Hartree

The hartree (symbol: E_h or Ha), also known as the Hartree energy, is the atomic unit of energy, named after the British physicist Douglas Hartree. It is defined as 2R_∞hc, where R_∞ is the Rydberg constant, h is the Planck constant and c is the speed of light. The 2010 CODATA recommended value is E_h = 4.359 744 34(19)×10−18 J= 27.211 385 05(60) eV. The 2006 CODATA recommended value was E_h = 4.359 743 94 (22)×10−18 J = 27.211 383 86(68) eV.