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

Zinc oxide nanostructures
are used in an ever increasing line of
applications in technology and biomedical fields. This requires a
detailed understanding of the phenomena that occur at the surface
particularly in aqueous environments and in contact with biomolecules.
In this work, we used ab initio molecular dynamics (AIMD) simulations
to determine structural details of ZnO surfaces in water and to develop
a general and transferable classical force field for hydrated ZnO
surfaces. AIMD simulations show that water molecules dissociate near
unmodified ZnO surfaces, forming hydroxyl groups at about 65% of the
surface 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 identified
by analysis of the specific connectivities of atoms. The analysis
of the electron density was then used to determine partial charges
and Lennard-Jones parameters for the identified force field atom types.
The obtained force field was validated by comparison with AIMD results
and 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 aqueous
and other fluid environments and in interaction with biomolecules.