Atomiyksiköitä

Atomiyksiköt, also called atomic units or Hartree units, are a natural system of units used primarily in atomic, molecular, and optical physics, as well as quantum chemistry. The system is based on setting the reduced Planck constant ħ, the elementary electric charge e, the electron mass me, and the Coulomb force constant (4πϵ0)−1 to unity. These choices simplify the Schrödinger equation and related expressions by eliminating many physical constants. In atomic units, the energy unit is the Hartree (equivalent to 2 R∞, twice the Rydberg constant energy), the length unit is the Bohr radius, the time unit equals ħ/Eh, and the velocity unit equals the fine-structure constant αc.

The concept was introduced by Douglas Hartree in the 1920s to streamline calculations of atomic structure. Since then, it has become the standard unit system for theoretical studies of electrons in atoms and molecules. Calculations performed in atomic units are dimensionless until a conversion back to SI units is required for comparison with experimental data. For example, one atomic unit of length is approximately 0.529 Å, and one Hartree of energy is about 27.211 eV.

Use of atomiyksiköt allows straightforward comparison of theoretical predictions with empirical measurements, enhances numerical stability in computational algorithms, and facilitates the exploration of scaling laws across different atomic systems. Despite its ubiquity in theory, practitioners often translate results into SI units for experimental interpretation, using conversion tables and software libraries that handle the necessary factors automatically.