Abstract
The structure of heavy and light water at 300 K was investigated
by using a joint approach in which the method of neutron di®raction with
oxygen isotope substitution was combined with path integral molecular dynamics
simulations. The di®raction results, which give intra-molecular O-D and O-H
bond distances of 0.985(5) and 0.990(5) ºA, were found to be in best agreement
with those obtained by using the °exible anharmonic TTM3-F water model. Both
techniques show a di®erence of '0.5% between the O-D and O-H intra-molecular
bond lengths and the results support a competing quantum e®ects model for
water in which its structural and dynamical properties are governed by an o®set
between intra-molecular and inter-molecular quantum contributions. Further
consideration of the O-O correlations is needed in order to improve agreement
with experiment.
