Potential energy surface for interactions between two hydrogen molecules.

Area of Science:

• * Physical Chemistry
• * Quantum Chemistry
• * Computational Molecular Science

Background:

• * Accurate potential energy surfaces are crucial for understanding intermolecular interactions.
• * Previous calculations for hydrogen molecule interactions lacked the desired precision.

Purpose of the Study:

• * To compute highly accurate nonrelativistic interaction energies for two ground-state hydrogen molecules.
• * To develop a precise four-dimensional potential energy surface for H2-H2 interactions.
• * To improve the calculation of the second virial coefficient for hydrogen.

Main Methods:

• * Employed the supermolecular coupled-cluster method with single, double, and noniterative triple excitations [CCSD(T)].
• * Utilized very large augmented quintuple zeta basis sets, supplemented with bond functions.
• * Performed symmetry-adapted perturbation theory and explicitly correlated Gaussian (ECG) calculations for validation and uncertainty estimation.

Main Results:

• * Achieved an accuracy of approximately 0.15 K (0.3%) at the potential well minimum.
• * Calculated interaction energies with an estimated uncertainty an order of magnitude better than previous studies.
• * The fitted potential's global minimum is -57.12 K for a T-shaped configuration at R=6.34 bohrs.

Conclusions:

• * The developed potential energy surface is highly accurate, significantly improving upon prior work.
• * Calculations of the second virial coefficient using this potential show substantially better agreement with experimental data.
• * This study sets a new benchmark for the accuracy of intermolecular potential calculations for small molecules.