H2S and HS- Adsorption on a Charged Cu Surface in an Electrolyte: Effect of Ionic Strength
ABSTRACTWe present a method for the calculation of the binding and rotational energies of neutral (H2S) and charged (HS-) molecules impinging upon a charged (Cu <100>) surface in the presence of an electrolyte. A molecular surface is constructed surrounding the H2S and HS- molecules forming boundary elements. A coupled Schrödinger-Poisson-Boltzmann iterative procedure treats the electronic structure of the molecules at the 6–31G**/MP2 level of theory and includes solvation effects through the single and double layers of charge induced by the electronic distribution. The molecule, together with its charged layers, forms a Molecular Single and Double Layer (MSDL), an object which then interacts with a Gouy-Chapman plane within the electrolyte. The additional induced charge at the molecular surface resulting from this electric field is obtained by solving a second set of boundary element equations. Repulsive interactions between the atoms of the molecule and those of the surface are obtained using a rigid-ion Hartree-Fock method. Binding energies of the molecule to the surface are determined as a function of the real surface charge imposed and also the ionic strength of the solution. It is found that surface charges can completely (180°) reorient these molecules and that the counterions in the solution can completely screen binding effects of even large surface charges.Work supported by the United States Department of Energy under contract #DE-AC04–94AL85000.