Calculation of Out‐of‐Plane Vibrations of a Porphin Molecule

Using the DFT/B3LYP method with the base set 631G^**, we carried out calculation of the frequencies of the normal vibrations of porphin and of its five isotopic types. Scaling of force constants for outofplane vibrations has been performed in independent natural coordinates. The symmetry coordinates are introduced and a force field for outof plane vibrations of a porphin molecule in independent coordinates of symmetry is obtained. A new correlation of the frequencies of vibrations in the type of the symmetry B _1u for the isotopic type of the d ₂ porphin molecule is suggested on the basis of discrete analysis of the distribution of a potential energy.     

Role of Interactions in Electronic Structure of a Two-Electron Quantum Dot Molecule

We have studied a two-electron quantum dot molecule in a magnetic field. The electron interaction is treated accurately by the direct diagonalization of the Hamiltonian matrix. We calculate two lowest energy levels of the two-electron quantum dot molecule in a magnetic field. Our results show that the electron interactions are significant, as they can change the total spin of the two-electron ground state of the system by adjusting the magnetic field between S = 0 and S = 1. The energy difference AE between the lowest S = 0 and S = 1 states is shown as a function of the axial magnetic field. We found that the energy difference between the lowest S = 0 and S = 1 states in the strong-B S = 0 state varies linearly. Our results provide a possible realization for a qubit to be fabricated by current growth techniques.     

Quantum–Chemical Calculations of the Spatial Structure of Bilirubin Molecule Fragments

Using the semiempirical methods MINDO/3, MNDO, AM1, and PM3 and the molecular mechanics (MM) method, we have calculated the geometrical structure of eight bilirubin molecule–fragments. For a number of molecules, calculations have also been made by the ab initio method. Effects arising as a result of successive complication of the molecular structure have been analyzed. The electronic spectra of the investigated molecules have been calculated by the CNDO/S and INDO/S methods. It is shown that the semiempirical quantum–chemical methods underestimate the contribution of conjugation effects to the geometrical structure of molecules, whereas the MM method overestimates it. Wave–like instabilities towards nonplanar distortions have been revealed in the five–membered rings A and D of the investigated molecules.     

Fluorescence as a Probe of Energy Dependence of Electron–Molecule Interaction

The fluorescence intensity dependences on electron kinetic energy, or fluorescence excitation functions, for some aromatic (perylene and p-terphenyl) and heterocyclic (biphenylfuran, oxazoles, and oxadiazoles) compounds are studied. It is found that the addition of phenyl rings to the above molecules result in a moderate decrease in excitation function. On the other hand, introducing heteroatoms such as oxygen or nitrogen leads to a substantial decrease in excitation function.     

Micro-Photoluminescence Investigation of Single Quantum Dot and its Molecule of CdSe/ZnSe

The single and a few coupled quantum dots are important for future quantum information sciences and their investigation is also a big challenge in physics. We investigate here the electronic and exciton states and their interaction with each other via micro photoluminescence. The luminescence for single and a few dots as well as a dot molecule of CdSe/ZnSe are measured with very high resolution, under liquid He temperature and magnetic fields and with different polarization of excitation laser. The observed sharp spectral lines are attributed to the atomlike transitions of exciton, trion, biexciton… in the investigated single QD or QD molecule. Band filling, Zeeman splitting, spin transition and their relaxation are observed and investigated＇from the spectra and compared with those of same material in different dimensions, and compared with the primary calculation as well. In addition, quite a few new phenomena, which can not be understood based on our present model and knowledge, are also observed; and some very interesting problems are left for further investigation.     

Dynamic Simulation of Single DNA Molecule at the Base Level

A mesoscopic discrete dsDNA model at the base level is proposed based on the statistical model (Phys. Rev. Lett.82 (1999) 4560). The numerical simulations reproduce the 65 pN plateau and those on the force vs extension for different supercoiling degrees are favourable with the experimental data. Our model has potential applications on the study of short DNA segments and provides a bridge between the statistical models and atomic modelling.     

Analysis of the Ro-Vibrational Structure of the Fundamental Band ν6 of 13CHF3 Molecule

Optics and Spectroscopy - The high-resolution IR spectrum of the fundamental band ν6 of 13CHF3 molecule, located in the region of 450–750 cm–1, has been investigated. The spectrum...     

High Two-Beam Coupling Coefficients of Monolithic Small Molecule at Low Electric Field

A novel full-functional photorefractive small molecular material, (9-ethyl-9H-carbazol-3-ylmethylene)-(4-nitrophenyl)-amine (ECYENPA), was synthesized and its photorefractivity was studied by two-beam coupling experiments at a wavelength of 632.8nm. The glass transition temperature of ECYENPA, as low as -5℃, results in the chromophore being orientated easily at room temperature. High two-beam coupling coefficient was obtained to be 232cm^-1 at an electric field of 44.6 V/μm.     

Significance of the Formal Quantum Number in the Highly Excited Vibration of the DCN Molecule

For the eigenstates of the highly excited vibration of the simple molecule DCN with two stretching modes,a classical approach in a multi-dimensional coset phase space is employed to show that the formal quantum numbers are related to regular or least “irregular” trajectories,with zero or least Lyapunov exponents,and are always located in the inner regions of the phase space.This property reflects that they are the approximate constants of motion.It is also demonstrated that formal quantum numbers correspond to the significant phase space dencity.     

Small Molecule Sorption and Desorption in and Out of Iota‐Carrageenan Gels

Small molecule sorption and desorption in and out of Iota‐Carrageenan was studied by using steady‐state fluorescence (SSF) technique. Pyranine dissolved in water used as fluorescence probe. Fluorescence emission intensity, I _p from pyranine was monitored for studying sorption and desorption processes at various temperatures. The Fickian model was applied to produce sorption, D_s, early desorption, D_ed, and desorption, D_d, coefficients. Corresponding activation energies were obtained and found to be 20.5 kJ mol^?1, 7.0 kJ mol^?1 and 34.9 kJ mol^?1, respectively. The observed D_ed value is an order of magnitude smaller than the D_s and D_d coefficients. On the other hand, sorption processes were shown to be twice as fast as desorption processes.     

Theoretical Investigation of a Single Molecule Device： Geometrical Configurations and Electronic Properties

Using the first-principle molecular dynamics simulations, we have studied the molecular geometrical configurations as well as the corresponding electronic structures of a single molecule device assembled by the mechanically controllable break junction technique with variations of the electrode distance. There are some very interesting features varying with the electrode distance.     

Single Molecule Fluorescence of Native and Refolded Peridinin–Chlorophyll–Protein Complexes

Single molecule spectroscopy was applied to study the optical properties of native and refolded peridinin-chlorophyll-protein (PCP) complexes. The native system is a trimer with six chlorophyll a (Chl a) molecules, while the refolded one contains two Chl a and resembles structurally and spectroscopically the PCP monomer. The fluorescence emission of single PCP complexes strongly broadens with increasing excitation power. Simultaneously, the distribution of fluorescence maximum frequencies is also broadened. These spectral changes are attributed to photoinduced conformational changes of the protein that influence the fluorescence of embedded chromophores. Comparison of fluorescence intensities measured for PCP complexes in two different solvents indicates that the native PCP trimers are preserved in EDTA Tris buffer, while in PVA polymer matrix only monomers are stable.     

Effects of Magnetic Field on the Valence Bond Property of the Double—Quantum—Dot Molecule

The effects of the magnetic field on the valence bond property of the double-quantum-dot molecule are numerically studied by the finite element method and perturbation approach because of the absence of cylindrical symmetry in the horizontally coupled dots.The calculation results show that the energy value of the ground state changes differently from that of the first excited state with increasing magnetic field strength,and they cross under a certain magnetic field.The increasing magnetic field makes the covalent bond state change into an ionic bond state,which agrees qualitatively with experimental results and and makes ionic bond states remain.The oscillator strength of transition between covalent bond states decreases distinctly with the increasing magnetic field strength,when the molecule is irradiated by polarized light.Such a phenomenon is possibly useful for actual applications.     

Dynamic Localization Condition of Two Electrons in a Strong dc-ac Biased Quantum Dot Molecule

We present a perturbation investigation of dynamic localization condition of two electrons in a strong dc-ac biased quantum dot molecule.By reducing the system to an Hubbard-type effective two-site model and by applying Floquet theory,we find that the dynamical localization phenomenon occurs under certain values of the large strength of the dc and ac field.This demonstrates the possibility of using appropriate dc-ac fields to manipulate dynamical localized states in mesoscopic devices,which is an essential component of practical schemesfor quantum information processing.Our conclusion is instructive to the field of quantum function devices.     

How Is a Protein Molecule Nearsighted？

The effect range of a local change of a protein molecule is calculated using a cluster method developed in this work based on the Gaussian software. This range is found to be about 8A°, which gives a concrete estimation on the “nearsightedness” by Kohn for protein molecules. The cluster method can be applied to calculation of the electronic density of a large molecule such as a motor protein and can provide a basis for the dynamical analysis of a single protein molecule.     

Charmonium and Meson–Molecule Hybrid Tetraquarks

In the X (3872) decay, both of the ${{J/{\psi\pi\pi}}}$ and ${{J/{\psi\pi\pi\pi}}}$ branching fractions are observed experimentally, and their sizes are comparable to each other. In order to clarify the mechanism to cause such a large isospin violation, we investigate X(3872) employing a model of coupled-channel two-meson scattering with a ${{\rm c}\bar{c}}$ core. The two-meson states consist of ${{D^0\overline{D}^{*0}}}$ , D ⁺ D ^*?, ${{J/{\psi\rho}}}$ , and ${{J/{\psi\omega}}}$ . The effects of the ρ and ω meson width are also taken into account. We calculate the transfer strength from the ${{{\rm c}\bar{c}}}$ core to the final two-meson states. It is found that very narrow ${{J/{\psi\rho}}}$ and ${{J/{\psi\omega}}}$ peaks appear very close to the ${{D^0\overline{D}^{*0}}}$ threshold for a wide range of variation in the parameter sets. The size of the ${{J/{\psi\rho}}}$ peak is almost the same as that of ${{J/{\psi\omega}}}$ , which is consistent with the experiments. The large width of the ρ meson makes the originally small isospin violation by about five times larger.     

Research on the Penetration Characteristic of Supersonic Molecule Beam on the HL-1M Tokamak

In the HL-1M plasma experiments, two refueling ways, the pellet injection and the gas puffing, are usually used. In recent years, a new refueling method, the supersonic molecule beam (SMB) injection, has been developed. SMB injection is an attempt to enhance the penetration depth and the fuelling efficiency of gas, as well as to reduce surface absorption of the injected particles and the impurity content in the plasma. In SMB injection experiments, the gas is injected into the plasma through a Laval nozzle at high gas pressure. In this case, the peak density and improving confinement have been achieved as in the case of a pellet injection.     

AFM‐Based Single Molecule Force Spectroscopy of Polymer Chains: Theoretical Models and Applications

Abstract

In recent years, remarkable advances in research of the mechanical and structural properties of single polymer chains have been achieved thanks to atomic force microscope (AFM)‐based single molecule force spectroscopy (SMFS). This technique offers great possibilities to investigate the mechanical properties of a single polymer chain by static/dynamic force‐extension measurements at the mesoscale level. Data are analyzed with the help of appropriate theoretical models, such as statistical mechanics models for freely jointed chains (FJC) or worm‐like chains (WLC), which can well describe the moderate entropy‐controlled stretch of most polymers, and with semiclassical models, which are being modified using quantum mechanics principles to account for entropic and enthalpic contributions to stretching in the high‐force Hookean regime. In this article we review the theoretical models of single chain stretching, the latest progress in force‐extension measurements by static and dynamic AFM modes for polymer chains dispersed in different solvents and subjected to a force that may induce their conformational transformations, as well as relevant applications.     

Effects of Electric Field on the Valence—Bond Property of an Electron in a Quantum—Dot Molecule

The electronic structure of the quantum-dot molecules in an electric field is investigated by the finite element method with the effective mass approximation.The numerical calculation results show that the valence bond of the quantum-dot molecule alternates between covalent bonds and ionic bonds as the electric field increases.The valence-bond property can be reflected by the oscillator strength of the intraband transition.The bound state with the highest energy level in the quantum-dot molecule gradually changes into a quasibound state when the electric field increases.