2024/02/13 by Jin, Jaehyeok, Reichman, David R., Dyre, Jeppe C. +1
#Chemical Physics (physics.chem-ph) #Computational Physics (physics.comp-ph) #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Soft Condensed Matter (cond-mat.soft) #Statistical Mechanics (cond-mat.stat-mech)
paper · doi:10.48550/arxiv.2402.08675
Understanding the structure and dynamics of liquids is pivotal for the study of larger spatiotemporal processes, especially in glass-forming materials at low temperatures. Density scaling, observed in many molecular systems through experiments, offers an efficient means for exploring a vast range of time scales along a one-dimensional phase diagram. However, the theoretical foundation provided by isomorph theory is of limited use for molecular systems, since currently no first-principles theory exists that can explain the origins of density scaling or make predictions based on it. In this work, we propose a first-principles framework employing coarse-graining in space and time. Spatial coarse-graining reduces a molecule to a center-of-mass-level description by eliminating fast degrees of freedom, while temporal coarse-graining involves averaging fluctuations or correlation functions over characteristic time scales. We show that both approaches enable ab initio estimation of the density scaling coefficient for ortho-terphenyl, consistent with experimental values. Building on these findings, we employ excess entropy scaling to derive a microscopic theory that underpins density scaling from fully atomistic simulations. Our results illuminate the role of coarse-graining in assessing slow fluctuations in molecules and unravel the microscopic nature of density scaling. Ultimately, our proposed framework enables systematic bottom-up approaches for predicting transport coefficients that are otherwise experimentally inaccessible and computationally prohibitive.