Calculated paramagnetic properties of the acute GaAs₂ and obtuse Ga₂As clusters

Dirac molecular orbital calculations are reported for the bent (C_2v) gallium arsenide GaAs₂ and Ga₂As clusters. The calculated clusters electronegativity (χ) and the calculated highest-occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap suggest that GaAs₂ should be softer and more reactive than Ga₂As. In GaAs₂, the unpaired electron spin spend 33.8% of its time on the apical Ga atom and 33.1% of its time on each basal As atom. In Ga₂As, the unpaired electron spin spend 69.4% of its time on the apical As atom and 15.3% of its time on each basal Ga atom. The calculations of the Zeeman (Δg_i) interaction for both clusters suggest that Δg_⊥>Δg_∥ for GaAs₂, while Δg_⊥>Δg_∥ for Ga₂As. We also calculated the hyperfine interactions (A_hfi) of the ⁶⁹Ga and ⁷⁵As nuclei for both clusters, and we have made an approximate decomposition of the total relativistic hyperfine tensors into Fermi, spin-dipolar, and orbital contributions, allowing us to identify some interesting features of relativistic effects on hyperfine interactions. The orbital contributions of each nuclei are substantial, thus providing an important contribution to the overall hyperfine coupling constants.