Importance of bond exchange in MnC structural stability and half-metallic ferromagnetism: A comprehensive benchmark density functional study

Recently, the first successful synthesis of bulk manganese monocarbide (MnC) has been reported. The compound crystallizes in the zinc-blende structure and has been proposed as a potential superhard material. In this work, we present a comprehensive first-principles study of the structural, electronic, and magnetic properties of MnC using several exchange-correlation approximations. We demonstrate that the SCAN meta-GGA (generalized gradient approximation) and the Perdew-Burke-Ernzerhof zero revised (PBE0r) hybrid functional outperform GGA–Perdew-Burke-Ernzerhof for solids (PBEsol), Heyd-Scuseria-Ernzerhof 2006 (HSE06), and the mean-field density functional theory [( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>DFT</a:mi> <a:mo>)</a:mo> <a:mo>]</a:mo> <a:mo>+</a:mo> <a:mi>U</a:mi> <a:mo>+</a:mo> <a:mi>V</a:mi> </a:mrow> </a:math> schemes in correctly predicting the experimentally observed zinc-blende structure as the ground state. Our analysis reveals that the bond-exchange interaction plays a decisive role in stabilizing this phase. At theoretical equilibrium, hybrid functionals (PBE0r and HSE06) predict a metallic ground state, whereas semilocal functionals (PBEsol and SCAN) and <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mi>DFT</b:mi> <b:mo>+</b:mo> <b:mi>U</b:mi> <b:mo>+</b:mo> <b:mi>V</b:mi> </b:mrow> </b:math> yield two distinct types of half-metallic ferromagnetism with opposite volume dependence, opening a debate on the origin and nature of this behavior. If confirmed experimentally, such a property would make MnC an attractive candidate for spintronic applications.