Theoretical exploration of the forces governing the interaction between gold–phthalocyanine and gold surface clusters

Here we aim to explore the nature of the forces governing the adsorption of gold–phthalocyanine on gold substrates. For this, we designed computational models of metal-free phthalocyanine and gold–phthalocyanine deposited over a gold metallic surface represented by cluster models of different sizes and geometries. Thereby, we were able to determine the role of the metal center and of the size of the substrate in the interaction process. For this purpose, we worked within the framework provided by density functional theory, were the inclusion of the semi-empirical correction of the dispersion forces of Grimme's group was indispensable. It has been shown that the interaction between molecules and surfaces is ruled by van der Waals attractive forces, which determine the stabilization of the studied systems and their geometric properties. Their contribution was characterized by energy decomposition analysis and through the visualization of the dispersion interactions by means of the NCI methodology. Moreover, calculations of Density of States (DOS) showed that the molecule-surface system displays a metal–organic interface evidenced by changes in their electronic structure, in agreement with a charge transfer process found to take place between the interacting parts.