Room temperature compressibility and diffusivity of liquid water from first principles

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Understanding water's anomalous properties is crucial in physical chemistry.
• Isothermal compressibility is a key property linked to water's behavior.

Purpose of the Study:

• To compute the isothermal compressibility of water using ab initio molecular dynamics.
• To evaluate the accuracy of different van der Waals density functionals in reproducing experimental data.
• To investigate the density dependence of the self-diffusion coefficient in water's anomalous region.

Main Methods:

• Ab initio molecular dynamics simulations were performed.
• Simulations included 200 water molecules across five different densities.
• Two distinct van der Waals density functionals were employed for calculations.

Main Results:

• Both density functionals predicted isothermal compressibilities within approximately 30% of experimental values.
• Only one functional accurately reproduced the density dependence of the self-diffusion coefficient in the anomalous region.
• Discrepancies were attributed to differences in the liquid's low- and high-density structures.

Conclusions:

• The choice of density functional significantly impacts the accurate prediction of water's dynamic properties.
• Ab initio molecular dynamics simulations provide valuable insights into water's anomalous behavior.
• Structural differences at varying densities are key to understanding functional performance.