We regret that there is an error with the author list in our original article. The authors Jussi Helminen, Paulus Hyvaori, and Ilkka Kilpelainen, all with the Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland, were mistakenly omitted. The author list should be as shown above in this Addition and Correction. Please note that Paulus Hyva¨ri passed away on March 27, 2018.