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arXiv · 2605.13703

Nonlinear dynamic elastic moduli from equilibrium stress fluctuations

F. E. Garbuzov·Y. M. Beltukov
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Abstract

Fluctuation formulas for elastic and viscoelastic moduli allow their computation from equilibrium molecular dynamics simulations, avoiding explicit nonequilibrium deformation protocols. While such expressions are well established for the quasi-static moduli, and also the linear dynamic moduli, no fluctuation formula exists for the nonlinear time-dependent moduli that govern anharmonic viscoelastic response under finite time-dependent strains. In this work we derive transient-time correlation function expressions for both the linear and the nonlinear dynamic moduli, starting from the DOLLS/SLLOD equations of motion for irrotational motion. The resulting formulas involve equilibrium time correlations of the stress tensor and Born-kinetic terms, and they recover the known quasi-static and linear dynamic results in the appropriate limits.

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F. E. Garbuzov, Y. M. Beltukov. 2026-05-13. Nonlinear dynamic elastic moduli from equilibrium stress fluctuations. https://arxiv.org/abs/2605.13703

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