Are recent water models obtained by fitting diffraction data consistent with infrared/Raman and x-ray absorption...

Area of Science:

• Computational chemistry and condensed matter physics.
• Spectroscopy and structural analysis of liquids.

Background:

• Accurate structural models of water are crucial for understanding its properties.
• Previous models derived from X-ray and neutron diffraction data have limitations.
• Discrepancies exist between diffraction-derived models and spectroscopic experimental data.

Purpose of the Study:

• To compute and compare X-ray absorption (XA) spectra from various water structural models.
• To evaluate the ability of theoretical models to reproduce experimental XA, IR, and Raman spectra.
• To identify limitations in current water models derived from diffraction data.

Main Methods:

• Calculation of X-ray absorption (XA) spectra using water structures from diffraction data fitting.
• Computation of electric field (E-field) distributions and infrared (IR) spectra.
• Utilized two established theoretical approaches for spectral calculations.

Main Results:

• Symmetric and asymmetric water models from diffraction data yield similar XA spectra, but do not match experimental results.
• Fitted models contain unphysical structures, such as hydrogen-hydrogen interactions.
• Modified asymmetric models show slight improvement but remain unsatisfactory; theoretical approaches yield discrepancies for asymmetric models and predict blueshifted Raman spectra for symmetric models.

Conclusions:

• No current water model adequately describes X-ray absorption, IR/Raman spectroscopy, and diffraction data simultaneously.
• Existing models derived from diffraction data possess unphysical characteristics.
• Further development of theoretical models for water structure and dynamics is required.