Hartree Units

(also atomic units), a natural system of units in which the following fundamental physical constants are set equal to unity: the charge e and mass m_e of the electron (e = 1.6021892 × 10^–19 coulombs and m_e = 0.9109534 × 10^–30 kg), the Bohr radius a₀ = 0.52917706 × 10^–10 m, and Planck’s constant ħ = h/2π = 1.0545887 ×, 10^–34 joules-sec. In other words, a₀ is taken as the unit of length, m_e is taken as the unit of mass, and the unit of time is approximately equal to 2.419 × 10^–17 sec. The use of Hartree units makes it possible to simplify the equations of quantum mechanics. The units were proposed by the English physicist D. Hartree in 1928.