Hartree energy

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:

CODATA Bull. 1986, 63, 1