# C01 - Adaptive coupling of scales in molecular dynamics and beyond to fluid dynamics

**Head(s):** Prof. Dr. Luigi Delle Site (FU Berlin), Prof. Dr.-Ing. Rupert Klein (FU Berlin)**Project member(s):** Dr. Sara Panahian Jand, Julian Friedrich Hille, Nelly Coulonges**Participating institution(s):** FU Berlin

**Project Summary:**

Current molecular science requires simulations that go beyond constant thermal or density fields and thus treats molecular systems embedded in arbitrarily fluctuating fields. Cell membranes in a realistic environment are subject to a fluctuating thermal field which has a major impact on their hydration properties and morphological structure. In technology, the possibility of externally modulating a thermal or density field in time could be used to build efficient devices, for example for phase separation of liquids in the context of water purification processes.

In this context the modeler/simulator question about a rigorous definition of boundary conditions that couple the particle domain to its simplified fluctuating environment becomes crucial. The physics is characterized by a situation of non-equilibrium at the boundary, so that the thermodynamic conditions of the particle domain adapt instantaneously to the information coming from the fluctuating environment and vice versa. In this project we have developed such an algorithm by coupling the AdResS scheme to a continuum fluctuating hydrodynamics scheme (FHD). The boundary conditions have been rigorously derived from a mathematical model of open system (Liouville hierarchy for open systems).

With the achievements so far, the project is ready to target its long-term goal:

(i) Study of phase separation in liquid mixtures via thermal gradient

(ii) Hydration-induced topological behaviour of biological membranes in a fluctuating thermal field

(iii) Hydrodynamic limit of the Liouville hierarchy for open systems

In parallel, the project will extend the current one-dimensional AdResS-FHD model to multiple space dimensions, and it will investigate other physically interesting problems that demonstrate the capabilities of the simulation technology as it evolves.