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Quantum theory

Helen H Fielding, Graham A Worth
Time-resolved photoelectron spectroscopy measurements combined with quantum chemistry and dynamics calculations allow unprecedented insight into the electronic relaxation mechanisms of photoexcited molecules in the gas-phase. In this Tutorial Review, we explain the essential concepts linking photoelectron spectroscopy measurements with electronic structure and how key features on the potential energy landscape are identified using quantum chemistry and quantum dynamics calculations. We illustrate how time-resolved photoelectron spectroscopy and theory work together using examples ranging in complexity from the prototypical organic molecule benzene to a pyrrole dimer bound by a weak N-Hπ interaction and the green fluorescent protein chromophore...
November 23, 2017: Chemical Society Reviews
Somayeh Khazaei, Daniel Sebastiani
We study the influence of rotational coupling between a pair of methyl rotators on the tunneling spectrum in condensed phase. Two interacting adjacent methyl groups are simulated within a coupled-pair model composed of static rotational potential created by the chemical environment and the interaction potential between two methyl groups. We solve the two-dimensional time-independent Schrödinger equation analytically by expanding the wave functions on the basis set of two independent free-rotor functions. We investigate three scenarios which differ with respect to the relative strength of single-rotor and coupling potential...
November 21, 2017: Journal of Chemical Physics
Sin-Mu Jhan, Bih-Yaw Jin
A simple molecular orbital treatment of local current distributions inside single molecular junctions is developed in this paper. Using the first-order perturbation theory and nonequilibrium Green's function techniques in the framework of Hückel theory, we show that the leading contributions to local current distributions are directly proportional to the off-diagonal elements of transition density matrices. Under the orbital approximation, the major contributions to local currents come from a few dominant molecular orbital pairs which are mixed by the interactions between the molecule and electrodes...
November 21, 2017: Journal of Chemical Physics
William K Peters, Vivek Tiwari, David M Jonas
The nonadiabatic states and dynamics are investigated for a linear vibronic coupling Hamiltonian with a static electronic splitting and weak off-diagonal Jahn-Teller coupling through a single vibration with a vibrational-electronic resonance. With a transformation of the electronic basis, this Hamiltonian is also applicable to the anti-correlated vibration in a symmetric homodimer with marginally strong constant off-diagonal coupling, where the non-adiabatic states and dynamics model electronic excitation energy transfer or self-exchange electron transfer...
November 21, 2017: Journal of Chemical Physics
Marissa L Weichman, Lan Cheng, Jongjin B Kim, John F Stanton, Daniel M Neumark
A joint experimental and theoretical study is reported on the low-lying vibronic level structure of the ground state of the methoxy radical using slow photoelectron velocity-map imaging spectroscopy of cryogenically cooled, mass-selected anions (cryo-SEVI) and Köppel-Domcke-Cederbaum (KDC) vibronic Hamiltonian calculations. The KDC vibronic model Hamiltonian in the present study was parametrized using high-level quantum chemistry, allowing the assignment of the cryo-SEVI spectra for vibronic levels of CH3O up to 2000 cm(-1) and of CD3O up to 1500 cm(-1) above the vibrational origin, using calculated vibronic wave functions...
June 14, 2017: Journal of Chemical Physics
WenJie Hou, YuanDong Wang, JianHua Wei, YiJing Yan
Pauli spin blockade (PSB) is a significant physical effect in double quantum dot (DQD) systems. In this paper, we start from the fundamental quantum model of the DQD with the electron-electron interaction being considered and then systematically study the PSB effect in DQD by using a recently developed nonperturbative method, the hierarchical equations of motion approach. By checking the current-voltage and nonequilibrium spectral function features, the physical picture of the PSB is explicitly elucidated. Then, various kinds of manipulation of PSBs are discussed, including gate voltage, exchange interaction, and electron spin resonance...
June 14, 2017: Journal of Chemical Physics
Xiang-Yang Liu, Ye-Guang Fang, Bin-Bin Xie, Wei-Hai Fang, Ganglong Cui
The photoinduced rearrangement reaction mechanism of 1,2,3-thiadiazole remains experimentally elusive. Two possible mechanisms have been proposed to date. The first is a stepwise mechanism via a thiocarbene intermediate; the second is an excited-state concerted rearrangement mechanism. Herein we have adopted both the electronic structure calculations and nonadiabatic dynamics simulations to study the photoinduced rearrangement reactions of 1,2,3-thiadiazole in the S2, S1, and S0 states in solution. On the basis of QM(CASPT2)/MM [quantum mechanics(complete active space self-consistent field second-order perturbation theory)/molecular mechanics] calculations, we have found that (1) the thiocarbene intermediate is not stable; thus, the stepwise mechanism should be unfavorable; (2) the excited-state decay from the S2 via S1 to S0 state is ultrafast and completed within ca...
June 14, 2017: Journal of Chemical Physics
Junwei Lucas Bao, Donald G Truhlar
This article reviews the fundamentals of variational transition state theory (VTST), its recent theoretical development, and some modern applications. The theoretical methods reviewed here include multidimensional quantum mechanical tunneling, multistructural VTST (MS-VTST), multi-path VTST (MP-VTST), both reaction-path VTST (RP-VTST) and variable reaction coordinate VTST (VRC-VTST), system-specific quantum Rice-Ramsperger-Kassel theory (SS-QRRK) for predicting pressure-dependent rate constants, and VTST in the solid phase, liquid phase, and enzymes...
November 22, 2017: Chemical Society Reviews
Sarabjeet Kaur, Purshotam Sharma, Stacey D Wetmore
The RNA world hypothesis assumes that RNA was the first informational polymer that originated from prebiotic chemical soup. However, since the reaction of d-ribose with canonical nucleobases (A, C, G and U) fails to yield ribonucleosides (rNs) in substantial amounts, the spontaneous origin of rNs and the subsequent synthesis of RNA remains an unsolved mystery. To this end, it has been suggested that RNA may have evolved from primitive genetic material (preRNA) composed of simpler prebiotic heterocycles that spontaneously form glycosidic bonds with ribose...
November 22, 2017: Physical Chemistry Chemical Physics: PCCP
Gabriel J Buralli, Andre N Petelski, Nélida M Peruchena, Gladis L Sosa, Darío J R Duarte
In the present work an in depth deep electronic study of multicenter XBs (FX)n/NH₃ (X = Cl, Br and n = 1-5) is conducted. The ways in which X∙∙∙X lateral contacts affect the electrostatic or covalent nature of the X∙∙∙N interactions are explored at the CCSD(T)/aug-cc-pVTZ level and in the framework of the quantum theory of atoms in molecules (QTAIM). Calculations show that relatively strong XBs have been found with interaction energies lying between -41 and -90 kJ mol(-1) for chlorine complexes, and between -56 and -113 kJ mol(-1) for bromine complexes...
November 22, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
J H Geesink, D K F Meijer
Solitons, as self-reinforcing solitary waves, interact with complex biological phenomena such as cellular self-organization. A soliton model is able to describe a spectrum of electromagnetism modalities that can be applied to understand the physical principles of biological effects in living cells, as caused by endogenous and exogenous electromagnetic fields and is compatible with quantum coherence. A bio-soliton model is proposed, that enables to predict which eigen-frequencies of non-thermal electromagnetic waves are life-sustaining and which are, in contrast, detrimental for living cells...
2017: Electromagnetic Biology and Medicine
Piero Macchi, Fabio Ragaini, Nicola Casati, Anna Krawczuk, Angelo Sironi
The accurate electron density distribution in Pd(Neoc)Cl2 (CO) (Neoc = 2,9-dimethyl-1,10-phenanthroline) was measured and calculated to investigate the chemical bonding features, the electrostatic forces and the polarizable bonds in this complex, which is a prototype of the proposed intermediate in the catalytic carbonylation of amines and nitroarenes. The quantum theory of atoms in molecules enables to investigate the nature of the elusive fifth coordination in the complex, which is approximately intermediate between a bypiramid penta-coordination and a square planar tetra-coordination...
November 21, 2017: Journal of Computational Chemistry
Amelia W Ray, Jianyi Ma, Rico Otto, Jun Li, Hua Guo, Robert E Continetti
The reaction F + H2O → HF + OH is a four-atom system that provides an important benchmark for reaction dynamics. Hydrogen atom transfer at the transition state for this reaction is expected to exhibit a strong dependence on reactant vibrational excitation. In the present study, the vibrational effects are examined by photodetachment of vibrationally excited F(-)(H2O) precursor anions using photoelectron-photofragment coincidence (PPC) spectroscopy and compared with full six-dimensional quantum dynamical calculations on ab initio potential energy surfaces...
November 1, 2017: Chemical Science
Guogang Yang, Sara Sangtarash, Zitong Liu, Xiaohui Li, Hatef Sadeghi, Zhibing Tan, Ruihao Li, Jueting Zheng, Xiaobiao Dong, Junyang Liu, Yang Yang, Jia Shi, Zongyuan Xiao, Guanxin Zhang, Colin Lambert, Wenjing Hong, Deqing Zhang
The protonation of azulene derivatives with quantum interference effects is studied by the conductance measurements of single-molecule junctions. Three azulene derivatives with different connectivities are synthesized and reacted with trifluoroacetic acid to form the protonated states. It is found that the protonated azulene molecular junctions produce more than one order of magnitude higher conductance than the neutral states, while the molecules with destructive interference show more significant changes...
November 1, 2017: Chemical Science
Anne Kathrine R Junker, Thomas Just Sørensen
The influence of an electron donating substituent on the photophysical properties of 1-azathioxanthone dyes has been investigated using optical spectroscopy and theoretical models. The motivation behind the study is based on the fact that thioxanthones are efficient triplet sensitizers, and thus promising sensitizers for lanthanide centered emission. By adding an aza group to one of the phenyl ring systems, direct coordination to a lanthanide center becomes possible, which makes azathoixanthones great candidates as antenna chromophores in lanthanide(III) based dyes...
November 21, 2017: Methods and Applications in Fluorescence
Loris Ercole, Aris Marcolongo, Stefano Baroni
The evaluation of transport coefficients in extended systems, such as thermal conductivity or shear viscosity, is known to require impractically long simulations, thus calling for a paradigm shift that would allow to deploy state-of-the-art quantum simulation methods. We introduce a new method to compute these coefficients from optimally short molecular dynamics simulations, based on the Green-Kubo theory of linear response and the cepstral analysis of time series. Information from the full sample power spectrum of the relevant current for a single and relatively short trajectory is leveraged to evaluate and optimally reduce the noise affecting its zero-frequency value, whose expectation is proportional to the corresponding conductivity...
November 20, 2017: Scientific Reports
Michel Van Wassenhoven, Martine Goyens, Marc Henry, Etienne Capieaux, Philippe Devos
BACKGROUND: NMR proton relaxation is sensitive to the dynamics of the water molecule H2O, through the interaction of the spin of the proton ((1)H) with external magnetic and electromagnetic fields. METHODS: We measured dilution and potentization processes through measurements of (1)H spin-lattice T1 and spin-spin T2 relaxation times. In order to interpret the recorded fluctuations in T1- or T2-values, experimental data were linearized by investigating how the area under a fluctuating time = f(dilution) curve (dilution integral or DI) changes with dilution...
November 2017: Homeopathy: the Journal of the Faculty of Homeopathy
Anton Georgiev, Anton Kostadinov, Deyan Ivanov, Deyan Dimov, Simeon Stoyanov, Lian Nedelchev, Dimana Nazarova, Denitsa Yancheva
This paper describes the synthesis, spectroscopic characterization and quantum mechanical calculations of three azo-azomethine dyes. The dyes were synthesized via condensation reaction between 4-(dimethylamino)benzaldehyde and three different 4-aminobenzene azo dyes. Quantum chemical calculations on the optimized molecular geometry and electron densities of the trans (E) and cis (Z) isomers and their vibrational frequencies have been computed by using DFT/B3LYP density-functional theory with 6-311++G(d,p) basis set in vacuo...
November 7, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
James McClory, David J Timson, Warispreet Singh, Jian Zhang, Meilan Huang
Isopentenyl phosphate kinase (IPK) catalyzes the Mg2+-ATP dependent phosphorylation reactions to produce isopentenyl diphosphate, an important precursor in the synthesis of isopentenols. However, the position of the divalent metal ion in the crystal structures of IPK in complex with ATP and its native substrate IP has not been definitively resolved, and as a result ambiguity surrounds the catalytic mechanism of IP, limiting its exploitation as a biofuel and in drug design. Here we report the conformational change caused by substrate binding and the catalytically competent structure in complex with the metal ion Mg2+ using molecular dynamic simulations and density functional theory-based quantum mechanics/molecular mechanics calculations (B97d/AMBER99)...
November 20, 2017: Journal of Physical Chemistry. B
Peter Woelfle
Quasiparticles are a powerful concept of condensed matter quantum theory. In this review the appearence and the properties of quasiparticles are presented in a unifying perspective. The principles behind the existence of quasiparticle excitations in both quantum disordered and ordered phases of fermionic and bosonic systems are discussed . The lifetime of quasiparticles is considered in particular near a continuous classical or quantum phase transition, when the nature of quasiparticles on both sides of a transition into an ordered state changes...
November 20, 2017: Reports on Progress in Physics
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