LOCALIZED LOW-FREQUENCY VIBRATIONAL MODES IN A SIMPLE MODEL GLASS

1991 ◽  
Vol 05 (11) ◽  
pp. 735-739 ◽  
Author(s):  
H.R. SCHOBER ◽  
BRIAN B. LAIRD
Keyword(s):  
Normal Mode Analysis ◽  
Low Frequency ◽  
Mode Analysis ◽  
Vibrational Modes ◽  
Zero Temperature ◽  
Localized Modes ◽  
Low Frequencies ◽  
Effective Masses ◽  
Model Glass ◽  
Soft Spheres

By molecular dynamics we produce a glass of soft spheres quenched to zero temperature. Normal mode analysis of the vibrational spectrum shows the existence of (quasi)localized modes at low frequencies. The structure of the glass around the centers of these modes deviates significantly from the average. The effective masses of these soft modes range upward from about 10 atomic masses.

scholarly journals Nonlinear modes disentangle glassy and Goldstone modes in structural glasses

2016 ◽  
Vol 1 (2) ◽  
Author(s):  
Luka Gartner ◽  
Edan Lerner
Keyword(s):  
Normal Mode Analysis ◽  
Low Frequency ◽  
Low Energy ◽  
Mode Analysis ◽  
Algebraic Equations ◽  
Low Frequencies ◽  
Nonlinear Modes ◽  
Selected Subset ◽  
Definition Of ◽  
Goldstone Modes

One outstanding problem in the physics of glassy solids is understanding the statistics and properties of low-energy excitations that stem from the disorder that characterizes these systems' microstructure. In this work we introduce a family of algebraic equations whose solutions represent collective displacement directions (modes) in the multi-dimensional configuration space of a structural glass. We explain why solutions of the algebraic equations, coined nonlinear glassy modes, are quasi-localized low-energy excitations. We present an iterative method to solve the algebraic equations, and use it to study the energetic and structural properties of a selected subset of their solutions constructed by starting from a normal mode analysis of the potential energy of a model glass. Our key result is that the structure and energies associated with harmonic glassy vibrational modes and their nonlinear counterparts converge in the limit of very low frequencies. As nonlinear modes never suffer hybridizations, our result implies that the presented theoretical framework constitutes a robust alternative definition of `soft glassy modes' in the thermodynamic limit, in which Goldstone modes overwhelm and destroy the identity of low-frequency harmonic glassy modes.

scholarly journals Continuum limit of the vibrational properties of amorphous solids

2017 ◽  
Vol 114 (46) ◽  
pp. E9767-E9774 ◽  
Author(s):  
Hideyuki Mizuno ◽  
Hayato Shiba ◽  
Atsushi Ikeda
Keyword(s):  
Large Scale ◽  
Continuum Limit ◽  
Scaling Law ◽  
Mean Field ◽  
Low Frequency ◽  
Amorphous Solids ◽  
Mode Analysis ◽  
Vibrational Modes ◽  
Phonon Modes ◽  
The Continuum

The low-frequency vibrational and low-temperature thermal properties of amorphous solids are markedly different from those of crystalline solids. This situation is counterintuitive because all solid materials are expected to behave as a homogeneous elastic body in the continuum limit, in which vibrational modes are phonons that follow the Debye law. A number of phenomenological explanations for this situation have been proposed, which assume elastic heterogeneities, soft localized vibrations, and so on. Microscopic mean-field theories have recently been developed to predict the universal non-Debye scaling law. Considering these theoretical arguments, it is absolutely necessary to directly observe the nature of the low-frequency vibrations of amorphous solids and determine the laws that such vibrations obey. Herein, we perform an extremely large-scale vibrational mode analysis of a model amorphous solid. We find that the scaling law predicted by the mean-field theory is violated at low frequency, and in the continuum limit, the vibrational modes converge to a mixture of phonon modes that follow the Debye law and soft localized modes that follow another universal non-Debye scaling law.

THZ-FREQUENCY SPECTROSCOPIC SENSING OF DNA AND RELATED BIOLOGICAL MATERIALS

2003 ◽  
Vol 13 (04) ◽  
pp. 903-936 ◽  
Author(s):  
T. GLOBUS ◽  
D. WOOLARD ◽  
M. BYKHOVSKAIA ◽  
B. GELMONT ◽  
L. WERBOS ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Normal Mode ◽  
Normal Mode Analysis ◽  
Low Frequency ◽  
Biological Materials ◽  
Mode Analysis ◽  
Resonance Structure ◽  
Terahertz Frequency ◽  
Dna Molecules ◽  
Phonon Modes

The terahertz frequency absorption spectra of DNA molecules reflect low-frequency internal helical vibrations involving rigidly bound subgroups that are connected by the weakest bonds, including the hydrogen bonds of the DNA base pairs, and/or non-bonded interactions. Although numerous difficulties make the direct identification of terahertz phonon modes in biological materials very challenging, recent studies have shown that such measurements are both possible and useful. Spectra of different DNA samples reveal a large number of modes and a reasonable level of sequence-specific uniqueness. This chapter utilizes computational methods for normal mode analysis and theoretical spectroscopy to predict the low-frequency vibrational absorption spectra of short artificial DNA and RNA. Here the experimental technique is described in detail, including the procedure for sample preparation. Careful attention was paid to the possibility of interference or etalon effects in the samples, and phenomena were clearly differentiated from the actual phonon modes. The results from Fourier-transform infrared spectroscopy of DNA macromolecules and related biological materials in the terahertz frequency range are presented. In addition, a strong anisotropy of terahertz characteristics is demonstrated. Detailed tests of the ability of normal mode analysis to reproduce RNA vibrational spectra are also conducted. A direct comparison demonstrates a correlation between calculated and experimentally observed spectra of the RNA polymers, thus confirming that the fundamental physical nature of the observed resonance structure is caused by the internal vibration modes in the macromolecules. Application of artificial neural network analysis for recognition and discrimination between different DNA molecules is discussed.

Low Frequency Raman Spectra in Water by Normal Mode Analysis

1994 ◽  
pp. 197-203
Author(s):  
Srikanth Sastry ◽  
H. Eugene Stanley ◽  
Francesco Sciortino
Keyword(s):  
Raman Spectra ◽  
Normal Mode ◽  
Normal Mode Analysis ◽  
Low Frequency ◽  
Mode Analysis

A minimal coarse-grained model for the low-frequency normal mode analysis of icosahedral viral capsids

Soft Matter ◽  
2020 ◽  
Vol 16 (14) ◽  
pp. 3443-3455 ◽  
Author(s):  
M. Martín-Bravo ◽  
J. M. Gomez Llorente ◽  
J. Hernández-Rojas
Keyword(s):  
Structural Properties ◽  
Normal Mode ◽  
Normal Mode Analysis ◽  
Low Frequency ◽  
Coarse Grained ◽  
Mode Analysis ◽  
Viral Capsids ◽  
Mode Spectrum ◽  
Coarse Grained Model

A minimal coarse-grained model unveils relevant structural properties of icosahedral viral capsids when fitted to reproduce their low-frequency normal-mode spectrum.

Low frequency depolarized Raman spectra in water: Results from normal mode analysis

1994 ◽  
Vol 100 (7) ◽  
pp. 5361-5366 ◽  
Author(s):  
Srikanth Sastry ◽  
H. Eugene Stanley ◽  
Francesco Sciortino
Keyword(s):  
Raman Spectra ◽  
Normal Mode ◽  
Normal Mode Analysis ◽  
Low Frequency ◽  
Mode Analysis

scholarly journals Probing the non-Debye low-frequency excitations in glasses through random pinning

2018 ◽  
Vol 115 (35) ◽  
pp. 8700-8704 ◽  
Author(s):  
Luca Angelani ◽  
Matteo Paoluzzi ◽  
Giorgio Parisi ◽  
Giancarlo Ruocco
Keyword(s):  
Density Of States ◽  
3D Model ◽  
Low Frequency ◽  
Particle Fraction ◽  
Localized Modes ◽  
Translational Invariance ◽  
Model Glass ◽  
And Shifts ◽  
Pinning Field ◽  
Finite Particle

We investigate the properties of the low-frequency spectrum in the density of states D(ω) of a 3D model glass former. To magnify the non-Debye sector of the spectrum, we introduce a random pinning field that freezes a finite particle fraction to break the translational invariance and shifts all of the vibrational frequencies of the extended modes toward higher frequencies. We show that non-Debye soft localized modes progressively emerge as the fraction p of pinned particles increases. Moreover, the low-frequency tail of D(ω) goes to zero as a power law ωδ(p), with 2≤δ(p)≤4 and δ=4 above a threshold fraction pth.

scholarly journals A minimalist network model for coarse-grained normal mode analysis and its application to biomolecular x-ray crystallography

2008 ◽  
Vol 105 (40) ◽  
pp. 15358-15363 ◽  
Author(s):  
Mingyang Lu ◽  
Jianpeng Ma
Keyword(s):  
Normal Mode ◽  
Network Model ◽  
Normal Mode Analysis ◽  
Low Frequency ◽  
Coarse Grained ◽  
Mode Analysis ◽  
Conformational Sampling ◽  
Structural Refinement ◽  
X Ray ◽  
X Ray Crystallography

In this article, we report a method for coarse-grained normal mode analysis called the minimalist network model. The main features of the method are that it can deliver accurate low-frequency modes on structures without undergoing initial energy minimization and that it also retains the details of molecular interactions. The method does not require any additional adjustable parameters after coarse graining and is computationally very fast. Tests on modeling the experimentally measured anisotropic displacement parameters in biomolecular x-ray crystallography demonstrate that the method can consistently perform better than other commonly used methods including our own one. We expect this method to be effective for applications such as structural refinement and conformational sampling.

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