OPTIMAL COUPLED-CLUSTER APPROXIMATION FOR THE LINEAR E-E JAHN-TELLER EFFECT

By introducing a slight modification to the successive coupled-cluster approximation, we have developed an optimal coupled-cluster approxima tion, which can take care of both the accuracies of the ground-state e nergy and wavefunction estimates, for the ground state of the linear E -e Jahn-Teller effect. Over the whole range of the coupling parameter, our results up to the third level of approximation show good agreemen t with the exact numerical diagonalization results and are better than those from earlier analytical treatments. The mathematical treatment in this work is simple and could be easily extended to the studies of other fermion-boson interacting systems.