Quantum effects and anharmonicity in the H2-Li(+)-benzene complex: a model for hydrogen storage materials

Area of Science:

• Computational Chemistry
• Materials Science
• Quantum Mechanics

Background:

• Hydrogen adsorption is key for materials like metal-organic frameworks (MOFs) and carbon-based materials.
• Accurate modeling of intermolecular interactions and quantum effects is essential for predicting material performance.

Purpose of the Study:

• To investigate quantum and anharmonic effects on hydrogen adsorption in a model H2-Li(+)-benzene system.
• To accurately calculate the binding enthalpy of hydrogen in this model system.

Main Methods:

• Employed three- and 8-dimensional quantum diffusion Monte Carlo (QDMC) and rigid-body diffusion Monte Carlo (RBDMC) simulations.
• Utilized potential energy surfaces interpolated from high-level electronic structure calculations (M05-2X/6-31+G(d,p) and M05-2X/6-311+G(2df,p)).

Main Results:

• Calculated 0 K H2 binding enthalpies (ΔH(bind) (0 K)) were 16.5 kJ mol⁻¹ (3D) and 12.4 kJ mol⁻¹ (8D), higher than harmonic approximations.
• Zero-point energy effects constitute 35% of ΔH(bind) (0 K), demonstrating their significant contribution.
• Simple corrections for H2 rotational modes accurately reproduced 8D anharmonic results, within 2%.

Conclusions:

• Quantum and anharmonic effects are critical for accurate hydrogen adsorption calculations in model systems.
• Neglecting zero-point energy leads to significant overestimation of binding enthalpies.
• QDMC and RBDMC simulations show H2 delocalization above the Li(+)-benzene system at 0 K.