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Direct assessment of quantum nuclear effects on hydrogen bond strength by constrained-centroid ab initio path integral molecular dynamics
 

Summary: Direct assessment of quantum nuclear effects on hydrogen bond strength
by constrained-centroid ab initio path integral molecular dynamics
Brent Walker and Angelos Michaelidesa
Department of Chemistry and London Centre for Nanotechnology, University College London,
London WC1E 6BT, United Kingdom
Received 20 August 2010; accepted 4 October 2010; published online 2 November 2010
The impact of quantum nuclear effects on hydrogen H- bond strength has been inferred in earlier
work from bond lengths obtained from path integral molecular dynamics PIMD simulations. To
obtain a direct quantitative assessment of such effects, we use constrained-centroid PIMD
simulations to calculate the free energy changes upon breaking the H-bonds in dimers of HF and
water. Comparing ab initio simulations performed using PIMD and classical nucleus molecular
dynamics MD , we find smaller dissociation free energies with the PIMD method. Specifically, at
50 K, the H-bond in HF 2 is about 30% weaker when quantum nuclear effects are included, while
that in H2O 2 is about 15% weaker. In a complementary set of simulations, we compare
unconstrained PIMD and classical nucleus MD simulations to assess the influence of quantum
nuclei on the structures of these systems. We find increased heavy atom distances, indicating
weakening of the H-bond consistent with that observed by direct calculation of the free energies of
dissociation. 2010 American Institute of Physics. doi:10.1063/1.3505038
I. INTRODUCTION
It is not difficult to illustrate the importance of hydrogen

  

Source: Alavi, Ali - Department of Chemistry, University of Cambridge

 

Collections: Chemistry