  In this study, we investigate the metal-insulator transition of charge
transfer type in high-temperature cuprates. We first show that we must
introduce a new band parameter in the three-band d-p model to reproduce the
Fermi surface of high temperature cuprates such as BSCCO, YBCO and Hg1201. We
present a new wave function of a Mott insulator based on the improved
Gutzwiller function, and show that there is a transition from a metal to a
charge-transfer insulator for such parameters by using the variational Monte
Carlo method. This transition occurs when the level difference
$\Delta_{dp}\equiv \epsilon_p-\epsilon_d$ between d and p orbitals reaches a
critical value $(\Delta_{dp})_c$. The energy gain $\Delta E$, measured from the
limit of large $\Delta_{dp}$, is proportional to $1/\Delta_{dp}$ for
$\Delta_{dp}>(\Delta_{dp})_c$: $\Delta E\propto -t_{dp}^2/\Delta_{dp}$. We
obtain $(\Delta_{dp})_c\simeq 2t_{dp}$ using the realistic band parameters.

Strongly Correlated Electrons