Anharmonische Gitterschwingungen und die lineare Kette

Hooton, D. J.

doi:10.1007/bf01330055

Cited by 25 publications

(14 citation statements)

References 7 publications

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“…(4). The kernel functions used to generate covariance matrices , are specified as Eq (5)(6)(7)(8)(9). After obtaining the coefficient vector , total energies of an arbitrary atomic configuration can be calculated using Eq (1-2), which completes the Gaussian process regression process.…”

Section: A Fitting Potential Energy Surface Using Gap Methodsmentioning

confidence: 99%

Temperature effect on the phonon dispersion stability of zirconium by machine learning driven atomistic simulations

Qian

Yang

2018

Phys. Rev. B

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It is well known that conventional harmonic lattice dynamics cannot be applied to dynamically unstable crystals at 0 K, such as high temperature body centered cubic (BCC) phase of crystalline Zr. Predicting phonon spectra at finite temperature requires the calculation of force constants to the third, fourth and even higher orders, however, it remains challenging to determine to which order the Taylor expansion of the potential energy surface for different materials should be cut off.Molecular dynamics, on the other hand, intrinsically includes arbitrary orders of phonon anharmonicity, however, its accuracy is severely limited by the empirical potential field used.Recently, machine learning algorithms emerge as a promising tool to build accurate potentials for molecular dynamics simulation. In this work, we approach the problem of predicting phonon dispersion at finite temperature by performing molecular dynamics simulations with machine learning-driven potential fields. We developed Gaussian approximation potential models for both the hexagonal closed-packed (HCP) phase and the body centered cubic (BCC) phase of Zirconium crystals. The developed potential field is first validated with static properties including energyvolume relationship, elastic constants and phonon dispersions at 0 K. Molecular dynamics

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Section: A Fitting Potential Energy Surface Using Gap Methodsmentioning

confidence: 99%

Temperature effect on the phonon dispersion stability of zirconium by machine learning driven atomistic simulations

Qian

Yang

2018

Phys. Rev. B

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“…One possible avenue involves the development of suitable effective pair interaction potentials to describe the ionic potential energy surface of the high-pressure phases 27 and their application within one of the implementations of the self-consistent harmonic approximation. [46][47][48][49] …”

Section: Concerted Hydrogen Motions: a Possibilitymentioning

confidence: 99%

Isotopic differentiation and sublattice melting in dense dynamic ice

2013

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The isotopes of hydrogen provide a unique exploratory laboratory for examining the role of zero point energy (ZPE) in determining the structural and dynamic features of the crystalline ices of water. There are two critical regions of high pressure: (i) near 1 TPa and (ii) near the predicted onset of metallization at around 5 TPa. At the lower pressure of the two, we see the expected small isotopic effects on phase transitions. Near metallization, however, the effects are much greater, leading to a situation where tritiated ice could skip almost entirely a phase available to the other isotopomers. For the higher pressure ices, we investigate in some detail the enthalpics of a dynamic proton sublattice, with the corresponding structures being quite ionic. The resistance toward diffusion of single protons in the ground state structures of high-pressure H 2 O is found to be large, in fact to the point that the ZPE reservoir cannot overcome these. However, the barriers toward a three-dimensional coherent or concerted motion of protons can be much lower, and the ensuing consequences are explored.

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“…This technique is based on the idea by Born and Hooton 262,268 that the atoms rarely occupy the positions where the phonon frequencies are negative, instead move into the effective potential of their non-stationary neighbors. This means that if we sampling the potential energy surface at probable atomic position for a given temperature, we should get a harmonic approximation that describes the system at elevated temperatures.…”

Section: Methods (Tdep)mentioning

confidence: 99%

Design of Transition-Metal Nitride Thin Films for Thermoelectrics

Kerdsongpanya

2015

Linköping Studies in Science and Technology. Dissertations

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Thermoelectric devices are one of the promising energy harvesting technologies, because of their ability to convert heat (temperature gradient) to electricity by the Seebeck effect. Furthermore, thermoelectric devices can be used for cooling or heating by the inverse effect (Peltier effect). Since this conversion process is clean, with no emission of greenhouse gases during the process, this technology is attractive for recovering waste heat in automobiles or industries into usable electricity. However, the conversion efficiency of such devices is rather low due to fundamental materials limitations manifested through the thermoelectric figure of merit (ZT ). Thus, there is high demand on finding materials with high ZT or strategies to improve ZT of materials.In this thesis, I discuss the basics of thermoelectrics and how to improve ZT of materials, including present-day strategies. Based on these ideas, I propose a new class of materials for thermoelectric applications: transition-metal nitrides, mainly ScN, CrN and their solid solutions. Here, I employed both experimental and theoretical methods to synthesize and study their thermoelectric properties. My study envisages ways for improving the thermoelectric figure of merit of ScN and possible new materials for thermoelectric applications.The results of my studies show that ScN is a promising thermoelectric material since it exhibits high thermoelectric power factor 2.5×10 −3 Wm −1 K −2 at 800 K, due to low metallic-like electrical resistivity while retained relatively large Seebeck coefficient. My studies on thermal conductivity of ScN also suggest a possibility to control thermal conductivity by tailoring the microstructure of ScN thin films. Furthermore, my theoretical studies on effects of impurities and stoichiometry on the electronic structure of ScN suggest the possibly to improve ScN ZT by stoichiometry tuning and doping. For CrN and Cr1−xScxN solid solution thin films, the results show that the power factor of CrN (8×10 −4Wm −1 K −2 at 770 K) can be retained for the solid solution Cr0.92Sc0.08N. Finally, density functional theory was used to enable a systematic predictionbased strategy for optimizing ScN thermoelectric properties via phase stability of solid solutions. Sc1−xGdxN and Sc1−xLuxN are stabilized as disordered solid solutions, while in the Sc-Nb-N and Sc-Ta-N systems, the inherently layered ternary structures ScNbN2 and ScTaN2 are stable. Svensk sammanfattningSedan den industriella revolutionen har fossila bränslen varit vår huvudkälla till energi i motorer för transport, elproduktion och uppvärmning av byggnader. Eftersom mänskligheten och vår teknik växer för varje år som går, fortsätter efterfrågan på fossila bränslen att öka. Med tanke på att fossila bränslen inte är förnybara, riskerar vi att de tar slut. Dessutom är resultatet av denna ständiga förbränning av fossila bränslen generering av växthusgaser, t.ex. kolmonoxid och koldioxid, som orsakar klimatförändringar, som ett ytterligare problem. Således finns det ett ökande behov...

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Anharmonische Gitterschwingungen und die lineare Kette

Cited by 25 publications

References 7 publications

Temperature effect on the phonon dispersion stability of zirconium by machine learning driven atomistic simulations

Temperature effect on the phonon dispersion stability of zirconium by machine learning driven atomistic simulations

Isotopic differentiation and sublattice melting in dense dynamic ice

Design of Transition-Metal Nitride Thin Films for Thermoelectrics

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