Higher order diffusion Monte Carlo propagators for linear rotors as diffusion on a sphere: development and...

Area of Science:

• Quantum chemistry
• Computational physics
• Chemical kinetics

Background:

• Diffusion Monte Carlo (DMC) simulations are crucial for studying quantum systems.
• Simulations involving linear rotors often employ simplified diffusion models.
• Understanding reaction dynamics in superfluid helium droplets is an ongoing challenge.

Purpose of the Study:

• To introduce a novel, higher-order diffusion kernel for DMC simulations of linear rotors.
• To enhance the accuracy and efficiency of dynamical correlation function calculations.
• To investigate the structure and energetics of O(2)@He(n) clusters and explain reaction quenching phenomena.

Main Methods:

• Developed a new rotational diffusion kernel based on particle diffusion on corrugated surfaces and linear molecule rotation isomorphism.
• Implemented and tested the new kernel in DMC simulations of model systems.
• Applied the algorithm to study O(2)@He(n) (n = 1-40) clusters.

Main Results:

• The new kernel demonstrates superior performance and second-order convergence with respect to the time step.
• This leads to an identical order of convergence for the diffusion part of the DMC projector.
• Simulations of O(2)@He(n) show O(2) localizing in the cluster core, while Mg@He(n) exhibits fluxional behavior at larger n.

Conclusions:

• The developed rotational diffusion kernel significantly improves DMC simulations for systems with linear rotors.
• The study provides insights into the behavior of O(2) and Mg within superfluid helium droplets.
• The observed localization and fluxional behavior are proposed as explanations for the quenching of O(2) and Mg reactions in larger helium droplets.