Continuum-based multiscale approach to predict the structure and theromdynamic properties of confined fluids*

We present a continuum-based theory to predict the structure and thermodynamic properties of fluids confined in multiple length-scales, ranging from few Angstroms to micron length channels. In this work, we introduce a free energy functional for classical DFT (cDFT) based on the empirical potential-based quasi-continuum theory (EQT). EQT is a simple and fast approach to predict the inhomogeneous density and potential profiles of confined fluids, and the results from EQT compare well with MD simulations. Using the density and potential profiles from EQT, we construct a grand potential functional for cDFT. EQT-cDFT based grand potential can be used to predict various thermodynamic properties of confined fluids. Here, we demonstrate applicability of the EQT-cDFT approach by simulating water confined inside slit-like channels of graphene at various thermodynamic states and channel widths. Using EQT-cDFT approach, we calculate the structure and thermodynamic properties of confined water, such as density profiles, adsorption, PMF profiles, surface tension, local pressure profiles, and solvation forces. It is found that the EQT-cDFT results compare well with the reference water MD simulation results.