Experimental and theoretical studies of effects of anharmonicity and high-temperature disorder on Raman scattering in fluorite crystals

1978 ◽  
Vol 360 (1702) ◽  
pp. 317-345 ◽  
Keyword(s):  
Raman Scattering ◽  
Fluorite Structure ◽  
Low Energy ◽  
Theoretical Studies ◽  
Nearest Neighbour ◽  
Anion Sublattice ◽  
Anion Vacancies ◽  
Polarized Raman ◽  
Experimental And Theoretical Studies ◽  
Raman Active Phonon

Some crystals with the fluorite structure, e.g. CaF 2 , SrF 2 , BaF 2 , SrCl 2 and PbF 2 , are known to exhibit a specific heat anomaly at temperatures T c well below the melting point. It is generally assumed that this anomaly is associated with the development of extensive disorder in the anion sublattice. To study this disorder we have carried out polarized Raman scattering investigations of these crystals in the temperature range 4-1420 K. Fluorite crystals have one Raman-active phonon with T 2g symmetry. We find th at the position and shape of this line below T c can be explained in detail by using third- and fourth-order anharmonicity. At T c and above additional scattering develops on the low-energy side of the T 2g phonon and this is accounted for by a theory of defect-induced scattering which includes effects of both anion vacancies and interstitials. Both force-constant and polarizability changes are considered in a nearest-neighbour approximation.

scholarly journals Graphene and related 2D materials for desalination : A review of recent patents

2020 ◽  
Author(s):  
Amall Ramanathan ◽  
Maha Aqra
Keyword(s):  
Energy Demand ◽  
High Efficiency ◽  
Sea Water ◽  
2D Materials ◽  
Water Desalination ◽  
Low Energy ◽  
Theoretical Studies ◽  
Great Progress ◽  
Experimental And Theoretical Studies ◽  
Growing Population

<p></p><p>The growing population and energy demand, coupled with the depleting fresh water resources has resulted in great progress in sea water desalination (SWD) technologies. Nanopores of 2D materials like graphene and its structural analogs are the latest innovations in membrane technology for SWD. The performance of these novel atomically thin nanopores as seen from various experimental and theoretical studies is highly encouraging with reports of water permeability 2-3 orders of magnitude greater than the conventional reverse osmosis (RO). The potential for high efficiency and the low energy requirements of these nanopores for desalination has led to tremendous efforts in fabrication and commercialization. We present here a review of the very recent patents associated with the preparation of these nanopores, the process and the efficiency of SWD. </p><br><p></p>

scholarly journals Combined Experimental and Theoretical Studies: Lattice-Dynamical Studies at High Pressures with the Help of Ab Initio Calculations

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1283
Author(s):  
Francisco Javier Manjón ◽  
Juan Ángel Sans ◽  
Placida Rodríguez-Hernández ◽  
Alfonso Muñoz
Keyword(s):  
Raman Scattering ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Phase Change Materials ◽  
High Pressures ◽  
Complete Characterization ◽  
Vibrational Properties ◽  
Theoretical Studies ◽  
Experimental And Theoretical Studies

Lattice dynamics studies are important for the proper characterization of materials, since these studies provide information on the structure and chemistry of materials via their vibrational properties. These studies are complementary to structural characterization, usually by means of electron, neutron, or X-ray diffraction measurements. In particular, Raman scattering and infrared absorption measurements are very powerful, and are the most common and easy techniques to obtain information on the vibrational modes at the Brillouin zone center. Unfortunately, many materials, like most minerals, cannot be obtained in a single crystal form, and one cannot play with the different scattering geometries in order to make a complete characterization of the Raman scattering tensor of the material. For this reason, the vibrational properties of many materials, some of them known for millennia, are poorly known even under room conditions. In this paper, we show that, although it seems contradictory, the combination of experimental and theoretical studies, like Raman scattering experiments conducted at high pressure and ab initio calculations, is of great help to obtain information on the vibrational properties of materials at different pressures, including at room pressure. The present paper does not include new experimental or computational results. Its focus is on stressing the importance of combined experimental and computational approaches to understand materials properties. For this purpose, we show examples of materials already studied in different fields, including some hot topic areas such as phase change materials, thermoelectric materials, topological insulators, and new subjects as metavalent bonding.

scholarly journals Very Low Energy Collision Induced Vibrational Relaxation: An Overview

1983 ◽  
Vol 2 (3-4) ◽  
pp. 137-166 ◽  
Author(s):  
Stuart A. Rice ◽  
Charles Cerjan
Keyword(s):  
Vibrational Relaxation ◽  
Polyatomic Molecules ◽  
Low Energy ◽  
Quantum Mechanical ◽  
Theoretical Studies ◽  
The Novel ◽  
Energy Collision ◽  
Quantum Mechanical Treatment ◽  
Experimental And Theoretical Studies ◽  
Full Quantum

Recent experimental and theoretical studies of very low energy collision induced vibrational relaxation in diatomic and polyatomic molecules are surveyed. Emphasis is placed on the novel features of the very low energy process; these require a full quantum mechanical treatment of the collision to account for the observations.

scholarly journals Graphene and related 2D materials for desalination : A review of recent patents

2020 ◽  
Author(s):  
Amall Ramanathan ◽  
Maha Aqra
Keyword(s):  
Energy Demand ◽  
High Efficiency ◽  
Sea Water ◽  
2D Materials ◽  
Water Desalination ◽  
Low Energy ◽  
Theoretical Studies ◽  
Great Progress ◽  
Experimental And Theoretical Studies ◽  
Growing Population

<p></p><p>The growing population and energy demand, coupled with the depleting fresh water resources has resulted in great progress in sea water desalination (SWD) technologies. Nanopores of 2D materials like graphene and its structural analogs are the latest innovations in membrane technology for SWD. The performance of these novel atomically thin nanopores as seen from various experimental and theoretical studies is highly encouraging with reports of water permeability 2-3 orders of magnitude greater than the conventional reverse osmosis (RO). The potential for high efficiency and the low energy requirements of these nanopores for desalination has led to tremendous efforts in fabrication and commercialization. We present here a review of the very recent patents associated with the preparation of these nanopores, the process and the efficiency of SWD. </p><br><p></p>

Experimental and Theoretical Studies of Low-Energy Penning Ionization of NH3, CH3F, and CHF3

ChemPhysChem ◽  
2016 ◽  
Vol 17 (22) ◽  
pp. 3776-3782 ◽  
Author(s):  
Krzysztof Jachymski ◽  
Michał Hapka ◽  
Justin Jankunas ◽  
Andreas Osterwalder
Keyword(s):  
Low Energy ◽  
Theoretical Studies ◽  
Penning Ionization ◽  
Experimental And Theoretical Studies

Graphene and Related 2D Materials for Desalination: A Review of Recent Patents

2020 ◽  
Vol 13 (3) ◽  
pp. 233-242
Keyword(s):  
Energy Demand ◽  
High Efficiency ◽  
Sea Water ◽  
2D Materials ◽  
Water Desalination ◽  
Low Energy ◽  
Theoretical Studies ◽  
Great Progress ◽  
Experimental And Theoretical Studies ◽  
Growing Population

Abstract: The growing population and energy demand, coupled with the depleting fresh water resources resulted in great progress in sea water desalination (SWD) technologies. Nanopores of 2D materials, like graphene and its structural analogs, are the latest innovations in membrane technology for SWD. The performance of these novel atomically thin nanopores, as seen from various experimental and theoretical studies, is highly encouraging with reports of water permeability 2-3 orders of magnitude greater than the conventional reverse osmosis (RO). The potential for high efficiency and the low energy requirements of these nanopores for desalination led to tremendous efforts in fabrication and commercialization. We present here a review of the very recent patents associated with the preparation of these nanopores, the process and the efficiency of SWD. Keywords: 2D nanopores, Graphene, Membrane, Patents, Desalination.

Low-energy conformational domains of polypeptides, characterized by a random-search and minimization procedure

1992 ◽  
Vol 70 (2) ◽  
pp. 596-603 ◽  
Author(s):  
André G. Michel ◽  
Chakib Ameziane-Hassani ◽  
Nathalie Bredin
Keyword(s):  
Random Search ◽  
Opioid Peptide ◽  
Low Energy ◽  
Theoretical Studies ◽  
Intrinsic Properties ◽  
Global Minima ◽  
Conformational Energy Calculations ◽  
Minimization Procedure ◽  
Geometrically Constrained ◽  
Experimental And Theoretical Studies

In the framework of molecular mechanics conformational energy calculations, a random-search and minimization procedure is presented to characterize low-energy domains of polypeptidic structures. Rather than striving for global minima, populations of conformers are randomly generated, and their energy is minimized in order to study their intrinsic properties. The application to the opioid peptide Met-Enkephalin allowed the identification of low-energy domains that are compared with previous results of conformational studies on this molecule. Our method gives a complete overview of the conformational behaviour of the polypeptide under study, including previously reported structures as determined from experimental and theoretical studies. To illustrate the usefulness of this method to determine bioactive peptidic structures and their active conformers, the application to geometrically constrained chemotactic tripeptides is presented. Keywords: peptides, conformation, theoretical prediction.

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