Hydrogen bonds: relation between lengths and electron densities at bond critical points T.-H. Tang, E. Deretey, S. J. Knak Jensen and I. G. Csizmadia Eur. Phys. J. D, 37 2 (2006) 217-222 Published online: 29 November 2005 DOI: 10.1140/epjd/e2005-00317-0