In-phase (constructive) overlap is the combination of atomic orbitals of the same sign, which increases the electron density in the region between the nuclei. This build-up of electron density holds the nuclei together, producing a bonding molecular orbital of lower energy. It contrasts with out-of-phase overlap, which produces an antibonding orbital.

同相(相长)重叠是符号相同的原子轨道组合,它使两核之间区域的电子密度增大。电子密度的这种积累把原子核结合在一起,形成能量较低的成键分子轨道。它与产生反键轨道的反相重叠相对。