Two-dimensional FeC compound with square and triangle lattice structure – Molecular dynamics and DFT study

The stability, electronic structure and magnetic behaviors of the two-dimensional (2D) FeC compounds with square and triangle lattice structure are studied by the density functional theory (DFT) calculations. We find that both forms of 2D FeC, one with a flat square lattice structure denoted as t-FeC and another with a puckered triangle lattice structure denoted at tr-FeC, are stable after DFT optimization. However, calculations of the phonon dispersion and binding energy show that the puckered 2D FeC with a triangle lattice structure is the most stable form. We find that both forms of the 2D FeC compounds are metallic and ferromagnetic materials, however, the mean atomic magnetic moment of Fe in the puckered 2D tr-FeC is significantly smaller than that of the flat 2D t-FeC. We check various interatomic potentials for the Fe-C systems implemented in the LAMMPS package and find that only 2D t-FeC can be formed ‘naturally’ from the melt while it does not occur for the 2D tr-FeC. The crystallization temperature (T_X≈2600K) and mean interatomic distance for the Fe-C pair of the flat 2D t-FeC have reasonable values. Various structural defects and mechanical behaviors of the flat 2D t-FeC compound are found and discussed.