Hartree energy

https://dx.doi.org/10.1351/goldbook.H02748
Atomic fundamental physical constant used as atomic unit of energy: E h = ℏ 2 m e a 0 2 = 4.359 7482 26 × 10 −18 J, where ℏ is the Planck constant divided by 2 π, m e the electron rest mass and a 0 the Bohr radius.
Source: