Density and thermodynamics of hydrogen adsorbed inside narrow carbon nanotubes

A model is proposed for calculating the thermodynamic functions and the equilibrium density of a one-dimensional chain of molecules (atoms) adsorbed inside a narrow nanotube. The model considers both the interaction between introduced atoms (molecules) and their interaction with the nanotube walls. The quantum-mechanical effects resulting in discrete energy levels of a particle and in its smeared position between neighbors are taken into account. In calculating the free energy at a nonzero temperature, the phonon contribution and the particle transitions to excited levels are considered. The model is applied to calculate the thermodynamic parameters of adsorbed hydrogen molecules inside extremely narrow single-wall carbon nanotubes of the (3,3) and (6,0) type. It is shown that external pressure gives rise to a sequence of first-order phase transitions, which change the density of adsorbed hydrogen molecules.     

Echo responses of an ensemble of cold atoms in optical lattices

The dynamics of an ultracold dilute boson gas in an optical lattice is described in the framework of the Bose-Hubbard model in which the parameters of the system are controlled by light. Within this model, an ensemble of Bose-Einstein condensates trapped in cells of a double optical lattice generates an echo response in the quantum-mechanical probability current. The echo signal is excited by biharmonic radiation pulses under two-photon (Raman) resonance conditions. The time profile of the echo signal and the role played by the inhomogeneous broadening and the interaction of atoms in the formation of the boson echo are discussed.     

Using a crystal as a universal generator of localized plastic flow autowaves

Patterns accompanying the development of a localized plastic flow in solids are considered. A correlation between products of the linear and rate parameters of elastic and plastic flows is revealed by analyzing localized plastic flows in metals and nonmetals. A relationship between the parameters of elasticity and plastic flow is hypothesized. A relationship between patterns in plastic flow and quantum-mechanical parameters is found.     

On the theory of the spontaneous magnetization of thin films. Part I

Conclusion From (3) it is seen that the quantum-mechanical theory of thin films leads to quite analogous results as for massive specimens. It is obvious that we should arrive at the same results as in (3) if from the very beginning we solved the whole problem by means of the theory of molecular fields putting the molecular fields of the individual atomic planes proportional to their magnetization. We shall therefore make use of this fact in the future by working with the method of molecular fields which permits of a somewhat more flexible procedure than the quantum-mechanical solution. At the same time, however, there appear in the equations constants of the molecular fields which are not more closely defined and which, as we know, are proportional to the exchange interaction energy between neighbours but with the present state of the theory this is not a disadvantage in comparison with the quantum-mechanical procedure, since the exchange integrals have not yet been calculated.A comparison of (3) with experiment will be left to the second part of this paper, where we shall compare the results of measurement with the equivalent equations in the molecular-field form.This paper was read at the international conference on magnetic phenomena in Moscow, 1956.     

Current trends in the theories of gas-surface interaction

Studies on gas-surface dynamics have acquired considerable importance recently not only for their intrinsic scientific interest but also for their technological potential. This article first briefly describes various experimental techniques and a number of interesting recent observations resulting from these techniques. It then discusses certain important theoretical methodologies being extensively used nowadays. There arethree broad overlapping streams of theoretical works, viz classical, semi-classical and quantum-mechanical. There are alsothree basic problems in gas-surface interaction, viz (i) the interface presents a manybody problem; (ii) the solid surface is “rough”; (iii) the number of diffractive and inelastic channels is enormously large. The semi-classical approaches appear to dominate over the others in variety and quantity. But the sources of benchmark theoretical results are still the rigorous classical-trajectory and close-coupling quantum-mechanical calculations. The coming years are likely to witness not only increased numerical accuracy through refinements in semi-classical and quantum-mechanical approaches, but also certain special approximate methods designed to yield deeper physical insights into the nature of gas-surface interaction. The authors felicitate Prof. D S Kothari on his eightieth birthday and dedicate this paper to him on this occasion. An erratum to this article is available at .     

Computation of the tunneling H-transfer reaction kinetics in the fluorene molecular crystal

The semi-empirical computation of the rate constant is fully performed for the photochemical bimolecular hydrogen atom transfer reaction in condensed phase, proceeding in the deep tunneling regime. For the system considered (fluorene + acridine in its first triplet state, inside the fluorene molecular crystal) the kinetics have been thoroughly investigated experimentally over wide temperature range (http://bernd-prass.de). In the present theoretical work the potential energy surface is constructed by means of the reported earlier QM/MM approach, covering the interaction of the reaction pair with the crystalline environment. Direct evaluation of two-dimensional tunneling amplitudes on this surface is made by means of the accurate quantum-mechanical numerical method. The kinetic part of the rate calculation invokes Golden Rule methodology in its recently elaborated modification while consistently accounting for the dynamical energy exchange between the tunneling pattern and the medium. The careful calibration of transition amplitudes for H- and D-transfer reactions provided the parameters controlling their exponential dependence on the promotion mode (i.e. the distance between the terminal heavy atoms of the reaction centre), which establishes the effective tunneling length of the transfer process. The experimental temperature dependence of the reaction rates for both cases is well reproduced by tuning the parameters of the phonon frequency spectrum projected on the promotion mode. The fitted values of these spectral density parameters are contained within the range located in the preliminary independent computation of the lattice dynamics for the fluorene crystal. Most difficult is the part of the computation concerned with the absolute values of rate constants for both H- and D-reactions. The magnitude of the isotope effect can be reasonably interpreted at a qualitative level by complementing the amplitude quantum-mechanical data with empirical Frank–Condon (FC) factors inherent to the reorganization of several intra-molecular modes, which is known to accompany the background transfer reaction. However, this treatment, based on the oversimplified one-dimensional model of such reorganization, is not fully consistent, since the pertaining FC parameters were found to differ significantly for the cases of H- and D-transfer.     

Simulation of interaction of oriented <Emphasis Type="Italic">J</Emphasis> aggregates with resonance laser radiation

The interaction of laser radiation with single J aggregates of cyanine dyes is theoretically analyzed and numerically simulated. The quantum-mechanical calculations of the equilibrium geometry and the energies and intensities of the lowest singlet electronic transitions in pseudoisocyanine chloride and its linear (chain) oligomers are fulfilled. The data of these calculations can serve as parameters of the analyzed model of interaction of J aggregates with radiation in the one-particle density matrix approximation. This model takes into account relaxation processes, the annihilation of excitations at neighboring molecules, and inhomogeneous broadening. Assuming that the inhomogeneous broadening is absent, calculations demonstrate the existence of spatial bistability, molecular switching waves, and dissipative solitons. The effect of the inhomogeneous broadening and the radiation intensity on the effective coherence length in linear (chain) J aggregates is analyzed.     

Si5++He相互作用时双活跃电子势能的计算

利用附加电子转移因子和开关函数的半经典近似和量子分子轨道方法,在0.3～3.0 KeV能区和2.0～20.0(a.u.)核间距的条件下,对Si5+离子与He原子相互作用过程中5个singlet 态和5个triplet态的双电子捕获势能进行了理论计算.通过参数优化,在比较了基通道电子转移势能和实验值之后,研究了主通道的电子转移势能.其结果说明了这一动力学过程中的避交叉(avoided crossings)性质,给出了双电子容易被捕获的不同核间距离点.     

Resonance phenomena in low-energy electron scattering by planar crystalline nanostructures

Multiple scattering of low-energy electrons by a nanostructure consisting of planar crystalline films is analyzed. It is demonstrated that, at a particular ratio between the geometric and potential parameters of the system, there arise resonance states of scattered electrons in which the transmission coefficient of electrons increases drastically. Narrow transparency windows that correspond to almost complete transmission of the electron beam are formed at specific distances between the films in the resonance structure. A method for quantum-mechanical calculation of the parameters of the resonance structure is proposed.     

Effective field theories for the heavy quarkonium

We briefly review how nonrelativistic effective field theories give us a definition of the QCD potentials and a coherent field-theory-derived quantum-mechanical scheme to calculate the properties of bound states made by two or more heavy quarks. In this framework heavy quarkonium properties depend only on the QCD parameters (quark masses and α _s ) and nonpotential corrections are systematically accounted for. The relation between the form of the nonperturbative potentials and the low-energy QCD dynamics is also discussed.     

Evolution of Berry's phase in a graded-index medium

Evolution of the polarization vector in an inhomogeneous isotropic medium is investigated using the quantum-mechanical formalism of coherent states. The relation between the fluctuations of Berry's phase of wave nature caused by the “spin-orbit” interaction of a photon and depolarization of an incident pure state of polarization is clarified.     

Cramér-Rao inequalities for operator-valued measures in quantum mechanics

The theory of estimation of parameters of quantum-mechanical density operators is expressed in terms of the measurement of operator-valued measures. Lower bounds on mean-square errors of parameter estimates are set by two quantum-mechanical forms of the Cramér-Rao inequality of classical statistics, derived here in terms of such measures. The results are exemplified by the simultaneous estimation of the real and imaginary parts of the complex amplitude of a coherent oscillation in the presence of thermal noise.This research was supported by grant NSF GK-33811 from the National Science Foundation.     

Numerical simulation of the intramolecular dynamics of photoisomerization

The results of mixed quantum-classical and quantum-mechanical numerical calculations of the intramolecular dynamics of photoisomerization under conditions similar to ordinary natural conditions, i.e., for irradiation of the molecule by a light pulse not shorter than the lifetime of the resonant excited electronic state of the molecule and with an intensity comparable to that of solar light at the Earth’s surface, are presented. It was concluded that the dynamics of such photoisomerization should be modeled using quantum-mechanical methods. The simplest approach to modeling the photoisomerization of a molecule with two isomeric forms can be based on the density matrix formalism for describing the interaction of a light pulse with a three-level system of Λ configuration.     

Quantum interference and Manley-Rowe relations in resonant four-wave frequency mixing in an optically thick Doppler-broadened medium

It is shown that under resonant interaction conditions certain notions in nonlinear optics which are based on the Manley-Rowe relations no longer hold because of the interference of elementary quantum-mechanical processes. This conclusion is illustrated by numerical examples corresponding to the experiments performed. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 862–866 (25 June 1999)     

Enhancing non-local correlations in the bipartite partitions of two qubit-system with non-mutual interaction

Several quantum-mechanical correlations, notably, quantum entanglement, measurement-induced nonlocality and Bell nonlocality are studied for a two qubit-system having no mutual interaction. Analytical expressions for the measures of these quantum-mechanical correlations of different bipartite partitions of the system are obtained, for initially two entangled qubits and the two photons are in their vacuum states. It is found that the qubits-fields interaction leads to the loss and gain of the initial quantum correlations. The lost initial quantum correlations transfer from the qubits to the cavity fields. It is found that the maximal violation of Bell’s inequality is occurring when the quantum correlations of both the logarithmic negativity and measurement-induced nonlocality reach particular values. The maximal violation of Bell’s inequality occurs only for certain bipartite partitions of the system. The frequency detuning leads to quick oscillations of the quantum correlations and inhibits their transfer from the qubits to the cavity modes. It is also found that the dynamical behavior of the quantum correlation clearly depends on the qubit distribution angle.     

Dipolar interaction and its interplay with interface roughness

We present a comparison of the strength of the classical dipolar interaction, relative to quantum-mechanical coupling mechanisms like RKKY and complete confinement, between two ferromagnetic films separated by a paramagnetic spacer. The classical dipolar coupling, which vanishes if the two interfaces are perfectly continuous and flat, builds up strength as the interface roughness grows for several models of interface topography. These numerical estimates, carried out for a Co/Cu/Co trilayer show that, in the presence of substantial surface roughness, the dipole-dipole interaction strength is comparable, and at times even larger, than those obtained using other well established mechanisms. These results are also in qualitative agreement with experimental measurements in a variety of multilayer systems. Thus, for rough interfaces, the dipolar interaction cannot be ignored.