Theoretical insight into the Jahn–Teller system NaCl:Rh 2+

Abstract

The RhCl 6 4− Jahn–Teller centre in NaCl has been explored through Density Functional calculations on clusters involving up to 39 atoms for different values of the Q θ (≈3 z 2− r 2) coordinate, where Q θ=( 12 /3)(R ax −R eq ), and R ax and R eq mean the axial and equatorial Rh 2+–Cl − distances. The equilibrium situation is found for Q θ=30.3 pm (R ax =270.7; R eq =244.5 pm) while another minimum is found at Q θ=−21.7 pm whose energy lies 213 cm −1 above. These facts and the different curvature at the two minima are all shown to arise from the anharmonicity of the E g mode. As a salient feature both the axial ( A s(ax)) and equatorial ( A s(eq)) isotropic superhyperfine constants are found to decrease when Q θ increases, A s(ax)/ A s(eq) being around 5 at equilibrium. This surprising result which is pointed out to be related to the 4d–5s hybridisation concurs with experimental findings. The crystal-field and charge transfer transitions calculated at the equilibrium geometry reasonably account for the experimental optical transitions of NaCl:Rh 2+.