On the principle of maximum overlap in valence bond theory

Revisitation of the Heitler-London theory for H2 shows that the exchange-overlap component of the bond energy has a strength which is maximum at the bond length. Making the usual assumptions typical of elementary Hückel theory including overlap it is similarly found that in the valence bond description of the chemical bond covalent bonding is strongest for atomic orbitals maximizing the strength of the complete exchange-overlap component of the bond energy.