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https://www.readbyqxmd.com/read/28437735/detective-quantum-efficiency-dqe-in-pet-scanners-a-simulation-study
#1
George E Karpetas, Christos M Michail, George P Fountos, Nektarios I Kalyvas, Ioannis G Valais, Ioannis S Kandarakis, George S Panayiotakis
The aim of the present study is to introduce the detective quantum efficiency (DQE) for the image quality assessment of positron emission tomography (PET) scanners. For this purpose, a thin layer chromatography (TLC) plane source was simulated using a previously validated, scanner and source geometry, Monte Carlo (MC) model. The model was developed with the Geant4 application for tomographic emission (GATE) MC package and reconstructed images obtained with the software for tomographic image reconstruction (STIR), with cluster computing...
April 12, 2017: Applied Radiation and Isotopes
https://www.readbyqxmd.com/read/28437618/state-of-the-art-calculations-of-sublimation-enthalpies-for-selected-molecular-crystals-and-their-computational-uncertainty
#2
Ctirad Červinka, Michal Fulem
A computational methodology for calculation of sublimation enthalpies of molecular crystals from first principles is developed and validated by comparison to critically evaluated literature experimental data. Temperature dependent sublimation enthalpies for a set of selected 22 molecular crystals in their low-temperature phases are calculated. The computational methodology consists in several building blocks based on high level electronic structure methods of quantum chemistry and statistical thermodynamics...
April 24, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28437115/development-and-implementation-of-advanced-fitting-methods-for-the-calculation-of-accurate-molecular-structures
#3
Marco Mendolicchio, Emanuele Penocchio, Daniele Licari, Nicola Tasinato, Vincenzo Barone
The determination of accurate equilibrium molecular structures plays a fundamental role for understanding many physical-chemical properties of molecules, ranging from the precise evaluation of the electronic structure to the analysis of dynamical and environmental effects in tuning their overall behavior. For this purpose the so-called semi-experimental approach, based on a non-linear least-squares fit of the moments of inertia associated to a set of available isotopologues, allows one to obtain very accurate results, without the unfavorable computational cost characterizing high-level quantum chemical methods...
April 24, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28437102/insights-into-the-complex-photophysics-and-photochemistry-of-the-simplest-nitroaromatic-compound-a-caspt2-casscf-study-on-nitrobenzene
#4
Angelo Giussani, Graham A Worth
Nitrobenzene is the simplest nitroaromatic compound and yet is characterized by a challenging and rich photophysics and photochemistry. In the present contribution the main decay paths undertaken by the system after UV absorption from both the brightest 1(La*) and the lowest 1(nA*) singlet excited states have been characterized by means of CASPT2//CASSCF computations. The obtained results match with the main photophysical properties experimentally reported: the lack of fluorescence and phosphorescence emission is justified by the presence of accessible conical intersections and intersystem crossing regions between respectively the 1(nA*) and 3(nA*) states with the ground state, while the high triplet quantum yield is attributable to the strong coupling between the 1(nA*) and 3(O*) states along the main decay path of the former...
April 24, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28437096/importance-of-mm-polarization-in-qm-mm-studies-of-enzymatic-reactions-assessment-of-the-qm-mm-drude-oscillator-model
#5
Abir Ganguly, Eliot Boulanger, Walter Thiel
For accurate quantum mechanics/molecular mechanics (QM/MM) studies of enzymatic reactions, it is desirable to include MM polarization, for example by using the Drude oscillator (DO) model. For a long time, such studies were hampered by the lack of well-tested polarizable force fields for proteins. Following up on a recent preliminary QM/MM-DO assessment (J. Chem. THEORY: Comput. 2014, 10, 1795-1809) we now report a comprehensive investigation of the effects of MM polarization on two enzymatic reactions, namely the Claisen rearrangement in chorismate mutase and the hydroxylation reaction in p-hydroxybenzoate hydrolase, using the QM/CHARMM-DO model and two QM methods (B3LYP, OM2)...
April 24, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28436661/performance-of-van-der-waals-corrected-functionals-for-guest-adsorption-in-the-m2-dobdc-metal-organic-frameworks
#6
Bess Vlaisavljevich, Johanna M Huck, Zeric Hulvey, Kyuho Lee, Jarad A Mason, Jeffrey B Neaton, Jeffrey R Long, Craig M Brown, Dario Alfè, Angelos Michaelides, Berend Smit
Small molecule binding in metal-organic frameworks (MOFs) can be accurately studied both experimentally and computationally, provided the proper tools are employed. Herein, we compare and contrast properties associated with guest binding by means of density functional theory (DFT) calculations using nine different functionals for the M2(dobdc) (dobdc4- = 2,5-dioxido,1,4-benzenedicarboxylate) series where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn. Additionally, we perform Quantum Monte Carlo (QMC) calculations for one system to determine if this method can be used to assess the performance of DFT...
April 24, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28436548/an-open-source-framework-for-analyzing-n-electron-dynamics-i-multideterminantal-wave-functions
#7
Vincent Pohl, Gunter Hermann, Jean Christophe Tremblay
The aim of the present contribution is to provide a framework for analyzing and visualizing the correlated many-electron dynamics of molecular systems, where an explicitly time-dependent electronic wave packet is represented as a linear combination of N-electron wave functions. The central quantity of interest is the electronic flux density, which contains all information about the transient electronic density, the associated phase, and their temporal evolution. It is computed from the associated one-electron operator by reducing the multideterminantal, many-electron wave packet using the Slater-Condon rules...
April 24, 2017: Journal of Computational Chemistry
https://www.readbyqxmd.com/read/28435665/a%C3%A2-voltage-dependent-fluorescent-indicator-for-optogenetic-applications-archaerhodopsin-3-structure-and-optical-properties-from-in-silico-modeling
#8
Dmitrii M Nikolaev, Anton Emelyanov, Vitaly M Boitsov, Maxim S Panov, Mikhail N Ryazantsev
It was demonstrated in recent studies that some rhodopsins can be used in optogenetics as fluorescent indicators of membrane voltage. One of the promising candidates for these applications is archaerhodopsin-3. However, the fluorescent signal for wild-type achaerhodopsin-3 is not strong enough for real applications. Rational design of mutants with an improved signal is an important task, which requires both experimental and theoretical studies. Herein, we used a homology-based computational approach to predict the three-dimensional structure of archaerhodopsin-3, and a Quantum Mechanics/Molecular Mechanics (QM/MM) hybrid approach with high-level multireference ab initio methodology (SORCI+Q/AMBER) to model optical properties of this protein...
2017: F1000Research
https://www.readbyqxmd.com/read/28434062/nlophoric-3-6-di-substituted-quinoxalin-carbazoles-synthesis-photophysical-properties-and-dft-studies
#9
Rahul D Telore, Amol G Jadhav, Nagaiyan Sekar
Synthesis of novel 3,6-di(substituted quinoxalin) carbazole fluorophores by the condensation of 1,1'-(9-ethyl-9H-carbazole-3,6-diyl)bis(2-bromoethanone) with methyl, chloro and unsubstituted o-phenylenediamine is presented. Synthesized derivatives are well characterized by (1)H NMR, (13)C NMR, FTIR and Mass spectroscopy. Photophysical studies are carried out using solvents of varying polarities revealed positive solvatochromism and intramolecular charge transfer from carbazole (Donor) to quinoxalin (Acceptor)...
April 22, 2017: Journal of Fluorescence
https://www.readbyqxmd.com/read/28433040/predicting-miscibility-of-binary-liquids-from-small-cluster-qce-calculations
#10
Johannes Ingenmey, Michael von Domaros, Barbara Kirchner
The quantum cluster equilibrium method is applied to model binary systems of molecular solvents. We minimize the computational effort as well as the experimental input and present the results obtained for the completely miscible acetonitrile/acetone, benzene/acetone, and water/acetone systems, as well as for the hardly miscible water/benzene system. Only clusters of sizes up to n = 3 are applied and these are optimized employing the low-cost functional PBEh-3c. The thermodynamic functions of the pure liquids are in reasonable agreement with experiments...
April 21, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28433028/incorporating-nuclear-vibrational-energies-into-the-atom-in-molecules-analysis-an-analytical-study
#11
Masumeh Gharabaghi, Shant Shahbazian
The quantum theory of atoms in molecules (QTAIM) is based on the clamped nucleus paradigm and solely working with the electronic wavefunctions, so does not include nuclear vibrations in the AIM analysis. On the other hand, the recently extended version of the QTAIM, called the multi-component QTAIM (MC-QTAIM), incorporates both electrons and quantum nuclei, i.e., those nuclei treated as quantum waves instead of clamped point charges, into the AIM analysis using non-adiabatic wavefunctions. Thus, the MC-QTAIM is the natural framework to incorporate the role of nuclear vibrations into the AIM analysis...
April 21, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28432857/on-the-importance-of-intramolecular-hydrogen-bond-cooperativity-in-d-glucose-an-nmr-and-qtaim-approach
#12
John S Lomas, Laurent Joubert
The idea that hydrogen bond cooperativity is responsible for the structure and reactivity of carbohydrates is examined. Density functional theory and gauge-including atomic orbital calculations on the known conformers of the α and β anomers of D-glucopyranose in the gas phase are used to compute proton NMR chemical shifts and interatomic distances, which are taken as criteria for probing intramolecular interactions. Atom-atom interaction energies are calculated by the interacting quantum atoms approach in the framework of the quantum theory of atoms in molecules...
April 22, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28430496/renormalized-stress-energy-tensor-of-an-evaporating-spinning-black-hole
#13
Adam Levi, Ehud Eilon, Amos Ori, Maarten van de Meent
We provide the first calculation of the renormalized stress-energy tensor (RSET) of a quantum field in Kerr spacetime (describing a stationary spinning black hole). More specifically, we employ a recently developed mode-sum regularization method to compute the RSET of a minimally coupled massless scalar field in the Unruh vacuum state, the quantum state corresponding to an evaporating black hole. The computation is done here for the case a=0.7M, using two different variants of the method: t splitting and φ splitting, yielding good agreement between the two (in the domain where both are applicable)...
April 7, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28426056/chemical-pathways-for-poly-anionic-isomerisation-in-the-metastable-anions-of-tetra-deprotonated-naphthalene-an-intra-molecular-inter-ring-proton-transfer
#14
Vikas, Poonam Sangwan, Ramanpreet Kaur
A surprising chemical pathway involving an intra-molecular proton-transfer between the two different aromatic rings of naphthalene is revealed while exploring the isomerisation in the metastable tetra-anionic species of tetra-deprotonated naphthalene. The pathways are explored through quantum-mechanical computations employing a global reaction route mapping (GRRM) strategy. Notably, several other pathways traced exhibit interesting aspects of poly-anionic isomerisation in the multiply-charged metastable molecular anions, which can provide valuable insights into the mechanisms of ring closure and expansion leading to species like azulenes, cyclodecapentaene, and phenylvinylacetylene...
April 20, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28422350/electronic-g-tensors-in-u-v-complexes-a-computational-study
#15
Helen Moylan, Joseph McDouall
The theory and computation of EPR parameters from first principles has seen a great deal of development over the past two decades. In particular, various techniques for the computation of the electronic g tensor have been implemented in many quantum chemistry packages. These methods have been successfully applied to paramagnetic organic species and transition metal systems. The situation is less well-understood and established in the case of actinide containing molecules and there is a dearth of experimental data available for validation of computations...
April 19, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28419898/theory-guided-access-to-efficient-photodegradation-of-the-simplest-perfluorocarboxylic-acid-trifluoroacetic-acid
#16
Cheng Luo, Wenyi Dong, Yurong Gu
The photodegradation approaches of perfluorocarboxylic acids have attracted considerable attention and have been developed extensively. However, the reaction channels along which the perfluorocarboxylic acid molecules dissociate remain to be deciphered by means of the quantum chemical method at the electronically excited state level of theory until now. Here we report the photodissociation mechanism of the simplest perfluorocarboxylic acid, trifluoroacetic acid, using the complete active space self-consistent field (CASSCF) and the multi-configurational second-order perturbation (CASPT2) methods...
March 30, 2017: Chemosphere
https://www.readbyqxmd.com/read/28418442/network-analysis-and-percolation-transition-in-hydrogen-bonded-clusters-nitric-acid-and-water-extracted-by-tributyl-phosphate
#17
Michael J Servis, David T Wu, Jenifer C Braley
Extraction of polar molecules by amphiphilic species results in a complex variety of clusters whose topologies and energetics control phase behavior and efficiency of liquid-liquid separations. A computational approach including quantum mechanical vibrational frequency calculations and molecular dynamics simulation with intermolecular network theory is used to provide a robust assessment of extractant and polar solute association through hydrogen bonding in the tributyl phosphate (TBP)/HNO3/H2O/dodecane system for the first time...
April 18, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28418036/maximal-violation-of-bell-inequalities-under-local-filtering
#18
Ming Li, Huihui Qin, Jing Wang, Shao-Ming Fei, Chang-Pu Sun
We investigate the behavior of the maximal violations of the CHSH inequality and Vèrtesi's inequality under the local filtering operations. An analytical method has been presented for general two-qubit systems to compute the maximal violation of the CHSH inequality and the lower bound of the maximal violation of Vértesi's inequality over the local filtering operations. We show by examples that there exist quantum states whose non-locality can be revealed after local filtering operation by the Vértesi's inequality instead of the CHSH inequality...
April 18, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28415190/density-functional-calculations-of-transport-properties-in-the-nondegenerate-limit-and-the-role-of-electron-electron-scattering
#19
Michael P Desjarlais, Christian R Scullard, Lorin X Benedict, Heather D Whitley, Ronald Redmer
We compute electrical and thermal conductivities of hydrogen plasmas in the nondegenerate regime using Kohn-Sham density functional theory (DFT) and an application of the Kubo-Greenwood response formula, and demonstrate that for thermal conductivity, the mean-field treatment of the electron-electron (e-e) interaction therein is insufficient to reproduce the weak-coupling limit obtained by plasma kinetic theories. An explicit e-e scattering correction to the DFT is posited by appealing to Matthiessen's Rule and the results of our computations of conductivities with the quantum Lenard-Balescu (QLB) equation...
March 2017: Physical Review. E
https://www.readbyqxmd.com/read/28409975/experimental-adiabatic-quantum-factorization-under-ambient-conditions-based-on-a-solid-state-single-spin-system
#20
Kebiao Xu, Tianyu Xie, Zhaokai Li, Xiangkun Xu, Mengqi Wang, Xiangyu Ye, Fei Kong, Jianpei Geng, Changkui Duan, Fazhan Shi, Jiangfeng Du
The adiabatic quantum computation is a universal and robust method of quantum computing. In this architecture, the problem can be solved by adiabatically evolving the quantum processor from the ground state of a simple initial Hamiltonian to that of a final one, which encodes the solution of the problem. Adiabatic quantum computation has been proved to be a compatible candidate for scalable quantum computation. In this Letter, we report on the experimental realization of an adiabatic quantum algorithm on a single solid spin system under ambient conditions...
March 31, 2017: Physical Review Letters
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