An Extended Mixed Quantum/Classical Approach for Quantitative Calculation of Complex Refractive Index

TL;DR

This paper extends a mixed quantum/classical method to directly compute the complex refractive index of water, accurately capturing spectral shapes and intensities, and highlighting the importance of local field effects.

Contribution

The authors develop an extended theoretical framework that allows direct calculation of water's complex refractive index, improving spectral intensity predictions.

Findings

Accurately reproduces experimental spectral shapes and intensities.

Shows local field effects are essential for spectral intensity accuracy.

Enables analysis of water in bulk, thin films, and clusters.

Abstract

The mixed quantum/classical approach of Skinner and co-workers has been widely used to calculate the line shapes of the infrared spectra of water (H2O), but less attention has been paid to the use of this approach in quantitatively calculating spectral intensity, thereby limiting direct comparisons of calculated and experimental spectra. Here, we extend this theoretical framework to facilitate direct computation of the full complex refractive index of water, replacing the normalized ordinate used in previous studies. Our results for the OH stretching region of H2O capture both the shapes and intensities of the experimental spectra. They reveal that inclusion of the local field effect is crucial to the accurate reproduction of spectral intensity. This extended approach enables new areas of analysis of the bulk, thin-film, and cluster spectra of water.