Theoretical study of the low lying states of Ga(2)X (X = P, As)

Since the low lying electronic states of Ga(2)X (X = P, As) are nearly degenerate, an accurate determination of the electronic structure of these states was incomplete in the previous works. In this study, the geometry optimization and vibrational frequency calculation have been performed at the various levels of theory, using the effective core pseudopotentials of the Ga and As atoms and the associated cc-pVTZ basis sets. The ground state of Ga(2)P is found to be the (2)A' state correlating with the (2)B(2) state in C(2v) structure, which lies 0.031 eV above the global minimum at the RCCSD(T) level. The equilibrium of the (2)A(1) state is optimized above that of the (2)B(2) state, and the (2)B(1) state, predicted previously as the ground state, has a stable minimum above the optimized geometries of the former states. Concerning the low lying states of Ga(2)As, our results confirm in general the previous studies. Because all the states of both compounds can be considered monoconfigurational around their equilibrium, the RCCSD(T) method is well adapted to acurrately describe both systems. In turn, we have applied our obtained information to analyze the Ga(2)P(-) and Ga(2)As(-) anion photoelectron spectra, to which it remains difficult to appropriately assign the low lying states of Ga(2)P and Ga(2)As. As a consequence, our analysis supports the previous assignment for Ga(2)P, but contrasts partially to that for Ga(2)As.