Electron phonon interactions and superconductivity in α ′ -TTF[Pd(dmit)2]2

A simple model is developed to understand superconductivity in α ^′ -TTF[Pd(dmit)₂]₂. We include electron-intra molecular and intermolecular phonon interactions as the mechanism of superconductivity. Intramolecular vibrations included are the eight symmetric A_g modes of the Pd(dmit)₂ molecule. Intermolecular vibrations included are the longitudinal acoustic and transverse acoustic (LA and TA) modes of the Pd(dmit)₂ column. All the electron-phonon coupling constants are calculated from first principles. We find that largest el-intramolecular vibration coupling is to the A_g mode with the highest frequency (1449 cm^-1). The el-intermolecular coupling to the LA mode is found to be larger than the total el-intramolecular couplings. We also find el-(TA)phonon coupling to be at least an order of magnitude smaller than el-(LA)phonon coupling. Estimate of superconducting transition temperature is comparable to experimental result. We also provide a detailed discussion, employing the results of recent numerical calculations on two-chain Hubbard model and the specific material parameters, on the relative importance of el-ph and Coulomb-origin mechanisms of superconductivity in α ^′ -TTF[Pd(dmit)₂]₂ and TTF[Ni(dmit) ₂ ] ₂ . Received 29 March 2001 and Received in final form 7 August 2001     

Probability diffusion in non-Markhovian,non-Gaussian molecular ensembles: A theoretical analysis and computer simulation

A theoretical generalisation of the Fokker/Planck equation for atomic and molecular diffusion is compared with the results of a molecular dynamics simulation of a triatomic molecule ofC _2v symmetry. The molecular dynamics results are non-Markhovian and non-Gaussian in nature, markedly so in the case of the centre of mass linear velocityV. This may be ascertained by simulating the long-time limit of the three dimensional kinetic energy autocorrelation function <V ²(t)V ²(0)>/<V ²(0)V ²(0)>, which falls well below the theoretical Gaussian value of 3/5. By expressing the Mori continued fraction as a multidimensional Markhovian chain of differential equations and expressing this in turn as a non-Gaussian probability-diffusion equation of the Kramers/Moyal type it is possible to account for the simulation results in a qualitative fashion.     

Theoretical study of molecular ordering in liquid crystals with the help of intermolecular interaction energy calculations

A theoretical analysis has been carried out to determine the molecular alignment of some nematic liquid crystals like DPAB (4, 4'-di-n-propoxy-azoxybenzene), EPAB (ethyl para-azoxybenzoate) and PAA (para-azoxyanisole). CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecules. Configurational energy has been computed using a modified Rayleigh-Schrodinger perturbation method at an interval of 1 Å in translation and 10° in rotation between a pair of DPAB molecules. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements between a molecular pair have been considered. A comparative picture of molecular parameters like total energy, binding energy, total dipole moment etc., has been obtained. An attempt has been made to explain the nematogenic behaviour of liquid crystal and thereby develop a molecular model for liquid crystallinity.     

Influence of molecular association on the solubility of methylxanthines in supercritical solvent CO<Subscript>2</Subscript>–methanol

Analysis of the experimental data on the solubility of methylxanthines (theophylline and theobromine) in supercritical (SC) solvent CO₂–methanol at various concentrations of methanol within the framework of the ASL model (Associated Solution + Lattice) based on molecular association theory and the simple lattice model is presented. Hetero-association of methylxanthines with the molecules of methanol is studied by means of ¹H NMR spectroscopy at 313 K. The contribution of molecular association to the solubility of methylxanthines in the mixed SC solvent CO₂–methanol is analyzed. It is shown that the presence of NH group in the molecule of methylxanthine, when passing from caffeine to theophylline or theobromine, leads to an increase of the contribution of the component related to molecular association to solubility.     

Constrained reaction coordinate dynamics for systems with constraints

In the context of molecular dynamics simulations of rare events, the application of constraints on a suitable reaction coordinate has often been found useful for sampling of the free energy barrier. The efficiency of these calculations is hampered by geometrical difficulties, related to the metric factor and inertial forces. Some years ago Mulders et al. [1996, J. chem. Phys., 104, 48691 suggested a way to simplify the approach. Their idea was demonstrated shortly afterwards by Sprik and Ciccotti [1998, J. chem. Phys., 109, 77371. The present paper extends these results to vector reaction coordinate and molecular systems modelled with holonomic constraints.     

EPR Investigations on Molecular Orientation of Paramagnetic Liquid Crystals in a Surface-Stabilized Liquid Crystal Cell: Studies on a Smectic C or Chiral Smectic C Phase

By electron paramagnetic resonance spectroscopy we investigated the molecular orientation in a surface-stabilized liquid crystal (LC) cell, which includes a racemic (±) or an enantiomerically enriched (S,S) paramagnetic LC, (2S,5S)-2,5-dimethyl-2-tridecyloxyphenyl-5-[4-(4-tridecyloxy-benzenecarbonyloxy)phenyl]pyrrolidine-1-oxy (2), whose spin source is fixed inside the rigid core. For both the smectic C (SmC) phase of (±)-2 and the chiral smectic C (SmC^*) phase of (S,S)-2 in a surface-stabilized LC cell (antiparallel configuration, thickness of 4 μm), the profile of the observed g-value as a function of the angle between the applied magnetic field and the cell plane could be explained by the orientation model, where, with some disordering, the molecules align uniformly with the direction which tilts from the normal line of the smectic layer being orthogonal to the rubbing direction on the cell surface. We divided the effect from the disordering into two parts, one of which is concerning the direction of the molecular long axis and the other is concerning the rotation around the molecular long axis. As a result of the analysis, the SmC^* phase gave quite lower ordering concerning the direction of the molecular long axis and a little lower ordering concerning the rotation around the molecular long axis than the SmC phase at the same temperature (80 °C). The obtained lower ordering in the SmC^* phase is probably due to the chirality that would result in the formation of a helical superstructure in a bulky state. Authors' address: Yohei Noda, Laboratory of Electron Spin Chemistry, Department of Chemistry, Graduate School of Science, Kyoto University, 606-8502 Kyoto, Japan     

Mechanism for giant electro-optic response of porphyrin J-aggregates in polymer film and aqueous solution

We report the dependence of the polarizability difference Δα on the orientational distribution of porphyrin J-aggregates. For quasi-one-dimensionally oriented aggregates in a polymer film, the red shift in Y ∥ F configuration was about 2 to 3 times smaller than that in Y ∥ F configuration, where Y is the orientational direction of the J-aggregates and F is the applied AC electric field vector. For an aqueous solution where J-aggregates were three-dimensionally oriented, the exciton band showed an electric-field-induced broadening. In addition, a red-shifted signal for two-dimensionally oriented aggregates in the polymer film was reduced by one order of magnitude at 77K compared with that at room temperature. These results were explained reasonably well by the molecular rearrangement model, which was applied to a variety of orientational distributions.     

Molecular effect on interatomic potentials

Abstract

In the low energy atomic collision of ε ≤ 0.1, the energy dissipation of projectile ion is mainly by the nuclear stopping. In this energy range Z-oscillation appears on ranges and range stragglings. In order to explain this osciallation from the viewpoint of molecular effect on interatomic potentials, an extended Hückel method is adopted for potential calculation. The Z-dependence on interatomic potentials to describe respective atomic collisions is similar to that of Z ₁-range oscillation. It suggests a possibility of molecular effect on the Z ₁-range oscillation.     

Molecular Structure of 3-Hydroxy-4-Pyrone

Abstract

Aerial parts of Erigeron annuus and E. strigosus afforded 3-hydroxy-4-pyrone, the molecular structure of which was determined by single crystal X-ray diffraction.     

Predictability of ion transport properties from the structure of solid electrolytes

The concept of bond valence (BV) is widely used in crystal chemical considerations, e.g. to assess equilibrium positions of atoms in crystal structures from an empirical relationship between bond lengthR _M−X and bond valenceS _A−X =exp [(R ₀ −R _M−X ) /b] as sites where the BV sumV(A)=∑ s _M−X equals the formal valenceV _id of the cationM ⁺ . Our modified BV approach that systematically accounts for the softness of the bond may then be effectively used to study the interplay between structure and properties of solid electrolytes. This is exemplified for correlations to experimental data from IR, NMR, and impedance spectroscopy. Combining the bond valence approach with reverse Monte Carlo (RMC) modeling or molecular dynamics (MD) simulations provides a deeper understanding of ion transport mechanisms, especially in highly disordered or amorphous solids. Local structure models for crystalline electrolytes are derived by combining crystallographic structure information with simulations. A method for the prediction of the activation energy of the ionic conductivity from the bond valence analysis of the crystal structure is proposed. Taking into account the mass dependence of the conversion factor from bond valence mismatch into an activation energy scale, we could establish a correlation that holds for different types of mobile ions. The strong coupling of the H⁺ transfer to the anion motion in proton conductors requires a special treatment. For glassy solid electrolytes RMC structure models are BV-analyzed to assess the total number of equilibrium sites and to identify transport pathways for the mobile ions. Recently, we have reported a correlation between the pathway volume fraction and the transport properties that permits to predict both absolute value and activation energy of the dc ionic conductivities of disordered solids (including mixed alkali glasses) directly from their structural models. Here we discuss a corresponding BV analysis of molecular dynamics simulation trajectories that allows quantifying the evolution of pathways in time and the influence of temperature on the transport pathways. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 — 18, 2004.     

The mutual interaction of molecular rotation and translation

The dynamics of molecular rototranslation are treated with an equation of motion with a non-Markovian, stochastic force/torque. It is shown that this Mori/Kubo/Zwanzig representation is equivalent to a multidimensional Markov equation which may be identified with analytical models of the molecular motion. Langevin and Fokker-Planck equations for two such models are derived from the general equations of motion. The analytical results are compared with a computer simulation of the velocity/angular velocity mixed autocorrelation function, C _vω(t) = <v(0) . ω(t)> for a triatomic of C _2v symmetry.     

Recent Analytical Applications of Molecular Spectroscopy in Bioorganometallic Chemistry—Part I: Metal Carbonyls

Abstract: This is the first part of a two-part review on the analytical applications of molecular spectroscopy in bioorganometallic chemistry since 2005. In this case, radiopharmaceutical studies are included and the review is focused particularly on biological molecules labeled with metal carbonyl fragments.     

Heterodyne coincidence spectroscopy

A new type of light-scattering experiment, which should measure directly the triple static structure factor S ⁽³⁾ (k, q) of a fluid, is proposed. S ⁽³⁾(k, q) is the full spatial Fourier transform of the equilibrium triplet distribution function g ⁽³⁾(r ₁, r ₂, r ₃). The experiment may also be used to study dynamic correlation functions of the form <a_k (t)a_q (t′)a_k_q(t″)> (where a_k () is the kth spatial Fourier component of the density), thereby giving new information on mode-mode coupling. The method obtains its information from triple correlations in the arrival of scattered photons at three detectors. The detectors must be operated in the heterodyne mode (i.e. with a local oscillator); the scattering volume must be much larger than the volume over which molecular positions are correlated. Comparison is made with previous analyses of other multi-detector experiments.     

Properties and structure of GaAs films grown by molecular beam epitaxy on GaAs substrates with the (100), (111)A, and (111)B orientations

The structural perfection of GaAs epitaxial films grown by molecular beam epitaxy on substrates with the (100), (111)A, and (111)B orientations is investigated by double-crystal and triple-crystal x-ray diffractometry. It is found that the ratio γ of the molecular fluxes of arsenic and gallium has a strong influence on the structural quality of the epitaxial films. The optimum values of the parameter γ are found for each of the substrate orientations (100), (111)A, and (111)B. Zh. Tekh. Fiz. 69, 68–72 (July 1999)     

Molecular and electronic structure of zwitterionic diamino-meta-quinonoid molecules

Quantum chemical calculations using molecular orbital (HF, CASSCF) and density functional theory (B3LYP) methods, in conjunction with the 6–311 + + G(d,p) basis set, have been applied to investigate the molecular and electronic structure of two diamino-meta-quinonoid molecules 1a and 2a, each containing a six-membered ring coupled with two exocyclic C = O bonds situated in a meta position, along with two amino substituents (NH₂ and NH-CH₃). It is confirmed that these substituted meta-quinone systems exhibit a zwitterionic structure in which the positively charged N-C-C(H)-C-N subunit, containing the two amino-groups, forms two chemical bonds with the negatively charged O-C-C(H)-C-O subunit. The negative charge amounts to about half of an electron. The charge separation has been approached in terms of geometries, vibrational frequencies, and electronic distribution. The ionization energy for molecule 1a is about 7.8±0.3eV. The quinonoid systems are essentially non-aromatic characterized by the NICS(+1) values of around 1.2 ppm.     

Primary isotopic effect on the magnetic shielding of tin nuclei (117Sn and 119Sn)

The Kirkwood-Buff statistical mechanical theory of surface tension γ for monatomic fluids is extended to molecular fluids. A rigorous expression for γ is derived in terms of the angular pair distribution function f(z ₁ R ₁₂θ₁θ₂) of an equilibrium fluid-fluid system (liquid-gas, liquid-liquid, or gas-gas). The Fowler approximation is applied for the liquid-gas case, and a simple expression for γ is derived in terms of the bulk liquid angular pair correlation function g(R ₁₂θ₁θ₂). Thermodynamic perturbation theory for g(R ₁₂θ₁θ₂) is also used to calculate γ theoretically. The theoretical results are compared with experimental values.     

Packing of molecules and hole formation in lyotropic systems

A vector field q (the order parameter of the molecular packing) describing the packing (specifically, the orientation) of membrane-forming amphiphilic molecules is introduced to describe the structures of lyotropic phases constructed from membranes. In the general case q·n≠0 (where n is the unit normal vector) and therefore the singularities of the vector field q are not determined uniquely by the topology of the surface. The condition q·n=0 signifies disruption of the packing of the molecules. This corresponds to holes, which can form in membranes when lyotropic systems are diluted. As an illustration, the simplest type of such singularities, in which the distribution of the field q around a hole is described by a part of an instanton with unit topological charge, is studied. It is shown that such a distribution guarantees the existence of a local minimum under the condition that the tension per unit length λ of the hole boundary is small compared with the deformation energy of the field q: λh/K≪l (K is the modulus of the orientational elasticity of the field q and h is the thickness of the membrane). The radius of the hole which is formed equals L≈2.52(K/λh)^1/3 and the energy E≈59.79K(λh/K)^1/3. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 575–580 (25 October 1996)     

Electronic structure,absorption spectra,and hyperpolarisabilities of some novel push–pull zinc porphyrins. A DFT/TDDFT study

DFT/TDDFT calculations have been performed on some novel push–pull zinc porphyrins (denoted ZnPor 1, ZnPor 2, and ZnPor 3). This theoretical work aims to investigate the electronic structure, absorption spectra, and hyperpolarisabilities of these molecules. To examine the effects of the peripheral substituents on the molecular properties, zinc porphine (ZnP) and zinc tetraphenylporphine (ZnTPP) were also included in the study. The orbital energy level patterns of the substituted zinc porphyrins are indeed rather different from those of ZnP and ZnTPP. The peripheral substitution breaks the molecular D_4h symmetry of the porphyrin, thereby leading to the splitting of the absorption Q band. On the other hand, the B band in the spectra may not arise only from a single excited state; instead, it could be made up of several states that are close in energy. The calculated hyperpolarisabilities (β _vec) increase strongly from ZnPor 1 to ZnPor 2 to ZnPor3. The latter two molecules were predicted to have a large β _vec value and thus may have potential application in the development of nonlinear optical (NLO) materials.     

Finite Maxwell field and electric displacement Hamiltonians derived from a current dependent Lagrangian

ABSTRACT

In the common Ewald summation technique for the evaluation of electrostatic forces, the average electric field E is strictly zero. Finite uniform E can be accounted for by adding it as a new degree of freedom in an extended Lagrangian. Representing the uniform polarization P as the time integral of the internal current and E as the time derivative of a uniform vector field A, we define such an extended Lagrangian coupling A to the total current j _t (internal plus external) and hence derive a Hamiltonian resembling the minimal coupling Hamiltonian of electrodynamics. Next, applying a procedure borrowed from nonrelativistic molecular electrodynamics the j _t · A coupling is transformed to P · D form where D is the electric displacement acting as an electrostatic boundary condition. The resulting Hamiltonian is identical to the constant-D Hamiltonian obtained by Stengel, Spaldin and Vanderbilt (SSV) using thermodynamic arguments. The corresponding SSV constant-E Hamiltonian is derived from an alternative extended Lagrangian.     

Constant pressure-constant temperature molecular dynamics: a correct constrained NPT ensemble using the molecular virial

In the present work we introduce a simple, Nosé—Hoover style isothermal—isobaric molecular dynamics method for systems with holonomic molecular constraints and the molecular representation of the virial. We prove, using the non-Hamiltonian dynamics approach, recently developed by Tuckerman et al. [1999, Europhys. Lett., 45, 149], that the phase space distribution, generated by our equations, samples the desired ensemble under all circumstances. We also write down the explicit reversible integrator for our equations. This integrator has been implemented in the last version of the DLProtein program.