Tunneling splittings from path-integral molecular dynamics using a Langevin thermostat

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Molecular Dynamics

Background:

• Calculating tunneling splittings in molecules is crucial for understanding reaction dynamics.
• Previous methods using path-integral molecular dynamics (PIMD) have limitations in accuracy and efficiency.
• Degenerate configurations in molecules and clusters present unique challenges for theoretical treatment.

Purpose of the Study:

• To develop and validate an improved PIMD method for calculating tunneling splittings.
• To apply the new method to complex systems like the water dimer.
• To enhance the accuracy and efficiency of stochastic calculations for molecular tunneling.

Main Methods:

• Utilized path-integral molecular dynamics (PIMD) with a Langevin thermostat.
• Employed thermodynamic integration along semiclassical instanton paths.
• Calculated tunneling splittings by sampling ratios of thermodynamic density matrices.

Main Results:

• Successfully applied the improved PIMD method to the water dimer and malonaldehyde.
• Achieved agreement within 20% for large splittings and 10% for smaller splittings in the water dimer compared to benchmark results.
• Refined previous PIMD calculations for one-dimensional models.

Conclusions:

• The developed PIMD method offers a robust and accurate approach for computing tunneling splittings.
• This method provides a physically motivated and efficient reaction coordinate for complex molecular systems.
• The findings pave the way for more precise theoretical investigations of quantum tunneling phenomena.