Structure prediction via global energy landscape exploration of the ternary rare-earth compound LaOI

Crystal structure prediction has been performed via the global exploration of the energy landscape of lanthanum oxyiodide (LaOI), using simulated annealing and involving over one million local optimizations. Afterwards, the most promising structure candidates among the minima found were subjected to local optimizations on ab initio level. Density functional theory (DFT) calculations were performed, using the GGA-PBE functional, together with the hybrid HSE06 exchange-correlation functional. Seven most relevant low-energy minima were found after the final ab initio relaxation. The global minimum found corresponds to the alpha-LaOI tetragonal structure in agreement with previous experimental and theoretical reports. The prediction of the additional beta-, gamma-, delta-, epsilon-, zeta-, and eta-LaOI modifications demonstrate the rich diversity of local cation-anion coordinations and structure types ranging from cubic and tetragonal, over rhombohedral and orthorhombic to monoclinic symmetry. Moreover, there are many previous experimental reports on related structures in the lanthanide oxyfluorides, which might guide possible future syntheses of LaOI-modifications. A successful synthesis of these novel LaOI materials could have multiple technological applications ranging from nano- and bio-materials to medicine, solid oxide fuel cells and photocatalytic materials.