Surface affinity of hydronium was explored using umbrella sampling molecular dynamics simulations 
with a refined polarizable potential. The polarizable interaction potential of H3O+ was 
reparameterized against accurate ab initio calculations for geometries including a water molecule 
approaching the Eigen cation from its oxygen side. Although there is no true hydrogen bonding with 
H3O+ acting as an acceptor, respecting in the force field the very shallow ab initio minimum 
corresponding to this interaction leads to a decrease in surface propensity of hydronium compared 
to previous results. Qualitatively, the mild surface affinity and strong surface orientation of 
hydronium is, nevertheless, robustly predicted by various computational approaches, as well as 
by spectroscopic experiments.