Metal–Metal Bonding Stabilized Ground State Structure of Early Transition Metal Monoxide TM–MO (TM = Ti, Hf, V, Ta)

Abstract

It is commonly believed that early transition metal monoxides (TM–MOs) crystallize in simple rock-salt structures (symmetry FM3M) for their ground states. Here, by combining structure-searching algorithm and first-principles calculations, we identified structures that are more stable than the ideal rock-salt for the early TM–MOs (TM = Ti, Hf, V, Ta). For TiO, HfO, and TaO, ground state symmetries of P62M), I41/AMD and P1 are obtained, respectively, which have distinct structural and electronic properties compared to the rock-salt structure. However, it is rather complex for the case of VO due to the existence of magnetic ordering. For VO, magnetic ordering behavior exists in the rock-salt and the predicted P1 structure according to the hybrid functional calculations. After relaxation, the magnetic ordering causes local distortion in the original rock-salt structure, leading to a R3M symmetry, which becomes more stable than the predicted P1 structure. Furthermore, the ionic TM–O bonding of the predic...