long-凯发网

a general formula of the long-range correlation energy ec for the π electron systems is given, which includes diagonal interactions and off-diagonal interactions and we put forward to a correlation hamiltonian at the first time. it is found that the effects of the off-diagonal interactions w and x on the correlation energies are opposite. the effect of w is to increase the correlation energies, but the effect of x is being counteracted by the integral term j due to |x|～|j |. the long-range correlation energies decrease with increasing the screening effect. at normal screening, the influence of w on the correlation energies can be neglected.