Anionic water pentamer and hexamer clusters: An extensive study of structures and energetics

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Physical Chemistry

Background:

• Anionic water clusters are crucial in atmospheric and biological processes.
• Understanding their energetics and structures is key to predicting their behavior.

Purpose of the Study:

• To investigate the structures and energetics of anionic pentamer and hexamer water clusters.
• To evaluate the accuracy of the density-fitted orbital-optimized linearized coupled-cluster doubles (DF-OLCCD) method against established high-level methods.

Main Methods:

• Employed high-level ab initio quantum chemical methods: coupled-cluster singles and doubles (CCSD), CCSD with perturbative triples [CCSD(T)], and DF-OLCCD.
• Calculations were performed at the complete basis set (CBS) limit, extrapolating from aug4-cc-pVTZ and aug4-cc-pVQZ basis sets.

Main Results:

• Reported structures and energetics for sixteen anionic pentamer and eighteen anionic hexamer clusters.
• Obtained vertical detachment energies (VDE) of 9.9 and 11.2 kcal mol⁻¹ for pentamers and hexamers, respectively, closely matching experimental values.
• Demonstrated strong binding energies (average -5.0 to -5.3 kcal mol⁻¹ per water molecule) due to hydrogen bonding.

Conclusions:

• The DF-OLCCD method provides results comparable in accuracy to CCSD(T) for anionic clusters.
• DF-OLCCD's efficiency makes it a valuable tool for high-accuracy computational studies of molecular systems.