihedral angles C6sbnd O4sbnd S1sbnd C5 and C25sbnd S22sbnd O19sbnd C16 to find the stable conformers of busulfan. In order to show the effects of long range interactions, the structures on the global minima of PES scan have been further optimized by B3LYP/6-311 ++G(d,p) method with and without empirical dispersion functional in Gaussian 09W package. The presence of n → σ* and σ → σ* interactions which lead to stability of the molecule have been predicted by natural bond orbital analysis. The strong and weak hydrogen bonds between the functional groups of busulfan were analyzed using quantum topological atoms in molecules analysis. In order to study the long-range forces, such as van der Waals interactions, steric effect in busulfan, the reduced density gradient as well as isosurface defining these interactions has been plotted using Multiwfn software. The spectroscopic characterization on the solid phase of busulfan has been studied by experimental FT-IR and FT-Raman spectra. From the 13C and 1H NMR spectra, the chemical shifts of individual C and H atoms of busulfan have been predicted. The maximum absorption wavelengths corresponding to the electronic transitions between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of busulfan have been found by UV-vis spectrum.

Simulated quantum computation of molecular energies.

PubMed

Aspuru-Guzik, Alán; Dutoi, Anthony D; Love, Peter J; Head-Gordon, Martin

2005-09-09

The calculation time for the energy of atoms and molecules scales exponentially with system size on a classical computer but polynomially using quantum algorithms. We demonstrate that such algorithms can be applied to problems of chemical interest using modest numbers of quantum bits. Calculations of the water and lithium hydride molecular ground-state energies have been carried out on a quantum computer simulator using a recursive phase-estimation algorithm. The recursive algorithm reduces the number of quantum bits required for the readout register from about 20 to 4. Mappings of the molecular wave function to the quantum bits are described. An adiabatic method for the preparation of a good approximate ground-state wave function is described and demonstrated for a stretched hydrogen molecule. The number of quantum bits required scales linearly with the number of basis functions, and the number of gates required grows polynomially with the number of quantum bits.

Ferritin-Templated Quantum-Dots for Quantum Logic Gates

NASA Technical Reports Server (NTRS)

Choi, Sang H.; Kim, Jae-Woo; Chu, Sang-Hyon; Park, Yeonjoon; King, Glen C.; Lillehei, Peter T.; Kim, Seon-Jeong; Elliott, James R.

2005-01-01

Quantum logic gates (QLGs) or other logic systems are based on quantum-dots (QD) with a stringent requirement of size uniformity. The QD are widely known building units for QLGs. The size control of QD is a critical issue in quantum-dot fabrication. The work presented here offers a new method to develop quantum-dots using a bio-template, called ferritin, that ensures QD production in uniform size of nano-scale proportion. The bio-template for uniform yield of QD is based on a ferritin protein that allows reconstitution of core material through the reduction and chelation processes. One of the biggest challenges for developing QLG is the requirement of ordered and uniform size of QD for arrays on a substrate with nanometer precision. The QD development by bio-template includes the electrochemical/chemical reconsitution of ferritins with different core materials, such as iron, cobalt, manganese, platinum, and nickel. The other bio-template method used in our laboratory is dendrimers, precisely defined chemical structures. With ferritin-templated QD, we fabricated the heptagonshaped patterned array via direct nano manipulation of the ferritin molecules with a tip of atomic force microscope (AFM). We also designed various nanofabrication methods of QD arrays using a wide range manipulation techniques. The precise control of the ferritin-templated QD for a patterned arrangement are offered by various methods, such as a site-specific immobilization of thiolated ferritins through local oxidation using the AFM tip, ferritin arrays induced by gold nanoparticle manipulation, thiolated ferritin positioning by shaving method, etc. In the signal measurements, the current-voltage curve is obtained by measuring the current through the ferritin, between the tip and the substrate for potential sweeping or at constant potential. The measured resistance near zero bias was 1.8 teraohm for single holoferritin and 5.7 teraohm for single apoferritin, respectively.

Nonequilibrium quantum mechanics: A "hot quantum soup" of paramagnons

NASA Astrophysics Data System (ADS)

Scammell, H. D.; Sushkov, O. P.

2017-01-01

Motivated by recent measurements of the lifetime (decay width) of paramagnons in quantum antiferromagnet TlCuCl3, we investigate paramagnon decay in a heat bath and formulate an appropriate quantum theory. Our formulation can be split into two regimes: (i) a nonperturbative, "hot quantum soup" regime where the paramagnon width is comparable to its energy; (ii) a usual perturbative regime where the paramagnon width is significantly lower than its energy. Close to the Neel temperature, the paramagnon width becomes comparable to its energy and falls into the hot quantum soup regime. To describe this regime, we develop a new finite frequency, finite temperature technique for a nonlinear quantum field theory; the "golden rule of quantum kinetics." The formulation is generic and applicable to any three-dimensional quantum antiferromagnet in the vicinity of a quantum critical point. Specifically, we apply our results to TlCuCl3 and find agreement with experimental data. Additionally, we show that logarithmic running of the coupling constant in the upper critical dimension changes the commonly accepted picture of the quantum disordered and quantum critical regimes.

Quantum dot nanoparticle conjugation, characterization, and applications in neuroscience

NASA Astrophysics Data System (ADS)

Pathak, Smita

Quantum dot are semiconducting nanoparticles that have been used for decades in a variety of applications such as solar cells, LEDs and medical imaging. Their use in the last area, however, has been extremely limited despite their potential as revolutionary new biological labeling tools. Quantum dots are much brighter and more stable than conventional fluorophores, making them optimal for high resolution imaging and long term studies. Prior work in this area involves synthesizing and chemically conjugating quantum dots to molecules of interest in-house. However this method is both time consuming and prone to human error. Additionally, non-specific binding and nanoparticle aggregation currently prevent researchers from utilizing this system to its fullest capacity. Another critical issue that has not been addressed is determining the number of ligands bound to nanoparticles, which is crucial for proper interpretation of results. In this work, methods to label fixed cells using two types of chemically modified quantum dots are studied. Reproducible non-specific artifact labeling is consistently demonstrated if antibody-quantum dot conditions are less than optimal. In order to explain this, antibodies bound to quantum dots were characterized and quantified. While other groups have qualitatively characterized antibody functionalized quantum dots using TEM, AFM, UV spectroscopy and gel electrophoresis, and in some cases have reported calculated estimates of the putative number of total antibodies bound to quantum dots, no quantitative experimental results had been reported prior to this work. The chemical functionalization and characterization of quantum dot nanocrystals achieved in this work elucidates binding mechanisms of ligands to nanoparticles and allows researchers to not only translate our tools to studies in their own areas of interest but also derive quantitative results from these studies. This research brings ease of use and increased reliability to

Quantum population and entanglement evolution in photosynthetic process

NASA Astrophysics Data System (ADS)

Zhu, Jing

Applications of the concepts of quantum information theory are usually related to the powerful and counter-intuitive quantum mechanical effects of superposition, interference and entanglement. In this thesis, I examine the role of coherence and entanglement in complex chemical systems. The research has focused mainly on two related projects: The first project is developing a theoretical model to explain the recent ultrafast experiments on excitonic migration in photosynthetic complexes that show long-lived coherence of the order of hundreds of femtoseconds and the second project developing the Grover algorithm for global optimization of complex systems. The first part can be divided into two sections. The first section is investigating the theoretical frame about the transfer of electronic excitation energy through the Fenna-Matthews-Olson (FMO) pigment-protein complex. The new developed modified scaled hierarchical equation of motion (HEOM) approach is employed for simulating the open quantum system. The second section is investigating the evolution of entanglement in the FMO complex based on the simulation result via scaled HEOM approach. We examine the role of multipartite entanglement in the FMO complex by direct computation of the convex roof optimization for a number of different measures, including pairwise, triplet, quadruple and quintuple sites entanglement. Our results support the hypothesis that multipartite entanglement is maximum primary along the two distinct electronic energy transfer pathways. The second part of this thesis can be separated into two sections. The first section demonstrated that a modified Grover's quantum algorithm can be applied to real problems of finding a global minimum using modest numbers of quantum bits. Calculations of the global minimum of simple test functions and Lennard-Jones clusters have been carried out on a quantum computer simulator using a modified Grover's algorithm. The second section is implementing the basic

Quantum dot-linked immunosorbent assay (QLISA) using orientation-directed antibodies.

PubMed

Suzuki, Miho; Udaka, Hikari; Fukuda, Takeshi

2017-09-05

An approach similar to the enzyme-linked immunosorbent assay (ELISA), with the advantage of saving time and effort but exhibiting high performance, was developed using orientation-directed half-part antibodies immobilized on CdSe/ZnS quantum dots. ELISA is a widely accepted assay used to detect the presence of a target substance. However, it takes time to quantify the target with specificity and sensitivity owing to signal amplification. In this study, CdSe/ZnS quantum dots are introduced as bright and photobleaching-tolerant fluorescent materials. Since hydrophilic surface coating of quantum dots rendered biocompatibility and functional groups for chemical reactions, the quantum dots were modified with half-sized antibodies after partial reduction. The half-sized antibody could be bound to a quantum dot through a unique thiol site to properly display the recognition domain for the core process of ELISA, which is an antigen-antibody interaction. The reducing conditions were investigated to generate efficient conjugates of quantum dots and half-sized antibodies. This was applied to IL-6 detection, as the quantification of IL-6 is significant owing to its close relationships with various biomedical phenomena that cause different diseases. An ELISA-like assay with CdSe/ZnS quantum dot institution (QLISA; Quantum dot-linked immunosorbent assay) was developed to detect 0.05ng/mL IL-6, which makes it sufficiently sensitive as an immunosorbent assay. Copyright © 2017 Elsevier B.V. All rights reserved.

On Macroscopic Quantum Phenomena in Biomolecules and Cells: From Levinthal to Hopfield

PubMed Central

Raković, Dejan; Dugić, Miroljub; Jeknić-Dugić, Jasmina; Plavšić, Milenko; Jaćimovski, Stevo; Šetrajčić, Jovan

2014-01-01

In the context of the macroscopic quantum phenomena of the second kind, we hereby seek for a solution-in-principle of the long standing problem of the polymer folding, which was considered by Levinthal as (semi)classically intractable. To illuminate it, we applied quantum-chemical and quantum decoherence approaches to conformational transitions. Our analyses imply the existence of novel macroscopic quantum biomolecular phenomena, with biomolecular chain folding in an open environment considered as a subtle interplay between energy and conformation eigenstates of this biomolecule, governed by quantum-chemical and quantum decoherence laws. On the other hand, within an open biological cell, a system of all identical (noninteracting and dynamically noncoupled) biomolecular proteins might be considered as corresponding spatial quantum ensemble of these identical biomolecular processors, providing spatially distributed quantum solution to a single corresponding biomolecular chain folding, whose density of conformational states might be represented as Hopfield-like quantum-holographic associative neural network too (providing an equivalent global quantum-informational alternative to standard molecular-biology local biochemical approach in biomolecules and cells and higher hierarchical levels of organism, as well). PMID:25028662

Spectroscopy of Single Free Standing Quantum Wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, M D; Hollars, C W; Huser, T

2006-03-14

We investigated the interaction of quantum confined exciton states GaAs quantum wells with native surface states. Single molecule photoluminescence (PL) spectroscopy, developed by T. Huser at LLNL was used to probe the unique bare quantum wells in the free standing quantum well structure. The latter was developed by the M. D. Williams at Clark Atlanta University. The goals of the project during this budget cycle were to procure samples containing GaAs free standing QWs, identify suitable regions for PL analysis at Lawrence Livermore, analyze the structures at room temperature and at liquid nitrogen temperatures. The specific regions of interest onmore » the sample structures were identified by scanning electron microscopy at Clark Atlanta prior to transport to LLNL. Previous attempts at other facilities using NSOM, cathodoluminescence, and conventional PL showed little luminescence activity at room temperature from the 200 {angstrom} thick wells. This suggested either excess recombination due to surface states in the quantum well region or insufficient absorption length for photoluminescence. The literature suggested that the effect of the defects could be eliminated by reducing the sample temperature below their associated activation energies. In our previous subcontract work with LLNL, a significant amount of effort was expended to modify the apparatus to allow low temperature measurements. The modifications were not successful and we concluded that in order to do the measurements at low temperature we would need to purchase a commercial optical cryostat to get reliable results. Ms. Rochelle Bryant worked during the summer as an intern at LLNL on the project under the supervision of C. Hollars and in collaboration with T. Huser and found that PL emission could be obtained at room temperature. This was a surprising result as the literature and our experience shows that there is no PL emission from GaAs at room temperature. We speculate that this is due to the

Optimal subsystem approach to multi-qubit quantum state discrimination and experimental investigation

NASA Astrophysics Data System (ADS)

Xue, ShiChuan; Wu, JunJie; Xu, Ping; Yang, XueJun

2018-02-01

Quantum computing is a significant computing capability which is superior to classical computing because of its superposition feature. Distinguishing several quantum states from quantum algorithm outputs is often a vital computational task. In most cases, the quantum states tend to be non-orthogonal due to superposition; quantum mechanics has proved that perfect outcomes could not be achieved by measurements, forcing repetitive measurement. Hence, it is important to determine the optimum measuring method which requires fewer repetitions and a lower error rate. However, extending current measurement approaches mainly aiming at quantum cryptography to multi-qubit situations for quantum computing confronts challenges, such as conducting global operations which has considerable costs in the experimental realm. Therefore, in this study, we have proposed an optimum subsystem method to avoid these difficulties. We have provided an analysis of the comparison between the reduced subsystem method and the global minimum error method for two-qubit problems; the conclusions have been verified experimentally. The results showed that the subsystem method could effectively discriminate non-orthogonal two-qubit states, such as separable states, entangled pure states, and mixed states; the cost of the experimental process had been significantly reduced, in most circumstances, with acceptable error rate. We believe the optimal subsystem method is the most valuable and promising approach for multi-qubit quantum computing applications.

Investigation of anticancer properties of caffeinated complexes via computational chemistry methods

NASA Astrophysics Data System (ADS)

Sayin, Koray; Üngördü, Ayhan

2018-03-01

Computational investigations were performed for 1,3,7-trimethylpurine-2,6-dione, 3,7-dimethylpurine-2,6-dione, their Ru(II) and Os(III) complexes. B3LYP/6-311 ++G(d,p)(LANL2DZ) level was used in numerical calculations. Geometric parameters, IR spectrum, 1H-, 13C and 15N NMR spectrum were examined in detail. Additionally, contour diagram of frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) maps, MEP contour and some quantum chemical descriptors were used in the determination of reactivity rankings and active sites. The electron density on the surface was similar to each other in studied complexes. Quantum chemical descriptors were investigated and the anticancer activity of complexes were more than cisplatin and their ligands. Additionally, molecular docking calculations were performed in water between related complexes and a protein (ID: 3WZE). The most interact complex was found as Os complex. The interaction energy was calculated as 342.9 kJ/mol.

Conformational analysis, spectroscopic, structure-activity relations and quantum chemical simulation studies of 4-(trifluoromethyl)benzylamine

NASA Astrophysics Data System (ADS)

Arjunan, V.; Devi, L.; Mohan, S.

2018-05-01

The FT-IR and FT-Raman spectra of 4-trifluoromethylbenzylamine (TFMBA) have been recorded in the range 4000-450 and 4000-100 cm-1 respectively. The conformational analysis of the compound has been carried out to attain stable geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compound are carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The experimental vibrational frequencies are compared with the wavenumbers obtained theoretically from the B3LYP gradient calculations employing the standard high level 6-311++G** and cc-pVTZ basis sets for the optimised geometry of the compound. The structural parameters, thermodynamic properties and vibrational frequencies of the normal modes obtained from the B3LYP methods are in good agreement with the experimental data. The 1H (400 MHz; CDCl3) and 13C (100 MHz; CDCl3) nuclear magnetic resonance (NMR) spectra were also recorded. The electronic properties, highest occupied molecular orbital and lowest unoccupied molecular orbital energies are measured by DFT approach. The charges of the atoms by natural bond orbital (NBO) analysis are determined by B3LYP/cc-pVTZ method. The structure-chemical reactivity relations of the compound are determined through chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods.

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

NASA Technical Reports Server (NTRS)

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

1997-01-01

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

Quantum transport under ac drive from the leads: A Redfield quantum master equation approach

NASA Astrophysics Data System (ADS)

Purkayastha, Archak; Dubi, Yonatan

2017-08-01

Evaluating the time-dependent dynamics of driven open quantum systems is relevant for a theoretical description of many systems, including molecular junctions, quantum dots, cavity-QED experiments, cold atoms experiments, and more. Here, we formulate a rigorous microscopic theory of an out-of-equilibrium open quantum system of noninteracting particles on a lattice weakly coupled bilinearly to multiple baths and driven by periodically varying thermodynamic parameters like temperature and chemical potential of the bath. The particles can be either bosonic or fermionic and the lattice can be of any dimension and geometry. Based on the Redfield quantum master equation under Born-Markov approximation, we derive a linear differential equation for an equal time two point correlation matrix, sometimes also called a single-particle density matrix, from which various physical observables, for example, current, can be calculated. Various interesting physical effects, such as resonance, can be directly read off from the equations. Thus, our theory is quite general and gives quite transparent and easy-to-calculate results. We validate our theory by comparing with exact numerical simulations. We apply our method to a generic open quantum system, namely, a double quantum dot coupled to leads with modulating chemical potentials. The two most important experimentally relevant insights from this are as follows: (i) Time-dependent measurements of current for symmetric oscillating voltages (with zero instantaneous voltage bias) can point to the degree of asymmetry in the system-bath coupling and (ii) under certain conditions time-dependent currents can exceed time-averaged currents by several orders of magnitude, and can therefore be detected even when the average current is below the measurement threshold.

Effects of multiple organic ligands on size uniformity and optical properties of ZnSe quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archana, J., E-mail: archana.jayaram@yahoo.com; Navaneethan, M.; Hayakawa, Y.

2012-08-15

Highlights: ► Highly monodispersed ZnSe quantum dots have been synthesized by wet chemical route. ► Strong quantum confinement effect have been observed in ∼ 4 nm ZnSe quantum dots. ► Enhanced ultraviolet near band emission have been obtained using long chain polymer. -- Abstract: The effects of multi-ligands on the formation and optical transitions of ZnSe quantum dots have been investigated. The dots are synthesized using 3-mercapto-1,2-propanediol and polyvinylpyrrolidone ligands, and have been characterized by X-ray diffraction, transmission electron microscopy (TEM), UV–visible absorption spectroscopy, photoluminescence spectroscopy, and Fourier transform infrared spectroscopy. TEM reveals high monodispersion with an average size ofmore » 4 nm. Polymer-stabilized, organic ligand-passivated ZnSe quantum dots exhibit strong UV emission at 326 nm and strong quantum confinement in the UV–visible absorption spectrum. Uniform size and suppressed surface trap emission are observed when the polymer ligand is used. The possible growth mechanism is discussed.« less

Generalized Hofmann quantum process fidelity bounds for quantum filters

NASA Astrophysics Data System (ADS)

Sedlák, Michal; Fiurášek, Jaromír

2016-04-01

We propose and investigate bounds on the quantum process fidelity of quantum filters, i.e., probabilistic quantum operations represented by a single Kraus operator K . These bounds generalize the Hofmann bounds on the quantum process fidelity of unitary operations [H. F. Hofmann, Phys. Rev. Lett. 94, 160504 (2005), 10.1103/PhysRevLett.94.160504] and are based on probing the quantum filter with pure states forming two mutually unbiased bases. Determination of these bounds therefore requires far fewer measurements than full quantum process tomography. We find that it is particularly suitable to construct one of the probe bases from the right eigenstates of K , because in this case the bounds are tight in the sense that if the actual filter coincides with the ideal one, then both the lower and the upper bounds are equal to 1. We theoretically investigate the application of these bounds to a two-qubit optical quantum filter formed by the interference of two photons on a partially polarizing beam splitter. For an experimentally convenient choice of factorized input states and measurements we study the tightness of the bounds. We show that more stringent bounds can be obtained by more sophisticated processing of the data using convex optimization and we compare our methods for different choices of the input probe states.

Quantum Yield Heterogeneity among Single Nonblinking Quantum Dots Revealed by Atomic Structure-Quantum Optics Correlation

DOE PAGES

Orfield, Noah J.; McBride, James R.; Wang, Feng; ...

2016-02-05

Physical variations in colloidal nanostructures give rise to heterogeneity in expressed optical behavior. This correlation between nanoscale structure and function demands interrogation of both atomic structure and photophysics at the level of single nanostructures to be fully understood. In this paper, by conducting detailed analyses of fine atomic structure, chemical composition, and time-resolved single-photon photoluminescence data for the same individual nanocrystals, we reveal inhomogeneity in the quantum yields of single nonblinking “giant” CdSe/CdS core/shell quantum dots (g-QDs). We find that each g-QD possesses distinctive single exciton and biexciton quantum yields that result mainly from variations in the degree of charging,more » rather than from volume or structure inhomogeneity. We further establish that there is a very limited nonemissive “dark” fraction (<2%) among the studied g-QDs and present direct evidence that the g-QD core must lack inorganic passivation for the g-QD to be “dark”. Finally and therefore, in contrast to conventional QDs, ensemble photoluminescence quantum yield is principally defined by charging processes rather than the existence of dark g-QDs.« less

Bohm's Quantum Potential and the Visualization of Molecular Structure

NASA Technical Reports Server (NTRS)

Levit, Creon; Chancellor, Marisa K. (Technical Monitor)

1997-01-01

David Bohm's ontological interpretation of quantum theory can shed light on otherwise counter-intuitive quantum mechanical phenomena including chemical bonding. In the field of quantum chemistry, Richard Bader has shown that the topology of the Laplacian of the electronic charge density characterizes many features of molecular structure and reactivity. Visual and computational examination suggests that the Laplacian of Bader and the quantum potential of Bohm are morphologically equivalent. It appears that Bohmian mechanics and the quantum potential can make chemistry as clear as they makes physics.

Chemical Bonding Technology: Direct Investigation of Interfacial Bonds

NASA Technical Reports Server (NTRS)

Koenig, J. L.; Boerio, F. J.; Plueddemann, E. P.; Miller, J.; Willis, P. B.; Cuddihy, E. F.

1986-01-01

This is the third Flat-Plate Solar Array (FSA) Project document reporting on chemical bonding technology for terrestrial photovoltaic (PV) modules. The impetus for this work originated in the late 1970s when PV modules employing silicone encapsulation materials were undergoing delamination during outdoor exposure. At that time, manufacturers were not employing adhesion promoters and, hence, module interfaces in common with the silicone materials were only in physical contact and therefore easily prone to separation if, for example, water were to penetrate to the interfaces. Delamination with silicone materials virtually vanished when adhesion promoters, recommended by silicone manufacturers, were used. The activities related to the direct investigation of chemically bonded interfaces are described.

The structure and photochemical transformation of cyclopropylacetylene radical cation as revealed by matrix EPR and quantum chemical study

NASA Astrophysics Data System (ADS)

Shiryaeva, Ekaterina S.; Tyurin, Daniil A.; Feldman, Vladimir I.

2012-05-01

The primary radical cation of cyclopropylacetylene was first characterized by EPR spectroscopy in low-temperature freon matrices. The assignment was confirmed by specific deuteration and quantum-chemical calculations at PBE0 and CCSD(T) levels. Photolysis with visible light led to irreversible transformation of the initial species to a ring-open structure. Detailed computational analysis of energy and magnetic resonance parameters of possible reaction products justified formation of pent-3-en-1-yne radical cation (presumably, a (Z)-isomer). This conclusion was also supported by the effect of specific deuteration.

Effects of quantum confinement and shape on band gap of core/shell quantum dots and nanowires

NASA Astrophysics Data System (ADS)

Gao, Faming

2011-05-01

A quantum confinement model for nanocrystals developed is extended to study for the optical gap shifts in core/shell quantum dots and nanowires. The chemical bond properties and gap shifts in the InP/ZnS, CdSe/CdS, CdSe/ZnS, and CdTe/ZnS core/shell quantum dots are calculated in detail. The calculated band gaps are in excellent agreement with experimental values. The effects of structural taping and twinning on quantum confinement of InP and Si nanowires are elucidated. It is found theoretically that a competition between the positive Kubo energy-gap shift and the negative surface energy shift plays the crucial role in the optical gaps of these nanosystems.

Graphene quantum dots, graphene oxide, carbon quantum dots and graphite nanocrystals in coals

NASA Astrophysics Data System (ADS)

Dong, Yongqiang; Lin, Jianpeng; Chen, Yingmei; Fu, Fengfu; Chi, Yuwu; Chen, Guonan

2014-06-01

Six coal samples of different ranks have been used to prepare single-layer graphene quantum dots (S-GQDs). After chemical oxidation and a series of centrifugation separation, every coal could be treated into two fractions, namely, CoalA and CoalB. According to the characterization results of TEM, AFM, XRD, Raman and FTIR, CoalA was revealed to be mainly composed of S-GQDs, which have an average height of about 0.5 nm and an average plane dimension of about 10 nm. The obtained S-GQDs showed excitation-dependent fluorescence and excellent electrochemiluminescence. CoalB was found to be some other carbon-based nanomaterials (CNMs), including agglomerated GQDs, graphene oxide, carbon quantum dots and agglomerated carbon nanocrystals. Generally, low-ranked coals might be more suitable for the preparation of S-GQDs. The production yield of S-GQDs from the six investigated coals decreased from 56.30% to 14.66% when the coal rank increased gradually. In contrast, high-ranked coals had high production yield of CoalB and might be more suitable for preparing other CNMs that were contained in CoalB, although those CNMs were difficult to separate from each other in our experiment.Six coal samples of different ranks have been used to prepare single-layer graphene quantum dots (S-GQDs). After chemical oxidation and a series of centrifugation separation, every coal could be treated into two fractions, namely, CoalA and CoalB. According to the characterization results of TEM, AFM, XRD, Raman and FTIR, CoalA was revealed to be mainly composed of S-GQDs, which have an average height of about 0.5 nm and an average plane dimension of about 10 nm. The obtained S-GQDs showed excitation-dependent fluorescence and excellent electrochemiluminescence. CoalB was found to be some other carbon-based nanomaterials (CNMs), including agglomerated GQDs, graphene oxide, carbon quantum dots and agglomerated carbon nanocrystals. Generally, low-ranked coals might be more suitable for the preparation of

The role of the interface in germanium quantum dots: when not only size matters for quantum confinement effects.

PubMed

Cosentino, S; Mio, A M; Barbagiovanni, E G; Raciti, R; Bahariqushchi, R; Miritello, M; Nicotra, G; Aydinli, A; Spinella, C; Terrasi, A; Mirabella, S

2015-07-14

Quantum confinement (QC) typically assumes a sharp interface between a nanostructure and its environment, leading to an abrupt change in the potential for confined electrons and holes. When the interface is not ideally sharp and clean, significant deviations from the QC rule appear and other parameters beyond the nanostructure size play a considerable role. In this work we elucidate the role of the interface on QC in Ge quantum dots (QDs) synthesized by rf-magnetron sputtering or plasma enhanced chemical vapor deposition (PECVD). Through a detailed electron energy loss spectroscopy (EELS) analysis we investigated the structural and chemical properties of QD interfaces. PECVD QDs exhibit a sharper interface compared to sputter ones, which also evidences a larger contribution of mixed Ge-oxide states. Such a difference strongly modifies the QC strength, as experimentally verified by light absorption spectroscopy. A large size-tuning of the optical bandgap and an increase in the oscillator strength occur when the interface is sharp. A spatially dependent effective mass (SPDEM) model is employed to account for the interface difference between Ge QDs, pointing out a larger reduction in the exciton effective mass in the sharper interface case. These results add new insights into the role of interfaces on confined systems, and open the route for reliable exploitation of QC effects.

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

DOE PAGES

Michael, Stephan; Chow, Weng; Schneider, Hans

2016-05-01

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. We study the influence of two important quantum-dot material parameters, here, 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 canmore » compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. 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.« less

Multiparty Quantum Key Agreement Based on Quantum Search Algorithm

PubMed Central

Cao, Hao; Ma, Wenping

2017-01-01

Quantum key agreement is an important topic that the shared key must be negotiated equally by all participants, and any nontrivial subset of participants cannot fully determine the shared key. To date, the embed modes of subkey in all the previously proposed quantum key agreement protocols are based on either BB84 or entangled states. The research of the quantum key agreement protocol based on quantum search algorithms is still blank. In this paper, on the basis of investigating the properties of quantum search algorithms, we propose the first quantum key agreement protocol whose embed mode of subkey is based on a quantum search algorithm known as Grover’s algorithm. A novel example of protocols with 5 – party is presented. The efficiency analysis shows that our protocol is prior to existing MQKA protocols. Furthermore it is secure against both external attack and internal attacks. PMID:28332610

Preface: Special Topic on Nuclear Quantum Effects

NASA Astrophysics Data System (ADS)

Tuckerman, Mark; Ceperley, David

2018-03-01

Although the observable universe strictly obeys the laws of quantum mechanics, in many instances, a classical description that either ignores quantum effects entirely or accounts for them at a very crude level is sufficient to describe a wide variety of phenomena. However, when this approximation breaks down, as is often the case for processes involving light nuclei, a full quantum treatment becomes indispensable. This Special Topic in The Journal of Chemical Physics showcases recent advances in our understanding of nuclear quantum effects in condensed phases as well as novel algorithmic developments and applications that have enhanced the capability to study these effects.

Preface: Special Topic on Nuclear Quantum Effects.

PubMed

Tuckerman, Mark; Ceperley, David

2018-03-14

Although the observable universe strictly obeys the laws of quantum mechanics, in many instances, a classical description that either ignores quantum effects entirely or accounts for them at a very crude level is sufficient to describe a wide variety of phenomena. However, when this approximation breaks down, as is often the case for processes involving light nuclei, a full quantum treatment becomes indispensable. This Special Topic in The Journal of Chemical Physics showcases recent advances in our understanding of nuclear quantum effects in condensed phases as well as novel algorithmic developments and applications that have enhanced the capability to study these effects.

Investigating and Improving Student Understanding of Key Ideas in Quantum Mechanics throughout Instruction

NASA Astrophysics Data System (ADS)

Emigh, Paul Jeffrey

This dissertation describes research on student understanding of quantum mechanics across multiple levels of instruction. The primary focus has been to identify patterns in student reasoning related to key concepts in quantum mechanics. The specific topics include quantum measurements, time dependence, vector spaces, and angular momentum. The research has spanned a variety of different quantum courses intended for introductory physics students, upper-division physics majors, and graduate students in physics. The results of this research have been used to develop a set of curriculum, Tutorials in Physics: Quantum Mechanics, for addressing the most persistent student difficulties. We document both the development of this curriculum and how it has impacted and improved student understanding of quantum mechanics.

Clinical Potential of Quantum Dots

PubMed Central

Iga, Arthur M.; Robertson, John H. P.; Winslet, Marc C.; Seifalian, Alexander M.

2007-01-01

Advances in nanotechnology have led to the development of novel fluorescent probes called quantum dots. Quantum dots have revolutionalized the processes of tagging molecules within research settings and are improving sentinel lymph node mapping and identification in vivo studies. As the unique physical and chemical properties of these fluorescent probes are being unraveled, new potential methods of early cancer detection, rapid spread and therapeutic management, that is, photodynamic therapy are being explored. Encouraging results of optical and real time identification of sentinel lymph nodes and lymph flow using quantum dots in vivo models are emerging. Quantum dots have also superseded many of the limitations of organic fluorophores and are a promising alternative as a research tool. In this review, we examine the promising clinical potential of quantum dots, their hindrances for clinical use and the current progress in abrogating their inherent toxicity. PMID:18317518

Interaction of surface hydroxyls with adsorbed molecules. A quantum-chemical study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geerlings, P.; Tariel, N.; Botrel, A.

1984-11-08

A study has been conducted to explain the interaction mechanisms of (bridging and terminal) surface hydroxyl groups with molecules, using ab initio, EHT, and CNDO/2-FA quantum-chemical calculations. Bond strength variations and charge shifts were found to be in complete agreement with Gutmann's rules, and provide a basis for the understanding of the Bronsted acid properties of zeolites and amorphous silica-alumina. A quantitative measure of the interaction strength is possible by referring to the experimentally determined donor number (Gutmann) following many molecules, but care should be taken for those molecules for which the donor strength was determined by indirect methods. Onlymore » a few exceptions to Gutmann's rules should exist, e.g., in those cases where the atom interacting with the proton is not the most electronegative of the donor molecule (such as for CO). Individual bonds in a given complex are more susceptible to perturbations (changes in composition and interactions with adsorbing molecules) if the coordination number increases. These rules are in agreement with the observations and apply to all reactions (inter- or intramolecular) involving a change in coordination. 52 references, 6 figures, 4 tables.« less

Conceptual versus Algorithmic Learning in High School Chemistry: The Case of Basic Quantum Chemical Concepts--Part 1. Statistical Analysis of a Quantitative Study

ERIC Educational Resources Information Center

Papaphotis, Georgios; Tsaparlis, Georgios

2008-01-01

Part 1 of the findings are presented of a quantitative study (n = 125) on basic quantum chemical concepts taught in the twelfth grade (age 17-18 years) in Greece. A paper-and-pencil test of fourteen questions was used. The study compared performance in five questions that tested recall of knowledge or application of algorithmic procedures (type-A…

Controlling the Properties of Matter with Quantum Dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klimov, Victor

2017-03-22

Solar cells and photodetectors could soon be made from new types of materials based on semiconductor quantum dots, thanks to new insights based on ultrafast measurements capturing real-time photoconversion processes. Photoconversion is a process wherein the energy of a photon, or quantum of light, is converted into other forms of energy, for example, chemical or electrical. Semiconductor quantum dots are chemically synthesized crystalline nanoparticles that have been studied for more than three decades in the context of various photoconversion schemes including photovoltaics (generation of photo-electricity) and photo-catalysis (generation of “solar fuels”). The appeal of quantum dots comes from the unmatchedmore » tunability of their physical properties, which can be adjusted by controlling the size, shape and composition of the dots. At Los Alamos, the research connects to the institutional mission of solving national security challenges through scientific excellence, in this case focusing on novel physical principles for highly efficient photoconversion, charge manipulation in exploratory device structures and novel nanomaterials.« less

Attachment of Quantum Dots on Zinc Oxide Nanorods

NASA Astrophysics Data System (ADS)

Seay, Jared; Liang, Huan; Harikumar, Parameswar

2011-03-01

ZnO nanorods grown by hydrothermal technique are of great interest for potential applications in photovoltaic and optoelectronic devices. In this study we investigate the optimization of the optical absorption properties by a low temperature, chemical bath deposition technique. Our group fabricated nanorods on indium tin oxide (ITO) substrate with precursor solution of zinc nitrate hexahydrate and hexamethylenetramine (1:1 molar ratio) at 95C for 9 hours. In order to optimize the light absorption characteristics of ZnO nanorods, CdSe/ZnS core-shell quantum dots (QDs) of various diameters were attached to the surface of ZnO nanostructures grown on ITO and gold-coated silicon substrates. Density of quantum dots was varied by controlling the number drops on the surface of the ZnO nanorods. For a 0.1 M concentration of QDs of 10 nm diameter, the PL intensity at 385 nm increased as the density of the quantum dots on ZnO nanostructures was increased. For quantum dots at 1 M concentration, the PL intensity at 385 nm increased at the beginning and then decreased at higher density. We will discuss the observed changes in PL intensity with QD concentration with ZnO-QD band structure and recombination-diffusion processes taking place at the interface.

Quantum Error Correction Protects Quantum Search Algorithms Against Decoherence

PubMed Central

Botsinis, Panagiotis; Babar, Zunaira; Alanis, Dimitrios; Chandra, Daryus; Nguyen, Hung; Ng, Soon Xin; Hanzo, Lajos

2016-01-01

When quantum computing becomes a wide-spread commercial reality, Quantum Search Algorithms (QSA) and especially Grover’s QSA will inevitably be one of their main applications, constituting their cornerstone. Most of the literature assumes that the quantum circuits are free from decoherence. Practically, decoherence will remain unavoidable as is the Gaussian noise of classic circuits imposed by the Brownian motion of electrons, hence it may have to be mitigated. In this contribution, we investigate the effect of quantum noise on the performance of QSAs, in terms of their success probability as a function of the database size to be searched, when decoherence is modelled by depolarizing channels’ deleterious effects imposed on the quantum gates. Moreover, we employ quantum error correction codes for limiting the effects of quantum noise and for correcting quantum flips. More specifically, we demonstrate that, when we search for a single solution in a database having 4096 entries using Grover’s QSA at an aggressive depolarizing probability of 10−3, the success probability of the search is 0.22 when no quantum coding is used, which is improved to 0.96 when Steane’s quantum error correction code is employed. Finally, apart from Steane’s code, the employment of Quantum Bose-Chaudhuri-Hocquenghem (QBCH) codes is also considered. PMID:27924865

Report: U.S. Chemical Safety and Hazard Investigation Board Needs to Complete More Timely Investigations

EPA Pesticide Factsheets

Report #13-P-0337, July 30, 2013. CSB does not have an effective management system to meet its established performance goal to “conduct incident investigations and safety studies concerning releases of hazardous chemical substances.”

Experimental investigation of a four-qubit linear-optical quantum logic circuit

NASA Astrophysics Data System (ADS)

Stárek, R.; Mičuda, M.; Miková, M.; Straka, I.; Dušek, M.; Ježek, M.; Fiurášek, J.

2016-09-01

We experimentally demonstrate and characterize a four-qubit linear-optical quantum logic circuit. Our robust and versatile scheme exploits encoding of two qubits into polarization and path degrees of single photons and involves two crossed inherently stable interferometers. This approach allows us to design a complex quantum logic circuit that combines a genuine four-qubit C3Z gate and several two-qubit and single-qubit gates. The C3Z gate introduces a sign flip if and only if all four qubits are in the computational state |1>. We verify high-fidelity performance of this central four-qubit gate using Hofmann bounds on quantum gate fidelity and Monte Carlo fidelity sampling. We also experimentally demonstrate that the quantum logic circuit can generate genuine multipartite entanglement and we certify the entanglement with the use of suitably tailored entanglement witnesses.

Experimental investigation of a four-qubit linear-optical quantum logic circuit.

PubMed

Stárek, R; Mičuda, M; Miková, M; Straka, I; Dušek, M; Ježek, M; Fiurášek, J

2016-09-20

We experimentally demonstrate and characterize a four-qubit linear-optical quantum logic circuit. Our robust and versatile scheme exploits encoding of two qubits into polarization and path degrees of single photons and involves two crossed inherently stable interferometers. This approach allows us to design a complex quantum logic circuit that combines a genuine four-qubit C(3)Z gate and several two-qubit and single-qubit gates. The C(3)Z gate introduces a sign flip if and only if all four qubits are in the computational state |1〉. We verify high-fidelity performance of this central four-qubit gate using Hofmann bounds on quantum gate fidelity and Monte Carlo fidelity sampling. We also experimentally demonstrate that the quantum logic circuit can generate genuine multipartite entanglement and we certify the entanglement with the use of suitably tailored entanglement witnesses.

Experimental investigation of a four-qubit linear-optical quantum logic circuit

PubMed Central

Stárek, R.; Mičuda, M.; Miková, M.; Straka, I.; Dušek, M.; Ježek, M.; Fiurášek, J.

2016-01-01

We experimentally demonstrate and characterize a four-qubit linear-optical quantum logic circuit. Our robust and versatile scheme exploits encoding of two qubits into polarization and path degrees of single photons and involves two crossed inherently stable interferometers. This approach allows us to design a complex quantum logic circuit that combines a genuine four-qubit C3Z gate and several two-qubit and single-qubit gates. The C3Z gate introduces a sign flip if and only if all four qubits are in the computational state |1〉. We verify high-fidelity performance of this central four-qubit gate using Hofmann bounds on quantum gate fidelity and Monte Carlo fidelity sampling. We also experimentally demonstrate that the quantum logic circuit can generate genuine multipartite entanglement and we certify the entanglement with the use of suitably tailored entanglement witnesses. PMID:27647176

Fluctuation theorems in feedback-controlled open quantum systems: Quantum coherence and absolute irreversibility

NASA Astrophysics Data System (ADS)

Murashita, Yûto; Gong, Zongping; Ashida, Yuto; Ueda, Masahito

2017-10-01

The thermodynamics of quantum coherence has attracted growing attention recently, where the thermodynamic advantage of quantum superposition is characterized in terms of quantum thermodynamics. We investigate the thermodynamic effects of quantum coherent driving in the context of the fluctuation theorem. We adopt a quantum-trajectory approach to investigate open quantum systems under feedback control. In these systems, the measurement backaction in the forward process plays a key role, and therefore the corresponding time-reversed quantum measurement and postselection must be considered in the backward process, in sharp contrast to the classical case. The state reduction associated with quantum measurement, in general, creates a zero-probability region in the space of quantum trajectories of the forward process, which causes singularly strong irreversibility with divergent entropy production (i.e., absolute irreversibility) and hence makes the ordinary fluctuation theorem break down. In the classical case, the error-free measurement ordinarily leads to absolute irreversibility, because the measurement restricts classical paths to the region compatible with the measurement outcome. In contrast, in open quantum systems, absolute irreversibility is suppressed even in the presence of the projective measurement due to those quantum rare events that go through the classically forbidden region with the aid of quantum coherent driving. This suppression of absolute irreversibility exemplifies the thermodynamic advantage of quantum coherent driving. Absolute irreversibility is shown to emerge in the absence of coherent driving after the measurement, especially in systems under time-delayed feedback control. We show that absolute irreversibility is mitigated by increasing the duration of quantum coherent driving or decreasing the delay time of feedback control.

Semiempirical Quantum Mechanical Methods for Noncovalent Interactions for Chemical and Biochemical Applications

PubMed Central

2016-01-01

Semiempirical (SE) methods can be derived from either Hartree–Fock or density functional theory by applying systematic approximations, leading to efficient computational schemes that are several orders of magnitude faster than ab initio calculations. Such numerical efficiency, in combination with modern computational facilities and linear scaling algorithms, allows application of SE methods to very large molecular systems with extensive conformational sampling. To reliably model the structure, dynamics, and reactivity of biological and other soft matter systems, however, good accuracy for the description of noncovalent interactions is required. In this review, we analyze popular SE approaches in terms of their ability to model noncovalent interactions, especially in the context of describing biomolecules, water solution, and organic materials. We discuss the most significant errors and proposed correction schemes, and we review their performance using standard test sets of molecular systems for quantum chemical methods and several recent applications. The general goal is to highlight both the value and limitations of SE methods and stimulate further developments that allow them to effectively complement ab initio methods in the analysis of complex molecular systems. PMID:27074247

Quantum chemical modeling of enzymatic reactions: the case of histone lysine methyltransferase.

PubMed

Georgieva, Polina; Himo, Fahmi

2010-06-01

Quantum chemical cluster models of enzyme active sites are today an important and powerful tool in the study of various aspects of enzymatic reactivity. This methodology has been applied to a wide spectrum of reactions and many important mechanistic problems have been solved. Herein, we report a systematic study of the reaction mechanism of the histone lysine methyltransferase (HKMT) SET7/9 enzyme, which catalyzes the methylation of the N-terminal histone tail of the chromatin structure. In this study, HKMT SET7/9 serves as a representative case to examine the modeling approach for the important class of methyl transfer enzymes. Active site models of different sizes are used to evaluate the methodology. In particular, the dependence of the calculated energies on the model size, the influence of the dielectric medium, and the particular choice of the dielectric constant are discussed. In addition, we examine the validity of some technical aspects, such as geometry optimization in solvent or with a large basis set, and the use of different density functional methods. Copyright 2010 Wiley Periodicals, Inc.

Quantum Feynman Ratchet

NASA Astrophysics Data System (ADS)

Goyal, Ketan; Kawai, Ryoichi

As nanotechnology advances, understanding of the thermodynamic properties of small systems becomes increasingly important. Such systems are found throughout physics, biology, and chemistry manifesting striking properties that are a direct result of their small dimensions where fluctuations become predominant. The standard theory of thermodynamics for macroscopic systems is powerless for such ever fluctuating systems. Furthermore, as small systems are inherently quantum mechanical, influence of quantum effects such as discreteness and quantum entanglement on their thermodynamic properties is of great interest. In particular, the quantum fluctuations due to quantum uncertainty principles may play a significant role. In this talk, we investigate thermodynamic properties of an autonomous quantum heat engine, resembling a quantum version of the Feynman Ratchet, in non-equilibrium condition based on the theory of open quantum systems. The heat engine consists of multiple subsystems individually contacted to different thermal environments.

Quantum chemical determination of Young's modulus of lignin. Calculations on a beta-O-4' model compound.

PubMed

Elder, Thomas

2007-11-01

The calculation of Young's modulus of lignin has been examined by subjecting a dimeric model compound to strain, coupled with the determination of energy and stress. The computational results, derived from quantum chemical calculations, are in agreement with available experimental results. Changes in geometry indicate that modifications in dihedral angles occur in response to linear strain. At larger levels of strain, bond rupture is evidenced by abrupt changes in energy, structure, and charge. Based on the current calculations, the bond scission may be occurring through a homolytic reaction between aliphatic carbon atoms. These results may have implications in the reactivity of lignin especially when subjected to processing methods that place large mechanical forces on the structure.

Evaluation of a chemical munition dumpsite in the Baltic Sea based on geophysical and chemical investigations.

PubMed

Missiaen, Tine; Söderström, Martin; Popescu, Irina; Vanninen, Paula

2010-08-01

This paper discusses the results of geophysical and chemical investigations carried out in a chemical munition dumpsite in the southern Baltic Sea, east of the island of Bornholm. After WW2 over 32,000 tons of chemical war material was dumped here including shells and bombs as well as small drums and containers. The geophysical investigations combined very-high-resolution seismics and gradiometric measurements. The results indicate the presence of a large number of objects buried just below the seafloor. The size of the objects and their distribution, with a marked increase in density towards the center of the dumpsite, suggests that we are dealing with dumped war material. Sediment and near-bottom water samples, taken within the dumpsite and in the surrounding area, were analysed for the presence of various chemical warfare agents (CWA) including Adamsite, Clark, sulphur mustard, tabun, chlorobenzene and arsine oil. The results indicate a widespread contamination that reaches far beyond the dumpsite boundary. CWA degradation products were found in most of the sediment samples. The contamination was mostly related to arsenic containing compounds; only one sample indicated the presence of sulfur mustard. Although the correlation between detected objects and CWA concentrations is not always straightforward, the overall results suggest that a lot of the dumped war material is leaking and that over the years the contamination has reached the seafloor sediments.

Nonlinear absorption properties of AlGaAs/GaAs multiple quantum wells grown by metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Lee, Hsing-Chung; Kost, A.; Kawase, M.; Hariz, A.; Dapkus, P. Daniel

1988-01-01

The nonlinear absorption properties of the excitonic resonances associated with multiple quantum wells (MQWs) in AlGaAs/GaAs grown by metalorganic chemical vapor deposition are reported. The dependence of the saturation properties on growth parameters, especially growth temperature, and the well width are described. The minimum measured saturation intensity for these materials is 250 W/sq cm, the lowest reported value to date. The low saturation intensities are the result of excellent minority carrier properties. A systematic study of minority carrier lifetimes in quantum wells are reported. Lifetimes range from 50-350 ns depending on growth temperature and well width. When corrected for lateral diffusion effects and the measured minority carrier lifetime, the saturation data suggest that saturation intensities as low as 2.3 W/sq cm can be achieved in this system. The first measurements of the dependence of the exciton area and the magnitude of the excitonic absorption on well width are prsented. The growth of MQW structures on transparent GaP substrates is demonstrated and the electroabsorption properties of these structures are reviewed.

Use of external cavity quantum cascade laser compliance voltage in real-time trace gas sensing of multiple chemicals

NASA Astrophysics Data System (ADS)

Phillips, Mark C.; Taubman, Matthew S.; Kriesel, Jason

2015-01-01

We describe a prototype trace gas sensor designed for real-time detection of multiple chemicals. The sensor uses an external cavity quantum cascade laser (ECQCL) swept over its tuning range of 940-1075 cm-1 (9.30-10.7 μm) at a 10 Hz repetition rate. The sensor was designed for operation in multiple modes, including gas sensing within a multi-pass Heriott cell and intracavity absorption sensing using the ECQCL compliance voltage. In addition, the ECQCL compliance voltage was used to reduce effects of long-term drifts in the ECQCL output power. The sensor was characterized for noise, drift, and detection of chemicals including ammonia, methanol, ethanol, isopropanol, Freon- 134a, Freon-152a, and diisopropyl methylphosphonate (DIMP). We also present use of the sensor for mobile detection of ammonia downwind of cattle facilities, in which concentrations were recorded at 1-s intervals.

Quantum Chemistry, 5th Edition by Ira N. Levine

NASA Astrophysics Data System (ADS)

Hinde, Robert J.

2000-12-01

Of course, there is no one- or two-week shortcut by which nonspecialists can master enough quantum mechanics to become informed users of quantum chemical techniques. Nevertheless, a text that integrated the fundamentals of quantum theory with a rigorous introduction to quantum chemistry could help instructors design a class that would benefit both these nonspecialists and graduate students in physical chemistry. Could such a class overcome the (undeserved) stigma associated with the physical chemistry curriculum? That remains to be seen.

Quantum communication complexity using the quantum Zeno effect

NASA Astrophysics Data System (ADS)

Tavakoli, Armin; Anwer, Hammad; Hameedi, Alley; Bourennane, Mohamed

2015-07-01

The quantum Zeno effect (QZE) is the phenomenon in which the unitary evolution of a quantum state is suppressed, e.g., due to frequent measurements. Here, we investigate the use of the QZE in a class of communication complexity problems (CCPs). Quantum entanglement is known to solve certain CCPs beyond classical constraints. However, recent developments have yielded CCPs for which superclassical results can be obtained using only communication of a single d -level quantum state (qudit) as a resource. In the class of CCPs considered here, we show quantum reduction of complexity in three ways: using (i) entanglement and the QZE, (ii) a single qudit and the QZE, and (iii) a single qudit. We have performed a proof of concept experimental demonstrations of three party CCP protocol based on single-qubit communication with and without QZE.

In situ electron-beam polymerization stabilized quantum dot micelles.

PubMed

Travert-Branger, Nathalie; Dubois, Fabien; Renault, Jean-Philippe; Pin, Serge; Mahler, Benoit; Gravel, Edmond; Dubertret, Benoit; Doris, Eric

2011-04-19

A polymerizable amphiphile polymer containing PEG was synthesized and used to encapsulate quantum dots in micelles. The quantum dot micelles were then polymerized using a "clean" electron beam process that did not require any post-irradiation purification. Fluorescence spectroscopy revealed that the polymerized micelles provided an organic coating that preserved the quantum dot fluorescence better than nonpolymerized micelles, even under harsh conditions. © 2011 American Chemical Society

Quantum-chemical, NMR, FT IR, and ESI MS studies of complexes of colchicine with Zn(II).

PubMed

Jankowski, Wojciech; Kurek, Joanna; Barczyński, Piotr; Hoffmann, Marcin

2017-04-01

Colchicine is a tropolone alkaloid from Colchicinum autumnale. It shows antifibrotic, antimitotic, and anti-inflammatory activities, and is used to treat gout and Mediterranean fever. In this work, complexes of colchicine with zinc(II) nitrate were synthesized and investigated using DFT, 1 H and 13 C NMR, FT IR, and ESI MS. The counterpoise-corrected and uncorrected interaction energies of these complexes were calculated. We also calculated their 1 H, 13 C NMR, and IR spectra and compared them with the corresponding experimentally obtained data. According to the ESI MS mass spectra, colchicine forms stable complexes with zinc(II) nitrate that have various stoichiometries: 2:1, 1:1:1, and 2:1:1 with respect to colchichine, Zn(II), and nitrate ion. All of the complexes were investigated using the quantum theory of atoms in molecules (QTAIM). The calculated and the measured spectra showed differences before and after the complexation process. Calculated electron densities and bond critical points indicated the presence of bonds between the ligands and the central cation in the investigated complexes that satisfied the quantum theory of atoms in molecules. Graphical Abstract DFT, NMR, FT IR, ESI MS, QTAIM and puckering studies of complexes of colchicine with Zn(II).

Magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 driven by the Stark effect

NASA Astrophysics Data System (ADS)

Zhang, Zuocheng; Feng, Xiao; Wang, Jing; Lian, Biao; Zhang, Jinsong; Chang, Cuizu; Guo, Minghua; Ou, Yunbo; Feng, Yang; Zhang, Shou-Cheng; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Yayu

2017-10-01

The recent experimental observation of the quantum anomalous Hall effect has cast significant attention on magnetic topological insulators. In these magnetic counterparts of conventional topological insulators such as Bi2Te3, a long-range ferromagnetic state can be established by chemical doping with transition-metal elements. However, a much richer electronic phase diagram can emerge and, in the specific case of Cr-doped Bi2(SexTe1-x)3, a magnetic quantum phase transition tuned by the actual chemical composition has been reported. From an application-oriented perspective, the relevance of these results hinges on the possibility to manipulate magnetism and electronic band topology by external perturbations such as an electric field generated by gate electrodes—similar to what has been achieved in conventional diluted magnetic semiconductors. Here, we investigate the magneto-transport properties of Cr-doped Bi2(SexTe1-x)3 with different compositions under the effect of a gate voltage. The electric field has a negligible effect on magnetic order for all investigated compositions, with the remarkable exception of the sample close to the topological quantum critical point, where the gate voltage reversibly drives a ferromagnetic-to-paramagnetic phase transition. Theoretical calculations show that a perpendicular electric field causes a shift in the electronic energy levels due to the Stark effect, which induces a topological quantum phase transition and, in turn, a magnetic phase transition.

Old Wine in New Bottles: Quantum Theory in Historical Perspective.

ERIC Educational Resources Information Center

Bent, Henry A.

1984-01-01

Discusses similarities between chemistry and three central concepts of quantum physics: (1) stationary states; (2) wave functions; and (3) complementarity. Based on these and other similarities, it is indicated that quantum physics is a chemical physics. (JN)

Nonlinear absorption in AlGaAs/GaAs multiple quantum well structures grown by metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Lee, H. C.; Hariz, A.; Dapkus, P. D.; Kost, A.; Kawase, M.

1987-01-01

This paper reports the study of growth conditions for achieving the sharp exciton resonances and low-intensity saturation of these resonances in AlGaAs-GaAs multiple quantum well structures grown by metalorganic chemical vapor deposition. Low growth temperature is necessary to observe this sharp resonance feature at room temperature. The optimal growth conditions are a tradeoff between the high temperatures required for high quality AlGaAs and low temperatures required for high-purity GaAs. A strong optical saturation of the excitonic absorption has been observed. A saturation density as low as 250 W/sq cm is reported.

Parameters for the RM1 Quantum Chemical Calculation of Complexes of the Trications of Thulium, Ytterbium and Lutetium

PubMed Central

Filho, Manoel A. M.; Dutra, José Diogo L.; Rocha, Gerd B.; Simas, Alfredo M.

2016-01-01

The RM1 quantum chemical model for the calculation of complexes of Tm(III), Yb(III) and Lu(III) is advanced. Subsequently, we tested the models by fully optimizing the geometries of 126 complexes. We then compared the optimized structures with known crystallographic ones from the Cambridge Structural Database. Results indicate that, for thulium complexes, the accuracy in terms of the distances between the lanthanide ion and its directly coordinated atoms is about 2%. Corresponding results for ytterbium and lutetium are both 3%, levels of accuracy useful for the design of lanthanide complexes, targeting their countless applications. PMID:27223475

Zinc sulfide quantum dots for photocatalytic and sensing applications

NASA Astrophysics Data System (ADS)

Sergeev, Alexander A.; Leonov, Andrei A.; Zhuikova, Elena I.; Postnova, Irina V.; Voznesenskiy, Sergey S.

2017-09-01

Herein, we report the photocatalytic and sensing applications of pure and Mn-doped ZnS quantum dots. The quantum dots were prepared by a chemical precipitation in an aqueous solution in the presence of glutathione as a stabilizing agent. The synthesized quantum dots were used as effective photocatalyst for the degradation of methylene blue dye. Interestingly, fully degradation of methylene blue dye was achieved in 5 min using pure ZnS quantum dots. Further, the synthesized quantum dots were used as efficient sensing element for methane fluorescent sensor. Interfering studies confirmed that the developed sensor possesses very good sensitivity and selectivity towards methane.

Quantum chemical investigation on the catalytic mechanism of vanadium iodoperoxidase and the iodination of common organic compounds

NASA Astrophysics Data System (ADS)

Gálvez, Óscar; Pacios, Luis F.

2010-05-01

Atmospheric iodine has received considerable attention in the two past decades due to both its potential role in the catalytic destruction of ozone (1) and its contribution to the formation of cloud condensation nuclei (2). It is generally assumed that iodine in the atmosphere has a natural origin since no anthropogenic sources are known. Seaweeds and marine phytoplankton release iodocarbons. In addition, IO and even I2, a major source of particle formation in coastal areas, are also detectable in the atmosphere above kelp beds. However, the reasons why iodocarbons are released by seaweeds and the mechanisms involved in their production remain largely unknown. It is currently well established that the general catalytic role of halide oxidation in marine algae is actually played by vanadium-dependent haloperoxidases enzymes, although relevant details such as protonation states of the vanadate cofactor or even key steps in the mechanism are still unknown. In this contribution, we focus on the iodoperoxidase VIPO enzyme. Quantum calculations on the vanadate cofactor were combined with structural analyses on a reliable three-dimensional model of the VIPO protein to investigate the steps along the catalytic mechanism that lead to the release of halide oxidation products. In addition, iodination reactions of several common organic compounds selected to account for representative volatile and non-volatile iodocarbons were thermodynamically studied by means of high-level ab initio correlated calculations. Free energies of reactions with the three possible iodinating species produced by the enzyme, namely HOI, I2, and I3- were calculated. Our results show that only hypoiodous acid give rise to clearly exoergonic iodination of organic substrates. (1) Saiz-Lopez, A.; Mahajan, A.S.; Salmon, R.A.; Bauguitte, J.B.; Jones, A.E.; Roscoe, H.K.; Plane, J.M.C. Science 2007, 317, 348-351 (2) O'Dowd, C.D.; Jimenez, J.L.; Bahreini, R.; Flagan, R.C.; Seinfeld, J.H.; Hämeri, K.; Pirjola

Generalized Geometric Quantum Speed Limits

NASA Astrophysics Data System (ADS)

Pires, Diego Paiva; Cianciaruso, Marco; Céleri, Lucas C.; Adesso, Gerardo; Soares-Pinto, Diogo O.

2016-04-01

The attempt to gain a theoretical understanding of the concept of time in quantum mechanics has triggered significant progress towards the search for faster and more efficient quantum technologies. One of such advances consists in the interpretation of the time-energy uncertainty relations as lower bounds for the minimal evolution time between two distinguishable states of a quantum system, also known as quantum speed limits. We investigate how the nonuniqueness of a bona fide measure of distinguishability defined on the quantum-state space affects the quantum speed limits and can be exploited in order to derive improved bounds. Specifically, we establish an infinite family of quantum speed limits valid for unitary and nonunitary evolutions, based on an elegant information geometric formalism. Our work unifies and generalizes existing results on quantum speed limits and provides instances of novel bounds that are tighter than any established one based on the conventional quantum Fisher information. We illustrate our findings with relevant examples, demonstrating the importance of choosing different information metrics for open system dynamics, as well as clarifying the roles of classical populations versus quantum coherences, in the determination and saturation of the speed limits. Our results can find applications in the optimization and control of quantum technologies such as quantum computation and metrology, and might provide new insights in fundamental investigations of quantum thermodynamics.

Numerical investigation of gapped edge states in fractional quantum Hall-superconductor heterostructures

NASA Astrophysics Data System (ADS)

Repellin, Cécile; Cook, Ashley M.; Neupert, Titus; Regnault, Nicolas

2018-03-01

Fractional quantum Hall-superconductor heterostructures may provide a platform towards non-abelian topological modes beyond Majoranas. However their quantitative theoretical study remains extremely challenging. We propose and implement a numerical setup for studying edge states of fractional quantum Hall droplets with a superconducting instability. The fully gapped edges carry a topological degree of freedom that can encode quantum information protected against local perturbations. We simulate such a system numerically using exact diagonalization by restricting the calculation to the quasihole-subspace of a (time-reversal symmetric) bilayer fractional quantum Hall system of Laughlin ν = 1/3 states. We show that the edge ground states are permuted by spin-dependent flux insertion and demonstrate their fractional 6π Josephson effect, evidencing their topological nature and the Cooper pairing of fractionalized quasiparticles. The versatility and efficiency of our setup make it a well suited method to tackle wider questions of edge phases and phase transitions in fractional quantum Hall systems.

Experimental investigation of terahertz quantum cascade laser with variable barrier heights

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Aiting; Vijayraghavan, Karun; Belkin, Mikhail A., E-mail: mbelkin@ece.utexas.edu

2014-04-28

We report an experimental study of terahertz quantum cascade lasers with variable barrier heights based on the Al{sub x}Ga{sub 1–x}As/GaAs material system. Two new designs are developed based on semiclassical ensemble Monte Carlo simulations using state-of-the-art Al{sub 0.15}Ga{sub 0.85}As/GaAs three-quantum-well resonant phonon depopulation active region design as a reference. The new designs achieved maximum lasing temperatures of 188 K and 172 K, as compared to the maximum lasing temperature of 191 K for the reference structure. These results demonstrate that terahertz quantum cascade laser designs with variable barrier heights provide a viable alternative to the traditional active region designs with fixed barrier composition.more » Additional design space offered by using variable barriers may lead to future improvements in the terahertz quantum cascade laser performance.« less

Path Integrals for Electronic Densities, Reactivity Indices, and Localization Functions in Quantum Systems

PubMed Central

Putz, Mihai V.

2009-01-01

The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI) development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr’s quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions – all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving) many-electronic systems. PMID:20087467

Path integrals for electronic densities, reactivity indices, and localization functions in quantum systems.

PubMed

Putz, Mihai V

2009-11-10

The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI) development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr's quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions - all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving) many-electronic systems.

Prospect of quantum anomalous Hall and quantum spin Hall effect in doped kagome lattice Mott insulators.

PubMed

Guterding, Daniel; Jeschke, Harald O; Valentí, Roser

2016-05-17

Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.

Remote explosive and chemical agent detection using broadly tunable mid-infrared external cavity quantum cascade lasers

NASA Astrophysics Data System (ADS)

Rayner, Timothy; Weida, Miles; Pushkarsky, Michael; Day, Timothy

2007-04-01

Terrorists both with IEDs and suicide bombers are targeting civilian infrastructures such as transportation systems. Although explosive detection technologies exist and are used effectively in aviation, these technologies do not lend themselves well to protecting open architecture soft targets, as they are focused on a checkpoint form factor that limits throughput. However, remote detection of explosives and other chemicals would enable these kinds of targets to be protected without interrupting the flow of commerce. Tunable mid-IR laser technology offers the opportunity to detect explosives and other chemicals remotely and quickly. Most chemical compounds, including explosives, have their fundamental vibrational modes in the mid-infrared region (3 to 15μm). There are a variety of techniques that focus on examining interactions that have proven effective in the laboratory but could never work in the field due to complexity, size, reliability and cost. Daylight Solutions has solved these problems by integrating quantum cascade gain media into external tunable cavities. This has resulted in miniaturized, broadly tunable mid-IR laser sources. The laser sources have a capability to tune to +/- 5% of their center wavelength, which means they can sweep through an entire absorption spectrum to ensure very good detection and false alarm performance compared with fixed wavelength devices. These devices are also highly portable, operate at room temperature, and generate 10's to 100's of mW in optical power, in pulsed and continuous wave configurations. Daylight Solutions is in the process of developing a variety of standoff explosive and chemical weapon detection systems using this technology.

Effect of hexagonal hillock on luminescence characteristic of multiple quantum wells structure

NASA Astrophysics Data System (ADS)

Du, Jinjuan; Xu, Shengrui; Li, Peixian; Zhang, Jincheng; Zhao, Ying; Peng, Ruoshi; Fan, Xiaomeng; Hao, Yue

2018-04-01

GaN based ultraviolet multiple quantum well structures grown on a c-plane sapphire substrate by metal organic chemical deposition showed a microstructure with a large amount of huge hexagonal hillocks. The polarity of the sample is confirmed by etching with sodium hydroxide solution. The luminous intensity distribution of a typical hexagonal hillock was investigated by the phototluminescent mapping and the luminous intensity at hillock top regions was found to be 15 times higher than that of the regions around hillocks. The reduction of dislocations, the decreasing of the quantum confirmed stack effect caused by semipolar plane and the inclination of the sidewalls of the hexagonal hillock were responsible for the enhancement of luminous intensity.

Bismuth as a versatile cation for luminescence in coordination polymers from BiX3/4,4'-bipy: understanding of photophysics by quantum chemical calculations and structural parallels to lanthanides.

PubMed

Sorg, Jens R; Wehner, Tobias; Matthes, Philipp R; Sure, Rebecca; Grimme, Stefan; Heine, Johanna; Müller-Buschbaum, Klaus

2018-05-16

Coordination polymers (CPs) with bismuth(iii) as a connectivity centre have been prepared from BiX3 (X = Cl-I) and 4,4'-bipyridine (bipy) in order to implement Bi-based luminescence. The products were obtained via different synthetic routes such as solution chemistry, melt syntheses or mechanochemical reactions. Five neutral and anionic 1D-CPs are presented that show a chemical parallel to trivalent lanthanides forming isostructural or closely related 1D-CPs, of which five additional compounds are described. Bi3+ proves to be a versatile cation for luminescence resulting from energy transfer processes between a metal and a ligand in the presented CPs. Quantum chemical calculations were carried out to investigate Bi3+-participation in the luminescence processes. The calculated results allow an assignment of the bright transitions composed of mainly metal-to-ligand-charge transfer (MLCT) character. These results show that Bi3+ can form strongly luminescent coordination compounds with N-donor ligands.

Synthesis, inhibition effects and quantum chemical studies of a novel coumarin derivative on the corrosion of mild steel in a hydrochloric acid solution.

PubMed

Al-Azawi, Khalida F; Al-Baghdadi, Shaimaa B; Mohamed, Ayad Z; Al-Amiery, Ahmed A; Abed, Talib K; Mohammed, Salam A; Kadhum, Abdul Amir H; Mohamad, Abu Bakar

2016-01-01

The acid corrosion inhibition process of mild steel in 1 M HCl by 4-[(2-amino-1, 3, 4-thiadiazol-5-yl)methoxy]coumarin (ATC), has been investigated using weight loss technique and scanning electron microscopy (SEM). ATC was synthesized, and its chemical structure was elucidated and confirmed using spectroscopic techniques (infrared and nuclear magnetic resonance spectroscopy). The results indicated that inhibition efficiencies were enhanced with an increase in concentration of inhibitor and decreased with a rise in temperature. The adsorption equilibrium constant (K) and standard free energy of adsorption (ΔGads) were calculated. Quantum chemical parameters such as highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy (EHOMO and ELUMO, respectively) and dipole moment (μ) were calculated and discussed. The results showed that the corrosion inhibition efficiency increased with an increase in both the EHOMO and μ values but with a decrease in the ELUMO value. Our research show that the synthesized macromolecule represents an excellent inhibitor for materials in acidic solutions. The efficiency of this macromolecule had maximum inhibition efficiency up to 96 % at 0.5 mM and diminishes with a higher temperature degree, which is revealing of chemical adsorption. An inhibitor molecule were absorbed by metal surface and follow Langmuir isotherms low and establishes an efficient macromolecule inhibitor having excellent inhibitive properties due to entity of S (sulfur) atom, N (nitrogen) atom and O (oxygen) atom.

Quantum chemical calculations in the structural analysis of phloretin

NASA Astrophysics Data System (ADS)

Gómez-Zavaglia, Andrea

2009-07-01

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

Ab initio quantum chemistry: methodology and applications.

PubMed

Friesner, Richard A

2005-05-10

This Perspective provides an overview of state-of-the-art ab initio quantum chemical methodology and applications. The methods that are discussed include coupled cluster theory, localized second-order Moller-Plesset perturbation theory, multireference perturbation approaches, and density functional theory. The accuracy of each approach for key chemical properties is summarized, and the computational performance is analyzed, emphasizing significant advances in algorithms and implementation over the past decade. Incorporation of a condensed-phase environment by means of mixed quantum mechanical/molecular mechanics or self-consistent reaction field techniques, is presented. A wide range of illustrative applications, focusing on materials science and biology, are discussed briefly.

Quantum state engineering in hybrid open quantum systems

NASA Astrophysics Data System (ADS)

Joshi, Chaitanya; Larson, Jonas; Spiller, Timothy P.

2016-04-01

We investigate a possibility to generate nonclassical states in light-matter coupled noisy quantum systems, namely, the anisotropic Rabi and Dicke models. In these hybrid quantum systems, a competing influence of coherent internal dynamics and environment-induced dissipation drives the system into nonequilibrium steady states (NESSs). Explicitly, for the anisotropic Rabi model, the steady state is given by an incoherent mixture of two states of opposite parities, but as each parity state displays light-matter entanglement, we also find that the full state is entangled. Furthermore, as a natural extension of the anisotropic Rabi model to an infinite spin subsystem, we next explored the NESS of the anisotropic Dicke model. The NESS of this linearized Dicke model is also an inseparable state of light and matter. With an aim to enrich the dynamics beyond the sustainable entanglement found for the NESS of these hybrid quantum systems, we also propose to combine an all-optical feedback strategy for quantum state protection and for establishing quantum control in these systems. Our present work further elucidates the relevance of such hybrid open quantum systems for potential applications in quantum architectures.

Investigation of thioglycerol stabilized ZnS quantum dots in electroluminescent device performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ethiraj, Anita Sagadevan, E-mail: anita.ethiraj@vit.ac.in; Center for Nanotechnology Research, VIT University, Vellore, TamilNadu-632014; Rhen, Dani

2016-05-06

The present work is focused on the investigation of thioglycerol (TG) stabilized Zinc Sulfide Quantum dots (ZnS QDs) in the hybrid electroluminescence (EL) device. Optical absorption spectroscopy clearly indicates the formation of narrow size distributed ZnS in the quantum confinement regime. X-ray Diffraction (XRD), Photoluminescence (PL), Energy Dispersive X-ray Spectroscopy (EDS) data supports the same. The hybrid EL device with structure of ITO (indium tin oxide)//PEDOT:PSS ((poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)//HTL (α NPD- N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-phenyl)-4,4′-diamine// PVK:ZnS QDs//ETL(PBD- 2-tert-butylphenyl- 5-biphenyl-1,3,4-oxadiazole)//LiF:Al (Device 1) was fabricated. Reference device without the ZnS QDs were also prepared (Device 2). The results show that the ZnS QDs based device exhibitedmore » bright electroluminescence emission of 24 cd/m{sup 2} at a driving voltage of 16 Volts under the forward bias conditions as compared to the reference device without the ZnS QDs, which showed 6 cd/m{sup 2} at ∼22 Volts.« less

Investigation on Adsorption and the Corrosion Inhibition Effect of Some Novel Hydrazide Derivatives for Mild Steel in HCl Solution

NASA Astrophysics Data System (ADS)

Singh, Dharmendra Kumar; Behera, Debasis; Singh, Mantu Kumar; Udayabhanu, G.; John, Rohith P.

2017-10-01

Two hydrazide derivatives, namely, N'-(thiophene-2-ylmethylene)nicotinic hydrazone (TNH) and N'-(pyrrol-2-ylmethylene)nicotinic hydrazone (PNH), have been synthesized and investigated as corrosion inhibitors for mild steel in 1 M HCl solution by electrochemical, weight loss, field emission-scanning electron microscope (FE-SEM), atomic force microscope (AFM), and quantum chemical calculation methods. The experimental results show that both the compounds are good inhibitors for mild steel in 1 M HCl. They act as mixed type inhibitors with predominating cathodic character. The adsorption of inhibitors obeys the Langmuir adsorption isotherm. Correlation between quantum chemical parameters and experimental results is discussed.

Quantum Effects in Biology

NASA Astrophysics Data System (ADS)

Mohseni, Masoud; Omar, Yasser; Engel, Gregory S.; Plenio, Martin B.

2014-08-01

List of contributors; Preface; Part I. Introduction: 1. Quantum biology: introduction Graham R. Fleming and Gregory D. Scholes; 2. Open quantum system approaches to biological systems Alireza Shabani, Masoud Mohseni, Seogjoo Jang, Akihito Ishizaki, Martin Plenio, Patrick Rebentrost, Alàn Aspuru-Guzik, Jianshu Cao, Seth Lloyd and Robert Silbey; 3. Generalized Förster resonance energy transfer Seogjoo Jang, Hoda Hossein-Nejad and Gregory D. Scholes; 4. Multidimensional electronic spectroscopy Tomáš Mančal; Part II. Quantum Effects in Bacterial Photosynthetic Energy Transfer: 5. Structure, function, and quantum dynamics of pigment protein complexes Ioan Kosztin and Klaus Schulten; 6. Direct observation of quantum coherence Gregory S. Engel; 7. Environment-assisted quantum transport Masoud Mohseni, Alàn Aspuru-Guzik, Patrick Rebentrost, Alireza Shabani, Seth Lloyd, Susana F. Huelga and Martin B. Plenio; Part III. Quantum Effects in Higher Organisms and Applications: 8. Excitation energy transfer in higher plants Elisabet Romero, Vladimir I. Novoderezhkin and Rienk van Grondelle; 9. Electron transfer in proteins Spiros S. Skourtis; 10. A chemical compass for bird navigation Ilia A. Solov'yov, Thorsten Ritz, Klaus Schulten and Peter J. Hore; 11. Quantum biology of retinal Klaus Schulten and Shigehiko Hayashi; 12. Quantum vibrational effects on sense of smell A. M. Stoneham, L. Turin, J. C. Brookes and A. P. Horsfield; 13. A perspective on possible manifestations of entanglement in biological systems Hans J. Briegel and Sandu Popescu; 14. Design and applications of bio-inspired quantum materials Mohan Sarovar, Dörthe M. Eisele and K. Birgitta Whaley; 15. Coherent excitons in carbon nanotubes Leonas Valkunas and Darius Abramavicius; Glossary; References; Index.

Two-qubit quantum cloning machine and quantum correlation broadcasting

NASA Astrophysics Data System (ADS)

Kheirollahi, Azam; Mohammadi, Hamidreza; Akhtarshenas, Seyed Javad

2016-11-01

Due to the axioms of quantum mechanics, perfect cloning of an unknown quantum state is impossible. But since imperfect cloning is still possible, a question arises: "Is there an optimal quantum cloning machine?" Buzek and Hillery answered this question and constructed their famous B-H quantum cloning machine. The B-H machine clones the state of an arbitrary single qubit in an optimal manner and hence it is universal. Generalizing this machine for a two-qubit system is straightforward, but during this procedure, except for product states, this machine loses its universality and becomes a state-dependent cloning machine. In this paper, we propose some classes of optimal universal local quantum state cloners for a particular class of two-qubit systems, more precisely, for a class of states with known Schmidt basis. We then extend our machine to the case that the Schmidt basis of the input state is deviated from the local computational basis of the machine. We show that more local quantum coherence existing in the input state corresponds to less fidelity between the input and output states. Also we present two classes of a state-dependent local quantum copying machine. Furthermore, we investigate local broadcasting of two aspects of quantum correlations, i.e., quantum entanglement and quantum discord, defined, respectively, within the entanglement-separability paradigm and from an information-theoretic perspective. The results show that although quantum correlation is, in general, very fragile during the broadcasting procedure, quantum discord is broadcasted more robustly than quantum entanglement.

Parallel Photonic Quantum Computation Assisted by Quantum Dots in One-Side Optical Microcavities

PubMed Central

Luo, Ming-Xing; Wang, Xiaojun

2014-01-01

Universal quantum logic gates are important elements for a quantum computer. In contrast to previous constructions on one degree of freedom (DOF) of quantum systems, we investigate the possibility of parallel quantum computations dependent on two DOFs of photon systems. We construct deterministic hyper-controlled-not (hyper-CNOT) gates operating on the spatial-mode and the polarization DOFs of two-photon or one-photon systems by exploring the giant optical circular birefringence induced by quantum-dot spins in one-sided optical microcavities. These hyper-CNOT gates show that the quantum states of two DOFs can be viewed as independent qubits without requiring auxiliary DOFs in theory. This result can reduce the quantum resources by half for quantum applications with large qubit systems, such as the quantum Shor algorithm. PMID:25030424

Parallel photonic quantum computation assisted by quantum dots in one-side optical microcavities.

PubMed

Luo, Ming-Xing; Wang, Xiaojun

2014-07-17

Universal quantum logic gates are important elements for a quantum computer. In contrast to previous constructions on one degree of freedom (DOF) of quantum systems, we investigate the possibility of parallel quantum computations dependent on two DOFs of photon systems. We construct deterministic hyper-controlled-not (hyper-CNOT) gates operating on the spatial-mode and the polarization DOFs of two-photon or one-photon systems by exploring the giant optical circular birefringence induced by quantum-dot spins in one-sided optical microcavities. These hyper-CNOT gates show that the quantum states of two DOFs can be viewed as independent qubits without requiring auxiliary DOFs in theory. This result can reduce the quantum resources by half for quantum applications with large qubit systems, such as the quantum Shor algorithm.

Electrostatic thin film chemical and biological sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prelas, Mark A.; Ghosh, Tushar K.; Tompson, Jr., Robert V.

A chemical and biological agent sensor includes an electrostatic thin film supported by a substrate. The film includes an electrostatic charged surface to attract predetermined biological and chemical agents of interest. A charge collector associated with said electrostatic thin film collects charge associated with surface defects in the electrostatic film induced by the predetermined biological and chemical agents of interest. A preferred sensing system includes a charge based deep level transient spectroscopy system to read out charges from the film and match responses to data sets regarding the agents of interest. A method for sensing biological and chemical agents includesmore » providing a thin sensing film having a predetermined electrostatic charge. The film is exposed to an environment suspected of containing the biological and chemical agents. Quantum surface effects on the film are measured. Biological and/or chemical agents can be detected, identified and quantified based on the measured quantum surface effects.« less

The study of metal sulphide nanomaterials obtained by chemical bath deposition and hot-injection technique

NASA Astrophysics Data System (ADS)

Maraeva, E. V.; Alexandrova, O. A.; Forostyanaya, N. A.; Levitskiy, V. S.; Mazing, D. S.; Maskaeva, L. N.; Markov, V. Ph; Moshnikov, V. A.; Shupta, A. A.; Spivak, Yu M.; Tulenin, S. S.

2015-11-01

In this study lead sulphide - cadmium sulphide based layers were obtained through chemical deposition of water solutions and cadmium sulphide quantum dots were formed through hot-injection technique. The article discusses the results of surface investigations with the use of atomic force microscopy, Raman spectroscopy and photoluminescence measurements.

Coherent control of diamond defects for quantum information science and quantum sensing

NASA Astrophysics Data System (ADS)

Maurer, Peter

. This opens the door for the engineering of nano-scaled chemical reactions to the study of temperature dependent biological processes. Finally, a novel technique is introduced that facilitates optical spin detection with nanoscale resolution based on an optical far-field technique; by combining this with a 'quantum Zeno' like effect coherent manipulation of nominally identical spins at a nanoscale is achieved.

High fidelity quantum teleportation assistance with quantum neural network

NASA Astrophysics Data System (ADS)

Huang, Chunhui; Wu, Bichun

2014-09-01

In this paper, a high fidelity scheme of quantum teleportation based on quantum neural network (QNN) is proposed. The QNN is composed of multi-bit control-not gates. The quantum teleportation of a qubit state via two-qubit entangled channels is investigated by solving the master equation in Lindblad operators with a noisy environment. To ensure the security of quantum teleportation, the indirect training of QNN is employed. Only 10% of teleported information is extracted for the training of QNN parameters. Then the outputs are corrected by the other QNN at Bob's side. We build a random series of numbers ranged in [0, π] as inputs and simulate the properties of our teleportation scheme. The results show that the fidelity of quantum teleportation system is significantly improved to approach 1 by the error-correction of QNN. It illustrates that the distortion can be eliminated perfectly and the high fidelity of quantum teleportation could be implemented.

Robust dynamical decoupling for quantum computing and quantum memory.

PubMed

Souza, Alexandre M; Alvarez, Gonzalo A; Suter, Dieter

2011-06-17

Dynamical decoupling (DD) is a popular technique for protecting qubits from the environment. However, unless special care is taken, experimental errors in the control pulses used in this technique can destroy the quantum information instead of preserving it. Here, we investigate techniques for making DD sequences robust against different types of experimental errors while retaining good decoupling efficiency in a fluctuating environment. We present experimental data from solid-state nuclear spin qubits and introduce a new DD sequence that is suitable for quantum computing and quantum memory.

LSE investigation of the thermal effect on band gap energy and thermodynamic parameters of BInGaAs/GaAs Single Quantum Well

NASA Astrophysics Data System (ADS)

Hidouri, T.; Saidi, F.; Maaref, H.; Rodriguez, Ph.; Auvray, L.

2016-12-01

In this paper, we report on the experimental and theoretical study of BInGaAs/GaAs Single Quantum Well elaborated by Metal Organic Chemical Vapor Deposition (MOCVD). We carried out the photoluminescence (PL) peak energy temperature-dependence over a temperature range of 10-300 K. It shows the S-shaped behavior as a result of a competition process between localized and delocalized states. We simulate the peak evolution by the empirical model and modified models. The first one is limited at high PL temperature. For the second one, a correction due to the thermal redistribution based on the Localized State Ensemble model (LSE). The new fit gives a good agreement between theoretical and experimental data in the entire temperature range. Furthermore, we have investigated an approximate analytical expressions and interpretation for the entropy and enthalpy of formation of electron-hole pairs in quaternary BInGaAs/GaAs SQW.

QSPR models for various physical properties of carbohydrates based on molecular mechanics and quantum chemical calculations.

PubMed

Dyekjaer, Jane Dannow; Jónsdóttir, Svava Osk

2004-01-22

Quantitative Structure-Property Relationships (QSPR) have been developed for a series of monosaccharides, including the physical properties of partial molar heat capacity, heat of solution, melting point, heat of fusion, glass-transition temperature, and solid state density. The models were based on molecular descriptors obtained from molecular mechanics and quantum chemical calculations, combined with other types of descriptors. Saccharides exhibit a large degree of conformational flexibility, therefore a methodology for selecting the energetically most favorable conformers has been developed, and was used for the development of the QSPR models. In most cases good correlations were obtained for monosaccharides. For five of the properties predictions were made for disaccharides, and the predicted values for the partial molar heat capacities were in excellent agreement with experimental values.

QuantumOptics.jl: A Julia framework for simulating open quantum systems

NASA Astrophysics Data System (ADS)

Krämer, Sebastian; Plankensteiner, David; Ostermann, Laurin; Ritsch, Helmut

2018-06-01

We present an open source computational framework geared towards the efficient numerical investigation of open quantum systems written in the Julia programming language. Built exclusively in Julia and based on standard quantum optics notation, the toolbox offers speed comparable to low-level statically typed languages, without compromising on the accessibility and code readability found in dynamic languages. After introducing the framework, we highlight its features and showcase implementations of generic quantum models. Finally, we compare its usability and performance to two well-established and widely used numerical quantum libraries.

Exploring the boundaries of quantum mechanics: advances in satellite quantum communications.

PubMed

Agnesi, Costantino; Vedovato, Francesco; Schiavon, Matteo; Dequal, Daniele; Calderaro, Luca; Tomasin, Marco; Marangon, Davide G; Stanco, Andrea; Luceri, Vincenza; Bianco, Giuseppe; Vallone, Giuseppe; Villoresi, Paolo

2018-07-13

Recent interest in quantum communications has stimulated great technological progress in satellite quantum technologies. These advances have rendered the aforesaid technologies mature enough to support the realization of experiments that test the foundations of quantum theory at unprecedented scales and in the unexplored space environment. Such experiments, in fact, could explore the boundaries of quantum theory and may provide new insights to investigate phenomena where gravity affects quantum objects. Here, we review recent results in satellite quantum communications and discuss possible phenomena that could be observable with current technologies. Furthermore, stressing the fact that space represents an incredible resource to realize new experiments aimed at highlighting some physical effects, we challenge the community to propose new experiments that unveil the interplay between quantum mechanics and gravity that could be realizable in the near future.This article is part of a discussion meeting issue 'Foundations of quantum mechanics and their impact on contemporary society'. © 2018 The Author(s).

Procedural Quantum Programming

NASA Astrophysics Data System (ADS)

Ömer, Bernhard

2002-09-01

While classical computing science has developed a variety of methods and programming languages around the concept of the universal computer, the typical description of quantum algorithms still uses a purely mathematical, non-constructive formalism which makes no difference between a hydrogen atom and a quantum computer. This paper investigates, how the concept of procedural programming languages, the most widely used classical formalism for describing and implementing algorithms, can be adopted to the field of quantum computing, and how non-classical features like the reversibility of unitary transformations, the non-observability of quantum states or the lack of copy and erase operations can be reflected semantically. It introduces the key concepts of procedural quantum programming (hybrid target architecture, operator hierarchy, quantum data types, memory management, etc.) and presents the experimental language QCL, which implements these principles.

Fano Effect and Quantum Entanglement in Hybrid Semiconductor Quantum Dot-Metal Nanoparticle System.

PubMed

He, Yong; Zhu, Ka-Di

2017-06-20

In this paper, we review the investigation for the light-matter interaction between surface plasmon field in metal nanoparticle (MNP) and the excitons in semiconductor quantum dots (SQDs) in hybrid SQD-MNP system under the full quantum description. The exciton-plasmon interaction gives rise to the modified decay rate and the exciton energy shift which are related to the exciton energy by using a quantum transformation method. We illustrate the responses of the hybrid SQD-MNP system to external field, and reveal Fano effect shown in the absorption spectrum. We demonstrate quantum entanglement between two SQD mediated by surface plasmon field. In the absence of a laser field, concurrence of quantum entanglement will disappear after a few ns. If the laser field is present, the steady states appear, so that quantum entanglement produced will reach a steady-state entanglement. Because one of all optical pathways to induce Fano effect refers to the generation of quantum entangled states, It is shown that the concurrence of quantum entanglement can be obtained by observation for Fano effect. In a hybrid system including two MNP and a SQD, because the two Fano quantum interference processes share a segment of all optical pathways, there is correlation between the Fano effects of the two MNP. The investigations for the light-matter interaction in hybrid SQD-MNP system can pave the way for the development of the optical processing devices and quantum information based on the exciton-plasmon interaction.

Fano Effect and Quantum Entanglement in Hybrid Semiconductor Quantum Dot-Metal Nanoparticle System

PubMed Central

He, Yong; Zhu, Ka-Di

2017-01-01

In this paper, we review the investigation for the light-matter interaction between surface plasmon field in metal nanoparticle (MNP) and the excitons in semiconductor quantum dots (SQDs) in hybrid SQD-MNP system under the full quantum description. The exciton-plasmon interaction gives rise to the modified decay rate and the exciton energy shift which are related to the exciton energy by using a quantum transformation method. We illustrate the responses of the hybrid SQD-MNP system to external field, and reveal Fano effect shown in the absorption spectrum. We demonstrate quantum entanglement between two SQD mediated by surface plasmon field. In the absence of a laser field, concurrence of quantum entanglement will disappear after a few ns. If the laser field is present, the steady states appear, so that quantum entanglement produced will reach a steady-state entanglement. Because one of all optical pathways to induce Fano effect refers to the generation of quantum entangled states, It is shown that the concurrence of quantum entanglement can be obtained by observation for Fano effect. In a hybrid system including two MNP and a SQD, because the two Fano quantum interference processes share a segment of all optical pathways, there is correlation between the Fano effects of the two MNP. The investigations for the light-matter interaction in hybrid SQD-MNP system can pave the way for the development of the optical processing devices and quantum information based on the exciton-plasmon interaction. PMID:28632165

Estimating system parameters for solvent-water and plant cuticle-water using quantum chemically estimated Abraham solute parameters.

PubMed

Liang, Yuzhen; Torralba-Sanchez, Tifany L; Di Toro, Dominic M

2018-04-18

Polyparameter Linear Free Energy Relationships (pp-LFERs) using Abraham system parameters have many useful applications. However, developing the Abraham system parameters depends on the availability and quality of the Abraham solute parameters. Using Quantum Chemically estimated Abraham solute Parameters (QCAP) is shown to produce pp-LFERs that have lower root mean square errors (RMSEs) of predictions for solvent-water partition coefficients than parameters that are estimated using other presently available methods. pp-LFERs system parameters are estimated for solvent-water, plant cuticle-water systems, and for novel compounds using QCAP solute parameters and experimental partition coefficients. Refitting the system parameter improves the calculation accuracy and eliminates the bias. Refitted models for solvent-water partition coefficients using QCAP solute parameters give better results (RMSE = 0.278 to 0.506 log units for 24 systems) than those based on ABSOLV (0.326 to 0.618) and QSPR (0.294 to 0.700) solute parameters. For munition constituents and munition-like compounds not included in the calibration of the refitted model, QCAP solute parameters produce pp-LFER models with much lower RMSEs for solvent-water partition coefficients (RMSE = 0.734 and 0.664 for original and refitted model, respectively) than ABSOLV (4.46 and 5.98) and QSPR (2.838 and 2.723). Refitting plant cuticle-water pp-LFER including munition constituents using QCAP solute parameters also results in lower RMSE (RMSE = 0.386) than that using ABSOLV (0.778) and QSPR (0.512) solute parameters. Therefore, for fitting a model in situations for which experimental data exist and system parameters can be re-estimated, or for which system parameters do not exist and need to be developed, QCAP is the quantum chemical method of choice.

Three isomers detected for the whisky lactone: 5-butyl-4-methyl tetrahydrofuran-2-one by Fourier transform microwave spectroscopy and quantum chemical calculations

NASA Astrophysics Data System (ADS)

Kawashima, Yoshiyuki; Katsuragi, Ryusuke; Hirota, Eizi

2017-05-01

The ground-state rotational spectra of the whisky lactone (WL) : 5-butyl-4-methyl tetrahydrofuran-2-one were observed and analyzed by molecular beam Fourier transform microwave spectroscopy combined with quantum chemical calculations. We have detected three stereo-isomers: the trans-TTT form with a methyl CH3 group attached to C(4) in an equatorial position (eq) and a butyl C4H9 group to C(5) in an eq position, for which 110 b-type and 113 a-type transitions were assigned, the cis-TTT form with a CH3 to C(4) in an axial position (ax) and a C4H9 to C(5) in eq, for which 96 a-type, 101 b-type, and 45 c-type transitions were observed, and the cis-GTT form with a CH3 to C(4) in ax and a C4H9 to C(5) in eq, for which 158 a-type, 52 b-type, and 17 c-type transitions were observed, where TTT and GTT denote the conformations about the C(6)sbnd C(5), C(7)sbnd C(6), and C(8)sbnd C(7) bonds, with T and G designating trans and gauche, respectively. The rotational constants thus derived agree with the predictions made by quantum chemical calculations, MP2/6-311++G(d, p) within 1.2%. The trans-TTT form was calculated to be the most stable. The splittings due to internal rotation of the terminal methyl in the butyl group were observed for all the three stereo-isomers and were analyzed by the XIAM program to determine the threefold potential barrier V3 to be 966.4 (25), 978.8 (11), and 1098.7 (48) in cm-1 for the trans-TTT (eq, eq), the cis-TTT (ax, eq), and the cis-GTT (ax, eq) forms, respectively, to be compared with quantum chemically calculated values: 1055, 1055, and 1053 in cm-1.

STRUCTURE-ACTIVITY RELATIONSHIP STUIDES AND THEIR ROLE IN PREDICTING AND INVESTIGATING CHEMICAL TOXICITY

EPA Science Inventory

Structure-Activity Relationship Studies and their Role in Predicting and Investigating Chemical Toxicity

Structure-activity relationships (SAR) represent attempts to generalize chemical information relative to biological activity for the twin purposes of generating insigh...

Synthesis of carbon-based quantum dots from starch extracts: Optical investigations.

PubMed

Al-Douri, Y; Badi, N; Voon, C H

2018-03-01

Carbon-based quantum dots (C-QDs) were synthesized through microwave-assisted carbonization of an aqueous starch suspension mediated by sulphuric and phosphoric acids. The as-prepared C-QDs showed blue, green and yellow luminescence without the addition of any surface-passivating agent. The C-QDs were further analyzed by UV-vis spectroscopy to measure the optical response of the organic compound. The energy gaps revealed narrow sizing of C-QDs in the semiconductor range. The optical refractive index and dielectric constant were investigated. The C-QDs size distribution was characterized. The results suggested an easy route to the large scale production of C-QDs materials. Copyright © 2017 John Wiley & Sons, Ltd.

Quantum radiation produced by the entanglement of quantum fields

NASA Astrophysics Data System (ADS)

Iso, Satoshi; Oshita, Naritaka; Tatsukawa, Rumi; Yamamoto, Kazuhiro; Zhang, Sen

2017-01-01

We investigate the quantum radiation produced by an Unruh-De Witt detector in a uniformly accelerating motion coupled to the vacuum fluctuations. Quantum radiation is nonvanishing, which is consistent with the previous calculation by Lin and Hu [Phys. Rev. D 73, 124018 (2006), 10.1103/PhysRevD.73.124018]. We infer that this quantum radiation from the Unruh-De Witt detector is generated by the nonlocal correlation of the Minkowski vacuum state, which has its origin in the entanglement of the state between the left and the right Rindler wedges.

Complete Quantum Control of a Single Silicon-Vacancy Center in a Diamond Nanopillar

NASA Astrophysics Data System (ADS)

Zhang, Jingyuan Linda; Lagoudakis, Konstantinos G.; Tzeng, Yan-Kai; Dory, Constantin; Radulaski, Marina; Kelaita, Yousif; Shen, Zhi-Xun; Melosh, Nicholas A.; Chu, Steven; Vuckovic, Jelena

Coherent quantum control of a quantum bit (qubit) is an important step towards its use in a quantum network. SiV- center in diamond offers excellent physical qualities such as low inhomogeneous broadening, fast photon emission, and a large Debye-Waller factor, while the fast spin manipulation and techniques to extend the spin coherence time are under active investigation. Here, we demonstrate full coherent control over the state of a single SiV- center in a diamond nanopillar using ultrafast optical pulses. The high quality of the chemical vapor deposition grown SiV- centers allows us to coherently manipulate and quasi-resonantly read out the state of the single SiV- center. Moreover, the SiV- centers being coherently controlled are integrated into diamond nanopillar arrays in a site-controlled, individually addressable manner with high yield, low strain, and high spectral stability, which paves the way for scalable on chip optically accessible quantum system in a quantum photonic network. Financial support is provided by the DOE Office of Basic Energy Sciences, Division of Materials Sciences through Stanford Institute for Materials and Energy Sciences (SIMES) under contract DE-AC02-76SF00515.

Darwinism in quantum systems?

NASA Astrophysics Data System (ADS)

Iqbal, A.; Toor, A. H.

2002-03-01

We investigate the role of quantum mechanical effects in the central stability concept of evolutionary game theory, i.e., an evolutionarily stable strategy (ESS). Using two and three-player symmetric quantum games we show how the presence of quantum phenomenon of entanglement can be crucial to decide the course of evolutionary dynamics in a population of interacting individuals.

Effect of Coulomb interaction on chemical potential of metal film

NASA Astrophysics Data System (ADS)

Kostrobij, P. P.; Markovych, B. M.

2018-07-01

The chemical potential of a metal film within the jellium model taking into account the Coulomb interaction between electrons is calculated. The surface potential is modelled as the infinite rectangular potential well. The behaviour of the chemical potential as a function of the film thickness is studied, the quantum size effect for this quantity is analysed. It is shown that taking into account the Coulomb interaction leads to a significant decrease of the chemical potential and to an enhancement of the quantum size effect.

Facile synthetic method for pristine graphene quantum dots and graphene oxide quantum dots: origin of blue and green luminescence.

PubMed

Liu, Fei; Jang, Min-Ho; Ha, Hyun Dong; Kim, Je-Hyung; Cho, Yong-Hoon; Seo, Tae Seok

2013-07-19

Pristine graphene quantum dots and graphene oxide quantum dots are synthesized by chemical exfoliation from the graphite nanoparticles with high uniformity in terms of shape (circle), size (less than 4 nm), and thickness (monolayer). The origin of the blue and green photoluminescence of GQDs and GOQDs is attributed to intrinsic and extrinsic energy states, respectively. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vibrational spectroscopic studies of Isoleucine by quantum chemical calculations.

PubMed

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

2014-04-24

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

Effect analysis of quantum chemical descriptors and substituent characteristics on Henry's law constants of polybrominated diphenyl ethers at different temperatures.

PubMed

Long, Jiang; Youli, Qiu; Yu, Li

2017-11-01

Twelve substituent descriptors, 17 quantum chemical descriptors and 1/T were selected to establish a quantitative structure-property relationship (QSPR) model of Henry's law constants for 7 polybrominated diphenyl ethers (PBDEs) at five different temperatures. Then, the lgH of 202 congeners at different temperatures were predicted. The variation rule and regulating mechanism of lgH was studied from the perspectives of both quantum chemical descriptors and substituent characteristics. The R 2 for modeling and testing sets of the final QSPR model are 0.977 and 0.979, respectively, thus indicating good fitness and predictive ability for Henry' law constants of PBDEs at different temperatures. The favorable hydrogen binding sites are the 5,5',6,6'-positions for high substituent congeners and the O atom of the ether bond for low substituent congeners, which affects the interaction between PBDEs and water molecules. lgH is negatively and linearly correlated with 1/T, and the variation trends of lgH with temperature are primarily regulated by individual substituent characteristics, wherein: the more substituents involved, the smaller the lgH. The significant sequence for the main effect of substituent positions is para>meta>ortho, where the ortho-positions are mainly involved in second-order interaction effect (64.01%). Having two substituents in the same ring also provides a significant effect, with 81.36% of second-order interaction effects, particularly where there is an adjacent distribution (55.02%). Copyright © 2017 Elsevier Inc. All rights reserved.

Quantum fluctuations of a fullerene cage modulate its internal magnetic environment.

PubMed

Kawatsu, Tsutomu; Tachikawa, Masanori

2018-01-17

To investigate the effect of quantum fluctuations on the magnetic environment inside a C 60 fullerene cage, we have calculated the nuclear magnetic shielding constant of protons in H 2 @C 60 and HD@C 60 systems by on-the-fly ab initio path integral simulation, including both thermal and nuclear quantum effects. The most dominant upfield from an isolated hydrogen molecule occurs due to the diamagnetic current of the C 60 cage, which is partly cancelled by the paramagnetic current, where the paramagnetic contribution is enlarged by the zero-point vibrational fluctuation of the C 60 carbon backbone structure via a widely distributed HOMO-LUMO gap. This quantum modulation mechanism of the nuclear magnetic shielding constant is newly proposed. Because this quantum effect is independent of the difference between H 2 and HD, the H 2 /HD isotope shift occurs in spite of the C 60 cage. The nuclear magnetic constants computed for H 2 @C 60 and HD@C 60 are 32.047 and 32.081 ppm, respectively, which are in reasonable agreement with the corresponding values of 32.19 and 32.23 ppm estimated from the experimental values of the chemical shifts.

Investigating the applicability of activity-based quantum mechanics in a few high school physics classrooms

NASA Astrophysics Data System (ADS)

Escalada, Lawrence Todd

Quantum physics is not traditionally introduced in high school physics courses because of the level of abstraction and mathematical formalism associated with the subject. As part of the Visual Quantum Mechanics project, activity-based instructional units have been developed that introduce quantum principles to students who have limited backgrounds in physics and mathematics. This study investigates the applicability of one unit, Solids & Light, that introduces quantum principles within the context of learning about light emitting diodes. An observation protocol, attitude surveys, and questionnaires were used to examine the implementation of materials and student-teacher interactions in various secondary physics classrooms. Aspects of Solids & Light including the use of hands-on activities, interactive computer programs, inexpensive materials, and the focus on conceptual understanding were very applicable in the various physics classrooms observed. Both teachers and students gave these instructional strategies favorable ratings in motivating students to make observations and to learn. These ratings were not significantly affected by gender or students, attitudes towards physics or computers. Solid's & Light was applicable in terms of content and teaching style for some teachers. However, a mismatch of teaching styles between some instructors and the unit posed some problems in determining applicability. Observations indicated that some instructors were not able to utilize the exploratory instructional strategy of Solid's & Light. Thus, Solids & Light must include additional support necessary to make the instructor comfortable with the subject matter and pedagogical style. With these revisions, Solids & Light, will have all the key components to make its implementation in a high school physics classroom a successful one.

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

ERIC Educational Resources Information Center

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);…

Simulation of n-qubit quantum systems. III. Quantum operations

NASA Astrophysics Data System (ADS)

Radtke, T.; Fritzsche, S.

2007-05-01

During the last decade, several quantum information protocols, such as quantum key distribution, teleportation or quantum computation, have attracted a lot of interest. Despite the recent success and research efforts in quantum information processing, however, we are just at the beginning of understanding the role of entanglement and the behavior of quantum systems in noisy environments, i.e. for nonideal implementations. Therefore, in order to facilitate the investigation of entanglement and decoherence in n-qubit quantum registers, here we present a revised version of the FEYNMAN program for working with quantum operations and their associated (Jamiołkowski) dual states. Based on the implementation of several popular decoherence models, we provide tools especially for the quantitative analysis of quantum operations. Apart from the implementation of different noise models, the current program extension may help investigate the fragility of many quantum states, one of the main obstacles in realizing quantum information protocols today. Program summaryTitle of program: Feynman Catalogue identifier: ADWE_v3_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v3_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: None Operating systems: Any system that supports MAPLE; tested under Microsoft Windows XP, SuSe Linux 10 Program language used:MAPLE 10 Typical time and memory requirements: Most commands that act upon quantum registers with five or less qubits take ⩽10 seconds of processor time (on a Pentium 4 processor with ⩾2 GHz or equivalent) and 5-20 MB of memory. Especially when working with symbolic expressions, however, the memory and time requirements critically depend on the number of qubits in the quantum registers, owing to the exponential dimension growth of the associated Hilbert space. For example, complex (symbolic) noise models (with several Kraus operators) for multi-qubit systems

[Bioinorganic chemical composition of the lens and methods of its investigation].

PubMed

Avetisov, S E; Novikov, I A; Pakhomova, N A; Motalov, V G

2018-01-01

Bioinorganic chemical composition of the lens of human and experimental animals (cows, dogs, rats, rabbits) have been analyzed in various studies. In most cases, the studies employed different methods to determine the gross (total) composition of chemical elements and their concentrations in the examined samples. Less frequently, they included an assessment of the distribution of chemical elements in the lens and correlation of their concentration with its morphological changes. Chemical elements from all groups (series) of the periodic classification system were discovered in the lens substance. Despite similar investigation methods, different authors obtained contradicting results on the chemical composition of the lens. This article presents data suggesting possible correlation between inorganic chemical elements in the lens substance with the development and formation of lenticular opacities. All currently employed methods are known to only analyze limited number of select chemical elements in the tissues and do not consider the whole range of elements that can be analyzed with existing technology; furthermore, the majority of studies are conducted on the animal model lens. Therefore, it is feasible to continue the development of the chemical microanalysis method by increasing the sensitivity of Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) with the purpose of assessing the gross chemical composition and distribution of the elements in the lens substance, as well as revealing possible correlation between element concentration and morphological changes in the lens.

Electronic and rovibrational quantum chemical analysis of C3P-: the next interstellar anion?

NASA Astrophysics Data System (ADS)

Fortenberry, Ryan C.; Lukemire, Joseph A.

2015-11-01

C3P- is analogous to the known interstellar anion C3N- with phosphorus replacing nitrogen in a simple step down the periodic table. In this work, it is shown that C3P- is likely to possess a dipole-bound excited state. It has been hypothesized and observationally supported that dipole-bound excited states are an avenue through which anions could be formed in the interstellar medium. Additionally, C3P- has a valence excited state that may lead to further stabilization of this molecule, and C3P- has a larger dipole moment than neutral C3P (˜6 D versus ˜4 D). As such, C3P- is probably a more detectable astromolecule than even its corresponding neutral radical. Highly accurate quantum chemical quartic force fields are also applied to C3P- and its singly 13C substituted isotopologues in order to provide structures, vibrational frequencies, and spectroscopic constants that may aid in its detection.

Are Cloned Quantum States Macroscopic?

NASA Astrophysics Data System (ADS)

Fröwis, F.; Dür, W.

2012-10-01

We study quantum states produced by optimal phase covariant quantum cloners. We argue that cloned quantum superpositions are not macroscopic superpositions in the spirit of Schrödinger’s cat, despite their large particle number. This is indicated by calculating several measures for macroscopic superpositions from the literature, as well as by investigating the distinguishability of the two superposed cloned states. The latter rapidly diminishes when considering imperfect detectors or noisy states and does not increase with the system size. In contrast, we find that cloned quantum states themselves are macroscopic, in the sense of both proposed measures and their usefulness in quantum metrology with an optimal scaling in system size. We investigate the applicability of cloned states for parameter estimation in the presence of different kinds of noise.

Using of Quantum Dots in Biology and Medicine.

PubMed

Pleskova, Svetlana; Mikheeva, Elza; Gornostaeva, Ekaterina

2018-01-01

Quantum dots are nanoparticles, which due to their unique physical and chemical (first of all optical) properties, are promising in biology and medicine. There are many ways for quantum dots synthesis, both in the form of nanoislands self-forming on the surfaces, which can be used as single-photon emitters in electronics for storing information, and in the form of colloidal quantum dots for diagnostic and therapeutic purposes in living systems. The paper describes the main methods of quantum dots synthesis and summarizes medical and biological ways of their use. The main emphasis is laid on the ways of quantum dots surface modification. Influence of the size and form of nanoparticles, charge on the surfaces of quantum dots, and cover type on the efficiency of internalization by cells and cell compartments is shown. The main mechanisms of penetration are considered.

Autonomy, explanation, and theoretical values: physicists and chemists on molecular quantum mechanics.

PubMed

Hendry, Robin Findlay

2003-05-01

The emergence of quantum chemistry in the early twentieth century was an international as well as an interdisciplinary affair, involving dialogue between physicists and chemists in Germany, the United States, and Britain. Historians of science have recently documented both the causes and effects of this internationalism and interdisciplinarity. Chemists and physicists involved in the development of quantum chemistry in its first few decades tended to argue for opposing views on acceptable standards of explanation in their field, although the debate did not divide along disciplinary lines. The purpose of this paper is to investigate these different positions, through the methodological reflections of John Clarke Slater, Linus Pauling, and Charles Coulson. Slater tended to argue for quantum-mechanical rigor and the application of fundamental principles as the values guiding models of molecular bonding. Although they were on different sides of the debate between the valence-bond and molecular-orbital approaches, Pauling and Coulson both emphasized the recovery of traditional chemical explanations and systematic explanatory power within chemistry.

Quantum Game of Life

NASA Astrophysics Data System (ADS)

Glick, Aaron; Carr, Lincoln; Calarco, Tommaso; Montangero, Simone

2014-03-01

In order to investigate the emergence of complexity in quantum systems, we present a quantum game of life, inspired by Conway's classic game of life. Through Matrix Product State (MPS) calculations, we simulate the evolution of quantum systems, dictated by a Hamiltonian that defines the rules of our quantum game. We analyze the system through a number of measures which elicit the emergence of complexity in terms of spatial organization, system dynamics, and non-local mutual information within the network. Funded by NSF

Recent advances in quantum scattering calculations on polyatomic bimolecular reactions.

PubMed

Fu, Bina; Shan, Xiao; Zhang, Dong H; Clary, David C

2017-12-11

This review surveys quantum scattering calculations on chemical reactions of polyatomic molecules in the gas phase published in the last ten years. These calculations are useful because they provide highly accurate information on the dynamics of chemical reactions which can be compared in detail with experimental results. They also serve as quantum mechanical benchmarks for testing approximate theories which can more readily be applied to more complicated reactions. This review includes theories for calculating quantities such as rate constants which have many important scientific applications.

Hybrid quantum chemical studies for the methanol formation reaction assisted by the proton transfer mechanism in supercritical water: CH3Cl+nH2O-->CH3OH+HCl+(n-1)H2O

NASA Astrophysics Data System (ADS)

Hori, T.; Takahashi, H.; Nitta, T.

2003-10-01

The proton transfer along the chain of hydrogen bonds is involved in many chemical reactions in aqueous solution and known to play a decisive role. We have performed the hybrid quantum chemical simulations for the methanol formation reaction catalyzed by the proton transfer mechanism [CH3Cl+nH2O→CH3OH+HCl+(n-1)H2O, n=3] in supercritical water (SCW) to investigate the role of water solvent on the reaction. In the simulation, the electronic state of the chemically active solutes (CH3Cl+3H2O) has been determined quantum mechanically, while the static water solvent has been represented by a classical model. The activation free energy for the water-catalytic reaction in SCW has been found to be 9.6 kcal/mol, which is much lower than that in the gas phase (29.2 kcal/mol). The fractional charge analysis has revealed that the notable charge separation in the solute complex takes place at the transition state (TS) and the resulting huge dipole gives rise to the considerable stabilization of the TS as compared to the reactant. It has been shown that the reaction assisted by the proton transfer mechanism is energetically much favored than the ionic SN2 reaction (CH3Cl+OH-→CH3OH+Cl-, 18.8 kcal/mol). The present calculations suggest that the proton migrations through the chain of hydrogen bonds can be regarded as a probable candidate responsible for the anomalous reactivities observed in SCW.

Investigating and improving student understanding of quantum mechanics in the context of single photon interference

NASA Astrophysics Data System (ADS)

Marshman, Emily; Singh, Chandralekha

2017-06-01

Single photon experiments involving a Mach-Zehnder interferometer can illustrate the fundamental principles of quantum mechanics, e.g., the wave-particle duality of a single photon, single photon interference, and the probabilistic nature of quantum measurement involving single photons. These experiments explicitly make the connection between the abstract quantum theory and concrete laboratory settings and have the potential to help students develop a solid grasp of the foundational issues in quantum mechanics. Here we describe students' conceptual difficulties with these topics in the context of Mach-Zehnder interferometer experiments with single photons and how the difficulties found in written surveys and individual interviews were used as a guide in the development of a Quantum Interactive Learning Tutorial (QuILT). The QuILT uses an inquiry-based approach to learning and takes into account the conceptual difficulties found via research to help upper-level undergraduate and graduate students learn about foundational quantum mechanics concepts using the concrete quantum optics context. It strives to help students learn the basics of quantum mechanics in the context of single photon experiment, develop the ability to apply fundamental quantum principles to experimental situations in quantum optics, and explore the differences between classical and quantum ideas in a concrete context. We discuss the findings from in-class evaluations suggesting that the QuILT was effective in helping students learn these abstract concepts.

Investigation of spin-zero bosons in q-deformed relativistic quantum mechanics

NASA Astrophysics Data System (ADS)

Sobhani, H.; Chung, W. S.; Hassanabadi, H.

2018-04-01

In this article, Scattering states of Klein-Gordon equation for three scatter potentials of single and double Dirac delta and a potential well in the q-deformed formalism of relativistic quantum mechanics have been derived. At first, we discussed how q-deformed formalism can be constructed and used. Postulates of this q-deformed quantum mechanics are noted. Then scattering problems for spin-zero bosons are studied.

Chemical investigation of predator-deterred macroalgae from the Antarctic peninsula.

PubMed

Ankisetty, Sridevi; Nandiraju, Santhisree; Win, Hla; Park, Young Chul; Amsler, Charles D; McClintock, James B; Baker, Jill A; Diyabalanage, Thushara K; Pasaribu, Albert; Singh, Maya P; Maiese, William M; Walsh, Rosa D; Zaworotko, Michael J; Baker, Bill J

2004-08-01

Chemical investigation of five Antarctic macroalgae whose tissues and crude extracts displayed ecologically relevant feeding deterrence in field bioassays was performed. Eleven compounds were characterized from the three red algae studied, of which four (1-3 and 9) were previously unreported, and four compounds were found from two brown algae, two (12 and 14) of which are new natural products. Several of these pure compounds have been individually investigated in ecological and/or pharmacological bioassays.

Investigating Learners' Epistemological Framings of Quantum Mechanics

ERIC Educational Resources Information Center

Dini, Vesal

2017-01-01

Classical mechanics challenges students to use their intuitions and experiences as a basis for understanding, in effect to approach learning as "a refinement of everyday thinking'' (Einstein, 1936). Moving on to quantum mechanics (QM), students, like physicists, need to adjust this approach, in particular with respect to the roles that…

Room-temperature processing of CdSe quantum dots with tunable sizes

NASA Astrophysics Data System (ADS)

Joo, So-Yeong; Jeong, Da-Woon; Lee, Chan-Gi; Kim, Bum-Sung; Park, Hyun-Su; Kim, Woo-Byoung

2017-06-01

In this work, CdSe quantum dots (QDs) with tunable sizes have been fabricated via photo-induced chemical etching at room temperature, and the related reaction mechanism was investigated. The surface of QDs was oxidized by the holes generated through photon irradiation of oxygen species, and the obtained oxide layer was dissolved in an aqueous solution of 3-amino-1-propanol (APOL) with an APOL:H2O volume ratio of 5:1. The generated electrons promoted QD surface interactions with amino groups, which ultimately passivated surface defects. The absorption and photoluminescence emission peaks of the produced QDs were clearly blue-shifted about 26 nm with increasing time, and the resulting quantum yield for an 8 h etched sample was increased from 20% to 26%, as compared to the initial sample.

Network-Forming Nanoclusters in Binary As-S/Se Glasses: From Ab Initio Quantum Chemical Modeling to Experimental Evidences.

PubMed

Hyla, M

2017-12-01

Network-forming As 2 (S/Se) m nanoclusters are employed to recognize expected variations in a vicinity of some remarkable compositions in binary As-Se/S glassy systems accepted as signatures of optimally constrained intermediate topological phases in earlier temperature-modulated differential scanning calorimetry experiments. The ab initio quantum chemical calculations performed using the cation-interlinking network cluster approach show similar oscillating character in tendency to local chemical decomposition but obvious step-like behavior in preference to global phase separation on boundary chemical compounds (pure chalcogen and stoichiometric arsenic chalcogenides). The onsets of stability are defined for chalcogen-rich glasses, these being connected with As 2 Se 5 (Z = 2.29) and As 2 S 6 (Z = 2.25) nanoclusters for As-Se and As-S glasses, respectively. The physical aging effects result preferentially from global phase separation in As-S glass system due to high localization of covalent bonding and local demixing on neighboring As 2 Se m+1 and As 2 Se m-1 nanoclusters in As-Se system. These nanoclusters well explain the lower limits of reversibility windows in temperature-modulated differential scanning calorimetry, but they cannot be accepted as signatures of topological phase transitions in respect to the rigidity theory.

Detection of multiple chemicals based on external cavity quantum cascade laser spectroscopy

NASA Astrophysics Data System (ADS)

Sun, Juan; Ding, Junya; Liu, Ningwu; Yang, Guangxiang; Li, Jingsong

2018-02-01

A laser spectroscopy system based on a broadband tunable external cavity quantum cascade laser (ECQCL) and a mini quartz crystal tuning fork (QCTF) detector was developed for standoff detection of volatile organic compounds (VOCs). The self-established spectral analysis model based on multiple algorithms for quantitative and qualitative analysis of VOC components (i.e. ethanol and acetone) was detailedly investigated in both closed cell and open path configurations. A good agreement was obtained between the experimentally observed spectra and the standard reference spectra. For open path detection of VOCs, the sensor system was demonstrated at a distance of 30 m. The preliminary laboratory results show that standoff detection of VOCs at a distance of over 100 m is very promising.

Quantum phase slips: from condensed matter to ultracold quantum gases.

PubMed

D'Errico, C; Abbate, S Scaffidi; Modugno, G

2017-12-13

Quantum phase slips (QPS) are the primary excitations in one-dimensional superfluids and superconductors at low temperatures. They have been well characterized in most condensed-matter systems, and signatures of their existence have been recently observed in superfluids based on quantum gases too. In this review, we briefly summarize the main results obtained on the investigation of phase slips from superconductors to quantum gases. In particular, we focus our attention on recent experimental results of the dissipation in one-dimensional Bose superfluids flowing along a shallow periodic potential, which show signatures of QPS.This article is part of the themed issue 'Breakdown of ergodicity in quantum systems: from solids to synthetic matter'. © 2017 The Author(s).

Atomic-scale investigation of nuclear quantum effects of surface water: Experiments and theory

NASA Astrophysics Data System (ADS)

Guo, Jing; Li, Xin-Zheng; Peng, Jinbo; Wang, En-Ge; Jiang, Ying

2017-12-01

Quantum behaviors of protons in terms of tunneling and zero-point motion have significant effects on the macroscopic properties, structure, and dynamics of water even at room temperature or higher. In spite of tremendous theoretical and experimental efforts, accurate and quantitative description of the nuclear quantum effects (NQEs) is still challenging. The main difficulty lies in that the NQEs are extremely susceptible to the structural inhomogeneity and local environments, especially when interfacial systems are concerned. In this review article, we will highlight the recent advances of scanning tunneling microscopy and spectroscopy (STM/S), which allows the access to the quantum degree of freedom of protons both in real and energy space. In addition, we will also introduce recent development of ab initio path-integral molecular dynamics (PIMD) simulations at surfaces/interfaces, in which both the electrons and nuclei are treated as quantum particles in contrast to traditional ab initio molecular dynamics (MD). Then we will discuss how the combination of STM/S and PIMD are used to directly visualize the concerted quantum tunneling of protons within the water clusters and quantify the impact of zero-point motion on the strength of a single hydrogen bond (H bond) at a water/solid interface. Those results may open up the new possibility of exploring the exotic quantum states of light nuclei at surfaces, as well as the quantum coupling between the electrons and nuclei.

Quantum kernel applications in medicinal chemistry.

PubMed

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.

Investigation of narrow-band thermal emission from intersubband transitions in quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Zoysa, M.; Hakubi Center, Kyoto University, Yoshida, Kyoto 606-8501; Asano, T.

2015-09-14

We investigate thermal emission from n-doped GaAs/AlGaAs quantum wells (QWs). Emission peaks with Lorentzian shapes (linewidth 11∼19 meV) that reflect transitions between the first and second conduction subbands are observed in the mid-infrared range. It is demonstrated that the emission characteristics can be tuned by modifying the QW parameters. The peak emissivity is increased from 0.3 to 0.9 by modifying the doping density, and the peak wavelength is tuned from 6 to 10 μm by changing the well width. The obtained results are useful for the design of narrow-band thermal emitters.

Spectral gain measurements of quantum confined emitters, and design and fabrication of intersubband quantum box laser structures

NASA Astrophysics Data System (ADS)

Tsvid, Gene

Semiconductor laser active regions are commonly characterized by photo- and electro-luminescence (PL, EL) and cavity length analysis. However quantitative spectral information is not readily extracted from PL and EL data and comparison of different active region materials can be difficult. More quantifiable spectral information is contained in the optical gain spectra. This work reports on spectral gain studies, using multi-segmented interband devices, of InGaAs quantum well and quantum dot active regions grown by metalorganic chemical vapor deposition (MOCVD). Using the fundamental connection between gain and spontaneous emission spectra, the spontaneous radiative current and spontaneous radiative efficiency is evaluated for these active regions. The spectral gain and spontaneous radiative efficiency measurements of 980 nm emitting InGaAs quantum well (QW) material provides a benchmark comparison to previous results obtained on highly-strained, 1200 nm emitting InGaAs QW material. These studies provide insight into carrier recombination and the role of the current injection efficiency in InGaAs QW lasers. The spectral gain of self-assembled MOCVD grown InGaAs quantum dots (QD) active regions are also investigated, allowing for comparison to InGaAs QW material. The second part of my talk will cover intersubband-transition QW and quantum-box (QB) lasers. Quantum cascade (QC) lasers have emerged as compact and technologically important light sources in the mid-infrared (IR) and far-IR wavelength ranges infringing on the near-IR and terahertz spectral regions respectively. However, the overall power conversion efficiency, so-called wallplug efficiency, of the best QC lasers, emitting around 5 microns, is ˜9% in CW operation and very unlikely to exceed 15%. In order to dramatically improve the wallplug efficiency of mid-IR lasers (i.e., to about 50%), intersubband QB (IQB) lasers have been proposed. The basic idea, the optimal design and the progress towards the

Surface Traps in Colloidal Quantum Dots: A Combined Experimental and Theoretical Perspective

PubMed Central

2017-01-01

Surface traps are ubiquitous to nanoscopic semiconductor materials. Understanding their atomistic origin and manipulating them chemically have capital importance to design defect-free colloidal quantum dots and make a leap forward in the development of efficient optoelectronic devices. Recent advances in computing power established computational chemistry as a powerful tool to describe accurately complex chemical species and nowadays it became conceivable to model colloidal quantum dots with realistic sizes and shapes. In this Perspective, we combine the knowledge gathered in recent experimental findings with the computation of quantum dot electronic structures. We analyze three different systems: namely, CdSe, PbS, and CsPbI3 as benchmark semiconductor nanocrystals showing how different types of trap states can form at their surface. In addition, we suggest experimental healing of such traps according to their chemical origin and nanocrystal composition. PMID:28972763

Surface Traps in Colloidal Quantum Dots: A Combined Experimental and Theoretical Perspective.

PubMed

Giansante, Carlo; Infante, Ivan

2017-10-19

Surface traps are ubiquitous to nanoscopic semiconductor materials. Understanding their atomistic origin and manipulating them chemically have capital importance to design defect-free colloidal quantum dots and make a leap forward in the development of efficient optoelectronic devices. Recent advances in computing power established computational chemistry as a powerful tool to describe accurately complex chemical species and nowadays it became conceivable to model colloidal quantum dots with realistic sizes and shapes. In this Perspective, we combine the knowledge gathered in recent experimental findings with the computation of quantum dot electronic structures. We analyze three different systems: namely, CdSe, PbS, and CsPbI 3 as benchmark semiconductor nanocrystals showing how different types of trap states can form at their surface. In addition, we suggest experimental healing of such traps according to their chemical origin and nanocrystal composition.

Photoisomerization in bacteriorhodopsin studied by FTIR, linear dichroism and photoselection experiments combined with quantum chemical theoretical analysis

NASA Astrophysics Data System (ADS)

Fahmy, K.; Siebert, F.; Großjean, M. F.; Tavan, P.

1989-12-01

Orientations of IR transition moments of the retinal chromophore of bacteriorhodopsin (BR) and of the apo-protein are investigated by FTIR linear dichroism and photoselection measurements. Low temperature difference spectra for the photoinduced transitions of BR to its photocycle intermediates K and L are evaluated using improved methods. Quantum chemical calculations of directions of IR and electronic transition moments of model chromophores are employed to analyze corresponding observations. The chromophore of light-adapted BR 568 is shown to exhibit small (15-30°) twists around the CC single bonds of retinals polyene chain but no large overall helicity (⩽15°). The average retinal plane is demonstrated to form an angle of 90±20° with the plane of the purple membrane. The C 9C 10 double bond of retinal is found approximately parallel to the plane of the membrane. Upon photoisomerization the orientation of the chromophore moiety from C 1 to C 13 is estimated to be largely conserved. The single bond twists of the chromophore in L are shown to be larger than those in BR 568. This result is in agreement with the previous prediction of increased single bond twists in L, which can cause a p K decrease of the chromophore and, thereby, enforce its deprotonation in the L→M transition [Schulten and Tavan, Nature, 272 (1978) 85].

One-way unlocalizable quantum discord

NASA Astrophysics Data System (ADS)

Xi, Zhengjun; Fan, Heng; Li, Yongming

2012-05-01

In this paper, we present the concept of the one-way unlocalizable quantum discord and investigate its properties. We provide a polygamy inequality for it in a tripartite pure quantum system of arbitrary dimension. Several tradeoff relations between the one-way unlocalizable quantum discord and other correlations are given. If the von Neumann measurement is made on a part of the system, we give two expressions of the one-way unlocalizable quantum discord in terms of partial distillable entanglement and quantum disturbance. Finally, we also provide a lower bound for bipartite shareability of quantum correlation beyond entanglement in a tripartite system.

Investigations of a voltage-biased microwave cavity for quantum measurements of nanomechanical resonators

NASA Astrophysics Data System (ADS)

Rouxinol, Francisco; Hao, Hugo; Lahaye, Matt

2015-03-01

Quantum electromechanical systems incorporating superconducting qubits have received extensive interest in recent years due to their promising prospects for studying fundamental topics of quantum mechanics such as quantum measurement, entanglement and decoherence in new macroscopic limits, also for their potential as elements in technological applications in quantum information network and weak force detector, to name a few. In this presentation we will discuss ours efforts toward to devise an electromechanical circuit to strongly couple a nanomechanical resonator to a superconductor qubit, where a high voltage dc-bias is required, to study quantum behavior of a mechanical resonator. Preliminary results of our latest generation of devices integrating a superconductor qubit into a high-Q voltage biased microwave cavities are presented. Developments in the circuit design to couple a mechanical resonator to a qubit in the high-Q voltage bias CPW cavity is discussed as well prospects of achieving single-phonon measurement resolution. National Science Foundation under Grant No. DMR-1056423 and Grant No. DMR-1312421.

Non-destructive state detection for quantum logic spectroscopy of molecular ions.

PubMed

Wolf, Fabian; Wan, Yong; Heip, Jan C; Gebert, Florian; Shi, Chunyan; Schmidt, Piet O

2016-02-25

Precision laser spectroscopy of cold and trapped molecular ions is a powerful tool in fundamental physics--used, for example, in determining fundamental constants, testing for their possible variation in the laboratory, and searching for a possible electric dipole moment of the electron. However, the absence of cycling transitions in molecules poses a challenge for direct laser cooling of the ions, and for controlling and detecting their quantum states. Previously used state-detection techniques based on photodissociation or chemical reactions are destructive and therefore inefficient, restricting the achievable resolution in laser spectroscopy. Here, we experimentally demonstrate non-destructive detection of the quantum state of a single trapped molecular ion through its strong Coulomb coupling to a well controlled, co-trapped atomic ion. An algorithm based on a state-dependent optical dipole force changes the internal state of the atom according to the internal state of the molecule. We show that individual quantum states in the molecular ion can be distinguished by the strength of their coupling to the optical dipole force. We also observe quantum jumps (induced by black-body radiation) between rotational states of a single molecular ion. Using the detuning dependence of the state-detection signal, we implement a variant of quantum logic spectroscopy of a molecular resonance. Our state-detection technique is relevant to a wide range of molecular ions, and could be applied to state-controlled quantum chemistry and to spectroscopic investigations of molecules that serve as probes for interstellar clouds.

Scrambling of quantum information in quantum many-body systems

NASA Astrophysics Data System (ADS)

Iyoda, Eiki; Sagawa, Takahiro

2018-04-01

We systematically investigate scrambling (or delocalizing) processes of quantum information encoded in quantum many-body systems by using numerical exact diagonalization. As a measure of scrambling, we adopt the tripartite mutual information (TMI) that becomes negative when quantum information is delocalized. We clarify that scrambling is an independent property of the integrability of Hamiltonians; TMI can be negative or positive for both integrable and nonintegrable systems. This implies that scrambling is a separate concept from conventional quantum chaos characterized by nonintegrability. Specifically, we argue that there are a few exceptional initial states that do not exhibit scrambling, and show that such exceptional initial states have small effective dimensions. Furthermore, we calculate TMI in the Sachdev-Ye-Kitaev (SYK) model, a fermionic toy model of quantum gravity. We find that disorder does not make scrambling slower but makes it smoother in the SYK model, in contrast to many-body localization in spin chains.

Quantum Transduction with Adaptive Control

NASA Astrophysics Data System (ADS)

Zhang, Mengzhen; Zou, Chang-Ling; Jiang, Liang

2018-01-01

Quantum transducers play a crucial role in hybrid quantum networks. A good quantum transducer can faithfully convert quantum signals from one mode to another with minimum decoherence. Most investigations of quantum transduction are based on the protocol of direct mode conversion. However, the direct protocol requires the matching condition, which in practice is not always feasible. Here we propose an adaptive protocol for quantum transducers, which can convert quantum signals without requiring the matching condition. The adaptive protocol only consists of Gaussian operations, feasible in various physical platforms. Moreover, we show that the adaptive protocol can be robust against imperfections associated with finite squeezing, thermal noise, and homodyne detection, and it can be implemented to realize quantum state transfer between microwave and optical modes.

Quantum Transduction with Adaptive Control.

PubMed

Zhang, Mengzhen; Zou, Chang-Ling; Jiang, Liang

2018-01-12

Quantum transducers play a crucial role in hybrid quantum networks. A good quantum transducer can faithfully convert quantum signals from one mode to another with minimum decoherence. Most investigations of quantum transduction are based on the protocol of direct mode conversion. However, the direct protocol requires the matching condition, which in practice is not always feasible. Here we propose an adaptive protocol for quantum transducers, which can convert quantum signals without requiring the matching condition. The adaptive protocol only consists of Gaussian operations, feasible in various physical platforms. Moreover, we show that the adaptive protocol can be robust against imperfections associated with finite squeezing, thermal noise, and homodyne detection, and it can be implemented to realize quantum state transfer between microwave and optical modes.

Conclusive identification of quantum channels via monogamy of quantum correlations

NASA Astrophysics Data System (ADS)

Kumar, Asutosh; Singha Roy, Sudipto; Pal, Amit Kumar; Prabhu, R.; Sen(De), Aditi; Sen, Ujjwal

2016-10-01

We investigate the action of global noise and local channels, namely, amplitude-damping, phase-damping, and depolarizing channels, on monogamy of quantum correlations, such as negativity and quantum discord, in three-qubit systems. We discuss the monotonic and non-monotonic variation, and robustness of the monogamy scores. By using monogamy scores, we propose a two-step protocol to conclusively identify the noise applied to the quantum system, by using generalized Greenberger-Horne-Zeilinger and generalized W states as resource states. We discuss a possible generalization of the results to higher number of parties.

Stability-Indicating TLC-Densitometric Assay for Methyltestosterone and Quantum Chemical Calculations.

PubMed

Musharraf, Syed Ghulam; Ul Arfeen, Qamar; Ul Haq, Faraz; Khatoon, Aliya; Azher Ali, Rahat

2017-10-01

Methyltestosterone is a synthetic testosterone derivative commonly used for the treatment of testosterone deficiency in males and one the anabolic steroids whose use is banned by World Anti-Doping Agency (WADA). This study presents a simple, cost-effective and rapid stability-indicating assay for densitometric quantification of methyltestosterone in pharmaceutical formulation. The developed method employed pre-coated TLC plates with mobile phase hexane:acetone (6.5:3.5 v/v). Limit of detection and limit of quantitation were found to be 2.06 and 6.24 ng/spot, respectively. Stress degradation study of methyltestosterone was conducted by applying various stress conditions such as hydrolysis under acidic, basic and neutral conditions, heating in anhydrous conditions and exposure to light. Methyltestosterone was found to be susceptible to photodegradation, acidic and basic hydrolysis. Degraded products were well resolved with significantly different Rf values. Acid degraded product was identified as 17,17-dimethyl-18-norandrosta-4,13(14)-dien-3-one through spectroscopic methods. The reactivity of methyltestosterone under applied stress conditions was also explained by quantum chemical calculations. The developed method is found to be repeatable, selective and accurate for quantification of methyltestosterone and can be employed for routine analysis. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

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

PubMed

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

2017-05-05

Dielectric studies using Time Domain Reflectometry method has been carried out on the binary solution of Ethyl acetate (EA) with Chlorobenzene (CBZ) over the entire composition range. Spectroscopic (FTIR and 13 C NMR) signatures of neat EA, CBZ and their equimolar binary solution have also been recorded. The results of the spectroscopic studies favour the presence of (CBZ) CH⋯OC (EA), (EA) methylene CH⋯π electrons (CBZ) and (EA) methyl CH⋯Cl (CBZ) contacts which have been validated using quantum chemical calculations. Dimerization of CBZ has been identified. Presence of β-clusters has been identified in all the solutions. Although EA and CBZ molecules have nearly equal molar volumes, CBZ molecules experience larger hindrance for the rotation than EA molecules. Very small excess dielectric constant (ε E ) values may be correlated with weak heteromolecular forces and/or closed heteromolecular association. Copyright © 2017 Elsevier B.V. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2017-05-01

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

Quantum Simulation and Quantum Sensing with Ultracold Strontium

DTIC Science & Technology

2015-09-18

quantum Kapitza pendulum , a novel Floquet system which we are investigating using modulated optical lattices. We have proposed and are developing...another goal of our AFOSR YIP project. To this end, we have developed the first theoretical treatment of a lattice-based quantum Kapitza pendulum . We have...classical single-particle analogue of this phase occurs in a rigid pendulum with an oscillating support (known as a Kapitza pendu- lum [9]). To prepare for

Nonvolatile Memories Using Quantum Dot (QD) Floating Gates Assembled on II-VI Tunnel Insulators

NASA Astrophysics Data System (ADS)

Suarez, E.; Gogna, M.; Al-Amoody, F.; Karmakar, S.; Ayers, J.; Heller, E.; Jain, F.

2010-07-01

This paper presents preliminary data on quantum dot gate nonvolatile memories using nearly lattice-matched ZnS/Zn0.95Mg0.05S/ZnS tunnel insulators. The GeO x -cladded Ge and SiO x -cladded Si quantum dots (QDs) are self-assembled site-specifically on the II-VI insulator grown epitaxially over the Si channel (formed between the source and drain region). The pseudomorphic II-VI stack serves both as a tunnel insulator and a high- κ dielectric. The effect of Mg incorporation in ZnMgS is also investigated. For the control gate insulator, we have used Si3N4 and SiO2 layers grown by plasma- enhanced chemical vapor deposition.

Interwell coupling effect in Si/SiGe quantum wells grown by ultra high vacuum chemical vapor deposition

PubMed Central

Wang, Rui; Lu, Fen; Fan, Wei Jun; Liu, Chong Yang; Loh, Ter-Hoe; Nguyen, Hoai Son; Narayanan, Balasubramanian

2007-01-01

Si/Si0.66Ge0.34coupled quantum well (CQW) structures with different barrier thickness of 40, 4 and 2 nm were grown on Si substrates using an ultra high vacuum chemical vapor deposition (UHV-CVD) system. The samples were characterized using high resolution x-ray diffraction (HRXRD), cross-sectional transmission electron microscopy (XTEM) and photoluminescence (PL) spectroscopy. Blue shift in PL peak energy due to interwell coupling was observed in the CQWs following increase in the Si barrier thickness. The Si/SiGe heterostructure growth process and theoretical band structure model was validated by comparing the energy of the no-phonon peak calculated by the 6 + 2-bandk·pmethod with experimental PL data. Close agreement between theoretical calculations and experimental data was obtained.

Thermal Quantum Discord and Super Quantum Discord Teleportation Via a Two-Qubit Spin-Squeezing Model

NASA Astrophysics Data System (ADS)

Ahadpour, S.; Mirmasoudi, F.

2018-04-01

We study thermal quantum correlations (quantum discord and super quantum discord) in a two-spin model in an external magnetic field and obtain relations between them and entanglement. We study their dependence on the magnetic field, the strength of the spin squeezing, and the temperature in detail. One interesting result is that when the entanglement suddenly disappears, quantum correlations still survive. We study thermal quantum teleportation in the framework of this model. The main goal is investigating the possibility of increasing the thermal quantum correlations of a teleported state in the presence of a magnetic field, strength of the spin squeezing, and temperature. We note that teleportation of quantum discord and super quantum discord can be realized over a larger temperature range than teleportation of entanglement. Our results show that quantum discord and super quantum discord can be a suitable measure for controlling quantum teleportation with fidelity. Moreover, the presence of entangled states is unnecessary for the exchange of quantum information.

How to compute isomerization energies of organic molecules with quantum chemical methods.

PubMed

Grimme, Stefan; Steinmetz, Marc; Korth, Martin

2007-03-16

The reaction energies for 34 typical organic isomerizations including oxygen and nitrogen heteroatoms are investigated with modern quantum chemical methods that have the perspective of also being applicable to large systems. The experimental reaction enthalpies are corrected for vibrational and thermal effects, and the thus derived "experimental" reaction energies are compared to corresponding theoretical data. A series of standard AO basis sets in combination with second-order perturbation theory (MP2, SCS-MP2), conventional density functionals (e.g., PBE, TPSS, B3-LYP, MPW1K, BMK), and new perturbative functionals (B2-PLYP, mPW2-PLYP) are tested. In three cases, obvious errors of the experimental values could be detected, and accurate coupled-cluster [CCSD(T)] reference values have been used instead. It is found that only triple-zeta quality AO basis sets provide results close enough to the basis set limit and that sets like the popular 6-31G(d) should be avoided in accurate work. Augmentation of small basis sets with diffuse functions has a notable effect in B3-LYP calculations that is attributed to intramolecular basis set superposition error and covers basic deficiencies of the functional. The new methods based on perturbation theory (SCS-MP2, X2-PLYP) are found to be clearly superior to many other approaches; that is, they provide mean absolute deviations of less than 1.2 kcal mol-1 and only a few (<10%) outliers. The best performance in the group of conventional functionals is found for the highly parametrized BMK hybrid meta-GGA. Contrary to accepted opinion, hybrid density functionals offer no real advantage over simple GGAs. For reasonably large AO basis sets, results of poor quality are obtained with the popular B3-LYP functional that cannot be recommended for thermochemical applications in organic chemistry. The results of this study are complementary to often used benchmarks based on atomization energies and should guide chemists in their search for

Computing protein infrared spectroscopy with quantum chemistry.

PubMed

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.

Simulation of quantum dynamics based on the quantum stochastic differential equation.

PubMed

Li, Ming

2013-01-01

The quantum stochastic differential equation derived from the Lindblad form quantum master equation is investigated. The general formulation in terms of environment operators representing the quantum state diffusion is given. The numerical simulation algorithm of stochastic process of direct photodetection of a driven two-level system for the predictions of the dynamical behavior is proposed. The effectiveness and superiority of the algorithm are verified by the performance analysis of the accuracy and the computational cost in comparison with the classical Runge-Kutta algorithm.

Hierarchical Equation of Motion Investigation of Decoherence and Relaxation Dynamics in Nonequilibrium Transport through Interacting Quantum Dots

NASA Astrophysics Data System (ADS)

Hartle, Rainer; Cohen, Guy; Reichman, David R.; Millis, Andrew J.

2014-03-01

A recently developed hierarchical quantum master equation approach is used to investigate nonequilibrium electron transport through an interacting double quantum dot system in the regime where the inter-dot coupling is weaker than the coupling to the electrodes. The corresponding eigenstates provide tunneling paths that may interfere constructively or destructively, depending on the energy of the tunneling electrons. Electron-electron interactions are shown to quench these interference effects in bias-voltage dependent ways, leading, in particular, to negative differential resistance, population inversion and an enhanced broadening of resonances in the respective transport characteristics. Relaxation times are found to be very long, and to be correlated with very slow dynamics of the inter-dot coherences (off diagonal density matrix elements). The ability of the hierarchical quantum master equation approach to access very long time scales is crucial for the study of this physics. This work is supported by the National Science Foundation (NSF DMR-1006282 and NSF CHE-1213247), the Yad Hanadiv-Rothschild Foundation (via a Rothschild Fellowship for GC) and the Alexander von Humboldt Foundation (via a Feodor Lynen fellowship for RH).

Nano Superconducting Quantum Interference device: A powerful tool for nanoscale investigations

NASA Astrophysics Data System (ADS)

Granata, Carmine; Vettoliere, Antonio

2016-02-01

The magnetic sensing at nanoscale level is a promising and interesting research topic of nanoscience. Indeed, magnetic imaging is a powerful tool for probing biological, chemical and physical systems. The study of small spin cluster, like magnetic molecules and nanoparticles, single electron, cold atom clouds, is one of the most stimulating challenges of applied and basic research of the next years. In particular, the magnetic nanoparticle investigation plays a fundamental role for the modern material science and its relative technological applications like ferrofluids, magnetic refrigeration and biomedical applications, including drug delivery, hyper-thermia cancer treatment and magnetic resonance imaging contrast-agent. Actually, one of the most ambitious goals of the high sensitivity magnetometry is the detection of elementary magnetic moment or spin. In this framework, several efforts have been devoted to the development of a high sensitivity magnetic nanosensor pushing sensing capability to the individual spin level. Among the different magnetic sensors, Superconducting QUantum Interference Devices (SQUIDs) exhibit an ultra high sensitivity and are widely employed in numerous applications. Basically, a SQUID consists of a superconducting ring (sensitive area) interrupted by two Josephson junctions. In the recent years, it has been proved that the magnetic response of nano-objects can be effectively measured by using a SQUID with a very small sensitive area (nanoSQUID). In fact, the sensor noise, expressed in terms of the elementary magnetic moment (spin or Bohr magneton), is linearly dependent on the SQUID loop side length. For this reason, SQUIDs have been progressively miniaturized in order to improve the sensitivity up to few spin per unit of bandwidth. With respect to other techniques, nanoSQUIDs offer the advantage of direct measurement of magnetization changes in small spin systems. In this review, we focus on nanoSQUIDs and its applications. In

Investigation on dielectrophoretic assembly of nanostructures and its application on chemical sensors

NASA Astrophysics Data System (ADS)

Tao, Quan

Because of their extraordinary characteristics such as quantum confinement and large surface-tovolume ratio, semiconducting nanostructures such as nanowires or nanotubes hold great potential in sensing chemical vapors. Nanowire or nanotube based gas sensors usually possess appealing advantages such as high sensitivity, high stability, fast recovery time, and electrically controllable properties. To better predict the composition and concentration of target gas, nanostructures made from heterogeneous materials are employed to provide more predictors. In recent years, nanowires and nanotubes can be synthesized routinely through different methods. The techniques of fabricating nanowire or nanotube based sensor arrays, however, encounter obstacles and deserve further investigations. Dielectrophoresis (DEP), which refers to the motion of submicron particles inside a non-uniform electric field, has long been recognized as a nondestructive, easily implementable, and efficient approach to manipulate nanostructures onto electronic circuitries. However, due to our limited understandings, devices fabricated through DEP often end up with unpredictable number of arbitrarily aligned nanostructures. In this study, we first optimize the classical DEP formulas such that it can be applied to a more general case that a nanostructure is subjected to a non-uniform electric field with arbitrary orientation. A comprehensive model is then constructed to investigate the trajectory and alignment of DEP assembled nanostructures, which can be verified by experimental observations. The simulation results assist us to fabricate a gas sensor array with zinc oxide (ZnO) nanowires and carbon nanotubes (CNTs). It is then demonstrated that the device can well sense ammonia (NH3) at room temperature, which circumvents the usually required high temperature condition for nanowire based gas sensor application. An effective approach to recover the device using DC biases to locally heat up the