Atomic unit

Atomic Unit (au) is a system of units that is primarily used in atomic physics, especially in the description of the properties of electrons. The atomic unit of length, for example, is the Bohr radius (approximately 0.529 Å).

Definition

The atomic unit system is based on the fundamental properties of the electron. The unit of mass is the electron mass (m_e), the unit of charge is the elementary charge (e), the unit of action (or angular momentum) is the reduced Planck constant (ħ), and the unit of energy is the Hartree energy (E_h).

Units

The atomic unit system includes units for length, mass, energy, time, and other physical quantities. For example, the atomic unit of length is the Bohr radius (a₀), which is the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state. The atomic unit of energy is the Hartree energy (E_h), which is the energy of the electron in the ground state of the hydrogen atom.

Use

The atomic unit system is widely used in atomic physics, especially in the description of the properties of electrons. It simplifies many equations and makes calculations easier. For example, in atomic units, the Schrödinger equation for the hydrogen atom takes a particularly simple form.

See also

• Bohr radius
• Hartree energy
• Electron
• Atomic physics