atomiyksikköinä

Atomiyksikköinä is a Finnish term that translates to "in atomic units" or "as atomic units". This refers to a system of natural units of measurement, primarily used in atomic and molecular physics, which are based on fundamental constants of nature. The key idea is to simplify equations by setting certain physical constants equal to one.

The most common system of atomic units, often called the Hartree system, defines the following constants as dimensionless and equal to 1: the elementary charge ($e$), the reduced Planck constant ($\hbar$), the electron mass ($m_e$), and the Coulomb constant ($k_e = 1/(4\pi\epsilon_0)$). This choice of fundamental constants leads to derived units for quantities like length, energy, and time. For instance, the atomic unit of length is the Bohr radius ($a_0$), and the atomic unit of energy is the Hartree ($E_h$).

Using atomic units significantly simplifies theoretical calculations in quantum mechanics. Many complex mathematical expressions become much more manageable, allowing physicists to focus on the core physics of the problem without being bogged down by numerical factors arising from the choice of arbitrary units. This system is particularly prevalent in computational chemistry and condensed matter physics where precise calculations of electronic structure and interactions are crucial. The dimensionless nature of quantities expressed in atomic units also aids in understanding scaling relationships and fundamental symmetries within physical systems.