band gap, carbides, MXene, quantum Monte Carlo, many-body methods, exciton, GW method

Sc2C(OH)2 is a prototypical non-magnetic member of MXenes, a promising transition-metal-based 2D materials family, with a direct band gap. We provide here benchmark of its fundamental gap ∆ obtained from many-body GW and fixed-node diffusion Monte Carlo (FNDMC) methods. Both approaches independently arrive at a similar value of ∆ ∼ 1.3 eV, suggesting validity of both methods. Such a band gap makes Sc2C(OH)2 a 2D semiconductor suitable for optoelectronic applications. Absorbance spectra and the first exciton binding energy (0.63 eV), based on the Bethe-Salpeter equation, are presented as well. The reported results may serve to delineate experimental uncertainties and enable selection of reasonable approximations, like DFT functionals, for use in modeling of related MXene/s.