The quantum structure of anionic hydrogen clusters

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Quantum Mechanics

Background:

• Understanding the behavior of hydrogen clusters is crucial for various chemical and physical processes.
• Previous studies have explored hydrogen-metal interactions, but modeling neutral hydrogen clusters with anions presents unique challenges.

Purpose of the Study:

• To develop and validate a flexible and polarizable interatomic potential for modeling hydrogen clusters interacting with a hydrogen anion.
• To investigate the structural, energetic, and vibrational properties of hydrogen clusters (H2)n H- for n = 1-54.

Main Methods:

• Development of a new interatomic potential parametrized against coupled cluster quantum chemical calculations.
• Path-integral molecular dynamics simulations at 1 K.
• Analysis of geometric structures, energetic stability, and vibrational delocalization.

Main Results:

• Identified equilibrium structures generally based on icosahedral shells with hydrogen molecules oriented towards the anion.
• Observed geometric magic numbers at cluster sizes n = 12, 32, and 44, consistent with mass spectrometry data.
• Correlated energetic stability with vibrational delocalization and noted finite size effects and increased molecular rotation in larger clusters.

Conclusions:

• The developed potential accurately models hydrogen clusters interacting with a hydrogen anion.
• Quantum nuclear effects play a significant role in the formation of the icosahedral structure, particularly for the 44-molecule cluster.
• The study provides insights into the interplay of structure, stability, and quantum effects in hydrogen cluster anions.