atomiyksiköinä

Atomiyksiköinä is a Finnish term that translates to "in atomic units" or "atomic units" when referring to a system of measurements. This system is primarily used in physics and chemistry to simplify calculations involving fundamental constants.

In the atomic unit system, several fundamental physical constants are set to unity (equal to 1). The most commonly used system is the Hartree atomic unit system, also known as the [^(1)] a.u. system. In this system, the electron rest mass, the elementary charge, and the reduced Planck constant are all defined as 1.

The consequences of these definitions are that the Bohr radius, the Hartree energy (which is twice the ionization energy of hydrogen), and the fine-structure constant also take on specific, often simple, numerical values within the system. For example, the Bohr radius, a fundamental length scale in atomic physics, becomes exactly 1 a.u. Similarly, the Hartree energy, a unit of energy, is also 1 a.u.

The advantage of using atomic units is that many equations in quantum mechanics and atomic physics become simpler and more elegant. Equations that would otherwise be cluttered with fundamental constants like h-bar (ħ) and m_e (electron mass) can be expressed more concisely. This simplification is particularly useful when dealing with atomic and molecular systems where these constants play a crucial role.

While widely used in theoretical atomic, molecular, and condensed matter physics, atomic units are not typically used in everyday scientific communication or experimental settings where SI units are standard. They are a specialized tool for theoretical calculations and conceptual understanding.