Partition-DFT on the water dimer.

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Quantum Chemistry

Background:

• The ground-state symmetry of water dimers shifts from C_s to C_2h as oxygen-oxygen distance decreases below ~2.5 Å.
• Understanding the energetic costs associated with these geometric changes is crucial for hydrogen bond studies.

Purpose of the Study:

• To investigate the energetic differences between C_s and C_2h water dimer geometries using Partition Density Functional Theory (PDFT).
• To analyze the monomer densities and partition potentials that contribute to hydrogen bond formation.

Main Methods:

• Application of Partition Density Functional Theory (PDFT) to water dimers across a range of O-O distances (1-5 Å).
• Calculation of the work required to deform isolated monomer densities for both C_s and C_2h geometries.
• Minimization of the sum of monomer energies to find unique monomer densities.

Main Results:

• The work of deforming monomer densities is consistently higher for the C_s geometry compared to the C_2h geometry for all investigated O-O distances.
• PDFT successfully identified unique monomer densities that accurately represent the dimer densities.

Conclusions:

• The energetic preference for the C_2h geometry is supported by the calculated deformation work.
• PDFT densities and partition potentials provide insights into the orbital interactions driving hydrogen bond formation in water dimers.