We propose a predictive Density Functional Theory (DFT) for the calculation of solvation free energies. Our approach is based on a Helmholtz free-energy functional that is consistent with the perturbed-chain SAFT (PC-SAFT) equation of state. This allows a coarse-grained description of the solvent, based on an inhomogeneous density of PC-SAFT segments. The solute, on the other hand, is described in full detail by atomistic Lennard-Jones interaction sites. The approach is entirely predictive, as it only takes the PC-SAFT parameters of the solvent and the force-field parameters of the solute as input. No adjustable parameters or empirical corrections are involved. The framework is applied to study self-solvation of n-alkanes and to the calculation of residual chemical potentials in binary solvent mixtures. Our DFT approach accurately predicts solvation free energies of small molecular solutes in three different solvents. Additionally, we show the calculated solvation free energies agree well with those obtained by molecular dynamics simulations and with the residual chemical potential calculated by the bulk PC-SAFT equation of state. We observe higher deviations for the solvation free energy of systems with significant solute-solvent Coulomb interactions.
Hydrogen is a promising energy carrier on a path toward a decarbonized society and economy. Green hydrogen (produced by water electrolysis) and turquoise hydrogen (produced by high temperature methane pyrolysis) are attractive CO 2 -free power-to-gas technologies in periods with a surplus of power from renewable energies. Hydrogen can be stored and subsequently converted back to electricity using a fuel cell at times of additional demand. As such, hydrogen, among other energy storage techniques like pumped hydroelectric storage and largescale batteries, can buffer the periodic fluctuations of renewable energies to stabilize the power grid (Bünger
This study analyzes
the adsorption behavior in two-dimensional
heterogeneous slit pores using nonlocal density functional theory
based on the perturbed-chain statistical associating fluid theory
(PC-SAFT) equation of state. Both chemical heterogeneity and surface
roughness on small atomistic scales are investigated. The solid structure
is considered as individual solid interaction sites whereby chemical
heterogeneity is introduced through the presence of different solid–fluid
sites and molecular roughness by varying the position of the interaction
sites in the first solid layers. The effect of both forms of heterogeneity
on the adsorption behavior is assessed individually. Effective one-dimensional
solid–fluid potentials provide a way to reduce the dimensionality
and computational demand of the density functional theory (DFT) calculations.
We determine one-dimensional free-energy-averaged (FEA) solid–fluid
potentials of methane and n-butane in the low-density
limit for solid systems with molecular roughness and chemical heterogeneity.
Using this effective one-dimensional solid–fluid potential
at any density, we find excellent agreement of adsorption isotherms
for both solid descriptions in systems with homogeneous slit pores.
Subcritical adsorption isotherms of n-butane in slit
pores with surface roughness show deviations at higher pressures due
to the formation of fluid layers in the one-dimensional FEA potential.
Chemical heterogeneity introduces a shift of the capillary condensation
pressure below the saturation pressure of the bulk liquid, which is
well described by the free-energy-averaged system.
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