Lattice Dynamics of Metal-Organic Frameworks (MOFs): Neutron Inelastic Scattering and First-Principles Calculations

TL;DR

This study combines neutron inelastic scattering and first-principles calculations to analyze the lattice dynamics and structural stability of MOF5, revealing its proximity to instability and detailed phonon behaviors.

Contribution

It provides the first combined experimental and theoretical analysis of MOF5's lattice dynamics, highlighting its near-instability and specific phonon modes.

Findings

MOF5 has an unusually small shear modulus c44 = 1.16 GPa.

Phonon dispersion and NIS spectra agree well with experiments.

MOF5 is close to structural instability and may form new phases under pressure.

Abstract

By combining neutron inelastic scattering (NIS) and first-principles calculations, we have investigated the lattice dynamics of MOF5. The structural stability of MOF5 was evaluated by calculating the three cubic elastic constants. We find that the shear modulus, c44 = 1.16 GPA, is unusually small, while two other moduli are relatively large (i.e. c11 = 29.42 GPa and c12 = 12.56 GPa). We predict that MOF5 is very close to structural instability and may yield interesting new phases under high pressure and strain. The phonon dispersion curves and phonon density of states were directly calculated and our simulated NIS spectrum agrees very well with our experimental data. Several interesting phonon modes are discussed, including the softest twisting modes of the organic linker.