  We study the relation between quantum entanglement and electron correlation
in quantum chemistry calculations. We prove that the Hartree-Fock (HF) wave
function does not violate Bell's inequality, thus is not entangled while the
configuration interaction (CI) wave function is entangled since it violates
Bell's inequality. Entanglement is related to electron correlation and might be
used as an alternative measure of the electron correlation in quantum chemistry
calculations. As an example we show the calculations of entanglement for the
H$_2$ molecule and how it is related to electron correlation of the system,
which is the difference between the exact and the HF energies.
