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# Science Fair Project Encyclopedia

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# Hartree energy

The Hartree energy (symbol Eh) is a physical constant used as atomic unit of energy, named after physicist Douglas Hartree.

It has a value of twice the absolute value of binding energy of the electron in the ground state of the hydrogen atom |W1| or the ionization energy.

$E_h = {\hbar^2 \over {m_e a^2_0}}$
= 4.359 743 81(34) × 10-18 J = 27.214 4 eV = 2 Ry

where:

$\hbar$ is the Planck's constant,
me is the electron rest mass