Long-range correlation energies calculations for excited states of π electronic systems

A general formula of long-range electron correlation energy in excited states of pi electron systems is presented for the first time. Effect of excited states upon the long-range electron correlations, which are related to problems of exciton and polaron, is discussed. It is found that because charge density distributions are different for removal (addition) of an electron from (into) pi electron system, the correlation energies of electron-type polaron and hole-type polaron are not the same even when the system tends to infinity. (C) 2010 Elsevier B.V. All rights reserved.