RANGE OF THE T-J MODEL PARAMETERS FOR CUO2 PLANES - EXPERIMENTAL-DATA CONSTRAINTS

The t-J-model effective hopping integral is determined from the three-band Hubbard model for the charge carriers in CuO2 planes. For this purpose the values of the superexchange constant J and the charge-transfer gap Egap are calculated in the framework of the three-band model. The energies of the local states for added electron and hole are obtained from the systematic analytical reduction of the three-band model and their kinetic energy is found from the accurate variational approach using the t-J model. Fitting values of J and Egap to the experimental data allows us to narrow the uncertainty region of the threeband model parameters. As a result, the t/J ratio of the t-J model is fixed in the range 2.4 2.7 for holes and 2.5 3.0 for electrons. This approach explains the formation of the Frenkel exciton and correctly describes the main features of the charge-transfer spectrum. © 1994 The American Physical Society.