Ab-initio crystal structure prediction. A case study: NaBH4

Crystal structure prediction from first principles is still one of the most challenging and interesting issue in condensed matter science. we explored the potential energy surface of NaBH4 by a combined ab-initio approach, based on global structure optimizations and quantum chemistry. In particular, we used simulated annealing (SA) and density functional theory (DFT) calculations. The methodology enabled the identification of several local minima, of which the global minimum corresponded to the tetragonal ground-state structure (P42/nmc), and the prediction of higher energy stable structures, among them a monoclinic (Pm) one was identified to be 22.75 kJ/mol above the ground-state at T=298 K. In between, orthorhombic and cubic structures were recovered, in particular those with Pnma   and F4¯3m symmetries.

The total electron energy difference of the calculated stable structures. Here, the tetragonal (IT 137) and the monoclinic (IT 6) symmetry groups corresponded to the lowest and the highest energy structures, respectively.Figure optionsDownload as PowerPoint slideHighlights
► Potential energy surface of NaBH4 is investigated.
► This is done a combination of global structure optimizations based on simulated annealing and density functional calculations.
► We successfully reproduced experimentally found tetragonal and orthorhombic structures of NaBH4.
► Furthermore, we found a new stable high energy structure.