Grand-Canonical-like adaptive resolution of molecules with electrons

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This project aims at merging the expertise of our two groups and build an interface between the adaptive resolution simulation technique of Berlin (AdResS code) with the constant chemical potential ab initio technique of Paderborn (ls++ code). The resulting code will allow us to simulate a quantum classical Grand Canonical molecular systems where molecules can change resolution from quantum to classical and vice versa according to the region where they are instantaneously located. The advantage, compared to standard open boundary QM/MM, is that the resulting method will be strictly based on conceptually well established physical principles of open systems. Contrary to QM/MM, the empirical input is minimal and as long as the principles of open systems are not violated, the simulation results will have physical consistency without the systematic need of post validation by larger full quantum calculations. We will then apply the new code to a relevant problem of physical chemistry, namely the calculation of the free energy of adsorption of phenylalanine on a metal, Pt(111) surface. For such a system, close to the surface, one needs electronic degrees of freedom to detect the interplay between hydration and adsorption, instead away from the surface water plays simply the role of a thermodynamic bath and thus can be treated classically or even at coarse-grained level, thus our new methodology represents a powerful tool for an efficient study of such systems.