Lattice oligomer dynamics

Exact results are obtained for the dynamics of short chains on the cubic lattice in the presence of excluded volume. The dynamics is used to evaluate the vector end-to-end length and squared length correlation functions. These functions are compared to those obtained by computer simulation by Kranbuehl and Verdier for longer chains. A coherent picture of the effects of excluded volume and chain length on the system properties sampled is found.     

Lattice dynamics of tetracyanoethylene

Lattice dynamics calculations for both crystalline forms of tetracyanoethylene are presented. The comparison of the calculated static and dynamical properties with the experimental data, leads us to suggest an improved parameter set for the “6-exp” potential function for crystals with cyano groups.     

Lattice dynamics of cuprous iodide

The lattice dynamics of cuprous iodide have been investigated on the basis of an ‘11-parameter’ rigid-ion model (RIM). The reported neutron scattering data of CuI are reasonably well decribed by the model, especially when an optimized procedure for the selection of parameters is used. Results are presented for the phonon dispersion curves of CuI. The critical point phonon (CPP) frequencies inferred from the model are shown to provide satisfactory assignments of the observed two-phonon features in the available Raman spectrum.     

Lattice dynamics of single-bonded cubic nitrogen

The first principle calculations of the lattice dynamical properties of the single-bonded cubic nitrogen were performed using the density-functional perturbation theory together with plane-wave expansion and nonlocal pseudopotentials. The equilibrium structure of the single-bonded cubic nitrogen was first evaluated via the minimization of the total energy. Then, the harmonic phonon dispersion curves and the density of phonon states of the single-bonded cubic nitrogen have been evaluated within the linear-response framework. Furthermore, the heat capacity, enthalpy, free energy, entropy and velocity of sound of the single-bonded cubic nitrogen were calculated.     

Lattice dynamics of solid hydrogen chloride

Lattice dynamics of solid hydrogen chloride is studied, assuming a rigid molecule, in the harmonic and pair potential (Lennard-Jones interaction) approximation between atoms with the inclusion of electrostatic interactions between point dipoles placed on atomic centres. The potential parameters for each of the different non-bonded atom pairs were obtained by means of an optimization routine to give a least-squares fit to observed zone centre (k = 0) frequencies, equilibrium conditions and lattice energy of the lattice.     

Conformation of p-terphenyl under hydrostatic pressure

The conformation of p-terphenyl (C18H14) and deuterated p-terphenyl (C18D14) has been investigated, using high-pressure infrared spectroscopy at liquid-helium temperatures. First-principles calculations, together with the experimental results, were performed to determine the structure of p-terphenyl in the twisted conformation. At low temperatures and pressures, p-terphenyl belongs to the C2 point group of symmetry. In this configuration, the central ring is twisted with respect to the plane of the outer rings. The symmetry of the molecule is nearly C2h, consistent with previous x-ray diffraction measurements.     

Photopolymerization of diacetylenes under hydrostatic pressure

Photopolymerization of diacetylene-bis (toluenesulfonate) (TS-6) under hydrostatic pressure up to 4 kbar has been studied employing timed-resolved absorption spectroscopy of the trimeric reaction intermediate. Formation of the biradical dimer is a non-thermal process occurring at a rate of 10⁷ s^?1 independent of both temperature and pressure. The rate constant for subsequent monomer addition increases exponentially with pressure delineating existence of a linear relationship between height of the energy barrier and reaction distance which is considered to be the key reaction parameter. Measurement of the photopolymerization yield in TS-6, TS-12 and 4-BCMU under pressure in conjunction with statistical considerations confirm (i) that formation of long chains is limited by preformed short chains and (ii) that in TS-6 and TS-12, yet not in 4-BCMU reaction-induced secondary-chain initiation is important.     

Lattice dynamics of solid α-carbon monoxide

The lattice dynamics of α-CO is studied assuming a fully-ordered antiferro P2₁3 structure, using a potential model which includes electrostatic, dispersion and exchange interactions. The coupling of translational and librational motions leads to mixed modes at finite wave vectors and to anomalous acoustic dispersion. Anharmonic frequency shifts and the damping due to phonon—phonon interactions are evaluated for the zero wave vector modes. The single-particle potential wells for the high-frequency librational modes are investigated and suggest that translation—rotation coupling plays a primary role in the molecular reorientations.     

Adam-Gibbs based model to describe the single component dynamics in miscible polymer blends under hydrostatic pressure

We present in this work a new model to describe the component segmental dynamics in miscible polymers blends as a function of pressure, temperature, and composition. The model is based on a combination of the Adam-Gibbs (AG) theory and the concept of the chain connectivity. In this paper we have extended our previous approach [D. Cangialosi et al. J. Chem. Phys. 123, 144908 (2005)] to include the effects of pressure in the component dynamics of miscible polymer blends. The resulting model has been tested on poly(vinyl methyl ether) (PVME)/polystyrene (PS) blends at different concentrations and in the temperature range where the system is in equilibrium. The results show an excellent agreement between the experimental and calculated relaxation times using only one fitting parameter. Once this parameter is known the model allows calculating the size of the relevant length scale where the segmental relaxation of the dielectrically active component takes place, i.e., the so called cooperative rearrangement region (CRR) in the AG framework. Thus the size of the CRR for PVME in the blends with PS has been determined as well as its dependence with pressure, temperature, and concentration.     

Structure formation under negative pressures

IR and Raman spectroscopy are used to study cubic and orthorhombic modifications of Sb₂O₃. Vibrational spectra are calculated in the approximation of density functional theory; the bands are assigned. Based on the assignment made, vibrational spectra of the α-Sb₃O₂F₅ compound are analyzed.     

Melting of icosahedral nickel clusters under hydrostatic pressure

The thermal stabilities and melting behavior of icosahedral nickel clusters under hydrostatic pressure have been studied by constant‐pressure molecular dynamics simulation. The potential energy and Lindemann index are calculated. The overall melting temperature exhibits a strong dependence on pressure. The Lindemann index of solid structure before melting varies slowly and is almost independent of pressure. However, after the clusters melt completely, the Lindemann index at the overall melting point strongly depends on pressure. The overall melting temperature is found to be increasing nonlinearly with increasing pressure, while the volume change during melting decreases linearly with increasing pressure. Under a high pressure and temperature environment, similar angular distributions were found between liquid and solid structures, indicating the existence of a converging local structure. © 2014 Wiley Periodicals, Inc.     

Lattice dynamics and interaction potentials in molecular crystals

This paper, based essentially on the work done in recent years in our laboratory, presents a critical analysis of harmonic and anharmonic calculations of crystal vibrations in the determination of intermolecular potentials. The main purpose is to show that the dynamical properties are specifically sensitive to different terms of the potential and thus that information extracted from vibrational spectra of crystals is of the greatest importance for the theory of intermolecular forces. The most important conclusion is that these calculations point to the development of anisotropic short-range potentials and orient future researches towards the more complex and elaborate anharmonic treatment of crystal vibrations.     

Lattice dynamics of carbon chain inside a carbon nanotube

Based on the density functional theory, we obtain the optimum geometry of carbon chain inside a carbon nanotube. The phonon spectrum and specific heat of such a chain and nanotube hybrid system are calculated in terms of lattice dynamics theory. Some new phonon branches that have been obtained come from the coupling vibrations of the nanotube and the chain. The bending and stretching modes of the chain appear at about 520 cm(-1)and 1935 cm(-1) at Gamma point, respectively. It is found that the softening of G modes results mainly from the chain induced variations in the bond length on nanotube, independent of van der Waals interaction, while the stiffening of radial breathing mode is developed by the competition between the two factors. In the low-frequency region, the vibrational density of states are very different from that of the bare nanotube. Its specific heat implies the underlying quantized phonon structures and much large thermal conductivity in the hybrid system. In addition, the chain-length dependent vibration modes are calculated, from which it is expected that a finite chain of about 14 carbon atoms in the nanotube may produce the experimental Raman peak at about 1850 cm(-1).     

Mixture model of water under high pressures

A remarkable characteristic of the thermal expansion coefficient is reported in respect of its temperature and pressure dependences. Then, on the basis of the mixture model, important predictions are derived on the properties and structure of water under high pressures.     

Bird muscles under hydrostatic high-pressure/temperature combinations

Breast muscles from three different birds were subjected to hydrostatic high-pressure (400 MPa)/temperature (10–75°C) combinations, and the denaturation-induced effects on the pressurized proteins monitored by DSC. Comparisons with parallel results from heating-alone processes were established. Actin was the most labile moiety to pressurization and myosin together with sarcoplasmic proteins were next in observing pressure-induced denaturation at low temperatures. Some myosin derivatives (fragments or aggregates) and collagen remained native-like under pressure at any temperature. As previously reported, pressure and temperature showed interdependent and antagonistic-like effects. Hydrostatic high-pressure caused severe proteins denaturation at non thermal denaturing temperatures. At thermally active conditions, pressure preserved proteins from subsequent thermal denaturation. This last effect was lower than in similar but destructured myosystems (batters) because of the absence of functional salts but presumably also by steric hindrance.     

Lattice theory of ultrafast excitonic and charge-transfer dynamics in DNA

We propose a lattice fermion model suitable for studying the ultrafast photoexcitation dynamics of ordered chains of deoxyribonucleic acid (DNA) polymers. The model includes both parallel (intrachain) and perpendicular (cross-chain) terms as well as diagonal cross-chain terms coupling neighboring bases. The general form of our Hamiltonian is borrowed from lattice fermion models of quantum chromodynamics. The band structure for this model can be determined analytically, and we use this as a basis for computing the singly excited states of the poly(dA)poly(dT) DNA duplex using configuration interaction singles. Parameters for the model are taken from various literature sources and our own ab initio calculations. Results indicate that the excited states consist of a low energy band of dark charge-separated states followed by separate bands of delocalized excitonic states which have weak mixing between the thymidine and adenosine sides of the DNA chain. We then propose a lattice exciton model based upon the transition dipole-dipole couplings between bases and compare the analytical results for the survival probability of an initially localized exciton to exact numerical results. The results herein underscore the competing role of excitonic and charge-transfer dynamics in these systems.