First-Principles Chemical Bonding Study of Manganese Carbodiimide, MnNCN, As Compared to Manganese Oxide, MnO.

We have performed an in-depth study of the chemical bonding in manganese oxide (MnO) and carbodiimide (MnNCN) from correlated spin-polarized density functional calculations. The chemical-bonding data were produced using the LOBSTER package, which has recently been enabled to process PAW-based output from Quantum ESPRESSO. Our results show that the ground states of MnO and MnNCN are similar, namely, antiferromagnetic structures whose axes are the MnO cubic [111] and the MnNCN hexagonal [001] axes, in agreement with experimental results. The results also evidence MnNCN being more covalent than MnO, in harmony with chemical intuition and spectroscopic data. In addition, the crystal orbital Hamilton population (COHP) analysis evidences that adopting the ground-state magnetic structures by MnO and MnNCN makes the cation-anion bonds optimized and annihilates obvious instability issues, that is, the existence of antibonding states in the vicinity of the Fermi level. We also detail the interactions involved in the systems using the recently introduced density-of-energy analysis and by partitioning the total and band-structure energies. While it is trivial that the total energy points toward the true magnetic ground state taken, the COHP integral of the metal-nonmetal bond is also capable of correctly delivering that particular information.