# SKM 2023 – wissenschaftliches Programm

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# DY: Fachverband Dynamik und Statistische Physik

## DY 23: Statistical Physics: General II

### DY 23.5: Vortrag

### Dienstag, 28. März 2023, 15:00–15:15, ZEU 250

**Effect of Frequency-Dependent Viscosity on Molecular Friction in Liquids** — •Henrik Kiefer^{1}, Domenico Vitali^{2}, Benjamin Dalton^{3}, Laura Scalfi^{4}, and Roland Netz^{5} — ^{1}Freie Universität Berlin, Department of Physics, Berlin, Germany — ^{2}Freie Universität Berlin, Department of Physics, Berlin, Germany — ^{3}Freie Universität Berlin, Department of Physics, Berlin, Germany — ^{4}Freie Universität Berlin, Department of Physics, Berlin, Germany — ^{5}Freie Universität Berlin, Department of Physics, Berlin, Germany

A fundamental problem in molecular dynamics is the relation between the frequency-dependent friction of a molecule in a liquid and the hydrodynamic properties of the liquid. We investigate this connection in the case of a water molecule moving in liquid water using all-atomistic molecular dynamics simulations and linear hydrodynamic theory. For this, we analytically calculate the frequency-dependent friction of a sphere with finite surface slip moving in a non-Newtonian compressible fluid by solving the linear transient Stokes equation, including frequency-dependent shear and volume viscosities, which are both determined from MD simulations of bulk liquid water. By fitting the effective sphere radius and the slip length, the frequency-dependent friction and velocity autocorrelation function from the transient Stokes equation and simulations quantitatively agree with the frequency-dependent friction of a single water molecule moving in liquid water, as defined by the generalized Langevin equation from MD simulation trajectories, provided accurate frequency-dependent viscosities are used.