Universal short-range ab initio atom-atom potentials for interaction energy contributions with an optimal repulsion functional form.

The repulsion term in conventional force fields constitutes a major source of error. Assuming that this could originate from a too simple analytical functional form, we analyzed various analytical functions using ab initio exchange component values as a reference and obtained (α + β R (-1))exp(-γ R) as the optimal form to represent the repulsion term. Universal exchange, delocalization, and electrostatic penetration potentials approximating the corresponding interaction energy components defined within hybrid variation-perturbation theory (HVPT) were derived using as a reference a training set of 660 biomolecular complexes.

Structure of alkylimidazolium-based ionic liquids at the interface with vacuum and water--a molecular dynamics study.

Ionic liquid (IL) interfaces with vacuum and water are studied by means of classical molecular dynamics simulations. Five ILs are compared: [C2mim][TfO], [C12mim][TfO], [C2mim][NTf2], [C8mim][NTf2] and [C12mim][NTf2], where [C2mim], [C8mim] and [C12mim] stand for 1-ethyl-, 1-octyl- and 1-dodecyl-3-methylimidazolium cation. Physical properties-density, thermal expansion coefficient, compressibility, surface tension, heat of vaporization, self-diffusion coefficient, electric conductivity and viscosity-are calculated and validated against experimental values.