Fluctuating hydrodynamics for multiscale simulation of inhomogeneous fluids: Mapping all-atom molecular dynamics to capillary waves

Abstract

We introduce a multiscale framework to simulate inhomogeneous fluids by coarse-graining an all-atom molecular dynamics (MD) trajectory onto sequential snapshots of hydrodynamic fields. We show that the field representation of an atomistic trajectory is quantitatively described by a dynamic field-theoretic model that couples hydrodynamic fluctuations with a Ginzburg-Landau free energy. For liquid-vapor interfaces of argon and water, the parameters of the field model can be adjusted to reproduce the bulk compressibility and surface tension calculated from the positions and forces of atoms in an MD simulation. These optimized parameters also enable the field model to reproduce the static and dynamic capillary wave spectra calculated from atomistic coordinates at the liquid-vapor interface. In addition, we show that a density-dependent gradient coefficient in the Ginzburg-Landau free energy enables bulk and interfacial fluctuations to be controlled separately. For water, this additional degree of freedom is necessary to capture both the bulk compressibility and surface tension emergent from the atomistic trajectory. The proposed multiscale framework illustrates that bottom-up coarse-graining and top-down phenomenology can be integrated with quantitative consistency to simulate the interfacial fluctuations in nanoscale transport processes.

Nonlinear hydrodynamic theory of crystallization

“…The kinetic equations were solved using a pseudo-spectral scheme with a 2 nd order Runge-Kutta time stepping (the grid spacing and time increment were ∆x = σ 0 /8 and ∆t = 0.025), respectively [25].…”

“…Our starting point is a recent work of Shang et al [25], which has successfully addressed multiphase liquid and liquidgas equilibrium interfaces. Considering isothermal processes, the respective dynamical equations read as:…”

“…Our paper is structured as follows: In section 2, we present the dynamical equations and the coupling between microscopic and macroscopic quantities on the basis of scale separation. To be able to address fluctuation phenomena (such as capillary waves at the crystal-liquid interface), we start from Fluctuating Nonlinear Hydrodynamics (FNH), a field-theoretic approach that couples hydrodynamic fluctuations with the free energy [25]. We then demonstrate the translational and rotational invariance of our model.…”

Critical dynamics of an isothermal compressible nonideal fluid

“…(39)] to the dynamic structure factor. The assumption of an exponential relaxation is well satisfied in the overdamped regime, after neglecting the shorttime, non-exponential part of C(k, t) caused by a finite residual speed of sound.…”

“…Recently, there has been growing interest in understanding the critical properties of these and related lipid bilayer systems [19][20][21][22][23][24][25][26][27][28], especially, since they constitute the building blocks that form the membranes of biological cells [29]. Isothermal non-ideal fluid models have also been used to study phase-separation [30][31][32][33][34][35][36], capillary waves [37][38][39] and supercooled liquids close to the glass transition [40][41][42][43][44]. All these works, however, did not address the critical dynamics of an isothermal fluid.…”