High accuracy ab initio potential energy surface for the H₂O-H van der Waals dimer

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Accurate potential energy surfaces (PES) are essential for understanding intermolecular interactions and dynamics.
• The water-hydrogen (H2O-H) van der Waals dimer is a fundamental system for studying hydrogen bonding and energy transfer.
• Previous studies may lack high-accuracy, three-dimensional PES representations suitable for advanced simulations.

Purpose of the Study:

• To construct a high-accuracy three-dimensional potential energy surface (PES) for the H2O-H van der Waals dimer.
• To determine the global minimum geometry and binding energy of the H2O-H system.
• To provide a reliable PES for future molecular dynamics simulations and theoretical investigations.

Main Methods:

• Ab initio calculations were performed using coupled-cluster single, double, and perturbative triple (CCSD(T)) level of theory.
• Scalar relativistic effects were included via the second-order Douglas-Kroll-Hess approximation with augmented correlation-consistent basis sets (aug-cc-pVnZ-DK).
• Calculations were extrapolated to the complete basis set (CBS) limit, and the counterpoise method was used to mitigate basis set superposition error.

Main Results:

• A PES was generated based on 1054 symmetry-unique H2O-H geometries, with a distance R ranging from 2.5 to 9.0 Å.
• The global minimum was found at a coplanar geometry with R = 3.41 Å and an angle of 122.25°, yielding a CBS binding energy of 61.297 cm⁻¹.
• The reproduced PES exhibits a mean absolute error of <0.02 cm⁻¹ for R ≥ 3.0 Å, demonstrating high accuracy.

Conclusions:

• A highly accurate three-dimensional PES for the H2O-H van der Waals dimer has been successfully developed.
• The global minimum configuration and binding energy provide critical insights into the dimer's stability.
• The generated PES is suitable for use in advanced molecular dynamics simulations, enabling further studies of H2O-H interactions.