Global search for minimum energy (H2O)n clusters, n = 3-5

Area of Science:

• Computational chemistry
• Physical chemistry
• Atmospheric science

Background:

• Understanding the structure and stability of water clusters is crucial for atmospheric chemistry.
• Previous studies have explored smaller water clusters, but comprehensive analyses of neutral trimers, tetramers, and pentamers are limited.

Purpose of the Study:

• To computationally determine the relative Gibbs free energy (deltaG(o)) for all possible conformers of neutral water clusters (H2O)n, where n = 3-5.
• To identify the most stable isomers of water trimers, tetramers, and pentamers at 298 K.
• To assess the significance of cyclic water clusters in atmospheric processes.

Main Methods:

• Utilized Gaussian-3 (G3) model chemistry for high-level energy calculations.
• Performed extensive conformational searches, generating thousands of initial structures for each cluster size.
• Employed sequential optimization steps: PM3, followed by Hartree-Fock/6-31G*, and finally G3 model chemistry.

Main Results:

• Identified only two stable conformers for water trimers.
• Discovered five stable tetramer conformers and ten stable pentamer conformers.
• Found that all linear starting structures converged to cyclic or three-dimensional configurations.
• The cyclic pentamer was determined to be the most stable isomer at 298 K.

Conclusions:

• The study provides a comprehensive set of stable isomers for neutral water clusters (H2O)3-5.
• Results indicate that cyclic water clusters, particularly tetramers and pentamers, are likely significant in the atmosphere.
• The findings contribute to a better understanding of water's role in atmospheric phenomena.