An ab initio molecular dynamics study on hydrogen bonds between water molecules.

Area of Science:

• Computational Chemistry
• Molecular Dynamics
• Quantum Chemistry

Background:

• Accurate identification of hydrogen bonds (H bonds) is essential for quantifying molecular interaction energies.
• Conventional geometric criteria for H bonds can lead to misidentification of non-H bonding cases as H-bonded.

Purpose of the Study:

• To investigate the misidentification of H bonds using conventional criteria.
• To propose refined geometric criteria for more accurate H-bond identification in molecular systems.

Main Methods:

• Systematic ab initio molecular dynamics calculations with dispersion correction (BLYP functionals) on two water molecules.
• Analysis of interaction energies at various orientations and distances.
• Statistical analysis using Car-Parrinello ab initio molecular dynamics for a 64-water molecule system.

Main Results:

• Conventional distance-angle criteria misidentify some non-H bonding water pairs as H-bonded due to short-range repulsions.
• Proposed criteria, including d(H···H) and a lower limit for r(O···H), improve H-bond identification accuracy.
• The refined criteria align well with binding energy criteria (E ≤ -10 kJ/mol) for the majority of H bonds.

Conclusions:

• Refined geometric criteria, incorporating hydrogen-hydrogen distance, enhance the accuracy of H-bond identification in water systems.
• Short-range repulsive interactions can be effectively accounted for by the proposed criteria, reducing misclassifications.
• While geometric criteria are powerful, complex quantum effects in H bonding necessitate a nuanced approach.