Atomic units

The atomic units (English: atomic units, au) form a natural unit system, which is mainly used in atomic and molecular physics and theoretical chemistry. The atomic units are based on the properties of the electron in the hydrogen atom.

The atomic units are:

• Length: the Bohr radius
• Mass: the atomic mass unit and the electron mass
• Charge: the elementary charge
• Energy: the Hartree energy

Also in use:

• Angular momentum is Planck's constant

• Time: the atomic time unit

The use of atomic units simplifies the Schrödinger equation. For example, the Hamiltonian results for an electron in a hydrogen atom to:

• In SI units:

• In atomic units:

In atomic units. The vacuum light velocity has a value, wherein the fine structure constant.

Values ​​in atomic units are formally dimensionless, quantities that are not dimensionless in SI units, but typically are the formal " unit characters " au marked (the points are part of the unit mark ). For example, a mass of 2 a.u. twice the electron mass, while an electric field strength of the field strength that prevails in a distance of one Bohr radius of an elementary charge.

Atomic units of magnetic quantities

Not clearly defined are basic units for sizes of the magnetic field as the magnetic flux density. Either for an electromagnetic wave in a vacuum as in SI units or in Gaussian units. This refers to the electric field strength and the vacuum speed of light. These different definitions have implications for all sizes, which are derived from the magnetic flux density. So is approximately the Bohr magneton only in SI -based atomic units. Various constant pre-factors arise when calculating the intensity of an electromagnetic wave from the electric field strength.