  The performance of gold nanoparticles (NPs) in applications depends
critically on the structure of the NP-solvent interface, at which the
electrostatic surface polarization is one of the key characteristics that
affects hydration, ionic adsorption, and electrochemical reactions. Here, we
demonstrate significant effects of explicit metal polarizability on the
solvation and electrostatic properties of bare gold NPs in aqueous electrolyte
solutions of sodium salts of various anions (Cl$^-$, BF$_4$$^-$, PF$_6$$^-$,
Nip$^-$(nitrophenolate), and 3- and 4-valent hexacyanoferrate (HCF)), using
classical molecular dynamics simulations with a polarizable core-shell model of
the gold atoms. We find considerable spatial heterogeneity of the polarization
and electrostatic potentials on the NP surface, mediated by a highly
facet-dependent structuring of the interfacial water molecules. Moreover,
ion-specific, facet-dependent ion adsorption leads to large alterations of the
interfacial polarization. Compared to non-polarizable NPs, polarizability
modifies water local dipole densities only slightly, but has substantial
effects on the electrostatic surface potentials, and leads to significant
lateral redistributions of ions on the NP surface. Besides, interfacial
polarization effects on the individual monovalent ions cancel out in the far
field, and effective Debye-H\"uckel surface potentials remain essentially
unaffected, as anticipated from continuum `image-charge' concepts. Hence, the
explicit charge response of metal NPs is crucial for the accurate description
and interpretation of interfacial electrostatics (as, e.g., for charge transfer
and interface polarization in catalysis and electrochemistry).
