Origin of structural stability of ScH3 molecular nanowires and their chemical-bonding behavior: Correlation effects of the Sc 3d electrons

A new stable transition-metal trihydride (ScH3) molecular nanowire was recently reported by Li et al. [J. Am. Chem. Soc. 139, 6290–6293 (2017)]. Of the two typical structures (T–ScH3 and O–ScH3), T–ScH3 is more stable than O–ScH3. However, the reason why O–ScH3 is less stable than T–ScH3 was not known. Using Perdew–Burke–Ernzerhof (PBE), PBE+U, SCAN, and HSE06, as well as crystal orbital Hamilton populations (COHPs), we investigate the orbital-projected band structures and chemical bonding of T–ScH3 and O–ScH3. It is found that the energies calculated by PBE, SCAN, and HSE06 indeed reveal that T–ScH3 is more stable than O–ScH3, and there is no occupied antibonding state at the Fermi level of the COHP curves of T–ScH3, supporting the stable Sc–H bonding of T–ScH3. To the contrary, the Sc–H bonding of O–ScH3 is unstable because there exist occupied antibonding states at the Fermi level of the COHP curves of O–ScH3. We found that the results of PBE+U are consistent with those of PBE, SCAN, and HSE06 in the case of U < Uc. However, when U > Uc, the results of PBE+U are opposite to those of PBE, SCAN, and HSE06.