Theoretical calculations have been performed on Si₂C using density functional theories (DFT) and conventionalab initio method employing 6-311G* basis set. Present calculations indicate that some of the DFT methods (B3LYP, B3P86, BHandH, BHandHLYP) employed in this study cannot predict the observed bent structure in the case of Si₂C cluster whereas, MP2, SVWN5 and B3PW91 calculations predict the bent structure, as observed by experiment.

Systematic investigation has been carried out to calculate critical points, charge density,ρ(r_c), and Laplacian of charge density, ∇²ρ(r_c), for weak complexes in the framework of MP2 and density functional theory (DFT). This study helps in assigning structures to van der Waals complexes such as Rg-HF, Rg-HCl, Rg-Li⁺ and Rg-Mg⁺, where Rg=He, Ne and Ar. The presence of (3, −1) critical points (bond critical points) in the complexes and the typical values ofρ(r) and ∇²ρ(r) at critical points indicate that closed-shell type of interaction is present in the molecules. The possible difference between the two types of bonding, rare gas-hydrogen bond interaction (Rg-H-X) and rare gas-halogen bond interaction (Rg-X-H), (where X=F and Cl) has also been analysed by computing the properties of charge density and Laplacian of charge density at the bond critical points.