atomic unit

The unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic and molecular masses. It is defined to be one twelfth of the mass of an unbound atom of the carbon-12 nuclide, at rest and in its ground state.1 u = 1/NA gram = 1/ (1000 NA) kg   (where NA is Avogadro's number)1 u ≈ 1.660538782(83) × 10−27 kg ≈ 931.494028(23) MeV/c2See 1 E-27 kg for a list of objects which have a mass of about 1 u.
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Atomic units (au) form a system of units convenient for atomic physics, electromagnetism, and quantum electrodynamics, especially when the focus is on the properties of electrons. There are two different kinds of atomic units, which one might name Hartree atomic units and Rydberg atomic units, which differ in the choice of the unit of mass and charge. This article deals with Hartree atomic units. In au, the numerical values of the following six physical constants are all unity by definition:Two properties of the electron, its mass and charge;Two properties of the hydrogen atom, its Bohr radius and the absolute value of its electric potential energy in the ground state;Two constants, Dirac's and that for Coulomb's Law.
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Compare with Bohr radius and hartree .A system of non-SI units used in quantum chemistry to simplify calculations and mathematical expressions. The definitions of atomic units include physical constants (like the speed of light, the rest mass of the electron, and other quantities that never change), so that all constants drop out of expressions when atomic units are used.

B: (Fisika) satuan atom
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