2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/166647The long-range correlation energies and the off-diagonal interactions are studied and a general formula for correlation energy $E_c$ of the $π$ electron systems is given, which is beyond the nearest-neighbor electron-electron interactions and includes the off-diagonal interactions. It is found that the effects of the off-diagonal interactions $W$ and $X$ on the correlation energies are opposite, but the influence of $X$ on the correlation energies is much stronger than that of $W$ on the correlation energies, and the correlation energies decrease with increasing the screening effect.5 pages, 2 tables, New version, SubmittedOther Condensed Mattertext