Explicit calculation of Coulomb correlation in bond orbitals

The Coulomb correlation is calculated explicitly in bond orbitals, such as the natural bond orbitals (NBOs). The dependence of the correlation from the weights of NBO structures is investigated in an analytical way. It is stressed that when the electrons of a molecular system are distributed in NBOs, they show significantly smaller correlations than when they were distributed in atomic orbital positions. The NBO-set which corresponds to the main bonding scheme of the molecule, exhibits the minimum Coulomb correlation.