Revisiting the question of what instantaneous normal modes tell us about liquid dynamics

The Journal of Chemical Physics, Journal Year: 2025, Volume and Issue: 162(11)

Published: March 18, 2025

The lack of a well-defined equilibrium reference configuration has long hindered comprehensive atomic-level understanding liquid dynamics and properties. Instantaneous Normal Mode (INM) approach, which involves diagonalizing the Hessian matrix potential energy in instantaneous configurations, emerged as promising framework this direction. However, several conceptual challenges remain, particularly related to approach’s inability capture anharmonic effects. In study, we present set “experimental facts” through INM analysis simulated systems, including Ar, Xe, N2, CS2, Ga, Pb, across wide temperature range from solid gas phase. First, examine density states (DOS) compare it DOS obtained velocity auto-correlation function. We then analyze dependence fraction unstable modes low-frequency slope search universal behaviors. Furthermore, explore relationship between INMs other properties liquids, liquid-like gas-like dynamical crossover momentum gap collective shear waves. addition, investigate spectrum at low temperatures system approaches phase, revealing significant even crystalline solids. Finally, confirm existence recently discussed cusp-like singularity eigenvalue uncover its complex temperature-dependent behavior, challenging current theoretical models.

Language: Английский

Revisiting the phonon theory of liquid heat capacity: Low-frequency shear modes and intramolecular vibrations

Physical review. B./Physical review. B, Journal Year: 2025, Volume and Issue: 111(14)

Published: April 2, 2025

Language: Английский