Hartree

1 hartree = 4.359 743 94(22) × 10−18 J 27.211 383 86(68) eV

Energy equivalents 1 hartree ≜ Mass 4.850 869 34(24) × 10−35 kg 2.921 262 2986(42) × 10−8 u Frequency/wavenumber 6.579 683 920 722(44) × 109 MHz 219 474.631 3705(15) cm−1 Temperature 315 774.65(55) K

The hartree (symbol: E_h), also known as the Hartree energy, is the atomic unit of energy, named after the British physicist Douglas Hartree. It is defined as the electric potential energy of the hydrogen atom in its ground state, and is equal to 2R_∞hc₀, where R_∞ is the Rydberg constant, h is the Planck constant and c₀ is the speed of light. The 2006 CODATA recommended value is E_h = 4.359 743 94(22) × 10⁻¹⁸ J = 27.211 383 86(68) eV.

The hartree energy is approximately twice the ionization energy of hydrogen: the relationship is not exact because the nucleus of the hydrogen atom does not have infinite mass. However, the relationship E_h = 2R_∞hc₀ is exact, as the effects of non-infinite nuclear mass are already considered in the Rydberg constant (hence the subscript infinity).

The hartree is usually used as a unit of energy in calculational chemistry: for experimental measurements at the atomic scale, the electronvolt (eV) or the reciprocal centimetre (cm⁻¹) are much more widely used.