Structural changes in the water tetramer. A combined Monte Carlo and DFT study

Area of Science:

• Computational chemistry
• Physical chemistry
• Quantum chemistry

Background:

• Water clusters are fundamental to understanding water's properties.
• Investigating the thermodynamic behavior of water clusters provides insights into hydrogen bonding.

Purpose of the Study:

• To calculate the heat capacity curve of the water tetramer.
• To explore the structural dynamics of water tetramers at various temperatures.
• To validate a computational methodology combining Monte Carlo and Density Functional Theory.

Main Methods:

• Parallel-tempering and multiple-histogram Monte Carlo simulations.
• Density Functional Theory (DFT) calculations with B97-1 functional and triple-zeta basis sets.
• Boltzmann-reweighting approach to integrate quantum chemistry with Monte Carlo.

Main Results:

• Well-converged thermodynamic data were obtained efficiently.
• A significant structural change was detected in the water tetramer between 50-200 K.
• The structural change involves the onset of water molecule rotations around hydrogen bonds.

Conclusions:

• The combined computational approach is effective for simulating thermodynamic properties of molecular clusters.
• The water tetramer exhibits temperature-dependent structural dynamics involving hydrogen bond rotations.
• The cluster's square cycle skeleton remains largely rigid during this transition.