Cooperation and Environment Characterize the Low-Lying Optical Spectrum of Liquid Water

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• The optical spectrum of liquid water exhibits unique features not fully explained by existing models.
• Understanding these spectral properties is crucial for various scientific disciplines.

Purpose of the Study:

• To elucidate the underlying mechanisms behind the optical spectrum of liquid water.
• To provide simple explanations for previously elusive spectral features.

Main Methods:

• Subsystem time-dependent density functional theory (TD-DFT) was employed for spectral analysis.
• The study focused on analyzing the joint density of states and many-body excitonic effects.

Main Results:

• The disordered environment in liquid water broadens the joint density of states, causing a red-shifted Urbach tail compared to water vapor.
• Confinement effects from the first solvation shell lead to a blue shift in the first absorption peak.
• Many-body excitonic effects significantly influence low-frequency spectral weights and contribute to the refractive index.

Conclusions:

• The study successfully explains key spectral features of liquid water through computational analysis.
• Disorder and solvation effects are identified as primary drivers of spectral shifts.
• Excitonic effects play a notable role in the optical properties of liquid water.