Recorded 28 October 2025. Davide Donadio of the University of California, Davis, presents "Molecular Dynamics of Solutions out of Equilibrium" at IPAM's Boundary Conditions for Atomistic Simulations in Macroscopic Electrochemical Cells Workshop. Abstract: Effective simulations of the electrochemical double layer, especially at low ionic concentrations, would require treating open systems in an out-of-equilibrium state in which particles are exchanged in a similar fashion as in the Grand Canonical ensemble. A similar problem is encountered while studying nucleation and crystal growth in heterogeneous solutions, in which the driving force depends on the composition of the fluid. In this talk, I will outline two different simulation methods to tackle equilibrium and out-of-equilibrium open systems. I will discuss the founding principles and the practical implementation of the Hamiltonian Adaptive Resolution Scheme (H-AdResS) for aqueous solutions. This approach, for which we have developed a solid statistical mechanics foundation, allows one to couple a high-resolution region, which can be treated quantum mechanically, to a lower-resolution region. The latter can be exploited as a reservoir of particles, thus effectively making the high-resolution region grand canonical. However, practical implementation issues have made this approach computationally ineffective and difficult to maintain in MD software packages. To circumvent these issues, we have recently developed a method to enforce a pseudo-grand-canonical ensemble in solutions through a membrane with harmonic volumetric restraints to control the solute osmotic pressure. The efficacy of this approach is tested on the case of ice growth from a NaCl solution. Learn more online at: https://www.ipam.ucla.edu/programs/workshops/workshop-iii-boundary-conditions-for-atomistic-simulations-in-macroscopic-electrochemical-cells/