© Paesani Research Group. All rights reserved.

46. Nuclear quantum effects in the reorientation of water.

      F. Paesani, S. Yoo, H.J. Bakker, S.S. Xantheas, J. Phys. Chem. Lett. 1, 2316 (2010). [link]

The molecular reorientation associated with the dynamics of the hydrogen-bond network in liquid water is

investigated using quantum molecular dynamics simulations performed with the ab-initio-based TTM3-F

interaction potential. The reorientation dynamics calculated at different temperatures are found to be in excellent

agreement with the corresponding experimental results obtained from polarization-resolved, femtosecond

mid-infrared, pump−probe spectroscopic measurements. A comparison with analogous results obtained from

classical molecular dynamics simulations with the same interaction potential clearly indicates that the explicit

inclusion of nuclear quantum effects is critical for reproducing the measured time dependence of the anisotropic

signal.

45. A quantitative assessment of the accuracy of centroid molecular dynamics for the calculation of the infrared

      spectrum of liquid water. F. Paesani, G.A. Voth, J. Chem. Phys. 132, 014105 (2010). [link]

A detailed analysis of the infrared lineshapes corresponding to the intramolecular bond vibrations of HOD in either

H2O or D2O is presented here in order to quantitatively assess the accuracy of centroid molecular dynamics in

reproducing the correct features of the infrared spectrum of water at ambient conditions. Through a direct comparison

with the results obtained from mixed quantum-classical calculations, it is shown that centroid molecular dynamics

provides accurate vibrational shifts and lineshapes when the intramolecular bond stretching vibrations are described

by a physically reasonable anharmonic potential. Artificially large redshifts due to a so-called “curvature problem” are

instead obtained with an unphysical shifted harmonic potential because the latter allows substantial probability density

at zero bond lengths.