The Dielectric Function for Water and Its Application to van der Waals Forces

Area of Science:

• Physical Chemistry
• Colloid and Surface Science
• Spectroscopy

Background:

• Accurate dielectric response of water is essential for Lifshitz theory calculations of van der Waals forces in aqueous systems.
• Existing dielectric response models for water (Parsegian-Weiss, Roth-Lenhoff) yield significant discrepancies in van der Waals force calculations.
• Previous models relied on fitting damped-harmonic-oscillator models to limited absorption data.

Purpose of the Study:

• To construct a more reliable dielectric response function, ε(iξ), for water at 298 K.
• To improve the accuracy of van der Waals force calculations in aqueous systems using Lifshitz theory.
• To provide a rigorous, model-independent representation of water's dielectric response.

Main Methods:

• Compiled recent and comprehensive spectral absorption data for water from diverse literature sources.
• Utilized direct integration of Kramers-Kronig relations to construct the dielectric response function ε(iξ).
• Incorporated spectral measurements across a broad frequency range (8-10 decades), including infrared, microwave, and X-ray inelastic scattering.

Main Results:

• Developed a new, model-independent dielectric response function, ε(iξ), for water at 298 K.
• The new ε(iξ) falls between the previously established Parsegian-Weiss and Roth-Lenhoff representations.
• This construction rigorously converts absorption data using Kramers-Kronig integration.

Conclusions:

• The newly constructed dielectric response function for water is considered the most reliable for van der Waals force calculations via Lifshitz theory.
• The methodology allows for the rigorous incorporation of diverse spectral data.
• The approach can be extended to construct dielectric responses at other temperatures.