Ultrafast pump-probe and 2DIR anisotropy and temperature-dependent dynamics of liquid water within the E3B model

Abstract

Recently, Tainter et al. [J. Chem. Phys. 134, 184501 (2011)] reparameterized a new rigid water model (E3B) that explicitly includes three-body interactions in its Hamiltonian. Compared to commonly used water models such as SPC/E and TIP4P, the new model shows better agreement with experiment for many physical properties including liquid density, melting temperature, virial coefficients, etc. However, the dynamics of the E3B model, especially as a function of temperature, has not been systematically evaluated. Experimental nonlinear vibrational spectroscopy is an ideal tool to study the dynamics of matter in condensed phases. In the present study, we calculate linear and nonlinear vibrational spectroscopy observables for liquid water using the E3B model at five temperatures: 10, 30, 50, 70 and 90 °C. Specifically, we calculate absorption and Raman spectra and pump-probe anisotropy for HOD in H2O at all temperatures, frequency-resolved pump-probe anisotropy for HOD in both H2O and D2O at 30 °C, and 2DIR anisotropy for HOD in D2O at 30 °C. In all cases, we find reasonable agreement with experiment, and for the ultrafast spectroscopy our results are a significant improvement over those of the SPC/E model. A likely reason for this improvement is that the three-body interaction terms in the E3B model are able to model cooperative hydrogen bonding. We also calculate rotational and frequency relaxation times at all temperatures, and fit the results to the Arrhenius equation. We find that the activation energy for hydrogen-bond switching in liquid water is 3.8 kcal/mol, which agrees well with the experimental value of 3.7 kcal/mol obtained from anisotropy decay experiments.

On the role of hydrogen-bond exchanges in the spectral diffusion of water

“…Ni and Skinner previously reported a spectral diffusion activation energy of 3.85 kcal/mol for the E3B2 water model from an Arrhenius analysis. 40 This is most directly comparable to E a for τ…”

“…These times are consistent with the ∼ 2 ps previously reported by Ni and Skinner for the E3B2 model. 40 This is quantitatively slower than that obtained for the SPC/E model, which represents the primary difference between the descriptions. Because of this behavior, we are able to resolve the FFCF for the E3B models out to longer times than that for SPC/E water.…”

“…( 1) or the timescale from a single exponential fit to C ω (t) for long times, e.g., t > 1.5 ps. 40 Note that the FFCF, under reasonable assumptions (at least for the neat liquid), 41 can be extracted from the center-line-slope of a 2D-IR spectrum and is thus experimentally accessible.…”

“…The former has been previously used to investigate water spectral diffusion and its temperature dependence. 40 The FFCFs obtained with these models are shown in Fig. 2 and the parameters obtained from fitting them are provided in Table I.…”

Charges of TIP4P water model for mixed quantum/classical calculations of OH stretching frequency in liquid water

“…F ull qu antu m ch e mi cal cal cu lati ons for th e p ote ntia l energies over a huge number of molecular configurations are very expensive and so a practical choice could be to employ a mixed quantum/classical theory. [9][10][11][12][13] In these methods, based on the assumption of adiabatic separation between the fast OH stretching motion and other slow degrees of freedom, a small subsystem including the stretching motion of a particular OH bond is treated by a full quantum chemical method while its interaction with the remainder of whole system (which is assumed to be frozen by the adiabatic approximation and treated by classical mechanics) is approximately described. 14 As an example, the potential energy curve v 0 for an OH stretchin g coordinate of an isolate d water mole cule is calculated by a quantum chemical ab initio method such as the coupled-cluster theory and the interaction energy curve int CM between the stretching motion and all other frozen degrees of freed om is approximatel y cal culated b y the Coulombic interaction energy between oscillating charges at the charge sites of the water molecule of interest and fixed charges at the charge sites of other water molecules.…”