A molecular orbital formed by the linear combination of atomic orbitals. The LCAO approximation arises because with an electron that is very close to a nucleus, the potential energy of the electron is dominated by the interaction between the electron and the nucleus. Thus, very close to the nucleus of an atom, A, in a molecule, the wave function of the molecule is very similar to the wave function of the atom A. The LCAO approximation shows the increase in electron density associated with chemical bonding. The LCAO method takes account of the symmetry of the molecule using symmetry-adapted linear combinations (SALC).