HF trimer: A new full-dimensional potential energy surface and rigorous 12D quantum calculations of vibrational states

Hydrogen bonds play a critical role in defining the structural and dynamical properties of water, aqueous solutions, and biomolecules such as DNA and proteins. Despite extensive studies using advanced experimental and theoretical approaches, the high dimensionality and complexity of bulk systems present challenges in characterizing hydrogen bonds, their cooperativity, and rearrangement dynamics quantitatively.

Noncovalently bound molecular trimers are essential in understanding these interactions, as they are the smallest clusters where significant nonadditive many-body interactions emerge. These trimers are ideal for testing the accuracy of computed three-body interactions by comparing high-level bound-state calculations on potential energy surfaces (PESs) with spectroscopic data.

While methods for full-dimensional quantum calculations of rovibrational states of molecular dimers are available, no comparable methodology for hydrogen-bonded molecular trimers was developed until recently. Over the past two years, we have developed a computational methodology for rigorous full-dimensional (12D) quantum calculations of fully coupled intramolecular and intermolecular vibrational states for hydrogen-bonded trimers of flexible diatomic molecules. Initially applied to the HF trimer and subsequently to the HCl trimer, this method uses ab initio many-body PESs, offering new accuracy levels in studying hydrogen-bonded trimer interactions.

In this presentation, I will introduce a new full-dimensional PES for the HF trimer, called PES-2024, based on advancements in ab initio electronic structure theory. To validate PES-2024, we conducted rigorous 12D quantum calculations of the fully coupled intra- and intermolecular vibrational states of the HF trimer, comparing results with experimental data and an older ab initio PES developed by Quack and Suhm (QSS PES). Our findings demonstrate that PES-2024 provides a more accurate depiction of the HF trimer’s intra- and intermolecular vibrations than the QSS PES.