Theoretical insight into the Jahn-Teller system NaCl : Rh2+

The RhC64- Jahn-Teller centre in NaCl has been explored through Density Fun ctional calculations on clusters involving up to 39 atoms for different val ues of the Q(theta) (approximate to 3z(2) - r(2)) coordinate, where Q(theta ) = (root 12/3)(R-ax - R-eq), and R-ax and R-eq mean the axial and equatori al Rh2+ -Cl- distances. The equilibrium situation is found for Q(theta) = 3 0.3 pm (R-ax = 270.7; R-eq = 244.5 pm) while another minimum is found at Q( theta) = - 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 anhar monicity of the E-g mode. As a salient feature both the axial (A,(ax)) and equatorial (A(s)(eq)) isotropic superhyperfine constants are found to decre ase when Q(theta) increases, A(s)(ax)/A(s)(eq) being around 5 at equilibriu m. This surprising result which is pointed out to be related to the 4d-5s h ybridisation concurs with experimental findings. The crystal-field and char ge transfer transitions calculated at the equilibrium geometry reasonably a ccount for the experimental optical transitions of NaCl:Rh2+. (C) 2001 Else vier Science Ltd. All rights reserved.