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 (chi) 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 (Delta g(i)) interaction for both clusters suggest that Delta g(perpendicular to) > Delta g(parallel to) for GaAs2, while Delta g(perpendicular to) < Delta g(parallel to) for Ga2As. We also calculated the hyperfine interactions (A(hfi)) of the Ga-69 and As-75 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. (C) 1999 American Institute of Physics. [S0021-9606(99)30120-3].