Molecular Physics

We measure the coherent nonlinear response of excitons in a single-layer of molybdenum disulphide embedded in hexagonal boron nitride, forming a h-BN/MoS 2 /h-BN heterostructure. Using four-wave mixing microscopy and imaging, we correlate the exciton homogeneous and inhomogeneous broadenings. We find that the exciton dynamics is governed by microscopic disorder on top of the ideal crystal properties. Analyzing the exciton ultra-fast density dynamics using amplitude and phase of the response, we investigate the relaxation pathways of the resonantly driven exciton population. The surface protection via encapsulation provides stable monolayer samples with low disorder, avoiding surface contaminations and the resulting exciton broadening and modifications of the dynamics. We identify areas localized to a few microns where the optical response is totally dominated by homogeneous broadening. Across the sample of tens of micrometers, weak inhomogeneous broadening and strain effects are observed, attributed to the remaining interaction with the h-BN and imperfections in the encapsulation process.

We present here a method for selecting optical patterns in a passive semiconductor microresonator, by using a spatial perturbation. A pattern is spontaneously generated in the system, and a switching beam causes this pattern to rotate even if the power in the switching beam is much lower than the power in the pattern. Thus, an all optical switch is realized, that operates at low light levels.

To model the double layer near an electrode, theories and simulations must include the different dielectric coefficients of the electrode, the commonly-postulated 'inner' layer, and the electrolyte. Recently, Boda et al. [D. Boda, D. Henderson, K.-Y. Chan, D.T. Wasan. Phys. Rev. E, 69, 046702, ( )] developed a technique to include inhomogeneous dielectric coefficients in arbitrary geometries in a simulation. Here, Monte Carlo simulation results based on this method are reported for the density profiles of 1:1, 2:2 and 2:1 aqueous electrolytes. The simulations include two dielectric boundaries, one from an inner layer of low dielectric coefficient and one from an uncharged metal electrode. In addition, an extension of a Poisson-Boltzmann (PB) type theory due to Onsager and Samara [L. Onsager, N.N.T. Samara. J. chem. Phys., 2, 528, (1934)] is developed and compared with our simulation results. This approach works best for 1:1 salts at low concentrations.

A comparison of the experimental momentum distribution of electrons in the highest occupied molecular orbital of N(CH,), with the electron momentum distribution of the boron-nitrogen bonding orbital of (CH,),N-BF, shows that the orbital of the complex has a larger relative density of high momentum electrons. This increase in high momentum components is associated n i t h the incrcasc in nodal surfaces in the orbital of the complex in comparison with the orbital of the amine. Qualitative agreement is seen in a comparison of the experimental momentum distributions with distributions calculated from small basis set ab initio position space orbital wave functions. The experimental results are also discussed in terms of the position apace autocorrelation function diffcrcncc M ( r ) . which is demonstrated to provide additional information concerning the orbital interactions. Thc bcn\iti\,it! and uccuracq with which (e,2e) spectroscopy can bc applied to the measurement of valence electron momentum distributions in gas-phase molecules by the present generation of high momentum resolution spectrometers has been well established during recent years.'-3 The basis of the spectroscopic technique is the observation of the high energy electron knock-out. or (e,2e), reaction. When the binding energy of electrons in a particular niolecular orbital differs sufficiently from the binding energy of othcr electrons in the molecule, it is possible to observe (e&) reactions involving essentially only the electrons of that orbital. The experimentally obtained momentum distribution p(p) is then the <phcrical average of the square modulus of the momentum space orbital wave function $ (p). In the work reported here, we have initiated an (e,2e) spectroscopic study of bonding interactions between molecules. Theoretical treatments of chemical reactivity and bonding have demonstrated that molecular interactions are often dominated by the frontier orbitals of the reactant molecule^.^ ( c . 7 ~) rpectroscopy. becnusc it can measure orbital specific momentum distributions. can provide information on such phenomena 215 clcctroii rcdihtribution and rchybridization associated with intcractiona of l'ronticr orbitals. The subject of this invcstigation is the reaction of boron trifluoride (BF,) and trimethylamine (N(CH,),) to form the electron donor-acccptor complex (CH,),N-BF,. Formation of the intermolecular bond involves the donation of charge density from the iionbondiiig highest occupied orbital of thc donor nioleculc Y(Cl13)3 to the antibonding T* lowest unoccupied orbital of the Lcni\ acid RF,. The transfer of electron density from the donor lea& to ;I nenkening of the bonds within the BF, moiety. and the complcu (CH1)?N-BF3 is therefore the product of what has been tcrmcd .in "incipient displacement r e a c t i ~n " . ~, ~ Our approach to tlic b t u d ) of the bonding interaction is to mcasurc thc niomciituiii di\tributions of two molecular orbitals: (i) the nonbonding hiyhcbt occupicd molecular orbital (HOMO) of Y(CH,), and (ii) thc boron-nitrogen bonding orbital of the complex complex (CH,),N-BF,. The orbital of ii is the HOMO of the complex and correlates with the HOMO of N(CH,), and the lowest unoccupied molecular orbital (LUMO) of BF,. By comparing the t \ r o momcntum diytributions. the rearrangement in momentum _-' Inslitutu for Ph!\ic,il Sciencc and Tcchnologq :

The quadrupole Carr± Purcell± Meiboom± Gill NMR experiment using magic-angle spinning (QCPMG-MAS) is analysed as a means of determining quadrupolar coupling and anisotropic chemical shielding tensors for half-integer I > 1/2 quadrupolar nuclei with large quadrupole coupling constants C Q . This is accomplished by numerical simulations and 87 Rb NMR experiments wih Rb2SO4 and Rb2CrO4 using di erent magnetic ® elds. It is demonstrated that (i) QCPMG-MAS experiments typically provide a sensitivity gain by more than an order of magnitude relative to quadrupolar-echo MAS experiments, (ii) non-secular secondorder terms do not a ect the spin evolution appreciably, and (iii) the e ect of ® nite RF pulses needs to be considered when 2x 2 Q / x 0 x RF > 0.1, where x Q 2p C Q / 4I 2I 1 , x RF is the RF amplitude, and x 0 the Larmor frequency. Using numerical simulations and iterative ® tting the magnitudes and relative orientation of 87 Rb quadrupolar coupling and chemical shielding tensors for Rb2SO4 and Rb2CrO4 have been determined.

Observing changes in molecular structure requires atomic-scale Ångstrom and femtosecond spatio-temporal resolution. We use the Fourier transform (FT) variant of laser-induced electron diffraction (LIED), FT-LIED, to directly retrieve the molecular structure of H2O + with picometre and femtosecond resolution without a priori knowledge of the molecular structure nor the use of retrieval algorithms or ab initio calculations. We identify a symmetrically stretched H2O + field-dressed structure that is most likely in the ground electronic state. We subsequently study the nuclear response of an isolated water molecule to an external laser field at four different field strengths. We show that upon increasing the laser field strength from 2.5 to 3.8 V/Å, the O-H bond is further stretched and the molecule slightly bends. The observed ultrafast structural changes lead to an increase in the dipole moment of water and, in turn, a stronger dipole interaction between the nuclear framework of the molecule and the intense laser field. Our results provide important insights into the coupling of the nuclear framework to a laser field as the molecular geometry of H2O + is altered in the presence of an external field. Water plays a crucial role in many physical, chemical and biological processes. In fact, modifying the geometric structure of water can, for example, influence the folding dynamics of proteins surrounded by water solvation shells. 2- 4 Such a modification of molecular structure can be accomplished by exposing molecules to strong fields with field strengths comparable to the Coulombic attraction between electrons and protons. Field-dressing the molecule can lead to a perturbation in its potential energy surfaces, and in turn could lead to a new energy minimum and possible modification of the equilibrium molecular structure on the nuclear (i.e. femtosecond; 1 fs = 10 -15 s) timescale. In fact, external fields with field strengths of around 0.5 V/Å have been theoretically reported to already cause structural changes in a water molecule. 5 Moreover, it is also reported that

In order to investigate the sample dependence of various properties of hydrogenated amorphous silicon (a-Si:H), we have generated four samples with 216 silicon atoms and 24 hydrogen atoms using the density functional based tight binding molecular dynamics simulations. The overall structural properties of these model samples are in agreement with the previous theoretical and experimental results. While the Si-Si and Si-H pair correlation functions are independent of preparation procedure as well as initial conditions, the H-H pair correlation functions are sample dependent. The distribution of hydrogen atoms in all the samples is nonuniform and depends upon the preparation procedure as well as the initial structure from which the hydrogenated amorphous silicon sample is generated. The Si-Si bond length and Si-Si-Si bond angle distributions are nearly independent of sample preparation procedure, but Si-H bond length distributions are sample dependent. The peaks in the vibrational density of states (VDOS) at high frequencies, which are due to the Si-H bond vibrations, are in reasonable accord with the experimental results. The positions of the high frequency peaks are found to be dependent on the local environment which changes from one sample to another. While the high frequency vibrational modes related to Si-Si bond vibrations are moderately localized, the vibrational modes related to Si-H bond vibrations in a-Si:H samples are highly localized. In samples generated from the liquid quench the free energy is smaller, whereas the entropy and specific heat are larger as compared to that of samples generated by hydrogenation of pure amorphous silicon samples. The total electronic density of states and local density of electronic states (LDOS) at Si atom sites are nearly sample independent, while the LDOS at the H atom sites are dependent on the sample preparation procedure.

We predict level degeneracy of the rotational type in diatomic molecules described by means of a cotangent-hindered rigid rotator. The problem is shown to be exactly solvable in terms of non-classical Romanovski polynomials. The energies of such a system are linear combinations of t(t + 1) and 1/[t(t + 1) + 1/4] terms with the non-negative integer principal quantum number t = n + | m| being the sum of the order n of the polynomials and the absolute value, | m|, of the square root of the separation constant between the polar and azimuthal angular motions. The latter obeys with respect to t same branching rule, | m| = 0, 1, ..., t, as does the magnetic quantum number with respect to the angular momentum, l, and in this fashion the t quantum number presents itself formally indistinguishable from l. In effect, the spectrum of the hindered rotator has the same (2t + 1)-fold level multiplicity as the unperturbed one. For low t values wave functions and excitation energies of the perturbed rotator differ from the ordinary spherical harmonics, and the l(l + 1) law, respectively, while approaching them asymptotically with the increase of t. In this fashion the breaking of the rotational symmetry at the level of the representation functions is opaqued by the level degeneracies. The model furthermore provides a tool for the description of rotational bands with anomalously large gaps between the ground state and its first excitation.

We present the quantum mechanics problem of the one-dimensional Schrödinger equation with the trigonometric Rosen-Morse potential. This potential is of possible interest to quark physics in so far as it captures the essentials of the QCD quark-gluon dynamics and (i) interpolates between a Coulomb-like potential (associated with one-gluon exchange) and the infinite wall potential (associated with asymptotic freedom), (ii) reproduces in the intermediary region the linear confinement potential (associated with multi-gluon self-interactions) as established by lattice QCD calculations of hadron properties. Moreover, its exact real solutions given here display a new class of real orthogonal polynomials and thereby interesting mathematical entities in their own.

We demonstrate that optical second-harmonic generation (SHG) from arrays of noncentrosymmetric gold nanoparticles depends essentially on particle geometry. We prepare nanoparticles with different geometrical shapes (L and T) but similar wavelengths for the polarization-dependent plasmon resonances. In contrast to recent interpretations emphasizing resonances at the fundamental frequency, the T shape leads to stronger SHG when only one, instead of both, polarization component of the fundamental field is resonant. This is explained by the character of plasmon oscillations supported by the two shapes. Our numerical simulations for both linear and second-order responses display unprecedented agreement with measurements.

The total cross-sections for the single electron-impact ionization of pyrimidine (C 4 H 4 N 2), 2-chloropyrimidine (2-C 4 H 3 ClN 2), 5-chloropyrimidine (5-C 4 H 3 ClN 2), 2bromopyrimidine (2-C 4 H 3 BrN 2) and 5-bromopyrimidine (5-C 4 H 3 BrN 2) molecules have been calculated with the binary-encounter-Bethe model from the ionization threshold up to 5 keV. The input data for the BEB calculations concerning electronic structure of the studied targets have been obtained with quantum chemical methods including the Hartree-Fock (H-F) and the outer valence Green function (OVGF) methods. The calculated cross-section for the ionization of the pyrimidine molecules due to electron impact is compared with available experimental and theoretical data. The question of the magnitude the pyrimidine ionization cross-section is also discussed, as is the efficiency of the ionization process of studied halogenated derivatives of pyrimidine.

Not Available Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints

The relation between the derivative of the energy with respect to occupation number and the orbital energy, ∂E/∂n i = i , was first introduced by Slater for approximate total energy expressions such as Hartree-Fock and exchange-only LDA, and his derivation holds also for hybrid functionals. We argue that Janak's extension of this relation to (exact) Kohn-Sham density functional theory is not valid. The reason is the nonexistence of systems with noninteger electron number, and therefore of the derivative of the total energy with respect to electron number, ∂E/∂N. How to handle the lack of a defined derivative ∂E/∂N at the integer point, is demonstrated using the Lagrange multiplier technique to enforce constraints. The well-known straight-line behaviour of the energy as derived from statistical physical considerations [J.P. Perdew, R.G. Parr, M. Levy and J.L. Balduz, Phys. Rev. Lett. 49, 1691Lett. 49, (1982))] for the average energy of a molecule in a macroscopic sample ('dilute gas') as a function of average electron number is not a property of a single molecule at T = 0. One may choose to represent the energy of a molecule in the nonphysical domain of noninteger densities by a straight-line functional, but the arbitrariness of this choice precludes the drawing of physical conclusions from it.

In this work, theoretical computations were performed using the Gaussian application. The results of theoretical calculations applying the density functional theory method (DFT) revealed that the azo group of -N=N-possesses a UV spectrum computed employing DFT-TD in the range of 250-500 nm. Several physical parameters were also calculated in this study, including Dipole moment (μ; Debye), HOMO and LUMO energies (EHOMO, ELUMO), energy gap (ΔEg in ev), ionization energy (IP in ev), electronic affinity, hardness, electronegativity, and the electrophiles (Ꞷ, Ꞷ, EA, ɳ, in ev), respectively.

There is a need to develop alternate energy sources in the coming century because fossil fuels will become depleted and their use may lead to global climate change. Inertial fusion can become such an energy source, but significant progress must be made before its promise is realized. The high-density approach to inertial fusion suggested by Nuckolls, et al., leads to reactors compatible with civilian power production. Methods to achieve the good control of hydrodynamic stability (adiabat shaping) and implosion symmetry required to achieve these high fuel densities will be discussed. Examples of symmetry control for targets driven by Z-pinches or heavy ion beams are given. Fast Ignition, a technique that achieves fusion ignition by igniting fusion fuel after it is assembled, will be described along with its gain curves. Fusion costs of energy for conventional hotspot ignition will be compared with those of Fast Ignition and their capital costs compared with advanced fission plants. Finally, techniques that may improve possible Fast Ignition gains by an order of magnitude and reduce driver scales by an order of magnitude below conventional ignition requirements are described. If these innovations are successful, the fusion specific capital costs can be reduced below 10% of the balance of plant.

This study explores the impact of a strong perpendicular laser field on the electronic structure and optical conductivity of bilayer graphene. Employing the Floquet-Bloch theorem and a four-band Hamiltonian model, we calculate the optical conductivity, unveiling modified optical properties due to the altered band structure. We investigate the effects of both circularly and linearly polarized dressing fields on the electronic structure and optical conductivity in the system. Under linear polarization, we observe a notable anisotropy in the band dispersion and optical conductivity, resulting in linear dichroism. In the case of circular polarization, we anticipate the emergence of induced Berry curvature and circular dichroism, especially close to the dynamical gaps. When circularly polarized light is applied alongside a bias potential, the band structure differs for right-handed and left-handed polarization. In this case, the longitudinal optical conductivity remains the same for both, while the transversal optical conductivity exhibits distinct results. Furthermore, the induced Berry curvature and valley asymmetry introduce the potential for generating a valley-polarized current, enabling valley-selective pumping and leading to circular dichroism.

As demonstrated in our previous work [J. Chem. Phys. 149, 174109 (2018)], the kinetic energy imparted to a quantum rotor by a non-resonant electromagnetic pulse with a Gaussian temporal profile exhibits quasi-periodic drops as a function of the pulse duration. Herein, we show that this behaviour can be reproduced with a simple waveform, namely a rectangular electric pulse of variable duration, and examine, both numerically and analytically, its causes. Our analysis reveals that the drops result from the oscillating populations that make up the wavepacket created by the pulse and that they are necessarily accompanied by drops in the orientation and by a restoration of the pre-pulse alignment of the rotor. Handy analytic formulae are derived that allow to predict the pulse durations leading to diminished kinetic energy transfer and orientation. Experimental scenarios are discussed where the phenomenon could be utilized or be detrimental.

The energy levels of methane molecule trapped, at low temperature, in small (s) and large (l) nano-cages of cubic sI clathrates are calculated in the Born-Oppenheimer approximation using the Extended Lakhlifi-Dahoo model based on pairwise atom-atom effective interaction potentials. In the s cage, the center of mass of CH 4 exhibits a slightly asymmetrical 3D oscillation motion with small amplitude around the cage center. Two methods were used to calculate the frequencies of such a motion: a 3D harmonic treatment and a 1D Discrete Variable Representation (DVR) treatment in the X, Y and Z directions. They give approximately the same values of, respectively, 133 cm -1 , 108 cm -1 and 120 cm -1 . In the l cage, the oscillations are anharmonic and characterized by large amplitude motions with frequencies of 63 cm -1 , 52 cm -1 and 47 cm -1 . In the s and l nano-cages, the molecule exhibits strongly perturbed rotational motion. The rotational level schemes are quite different from that of the molecular free rotational motion, and for each nano-cage, the obtained levels are described as combination of the free rotation levels.

The localized surface plasmon resonance (LSPR) spectral band of a gold or silver nanoparticle is observed to shift as a result of the near-field plasmonic field of another nanoparticle. The dependence of the observed shift on the interparticle distance is used as a ruler in biological systems and gave rise to a plasmonic ruler equation in which the fractional shift in the dipole resonance is found to decrease near exponentially with the interparticle separation in units of the particle size. The exponential decay length constant was observed to be consistent among a small range of nanoparticle sizes, shapes, and types of metal. The equation was derived from the observed results on disks and spherical nanoparticles and confirmed using results on a DNA conjugated nanosphere system. The aim of the present paper is to use electron beam lithography and DDA calculations to examine the constancy of the exponential decay length value in the plasmonic ruler equation on particle size and shape of a number of particles including nanoparticles of different symmetry and orientations. The results suggest that the exponent is almost independent of the size of the nanoparticle but very sensitive to the shape. A discussion of the nanoparticles most suitable for different applications in biological systems and a comparison of the plasmonic ruler with Forster resonance energy transfer (FRET) is mentioned.

Straipsnyje pateikiama vadybinės kompetencijos samprata, jos įvertinimo ir taikymo galimybės mokymo procese. Formuluojami vadybinės kompetencijos nustatymo kriterijai bei siūloma metodika skirta neformaliu ir savaiminiu būdu įgytų vadybinių kompetencijų įvertinimuiThe article provides the concept of managerial competence, the possibilities to form and assess it in the teaching process. The authors enunciate criteria for the evaluation of managerial competence and propose the model for the assessment of managerial competences acquired by non-formal and informal learningVytauto Didžiojo universiteta

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Femtosecond optical Kerr dynamics in various transparent liquids were measured using incoherent light with a 60 fs autocorrelation width. From the measurement of the optical Kerr effect (OKE) of binary mixtures of CS2 and various liquids, the contribution of the intermolecular interaction-induced polarizability change to the OKE was found to be affected remarkably by the femtosecond molecular dynamics of CS2. Especially, data from diluted solutions of CS2 in nonviscous solvents composed of molecules with a low molecular weight are consistent with the binary collision model in free space. An oscillatory feature, which was attributed to an intermolecular vibrational mode, was found in the OKE dynamics of neat benzene and several benzene derivatives. A theoretical expression for the delay-time dependence of the signal intensity was also derived with no restriction on the statistical properties of the incoherent light. It is expressed in terms of the autocorrelation function of the inte...

Four proteins are selected to represent each of the four different CATH classes and, for each protein, three decoys are built with structures that are totally alien to the native state. The decoys are scored against the native state with the help of the AMBER force field, using three measures: the average energy, the average fluctuation and the resistance to a heat pulse. Two sets of simulations are performed, one with explicit solvent and another set with implicit solvent. The overall conclusion is that of these three measures that which is most successful in picking out the native states is the last one since the native structures take a consistently longer time to be destabilized in this manner. But the general conclusion is also that none of measures is completely effective in discriminating all the decoys, a result that supports other studies according to which the native state is reached by a kinetic step.

Thermoplastic urethane (TPU) nanocomposite was prepared successfully by dispersion at high shear stress of the nanoclay in polyol and further bulk polymerization. Our results from DSC studies showed an increase in decomposition temperature when nanoclay was loaded at 3,5% on elastomeric PU made from TDI, PTMEG and BDO, while not when nanoclay content was lower (1,5%). The exotherms at 370-375ºC could be adscribed to the decomposition of the hard segments according to previous work.

Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angström spatial precision is one of the critical challenges in the chemical sciences, as the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. Here we report a gas-phase electron diffraction experiment using megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved a combination of 100 fs root-mean-squared temporal resolution and sub-Angstrom (0.76 Å) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomica...

Aqueous solutions of rare gases are studied by computer simulation employing a polarizable potential for both water and solutes. The use of a polarizable potential allows to study the systems from ambient to supercritical conditions for water. In particular the effects of increasing the concentration and the size of the apolar solutes are considered in an extended range of temperatures. By comparing the results at increasing temperature it appears clearly the change of behaviour from the tendency to demix at ambient conditions to a regime of complete solubility in the supercritical region. In this respect the role of the hydrogen bond network of water is evidenced.

The two-photon spectrum of the 2 1 A g Á 1 1 A g transition in trans-stilbene has been calculated at the complete active space self-consistent ®eld (CASSCF) level of theory. Energies were obtained at the complete active space second-order perturbation (CASPT2) level of theory, while the geometries of both the initial and ®nal states were optimized at the CASSCF level. The energy and the geometry optimizations were performed using an active space of 14 electrons in 14 active º orbitals. The vibrational frequencies of both states and the two-photon transition (TPT) cross-section were calculated with a smaller active space where the two lowest º orbitals were kept inactive. A newly implemented algorithm, in the quantum chemical package Molcas was used to determine the two-photon transition intensity. This method requires only the linear response of the CASSCF wavefunction. Furthermore, the vibronic structure of this TPT was studied. The Franck±Condon factors were obtained by calculating the overlap between the vibrational states involved, which were determined from the force ®elds of both the initial and ®nal states, at the CASSCF level of theory. The results are in agreement with experiment.

The effect of repulsive interactions (geometrical packing of molecules) on mixing properties is examined considering hard sphere solutes of different diameters in the hard sphere and pseudo-hard body solvents. It is shown that the fluid of pseudo-hard bodies, representing repulsive interactions in water, captures, without any parameter adjustment, the experimentally observed decrease of the partial molar volume of nonpolar solutes (hard spheres) at their low concentrations when compared to that in a nonpolar (hard sphere) solvent.

Molecular simulation data of the vapour-liquid equilibria (VLE) published in the period [2005][2006][2007][2008][2009][2010][2011][2012][2013][2014][2015][2016] and listed in the Web-of-Science collection have been scrutinised and their correctness examined using the recently proposed exact compressibility factor criterion [I. Nezbeda, J. Chem. Eng. Data 61, 3964 (2016)]. It turns out that a large number of the examined data are very inaccurate, if not completely wrong, and this is illustrated by several examples. This problem goes, unfortunately, unnoticed and the data are further used by other researchers. The finding goes hand-in-hand with the becoming practice of ignoring the common etiquette of presenting (pseudo)experimental data, i.e. to provide sufficient information both on technical details and on data post-simulation processing which could enable anyone their independent check and further reliable use. Moreover, the problem of the correctness of published data does not concern only VLE data but any simulation results and these cases along with potential reasons are therefore also briefly discussed. An appeal is therefore made both to the community of simulators and users to examine data using available tools before publishing or using them. Similarly, an appeal is made also to reviewers to insist that the submitted papers with simulation data do contain all necessary details.

Thermodynamic properties of binary mixtures of hard spheres of various size and pseudo-hard bodies, mimicking the short-range non-additive repulsive interactions in realistic models of water, have been determined over the entire concentration range using standard NVT Monte Carlo simulations. Virial coefficients of the mixture have also been computed. Having no other theoretical tool currently available, a perturbed virial expansion is examined with respect to its potential to estimate/predict the properties of the mixture without resorting to any fitting of simulation data. The perturbed virial expansion is found to perform quite accurately for the mixtures containing larger spheres, whereas for small spheres dissolved in water the result is only qualitatively correct.

The article presents a theoretical framework for molecular dynamics simulations of complex systems subject to any combination of holonomic and non-holonomic constraints. Using the concept of constrained inverse matrices both the particle accelerations and the associated constraint forces can be determined from given external forces and kinematical conditions. The formalism enables in particular the construction of explicit kinematical conditions which lead to the well-known Nosé-Hoover type equations of motion for the simulation of non-standard molecular dynamics ensembles. Illustrations are given for a few examples and an outline is presented for a numerical implementation of the method.

The scattering law for inelastic neutron scattering from classical systems is derived by treating the wavefunctions of the scattering system in the stationary phase approximation and taking the classical limit of the Wigner phase space distribution function. In this way recoil effects are properly accounted for and the scattering law fulfils the relation of detailed balance. It is shown why classical van Hove correlation functions do not properly describe neutron scattering from classical systems.

The low-frequency dynamics (&lt;20 meV) of pure and sodium-doped trans polyacetylene are investigated using a combination of incoherent neutron scattering spectroscopy and molecular dynamics simulations. The simulations are performed using a molecular mechanics potential function and including explicitly the three-dimensional crystal environments of the molecules. Both the experiments and the simulations indicate that doping results in a marked change in the vibrational density of states of the polyene chains in the direction perpendicular to the chain axes, a broad minimum appearing at ∼16 meV. This spectral region is dominated by intramolecular torsional displacements. The results also suggest that the mean-square displacements of the polyacetylene atoms become more isotropic on doping. The contributions of various rigid-body motions to the simulation-derived mean-square displacements and vibrations are described.

Laser measurements of the intensity of (201) 3 22 -(000) 2 21 near-infrared water absorption line at 10670.1 cm -1 are made using three different Herriott cells. These measurements determine the line intensity with an standard deviation below of 0.3 % by consideration of the new geometrically derived formula for the optical path length without approximations. This determination together with the current accepted value leads to an overall uncertainty of 0.7 % of the experimentally assessed line intensity which is compared with previous ab initio predictions. It is found that steady improvements in the both the dipole moment surface (DMS) and potential energy surface (PES) used in the theoretical studies leads to systematic better agreement with the observation, with the most recent prediction agreeing closely with the experiment.

We study the spectrum of vibrational modes in metal nanoparticles with a dielectric core. Vibrational modes are excited by the rapid heating of the particle lattice that takes place after laser excitation, and can be monitored by means of pump-probe spectroscopy as coherent oscillations of transient optical spectra. In nanoshells, the presence of two metal surfaces results in a substantially different energy spectrum of acoustic vibrations than for solid particles. We calculated the energy spectrum as well as the damping of nanoshell vibrational modes. The oscillator strength of fundamental breathing mode is larger than that in solid nanoparticles. At the same time, in very thin nanoshells, the fundamental mode is overdamped due to instantaneous energy transfer to the surrounding medium.

The results obtained from theoretical calculations using the Gaussian 09 program using density functional (DFT) theory through calculated each of structural, electronic, thermal, and mechanical properties such as Poisson's ratio, Young's modulus, and shear modulus from the elastic constants calculated for Ni2Ti. Also, that prepared these alloys and tested on people of both sexes to learn how important it is to improve orthodontic treatments and found that the results obtained in experimental and theoretical compatible to some extent.

Yukawa mixtures are important microscopic models of liquids. In order to obtain their properties, we must have accurate and consistent theories, without the issues arising from the multi-valued pressures and chemical potentials due to inconsistencies in the theory. This work tests two selfconsistent integral equation theories (IETs): the modified hypernetted-chain (MHNC) theory and the zero-separation (ZSEP) based theory. These equations, by construction, automatically satisfy the pressure consistency the Gibbs-Duhem relation, as well as the zero-separation theorem. To verify, new Monte-Carlo (MC) simulations are carried out for temperatures 0.7 < T * < 1.1 and densities 0.4 < ρ * < 0.5. The Yukawa interactions u ij are symmetric (u 11 = u 22 ). The unlike u 12 is made weaker than the like-type by a factor α < 1. The structures, exemplified by the radial distribution functions, are accurately reproduced by both MHNC and ZSEP. The internal energies are predicted to within 1% of the MC data, the pressures to within 4%; and the chemical potentials to less than 3%. The vapour-liquid phase envelope is determined for a typical mixture. In this case the performance of both IETs is also shown to be satisfactory.

Taylor & Francis makes every effort to ensure the accuracy of all the information (the "Content") contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.

In this work the path integral formulation for rigid rotors, proposed by Müser and Berne [Phys. Rev. Lett. 77, 2638 (1996)], is described in detail. It is shown how this formulation can be used to perform Monte Carlo simulations of water. Our numerical results show that whereas some properties of water can be accurately reproduced using classical simulations with an empirical potential which, implicitly, includes quantum effects, other properties can only be described quantitatively when quantum effects are explicitly incorporated. In particular, quantum effects are extremely relevant when it comes to describing the equation of state of the ice phases at low temperatures, the structure of the ices at low temperatures, and the heat capacity of both liquid water and the ice phases. They also play a minor role in the relative stability of the ice phases.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Charge-dipole interactions are very common interactions among atoms and molecules, especially materials that can emit light or contain free charges. The second-order charge-dipole interactions, proportional to 1 R 4 , are stronger than the second-order dipole-dipole interactions or van der Waals interactions, proportional to 1 R 6 , at longer distances. In reality, there is more than one atom or charge; therefore, we focus on few-body charge-dipole interactions, such as charge-dipole-dipole interactions. Laser cooling and trapping allow us to study such interactions with much higher precision. In this article, charge-dipole interactions will be investigated in cold gases. To increase the interaction strength, we excite the cold atoms to highly excited states, Rydberg states. Here, we treat one Rydberg atom as a dipole; the excited electron and the ion core are the two poles of an electric dipole. Specifically, we study charge-atom interactions in cold Rydberg gases. The laser-cooled lower level atoms were excited to highly excited states, and we scanned a microwave to look at the line shape of a particular transition between two Rydberg states. It has been shown that adding a charge can enhance atom-atom interactions under certain circumstances.

An interpretation of the Raman spectra of GaAs/A1As ultrathin-layer superlattices based on the microscopic analysis of the optical vibrational modes has been reported. The difFerence between normal and inverted interfaces is responsible for the lack of the inversion symmetry of the layers with respect to the central plane, therefore confined modes can no longer be considered as even or odd ones. All the optical vibrational modes, independently of their quantum index, are now active in Raman scattering. Our results show the evidence of the strong difFerence between the distribution of the Ga and Al atoms at the normal and inverted interfaces.