Dirichlet boundary conditions and effect of confinement on chemical reactivity.

To understand the source of discrepancy in the qualitative trends in the reactivity of the spherically confined atoms/ions when the high pressure is generated through the use of a proper Dirichlet boundary condition [J. Chem. Sci. 2005, 117, 379; Phys. Chem. Chem. Phys. 2008, 10, 1406] and of a cutoff function [Chem. Phys. Lett. 2003, 372, 805; J. Phys. Chem. A 2003, 107, 4877], a modified Herman-Skilman program is run. Results obtained from different formulas of reactivity parameters are analyzed. Change in reactivity for different electronic configurations is also reported. It is observed that the use of different formulas is the major source of discrepancy and not the Dirichlet condition, although the latter is highly recommended. As the cutoff radius of the confining spherical box decreases, the energy of the atom/ion increases, the electronegativity decreases, and the hardness increases and ultimately slightly decreases in an ultraconfined situation. For small R(C) values, softness decreases and electrophilicity increases and attains relatively small values. The reactivity of confined atoms/ions is put in a proper perspective.