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The hartree (symbol: Eh or Ha), also known as the Hartree energy, is the unit of energy in the Hartree atomic units system, named after the British physicist Douglas Hartree. Its CODATA recommended value is Eh = 4.3597447222071(85)×10−18 J[1] = 27.211386245988(53) eV.[2]

The hartree energy is approximately the electric potential energy of the hydrogen atom in its ground state and, by the virial theorem, approximately twice its ionization energy; the relationships are not exact because of the finite mass of the nucleus of the hydrogen atom and relativistic corrections.

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

Other relationships[edit]

= 2 Ry = 2 Rhc
27.211386245988(53) eV
4.3597447222071(85)×10−18 J
4.3597447222071(85)×10−11 erg
2625.4996394799(50) kJ/mol
627.5094740631(12) kcal/mol
219474.63136320(43) cm−1
6579.683920502(13) THz
315775.02480407(61) K


Note that since the Bohr radius is defined as , one may write the Hartree energy as in Gaussian units where .

Effective hartree units are used in semiconductor physics where is replaced by and is the static dielectric constant. Also, the electron mass is replaced by the effective band mass . The effective hartree in semiconductors becomes small enough to be measured in millielectronvolts (meV).[3]


  1. ^ "2018 CODATA Value: Hartree energy". The NIST Reference on Constants, Units, and Uncertainty. NIST. 20 May 2019. Retrieved 2019-05-20.
  2. ^ "2018 CODATA Value: Hartree energy in eV". The NIST Reference on Constants, Units, and Uncertainty. NIST. 20 May 2019. Retrieved 2019-09-01.
  3. ^ Tsuneya Ando, Alan B. Fowler, and Frank Stern Rev. Mod. Phys. 54, 437 (1982)