Revisiting the Strongly Correlated Si-Terminated 3C-SiC(001)‑p(2 × 1) Reconstructed Surface with Single- and Multiconfigurational Methods

Restricted and unrestricted single- and multiconfigurational calculations have been carried out to understand the nature of the spatial and electronic structure of the Si-terminated (001) surface of cubic silicon carbide (3C-SiC) and its p(2 × 1) reconstruction with unbuckled Si dimers. The restricted single-configurational calculations on periodic slab models show weak reconstruction and thus long dimer bonds caused by the enforced double occupation of the bonding interdimer (ID) surface state band. The unrestricted calculations, on the other hand, allow stronger reconstruction due to spin symmetry breaking of this surface state, resulting in a fully radicalic but spin-contaminated electronic structure. High-level multiconfigurational calculations on H-saturated cluster models with multiple Si dimers reveal the strong/static correlation of the bonding and antibonding ID surface states as well as the interaction of neighboring dimers to play a crucial role for the correct description of the spatial and electronic structure of the surface, which appears to be in between the restricted and unrestricted single-configurational solutions. The multiconfigurational character of the ideal p(1 × 1) surface could also be shown, implying that both surfaces cannot be correctly described by single-configurational methods. Excited-state calculations of the p(2 × 1) and p(1 × 1) cluster models suggest the respective surfaces to be semiconducting.