A solid-state density functional theory investigation of the structure and vibrational modes of vanadium phosphate polymorphs

The experimental mid-infrared spectra and structures of the α1, α2, and β phases of vanadium phosphate (VOPO4) are compared to solid-state density functional theory (DFT) simulations. The effect of basis set is also explored in the orbital descriptions of oxygen, and it is shown that there are drastic changes in the results for each crystal phase. Overall, there was a good agreement in both bond lengths and angles as well as the infrared vibrational modes between the experimental and theoretically obtained values. These results indicate that solid-state DFT provides sufficiently high accuracy to be able to distinguish between energetically similar yet distinct crystalline polymorphs, providing a tool for understanding and predicting the complex polymorphism in VOPO4 and other inorganic solids.