Skip to content
Free planNo credit card requiredStart writing
AI for Research home
AI for Research home
Dashboard
Sign inGet started

Search 250 million research papers

Read the abstract, see who wrote it and who cites it, and get the citation in APA, MLA, Chicago or Harvard.

About 6,153 papers for “Anharmonicity”

electrical anharmonicity

2024

Citation: 'electrical anharmonicity' in the IUPAC Compendium of Chemical Terminology, 5th ed.; International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.08591 • License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International for individual terms. Requests for commercial usage of the compendium should be directed to IUPAC.

Cited by 0

mechanical anharmonicity

2024

Citation: 'mechanical anharmonicity' in the IUPAC Compendium of Chemical Terminology, 5th ed.; International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.08635 • License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International for individual terms. Requests for commercial usage of the compendium should be directed to IUPAC.

Cited by 0

Anharmonicity in Diffusion * *

C. P. Flynn · Zeitschrift für Naturforschung A · 1971

Abstract It is emphasized that anharmonic effects are important in determining the parameters describing diffusion processes at elevated temperatures in crystals. The relevance of anharmonicity to the reaction rate and the dynamical theories of diffusion, and to models of defect formation and migra­tion, is discussed. A comparison is made between the theoretical results and some collected experi­mental data pertaiining mainly to ionic crystals

Cited by 17Open access

Anharmonicity measure for materials

Florian Knoop, Thomas A. R. Purcell, Matthias Scheffler et al. · Physical Review Materials · 2020

Theoretical frameworks used to qualitatively and quantitatively describe nuclear dynamics in solids are often based on the harmonic approximation. However, this approximation is known to become inaccurate or to break down completely in many modern functional materials. Interestingly, there is no reliable measure to quantify anharmonicity so far. Thus, a systematic classification of materials in terms of anharmonicity and a benchmark of methodologies that may be appropriate for different strengths of anharmonicity is currently impossible. In this work, we derive and discuss a statistical measure that reliably classifies compounds across temperature regimes and material classes by their ``degree of anharmonicity.'' This enables us to distinguish ``harmonic'' materials, for which anharmonic effects constitute a small perturbation on top of the harmonic approximation, from strongly ``anharmonic'' materials, for which anharmonic effects become significant or even dominant and the treatment of anharmonicity in terms of perturbation theory is more than questionable. We show that the analysis of this measure in real and reciprocal space is able to shed light on the underlying microscopic mechanisms, even at conditions close to more complicated dynamical processes, e.g., phase transitions or defect formation. Eventually, we demonstrate that the developed approach is computationally efficient and enables rapid high-throughput searches by scanning over a set of several hundred binary solids. The results show that strong anharmonic effects beyond the perturbative limit are not only active in complex materials or close to phase transitions, but already at moderate temperatures in simple binary compounds.

Cited by 86Open access

Anharmonicity in Crystal Vibrations

Arieh Warshel · The Journal of Chemical Physics · 1971

A scheme for the calculation of anharmonicity in crystal vibrations is developed for crystals with one molecule per unit cell. This method is applied to n-hexane crystal. It is found that the contribution from anharmonicity can be very important in lattice vibrations of molecular crystals. Hence, the use of harmonic crystal vibrations for evaluation of nonbonded potentials without an anharmonicity correction can lead to an inconsistent potential.

Cited by 10

Anharmonicity of Amide Modes

Jianping Wang, Robin M. Hochstrasser · The Journal of Physical Chemistry B · 2005

The principal contributions to the anharmonic coupling of amide vibrations are explored with the objective of comparing recent experiments with density functional theory and evaluating simple models of mode coupling. Experimental information obtained by means of two-dimensional infrared spectroscopy (2D IR) is reasonably well predicted by the computed one- and two-quantum anharmonic modes of amide-A, -I, and -II types in mono-, di- and tripeptides. The expansion of the vibrational energy up to the cubic and quartic coupling of harmonic modes suggested criteria to assess how localized are the forces determining the anharmonicity. The off-diagonal anharmonicity between an amide-A and one other amide mode was shown to be mainly determined by forces involving only these two modes, whereas the off-diagonal anharmonicity of two amide-I modes in peptides depended significantly on forces due to motions other than those of the amide-I type. Both the diagonal and off-diagonal anharmonicities exhibit sensitivity to peptide structures. These results should prove useful in linking 2D IR experimental results to secondary structure. Further, the results are used to evaluate the vibrational exciton model for the mixed-mode anharmonicities of the amide-I transitions.

Cited by 92

Anharmonicity in Sodium Chloride

K. D. Swartz · The Journal of the Acoustical Society of America · 1967

The full set of third-order elastic constants of NaCl was measured and compared to some combinations of these constants that have been reported in the literature. The Cauchy relations were found to be reasonably well satisfied. For NaCl, C111 is large (of the order of 1013 dyn/cm2) and negative, C112 and C166 are smaller (of the order of 0.5×1012 dyn/cm2) and negative, and C123, C456, and C144 are small (of the order of 1011 dyn/cm2) and positive. It is shown that the closed-shell repulsive interaction between nearest and next-nearest neighbors gives the major contribution to the third-order elastic constants of NaCl and completely dominates the contributions to the fourth-order elastic constants. These fourth-order elastic constants are evaluated from the experimentally measured temperature coefficients of the second-order elastic constants. The Grüneisen parameter of 1.588 calculated from the measured second- and third-order elastic constants compares well with the Grüneisen constant of 1.64 obtained from thermodynamic measurements. Comparison of the third-order elastic constants obtained with linear combinations given by other methods shows that the two-specimen method used here gives results in fair agreement with one-specimen ultrasonic methods but not with optical methods.

Cited by 49

On anharmonicity in cadmium

D. W. Field · Acta Crystallographica Section A · 1982

Recent X-ray diffraction data on cadmium [Rossmanith (1978). Acta Cryst. A34, 497-500] have been reanalysed using a temperature factor based on an anharmonic one-particle potential to fourth order for the atoms, and values for the anharmonic parameters have been obtained. The fourth-order parameters α40 and β20 are found not to be significantly different from zero, while the other fourth-order parameter γ00 is found to be strongly correlated to the extinction correction and harmonic parameters. The third-order antisymmetric parameter is found to have a value of 57 ± 16 eV nm-3, which is in reasonable agreement with a recent measurement. The application of the extinction correction is shown to affect substantially the values for the potential parameters.

Cited by 3

Anharmonicity measure for materials: Figures

Florian Knoop, Thomas A. R. Purcell · Figshare · 2020

This dataset contains the raw data and scripts to create figures in <br>Florian Knoop, Thomas A. R. Purcell, Matthias Scheffler, and Christian Carbogno, Phys. Rev. Materials 4, 083809 (2020)

Cited by 1Open access

Anharmonicity in Vibrational State Sums

Kenneth A. Wilde · The Journal of Chemical Physics · 1964

Refinements have been made in the treatment of vibrational state sums. These modifications are particularly important at energies greater than the dissociation energies. It was not possible to extend the available analytical treatments of harmonic oscillators, and numerical sums were computed for several anharmonic examples and compared with previous work. Values of the empirical correction factor a were given and the previously derived approximate equations involving a extended to the anharmonic case.

Cited by 20