Revisiting the manganese dimer on the base of first-principles theory

Manganese is one of the most intriguing elements showing multiple magnetic phases. In order to shed some light on the complex behavior, the manganese dimer has been the focus of extensive interest in theoretical research. Various quantum techniques have been utilized to comprehend the characteristics of the Mn dimer. Several approaches and functionals have been employed that suggest that the ferromagnetic (FM) state is its lowest energy configuration. Nevertheless, these findings are inconsistent with the experimental results showing that Mn2 has an antiferromagnetic (AFM) Σg+1 configuration at an interatomic Mn-Mn distance of dMn-Mn = 3.40 Å. This work presents a comparative assessment of outcomes obtained through several levels of the exchange-correlation functional: generalized gradient approximation (GGA), meta-GGA, GGA+U, and the hybrid Heyd-Scuseria-Ernzerhof (HSE06), the Perdew-Burke-Ernzerhof 0, and the Becke, 3-parameter, Lee-Yang-Parr. The results of our investigation are discussed based on previous theoretical and experimental reports. We found that the best description is obtained with the hybrid HSE06 functional. The Mn2 has a FM coupling at short distances and the characteristic AFM Σg+1 state at dMn-Mn = 3.27 Å. Furthermore, we obtained a magnetic moment (μ) per Mn atom of μ = 4.527 μB, a stretching frequency of ω = 80 cm-1, and a binding energy of Eb = -195 meV, which is in good agreement with the experimental results.