Tunneling time in driven double-well system using entangled molecular dynamics method

We calculate quantum tunneling time in the double-well system without perturbation and with symmetry-breaking driven force using the entangled trajectory molecular dynamics method in the present article. Without perturbation, quantum tunneling time decreased with the increase of the energy, and the different contributions of the barrier traversal time and the intrinsic decay time have been shown. The tunneling time dependence on the amplitude and frequency of the symmetry-breaking driven force are present. In the case of weak driven force, tunneling time has a minimum value in the resonant frequency. For strong driven force, chaos brings a huge change to quantum dynamics, tunneling time significantly becomes short. Finally, we directly show the enhancement of quantum tunneling process by chaotic behavior of entangled trajectories and indicate that it was caused by quantum effect.     

Quantum tunneling effect in entanglement dynamics

Quantum tunneling effect in entanglement dynamics between two coupled particles with separable Gaussian initial state is investigated using entangled trajectory molecular dynamics method in terms of the reduced‐density linear entropy. It has been presented through showing distinguish contribution of single trajectory to linear entropy between classical trajectory and entangled trajectory with same initial state. We find that quantum tunneling effect makes single trajectory's contribution remarkably decrease under quantum dynamics compared to classical dynamics. The nonlocality of quantum entanglement is presented, and the energy transfer between two coupled particles through quantum correlations and classical ones is also discussed in the end. © 2015 Wiley Periodicals, Inc.     

Quantum tunneling in a periodically driven double well system: Entangled trajectory molecular dynamics method

We study a wavepacket tunneling in one‐dimensional periodically driven double‐well system using entangled trajectory molecular dynamics method. The tunneling dynamics dependents on the amplitude and frequency of the driven force are present. Both resonant and nonresonant tunneling process are enhanced by the driven force when the system is chaotic under classical dynamics. We give entangled trajectory in phase space compared to corresponding classical trajectory with same initial state to visually show quantum tunneling process. The average values of quantum tunneling probability after long time evolution have been shown in the parameter spaces, the effect of resonance and chaos on the tunneling dynamics are present. The relation between chaos and the uncertainly product is discussed in the end. © 2016 Wiley Periodicals, Inc.     

Quantum tautomerization in porphycene and its isotopomers: Path-integral molecular dynamics simulations

Path-integral molecular dynamics simulations have been performed for porphycene and its isotopic variants in order to understand the effect of isotopic substitution of inner protons on the double proton transfer mechanism. We have used an on-the-fly direct dynamics technique at the semiempirical PM6 level combined with specific reaction parameterization. Our quantum simulations show that double proton transfer of the unsubstituted porphycene at T = 300 K mainly occurs via a so-called concerted mechanism through the D_2h second-order saddle point. In addition, we found that both isotopic substitution and temperature significantly affect the double proton transfer mechanism. For example, the contribution of the stepwise mechanism increases with a temperature increase. We have also carried out hypothetical simulations with the porphycene configurations being completely planar. It has been found that out-of-plane vibrational motions significantly decrease the contribution of the concerted proton transfer mechanism.     

Some Mathematical and Algorithmic Challenges in the Control of Quantum Dynamics Phenomena

The theory and practice of control over quantum mechanical phenomena is receiving increasing attention, underscored by striking experimental successes. Nevertheless, many questions of fundamental and practical relevance to the field remain unresolved. With the aim of stimulating further development, this paper formulates a number of theoretical questions, divided into three categories. First, questions related to control law design are discussed, with an emphasis on controllability and optimal control theory. This leads to the second category of open problems relevant to closed loop laboratory implementation of quantum control, including learning and feedback methods. The sensitive dependence of control on basic quantum mechanical interactions motivates the third section, which treats coherent dynamical techniques for identifying the system Hamiltonian. An open issue overarching all of these directions is the need to discover general rules for the control of quantum systems. Although the list of issues raised in this paper is extensive, it should be viewed not as a complete menu for exploration, but rather as a springboard to new challenges as the field evolves.     

异丙基膦酸单烷基酯萃取剂的量子化学研究

用分子力学、分子动力学及半经验量子化学方法研究了异丙基膦酸单烷基酯系列稀土萃取剂的空间结构和电子结构、结果表明，烷氧基上的取代基对空间位阻的影响比主碳链大。与稀土原子配位的磷酰氧原子在ＨＯＭＯ中的贡献较大，而ＬＵＭＯ轨道则主要由非配位原子的轨道组成。萃取剂中磷原子、磷酰氧原子以及羟基中氧原子上的电荷分布均随结构的变化呈规律性变化。磷原子和磷酰氧原子上的电荷分布与萃取剂的ｐＫａ值呈线性关系。     

Localization in some discontinuously and randomly driven quantum systems

A charged particle moving in a harmonic, symmetric double well, a square well, or a Morse potential is allowed to interact with a discontinuously reversing spatially homogeneous electric field. Randomly reversing field is seen to cause localization in the quantum system. A critical reversal frequency is seen to exist below which no localization is manifested in the harmonic, double and square well. In the Morse case, there is dissociation if the upper limit of the interval between random kicks exceeds τ_max. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Quantum dynamics of a system of coupled nonlinear oscillators: Spectral and information entropy‐based analysis

The quantum dynamics of the evolution of a system of a few coupled nonlinear oscillators is studied. The spectral entropy and the quantal information entropy, as well as their correlation functions, are computed and used to identify distinctive phases of the evolution. The two entropy functions lead to similar conclusions. It appears that adiabatic switching of the nonlinear interaction does not affect the nature of the short time dynamics but affects the dynamics over intermediate time scales. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Quantum interference effects in the Br2 electronic predissociation: Dependence upon the molecular properties

The occurrence of quantum interference in the Br₂ electronic predissociation has been observed for the first time. It is also shown that the quantum interference effects are strongly dependent upon the representation of the molecular properties, such as the kinetic coupling and the transition dipole moment. The fast Fourier transform method implemented within the wave packet formalism was used to simulate the time evolution of the molecular system under the influence of single monochromatic ultrashort laser pulses. The quantum interference has been inferred from the oscillatory behavior of the autocorrelation functions, which have also been used to calculate the cross-sections, the branching ratios, and the selectivity. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Quantum dynamics of dissociative adsorption of H2 and D2: The time-dependent wave packet method

A time-dependent quantum wave packet method was used to study the dynamics of dissociative adsorption of H₂ and D₂ on a flat and static surface. The molecule-surface interaction is described using a modified London-Eyring-Polanyi-Sato (LEPS) type potential for the H₂/Ni(100) system. The three-dimensional (3-D) dissociation probabilities were calculated for different initial rovibrational states as a function of initial incident energies. Our results show that the dissociation of the diatomic rotational states whose quantum numbers satisfyj+m = odd is forbidden at low energies for the homonuclear H_z and D₂ due to the selection rule. The effect of the rotational orientation of diatoms on adsorption predicts that the in-plane rotation (m = j) is more favorable for dissociation than the out-of-plane rotation (m = 0). Enhanced dissociation for vibrationally excited molecules and the significant enhancement of the dissociation probability of H2 when compared to D₂ were explained reasonably in terms of quantum mechanical zero-point energies, the tunneling effect and the reflection from an activation barrier. Project supported by the National Natural Science Foundation of China (Grant No. 19694033) and partially by the Science Foundation for Overseas Chinese Scholars and Students, administered by the State Education Commission of China (Grant No. 1992), by the State Key Laboratory of Theoretical and Computational Chemistry of Jilin University at Changchun (Grant No. 98011, and by the Natural Science Foundation of Shandong Province (Grant No. Y96B03022)     

Quantum dynamics of dissociative adsorption of H_2 and D_2:The time-dependent wave packet method

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Wave packet and quasiclassical trajectory calculations for the N(D) + H2 reaction and its isotopic variants

The N(²D) + H₂(v = 0, j = 0) reaction and its HD and D₂ isotopic variants have been studied by means of quantum mechanical real wave packet and wave packet with split operator and quasiclassical trajectory methodologies on the potential energy surface of Ho et al. [J. Chem. Phys. 119 (2003) 6]. Total initial state-selected and final state-resolved reaction probabilities and product rotational distributions have been calculated for total angular momentum J = 0 in a broad range of collision energies. The real wave packet results are in very good agreement with the corresponding split operator wave packet calculations. A reasonable overall good agreement has been found between the wave packet and quasiclassical trajectory results. Integral cross-sections and thermal rate constants have been calculated from the wave packet reaction probabilities by means of standard J-shifting, refined J-shifting and uniform J-shifting methods in combination with the centrifugal sudden approximation for J > 0. Comparisons with available exact wave packet, quasiclassical trajectory and experimental results are made and discussed.     

三维含时量子散射研究H + CIH体系

用三维含时量子散射理论模拟了H+CIH体系在BW2,mBW2,G3势能面上的动力学行为,其计算结果表明,振动量子态对反应几率影响很大;势能面的地形对转动量子态如何影响反应几率起重要作用;反应几率表现出“黄金规则”,此外,BW2,mBW2势能面上的反应几率几乎相同,而G3势能面上的反应几率较前者低,大概由于G3的势垒高的缘故。     

功能化PbS量子点的水相合成及结构表征

在水溶液中以Pb(NO3)2和Na2S为原料,巯基乙酸为稳定剂,合成了水溶性PbS量子点.用透射电子显微镜、扫描电子显微镜、粒度分析仪和红外光谱对PbS量子点进行了表征,结果表明所合成的PbS量子点的平均粒径为25 nm左右,分散性好,且巯基乙酸成功修饰于PbS纳米粒子表面,使其具有进一步与生物分子偶联的作用.     

Quantum dynamics study of the excited-state double-proton transfer in 2,2'-bipyridyl-3,3'-diol.

Density functional theory and quantum dynamics simulations have been used to study the double-proton transfer reaction in 2,2'-bipyridyl-3,3'-diol in the first singlet excited electronic state. This process is experimentally known to be branched: It consists of a fast, concerted reaction mechanism (tau approximately 100 fs) and a stepwise reaction mechanism [with a fast initial step (tau approximately 100 fs) and a slower final step (tau approximately 10 ps)]. Quantum dynamics simulations on a two-dimensional model reveal that the concerted reaction occurs despite the nonexistence of a concerted reaction path, but they fail to explain the relative slowness of the stepwise mechanism. A qualitative simulation using a three-dimensional model suggests that internal vibrational relaxation (IVR) might be the reason why the second stage of the stepwise mechanism is so slow.     

Quantum trajectory method calculation of collinear collisions in the hydrogen exchange reaction H + ClH′ → HCl + H′

The quantum trajectory method was used to study the collinear reaction H + ClH′ → HCl + H′. The potential energy surface was calculated on the QCISD(T)/6-311++G(3df,3pd) level. The reaction probabilities are in good accord with the results obtained by solving the Schroedinger equation using the finite difference method. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 3, pp. 156-159, May-June, 2009.     

Quantum dynamics of relaxation of a pair of coupled Morse oscillators: Effects of mass and electrical asymmetries

A multiconfiguration time‐dependent Hartree method based recipe is used to study the role of mass and electrical asymmetry in controlling the quantum dynamics of relaxation of a locally excited O? H bond in a water molecule, modeled by a pair of interacting Morse oscillators. The fast periodic energy transfer between the two equivalent O? H bonds in H? O? H is replaced by a rather slow process when one of the H atom is replaced by a deuterium atom. Application of static electric field along the O? D bond in HOD molecule is seen to either enhance or damp the relaxation rate, depending on the strength of the applied field. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Quantum dynamics through conical intersections in macrosystems: Combining effective modes and time-dependent Hartree

We address the nonadiabatic quantum dynamics of (macro)systems involving a vast number of nuclear degrees of freedom (modes) in the presence of conical intersections. The macrosystem is first decomposed into a system part carrying a few, strongly coupled modes, and an environment, comprising the remaining modes. By successively transforming the modes of the environment, a hierarchy of effective Hamiltonians for the environment can be constructed. Each effective Hamiltonian depends on a reduced number of effective modes, which carry cumulative effects. The environment is described by a few effective modes augmented by a residual environment. In practice, the effective modes can be added to the system’s modes and the quantum dynamics of the entire macrosystem can be accurately calculated on a limited time-interval. For longer times, however, the residual environment plays a role. We investigate the possibility to treat fully quantum mechanically the system plus a few effective environmental modes, augmented by the dynamics of the residual environment treated by the time-dependent Hartree (TDH) approximation. While the TDH approximation is known to fail to correctly reproduce the dynamics in the presence of conical intersections, it is shown that its use on top of the effective-mode formalism leads to much better results. Two numerical examples are presented and discussed; one of them is known to be a critical case for the TDH approximation.