Insights in quantum dynamical effects in the infrared spectroscopy of liquid water from a semiclassical study with an ab initio-based flexible and polarizable force field

Abstract

The dynamical properties of liquid water play an important role in many processes in nature. In this paper, we focus on the infrared (IR) absorption spectrum of liquid water based on the linearized semiclassical initial value representation (LSC-IVR) with the local Gaussian approximation (LGA) [J. Liu and W. H. Miller, J. Chem. Phys. 131, 074113 (2009)] and an ab initio based, flexible, polarizable Thole-type model (TTM3-F) [G. S. Fanourgakis and S. S. Xantheas, J. Chem. Phys. 128, 074506 (2008)]. Although the LSC-IVR (LGA) gives the exact result for the isolated three-dimensional shifted harmonic stretching model, it yields a blueshifted peak position for the more realistic anharmonic stretching potential. By using the short-time information of the LSC-IVR correlation function; however, it is shown how one can obtain more accurate results for the position of the stretching peak. Due to the physical decay in the condensed phase system, the LSC-IVR (LGA) is a good and practical approximate quantum approach for the IR spectrum of liquid water. The present results offer valuable insight into future attempts to improve the accuracy of the TTM3-F potential or other ab initio-based models in reproducing the IR spectrum of liquid water.

2D-Raman-THz spectroscopy: A sensitive test of polarizable water models

“…That band is better represented in more sophisticated polarizable models of water, [43][44][45] presumably since those are polarizable also at the hydrogen sites and as such feel more closely the formation of a hydrogen bond, or since those are flexible models. It is however very well established that this band originates from charge flows between water molecules upon hydrogen bonding, 5,[36][37][38][39] and it is quite questionable whether polarizability can describe that effect.…”

“…Apart from a few exceptions, [43][44][45] water models are not typically validated against experimental THz and/or Raman spectra. The development of polarizable water models is currently a very active field of research, because they will be a cornerstone for the next generation of MD force fields for biomolecular simulations.…”

“…32 It is well established that simple point charge models of water, such as TIP4P/2005 34 or SPC/E, 35 cannot account for the intensity of that band, since that band originates from charge flows within and between water molecules upon hydrogen bonding. 5,[36][37][38][39] Adding polarizability to a water model, either in an ad hoc manner to a trajectory that has been precalculated with the help of a pointcharge model, [39][40][41][42] or explicitly as part of the force field, [43][44][45] reveals the band in the THz absorption spectrum, albeit, often, with severely underestimated intensity.…”

Role of sampling in evaluating classical time autocorrelation functions

“…Numerical statistical errors were estimated by averaging these errors over 100 independent simulations, each with the same number of unique trajectories N uniq = 5 × 10 5 . In order to compare with the analytical results, the effect of correlation was removed by converting the numerical statistical error σ to an error per trajectory σ 1 := (N/N corr ) 1/2 σ .…”

“…1,2 Examples include the optical absorption line shapes computed from the dipole time autocorrelation function, the diffusion coefficient computed from the velocity time autocorrelation function, and various relaxation properties. 3 More general time correlation functions are in fact the principal ingredients of semiclassical 4,5 and path-integral [6][7][8][9][10][11] calculations of quantum dynamical properties. Trajectory-based methods for computing time correlation functions, however, may become too expensive in many-dimensional systems.…”