Search results for "Normal mode"
showing 10 items of 75 documents
On the interpretation of the experimental Raman spectrum of β-eucryptite LiAlSiO4 from atomistic computer modeling
2000
Abstract The vibrational spectrum of β-eucryptite LiAlSiO4 with stuffed high quartz structure – commercially relevant for zero-expansion glass ceramics – was calculated by lattice energy minimization and diagonalization of the dynamical matrix using an ab initio based ion-pair shell model potential. A full symmetry analysis of the vibrational modes was carried out. Raman activity of vibrations was calculated under parameterization of individual polarizability factors for each type of interatomic bonds in β-eucryptite LiAlSiO4. Calculated vibrational energies agree with the experimental energies within ±2.3%. Agreement of calculated spectroscopic Raman intensities with experimental intensiti…
Non-Markovian dynamics from band edge effects and static disorder
2017
It was recently shown [S. Lorenzo et al., Sci. Rep. 7, 42729 (2017)] that the presence of static disorder in a bosonic bath - whose normal modes thus become all Anderson-localised - leads to non-Markovianity in the emission of an atom weakly coupled to it (a process which in absence of disorder is fully Markovian). Here, we extend the above analysis beyond the weak-coupling regime for a finite-band bath so as to account for band edge effects. We study the interplay of these with static disorder in the emergence of non-Markovian behaviour in terms of a suitable non-Markovianity measure.
Quantum non-Markovianity induced by Anderson localization
2017
As discovered by P. W. Anderson, excitations do not propagate freely in a disordered lattice, but, due to destructive interference, they localise. As a consequence when an atom interacts with a disordered lattice one indeed observes, a non-trivial excitation exchange between atom and lattice. Such non-trivial atomic dynamics will in general be characterised also by a non-trivial quantum information backflow, a clear signature of non-Markovian dynamics. To investigate the above scenario we consider a quantum emitter, or atom, weakly coupled to a uniform coupled-cavity array (CCA). If initially excited, in the absence of disorder, the emitter undergoes a Markovian spontaneous emission by rele…
Frequency Range Selection Method for Vibrational Spectra
2018
Theoretical calculations of vibrational properties are widely used to explain and predict experimental spectra. However, with standard quantum chemical methods all molecular motions are considered, which is rather time-consuming for large molecules. Because typically only a specific spectral region is of experimental interest, we propose here an efficient method that allows calculation of only a selected frequency interval. After a computationally cheap low-level estimate of the molecular motions, the computational time is proportional to the number of normal modes needed to describe this frequency range. Results for a medium-sized molecule show a reduction in computational time of up to 1 …
Eulerian models of the rotating flexible wheelset for high frequency railway dynamics
2019
Abstract In this paper three formulations based on an Eulerian approach are presented to obtain the dynamic response of an elastic solid of revolution, which rotates around its main axis at constant angular velocity. The formulations are especially suitable for the study of the interaction of a solid with a non-rotating structure, such as occurs in the coupled dynamics of a railway wheelset with the track. With respect to previous publications that may adopt similar hypotheses, this paper proposes more compact formulations and eliminates certain numerical problems associated with the presence of second-order derivatives with respect to the spatial coordinates. Three different models are dev…
Level statistics and Anderson delocalization in two-dimensional granular materials
2020
Contrary to the theoretical predictions that all waves in two-dimensional disordered materials are localized, Anderson localization is observed only for sufficiently high frequencies in an isotropically jammed two-dimensional disordered granular packing of photoelastic disks. More specifically, we have performed an experiment in analyzing the level statistics of normal mode vibrations. We observe delocalized modes in the low-frequency boson-peak regime and localized modes in the high frequency regime with the crossover frequency just below the Debye frequency. We find that the level-distance distribution obeys Gaussian-Orthogonal-Ensemble (GOE) statistics, i.e. Wigner-Dyson distribution, in…
Coriolis interaction parameters of the (2100; F2) bands of SiH4 and GeH4. A test of local mode models
1995
Abstract The high-resolution spectra of the (2100; F 2 , N ), N = 1 and 2, bands of SiH 4 and GeH 4 have been recorded and preliminary analyzed. The Coriolis interaction parameter 2 Bζ 3 is obtained; it provides a test of three widely used models: the harmonically coupled anharmonic oscillators model with two different kinds of variables, and the normal mode model with Darling-Dennison resonance included.
Analysis of the transition from normal modes to local modes in a system of two harmonically coupled Morse oscillators
1992
The system consisting of two Morse oscillators coupled via either a potential or a kinetic quadratic term is considered. The corresponding classical equations of motion have been numerically integrated and the initial conditions have been systematically analyzed in the regime of low total excitation energy of the system. Particular attention was paid to the full characterization of an intermediate type of motion, herein called transition mode, which appears at total energy values in between those typical of normal modes and those where local and normal modes coexist. A previously proposed perturbative approach (Jaffe C, Brumer P (1980) J Chem Phys 73:5646) is reanalyzed and compared with th…
Longitudinal versus transverse spheroidal vibrational modes of an elastic sphere
2005
Analysis of the spheroidal modes of vibration of a free elastic sphere show that they can be qualitatively grouped into two categories: primarily longitudinal and primarily transverse. This is not a sharp distinction. However, there is a relatively stark contrast between the two kinds of modes. Primarily transverse modes have a small divergence and have frequencies that are almost functionally independent of the longitudinal speed of sound. Analysis of inelastic light scattering intensity from confined acoustic phonons in nanoparticles requires an understanding of this qualitative distinction between different spheroidal modes. In addition, some common misconceptions about spheroidal modes …
Optical phonon modes of wurtzite InP
2013
Optical vibration modes of InP nanowires in the wurtzite phase were investigated by Raman scattering spectroscopy. The wires were grown along the [0001] axis by the vapor-liquid-solid method. The A1(TO), E2h, and E1(TO) phonon modes of the wurtzite symmetry were identified by using light linearly polarized along different directions in backscattering configuration. Additionally, forbidden longitudinal optical modes have also been observed. Furthermore, by applying an extended 11-parameter rigid-ion model, the complete dispersion relations of InP in the wurtzite phase have been calculated, showing a good agreement with the Raman experimental data.