The structure of liquid water beyond the first hydration shell

Area of Science:

• Physical Chemistry
• Liquid State Physics
• Materials Science

Background:

• Consensus exists on the tetrahedral short-range order in the first coordination shells of liquid water.
• Limited understanding of longer-range molecular structure and the influence of local tetrahedral arrangements.

Purpose of the Study:

• Investigate molecular arrangements and their importance at different distance ranges in liquid water.
• Characterize the transition in structural order at larger distances.

Main Methods:

• Utilized an expansion of distance-dependent excess entropy.
• Decomposed excess entropy into components related to relative molecular position and orientation.

Main Results:

• Identified a transition in liquid water structure around 6 Å.
• Shorter distances (up to ~6 Å) show predominantly orientational order.
• Larger distances (up to ~9 Å) reveal predominantly positional order with preserved tetrahedral symmetry.

Conclusions:

• Liquid water exhibits distinct orientational and positional ordering regimes at different length scales.
• The tetrahedral symmetry of the first coordination shell influences longer-range positional order.