p-H2 vs o-D2 clusters: From liquid-like to glass-like behavior.

Area of Science:

• Quantum chemistry
• Computational physics
• Materials science

Background:

• Para-hydrogen (p-H2) clusters are studied for their unique structural properties and computational challenges.
• Previous studies lack consensus on cluster energetics and structures due to size dependencies and numerical limitations.

Purpose of the Study:

• Accurately determine the energetic and structural properties of small para-hydrogen clusters (LJ34-39).
• Investigate the influence of the quantum delocalization parameter (Λ) on cluster behavior, comparing hydrogen and deuterium regimes.

Main Methods:

• Utilized Diffusion Monte Carlo (DMC) simulations.
• Focused on a specific size range of Lennard-Jones clusters (LJ34-39).
• Varied the quantum delocalization parameter Λ between hydrogen and deuterium values.

Main Results:

• Demonstrated strongly delocalized ground state wavefunctions for (p-H2)N clusters across numerous identical isomers.
• Showed that ortho-deuterium (o-D2) clusters exhibit localized yet disordered ground states.
• Observed non-ergodic system dynamics in the o-D2 regime, with DMC walkers getting trapped.

Conclusions:

• The transition from p-H2 to o-D2 clusters, driven by decreasing Λ, resembles a liquid-glass transition.
• The study highlights the critical role of quantum effects in determining cluster properties.
• Suggests DMC method's limitations in non-ergodic regimes.