A combined instantaneous normal mode and time correlation function description of the infrared vibrational spectrum of ambient water

Abstract

A formal connection is made between the vibrational density of states (DOS) of a liquid and its approximation by way of instantaneous normal modes (INMs). This analysis leads to a quantum generalization of the INM method (QINM), and to the possibility of evaluating the classical DOS exactly. Further, INM approximations to spectroscopic quantities (e.g., infrared absorption and Raman scattering) follow in a consistent manner by evaluating the appropriate golden rule expressions for harmonic oscillators, using the INM or QINM DOS in place of the true DOS. INM and QINM methods are then applied along with traditional time correlation function (TCF) methods to analyze the entire infrared (IR) spectrum of ambient water. The INM and TCF approaches are found to offer complimentary information. TCF methods are shown to offer an unexpectedly accurate description of the O–H stretching line shape. Further, the 19-fold enhancement in liquid phase absorption compared to the gas phase is also reproduced. INM and QINM methods are used to analyze the molecular origin of the water spectrum, and prove especially effective in analyzing the broad O–H stretching absorption. Further, it is argued that a motional narrowing picture is qualitatively useful in analyzing INM approximations to spectroscopy.

Hydrogen bonds of interfacial water in human breast cancer tissue compared to lipid and DNA interfaces

“…The calculations of the vibrational band shapes of the OH stretching mode involved in H-bond interactions have a long history and have captured the attention of a number of papers [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61]. In order to explain spectacular features in frequency shifts, band shapes, and bandwidths of the components the OH stretching modes the linear and nonlinear response theory [43][44][45], quantum ab inito calculations for possible cluster structures [62][63][64][65][66][67][68], classical [69][70][71][72][73] and mixed quantum/classical molecular dynamics simulations [74][75][76] have been used.…”

Vibrational Line Shapes, Spectral Diffusion, and Hydrogen Bonding in Liquid Water

“…); and third, vibrational energy relaxation is automatically included (see below). Results from several of these classical approaches have appeared in the literature [79,[87][88][89][90][91].…”

“…A related approach was also presented by Reimers and Watts [159]. Classical line shape calculations using an MD simulation of flexible molecules [79,[87][88][89][90], or from a Car-Parrinello simulation [91], have also been performed. Very recently mixed quantum/classical approaches that include dynamical effects have been presented by Buch et al [71,110] and by Torii [97].…”

Inelastic effects in electron tunneling through water layers

“…Instead we use previous work that indicate that on timescales shorter than ~100fs the nuclear dynamics of different solvents, including water, can be reliably described in the instantaneous normal mode picture. [35][36][37][38] In this approach each static liquid configuration sampled from the equilibrium ensemble is used as a reference for expanding the nuclear potential up to second order in the deviations of the nuclear coordinates from this reference configuration. Diagonalizing the Hessian matrix associated with the second order derivatives of the nuclear potential about this reference point then yields a set of 'instantaneous normal modes' (INMs) whose dynamics describes the short time evolution of the liquid about that configuration.…”