Surface melting of ice below the bulk melting point is well-established but little-understood phenomenon. In order to investigate the effects of impurities on the surface melting, we performed molecular dynamics simulations of ice surfaces containing NO3-, Cl-, Na+, and H+. The vibrational density of state showed that collective dangling vibrations of the free O-H bonds are excited around the ions with the negative charge. This mode is not excited around the positive ions. We conclude that the collective vibration is the dominant factor governing the enhancement of the surface melting. (c) 2005 Elsevier B.V. All rights reserved.