Theoretical study on the structural evolution and hydrogen storage in NbHn (n = 2–15) clusters

Abstract

Niobium hydrides are attractive superconductors. Exploring the formation process of niobium hydrides is essential to elucidate the mechanism of superconductivity. One of the key issues is to clarify the atomic stacking patterns of Nb and H atoms, i.e., the structural evolution of Nb–H clusters. Here, the low-energy structural isomers of NbHn (n = 2–15) clusters are determined using the CALYPSO method combined with density functional theory calculations. Geometries were fully optimized at the B3LYP/LANL2DZ/6–311++G(d) level of theory to determine global minimum structures for each size. The results indicate that NbH13 is the most stable cluster in this size range. The 4d atomic orbital of Nb and the hydrogen 1s atomic orbital participate largely to the internal binding of the NbH13 cluster. They hydrogen storage density and adsorption energy of this cluster are calculated to be 12.4 wt% and 2.58 eV, respectively. The high hydrogen storage density, suitable hydrogen adsorption energy, and high stability of NbH13 shows promise as a hydrogen storage material. These results provide fundamental information for further design of metal hydrogen storage materials.