Argentophillic interactions in argentum chalcogenides: First principles calculations and topological analysis of electron density

The plasticity of Ag2S and Ag2Se crystals important for applications is associated mainly with Ag-Ag metallophilic bonds, which are related to van der Waals interactions and therefore are not directed. This is demonstrated by the first principles DFT M06 LCAO calculations of Ag2X (X = S, Se) crystals (periodic model) and hypothetical molecules XnAg2n (X = S, Se; n = 1, 2, 4) in gas phase (molecular model). A topological analysis of the calculated electron density, was performed both for periodic and molecular models of Ag2X (X = S, Se). It was found that Ag-Ag interatomic distances are close in periodic and molecular models. The numerical values of electron density, its Laplacian, kinetic, and potential energy densities are also close in both models and confirm the existence of Ag-Ag metallophilic bonds.