Quantum chemistry can describe motions, including changes in bonding

Quantum chemistry (QC) calculates molecular properties based on numerical approximations to the actual physics that determines those properties. In contrast to molecular mechanics, it has no built-in concept of a “molecular bond.” Instead, the behavior we call bonding arises from modeling of the behavior of electrons and nuclei, interacting according to the laws of quantum mechanics. As a consequence, QC can describe molecular transformations involving the making and breaking of bonds (though some methods provide better estimates of the energies of stable structures than of transition states between them).