Ab Initio Derived Classical Force Field for Molecular Dynamics Simulations of ZnO Surfaces in Biological Environment

Zinc oxide nanostructuresare used in an ever increasing line ofapplications in technology and biomedical fields. This requires adetailed understanding of the phenomena that occur at the surfaceparticularly in aqueous environments and in contact with biomolecules.In this work, we used ab initio molecular dynamics (AIMD) simulationsto determine structural details of ZnO surfaces in water and to developa general and transferable classical force field for hydrated ZnOsurfaces. AIMD simulations show that water molecules dissociate nearunmodified ZnO surfaces, forming hydroxyl groups at about 65% of thesurface Zn atoms and protonating 3-coordinated surface oxygen atoms,while the rest of the surface Zn atoms bind molecularly adsorbed waters.Several force field atom types for ZnO surface atoms were identifiedby analysis of the specific connectivities of atoms. The analysisof the electron density was then used to determine partial chargesand Lennard-Jones parameters for the identified force field atom types.The obtained force field was validated by comparison with AIMD resultsand with available experimental data on adsorption and immersion enthalpies,as well as adsorption free energies of several amino acids in methanol.The developed force field can be used for modeling of ZnO in aqueousand other fluid environments and in interaction with biomolecules.