Classical, quantum, and thermodynamics of a lattice model exhibiting structural negative thermal expansion

Occhialini, Connor A.; Handunkanda, Sahan; Curry, Erin; Hancock, Jason

doi:10.1103/physrevb.95.094106

Cited by 5 publications

(2 citation statements)

References 54 publications

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“…On the basis of our experimental observations, we developed a simple theoretical description of the NTE effect in ScF 3 , which is rooted in entropic elasticity of an underconstrained floppy network, similar in spirit to the celebrated Flory–de Gennes theory of polymer elasticity ( 28 , 29 ). Our approach presents a paradigm shift, where instead of focusing on peculiar energetics of low-energy lattice vibrations, such as RUM ( 2 – 5 , 7 , 9 – 11 , 30 , 33 – 35 ), these vibrations are approximated by Einstein local phonon modes, and the focus is on their entropic contribution to free energy. Our results provide not only a clear understanding of the entropic elasticity origin of the NTE effect in the practically important class of materials and temperature range, including at and above room temperature, but also an accurate, quantitative, textbook description of NTE, thus opening new avenues for predictive modeling of this effect in solids.…”

Section: Resultsmentioning

confidence: 99%

Entropic elasticity and negative thermal expansion in a simple cubic crystal

et al. 2019

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Section: Resultsmentioning

confidence: 99%

Entropic elasticity and negative thermal expansion in a simple cubic crystal

et al. 2019

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“…Examples of this type of NTE are found in InVar [1], anti-perovskites [2,3], ruthenates [4], and charge-transfer insulators [5,6]. In contrast, a second type of NTE is realized from intrinsic dynamical origins, also referred to as structural NTE (SNTE) [7], which is not obviously resultant from phase competition and does not require quenched disorder but seems to arise from intrinsic geometrical modes with tendencies to draw in the lattice dimensions when thermally activated. Unlike the broadened phase transition type, SNTE appears in a wide variety of lattice systems [8,9] without necessarily constraining the magnetic or electronic phase diagram.…”

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Negative thermal expansion near two structural quantum phase transitions

Occhialini

Handunkanda

Said

et al. 2017

Phys. Rev. Materials

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Recent experimental work has revealed that the unusually strong, isotropic structural negative thermal expansion in cubic perovskite ionic insulator ScF3 occurs in excited states above a ground state tuned very near a structural quantum phase transition, posing a question of fundamental interest as to whether this special circumstance is related to the anomalous behavior. To test this hypothesis, we report an elastic and inelastic X-ray scattering study of a second system Hg2I2 also tuned near a structural quantum phase transition while retaining stoichiometric composition and high crystallinity. We find similar behavior and significant negative thermal expansion below 100K for dimensions along the body-centered-tetragonal c axis, bolstering the connection between negative thermal expansion and zero temperature structural transitions. We identify the common traits between these systems and propose a set of materials design principles that can guide discovery of new materials exhibiting negative thermal expansion.Comment: 8 pages, 4 figures, accepted, Phys. Rev. Mat. 2017, 8 pages, 4 figure

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Equation of state predictions for ScF3 and CaZrF6 with neural network-driven molecular dynamics

Stoppelman,

Wilkinson,

McDaniel

2023

The Journal of Chemical Physics

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In silico property prediction based on density functional theory (DFT) is increasingly performed for crystalline materials. Whether quantitative agreement with experiment can be achieved with current methods is often an unresolved question, and may require detailed examination of physical effects such as electron correlation, reciprocal space sampling, phonon anharmonicity, and nuclear quantum effects (NQE), among others. In this work, we attempt first-principles equation of state prediction for the crystalline materials ScF3 and CaZrF6, which are known to exhibit negative thermal expansion (NTE) over a broad temperature range. We develop neural network (NN) potentials for both ScF3 and CaZrF6 trained to extensive DFT data, and conduct direct molecular dynamics prediction of the equation(s) of state over a broad temperature/pressure range. The NN potentials serve as surrogates of the DFT Hamiltonian with enhanced computational efficiency allowing for simulations with larger supercells and inclusion of NQE utilizing path integral approaches. The conclusion of the study is mixed: while some equation of state behavior is predicted in semiquantitative agreement with experiment, the pressure-induced softening phenomenon observed for ScF3 is not captured in our simulations. We show that NQE have a moderate effect on NTE at low temperature but does not significantly contribute to equation of state predictions at increasing temperature. Overall, while the NN potentials are valuable for property prediction of these NTE (and related) materials, we infer that a higher level of electron correlation, beyond the generalized gradient approximation density functional employed here, is necessary for achieving quantitative agreement with experiment.

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Classical, quantum, and thermodynamics of a lattice model exhibiting structural negative thermal expansion

Cited by 5 publications

References 54 publications

Entropic elasticity and negative thermal expansion in a simple cubic crystal

Entropic elasticity and negative thermal expansion in a simple cubic crystal

Negative thermal expansion near two structural quantum phase transitions

Equation of state predictions for ScF3 and CaZrF6 with neural network-driven molecular dynamics

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