Geometries, Electronic g-tensor Elements, Hyperfine Coupling Constants, and Vertical Excitation Energies for Small Gallium Arsenide Doublet Radicals, GaxAsy (x + y = 3, 5)

Abstract

Geometries of the gallium arsenide doublet radicals GaAs 2 , Ga 2 As, Ga 2 As 3 , Ga 3 As 2 , GaAs 4 , and Ga 4 As were optimized by the B3LYP/6-311+G(2df) method and compared with literature values. For the global minimum, as well as for isomers lying up to 0.2 eV higher, hyperfine coupling constants (HFCC) and electron-spin g-tensors were calculated. For HFCCs the B3LYP/6-311+G(2df) method was used, whereas for g-tensors second-order perturbation calculations with multireference configuration interaction wave functions and a valence triple-< basis set with polarization functions (TZVP) were performed. Generally, due to the low s-spin and high p-spin densities, A i s o values are small, and A d i p 's large. The g-shifts (Δg = g - g e ) are on the order of 100 000 ppm, caused by large spin-orbit couplings and low excitation energies. For the experimentally known Ga 2 As 3 , values calculated for the D 3 h structure are (A's in MHz, Δg's in ppm) A i s o ( 6 9 Ga) = 1325 (1524); A i s o ( 7 5 As) = -23 (65); A d i p ( 6 9 Ga) = 65 (87); A d i p ( 7 5 As) = 36 (0); Δg⊥ = -73 410 (-82 300); and Δg∥ = 6460 (0), with magnetic parameters derived from the experimental values in parentheses. Mulliken spin densities are shown to be a good measure of A d i p values. Vertical excitation energies, as obtained from the g-tensor calculations, are also tabulated.