Hartree

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The hartree (symbol: Eh), 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 2Rhc0, where R is the Rydberg constant, h is the Planck constant and c0 is the speed of light. The 2006 CODATA recommended value is Eh = 4.359 743 94(22) × 10−18 J = 27.211 383 86(68) eV.[1]

The hartree energy is approximately twice the ionization energy of hydrogen: the relationship is no exact because the nucleus of the hydrogen atom does not have infinite mass. However, the relationship Eh = 2Rhc0 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.

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