Accurate calculation of tunneling splittings in water clusters using path-integral based methods

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Computational Physics

Background:

• Tunneling splittings in molecular rovibrational spectra provide evidence of quantum tunneling.
• Accurate calculation requires high-fidelity interatomic potentials and quantum mechanical treatment of nuclei.
• Previous theoretical efforts have focused on various computational approaches.

Approach:

• This perspective reviews two path-integral based methods for calculating tunneling splittings: ring-polymer instanton and path-integral molecular dynamics (PIMD).
• It demonstrates the ring-polymer instanton method as a semiclassical approximation to PIMD.
• Focuses on methods with computational costs that scale favorably with system size.

Key Points:

• PIMD is presented as the rigorous approach for ground-state tunneling splitting calculations.
• The ring-polymer instanton method offers a computationally cheaper alternative with some accuracy trade-off.
• These calculations are crucial for testing and calibrating potential energy surfaces with spectroscopic accuracy.

Conclusions:

• Recent advancements in water cluster calculations are highlighted.
• The review discusses current challenges in the field of quantum tunneling calculations.
• Path-integral methods provide a powerful toolkit for understanding molecular quantum dynamics.