Unraveling the electronic structure, mechanical, and dielectric properties of ZnPurBr-MOF: Ab initio calculations

A novel nanocrystalline metal–organic framework (MOF), ZnPurBr, was recently discovered to undergo an unusual thermal solid–solid phase transition, resulting in a stable high-temperature phase structure, ZnPurBr-HT. In order to fully elucidate this fascinating phase transition, the structural, electronic, optical, and mechanical properties of the ZnPurBr high and low temperature phases are thoroughly investigated through first-principles calculations. This study confirms the retention of the metal tetrahedral bonding and the integrity of the framework during phase transition. Calculations on the electronic and optical properties show that ZnPurBr is a semiconductor and has low refractive indexes at both phases; however, increases in the dielectric constants and the plasmon frequency upon going through the phase transition can be clearly captured. Tensorial analysis of the elastic constants for both phases shows that the high temperature phase is stiffer than its low temperature counterpart, but less anisotropic. Importantly, the techniques used for the modeling and physical properties calculations can be easily be applied to other MOFs, which can certainly reveal many of the interesting features hitherto undiscovered.