Develop Quantum Vibrational Perturbation Method And Apply It To HCl-H₂O Clusters And Acetone-Water Solution

One-or two-dimensional(1D or 2D)infrared(IR)spectra of site-specific probes provide an opportunity to gain a molecular-level understanding of the local hydrogen-bonding network,conformational dynamics,and long-range electrostatic interactions in condensed-phase and biological systems.However,up to date,quantitative interpretation of experimental spectra is still a major challenge due to the fast time scale,nuclear quantum effects and large-scale systems with complicated surrounding solvent.A challenge in computation is to determine the time-dependent vibrational frequencies that incorporate explicitly both nuclear quantum effects of vibrational motions and an electronic structural representation of the potential energy surface.In this work,we propose a quick and accurate new approach to simulate 1D or 2D-IR spectra,which is a semi-classical method through a combination of the classical sampling the intermolecular structures and density distribution by ab initio molecular dynamics(AIMD)simulation,and quantum treatment of the time-depended transition frequencies of a specific vibrational mode based on the first-order perturbation approximation.Computational efficiency is achieved through the use of discrete variable representation of the vibrational wave functions,a perturbation theory to evaluate the vibrational energy shifts due to solvent dynamic fluctuations,and a combined QM/MM potential for the systems.It was found that first-order perturbation is sufficiently accurate,enabling time-dependent vibrational frequencies to be obtained on the fly in molecular dynamics.The QVP method is illustrated on the mode-specific linear and 2D-IR spectra of the H-Cl stretching frequency in the HCl-water clusters and the carbonyl stretching vibration of acetone in aqueous solution.To further reduce computational cost,a hybrid strategy was proposed,and it was found that the computed vibrational spectral peak position and line shape are in agreement with experiment.In addition,it was found that anharmonicity is significant in the H-Cl stretching mode and hydrogen-bonding interactions further enhance anharmonic effects.