hartree

A Hartree (symbol Eh) is the atomic unit of energy and is named after physicist Douglas Hartree.The Hartree energy is equal to the absolute value of the electric potential energy of the hydrogen atom in its ground state. This is also almost exactly twice the absolute value of the binding energy (or ionization energy) of the electron in the ground state hydrogen atom, |W1| (it is not exactly equal to twice the ionization energy, because of the finite mass of the proton; see reduced mass).
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(Eh) Compare with atomic unit .The atomic unit of energy, equal to 4.359 743 81 × 10-18 J ± 0.000 000 34 × 10-18 J [1998 CODATA values ].