Atomic, molecular, and optical physics electron is treated quantum mechanically. In low speed collisions the approximation fails. Classical Monte-Carlo methods for the dynamics of electrons can be described as semi-classical in that the initial conditions are calculated using a fully quantum treatment, but all further treatment is classical. Atomic, Molecular and Optical physics frequently considers atoms and molecules in isolation. Atomic models will consist of a single nucleus that may be surrounded by one or more bound electrons, whilst molecular models are typically concerned with molecular hydrogen and its molecular hydrogen ion. It is concerned with processes such as ionization, above threshold ionization and excitation
Comparison of chemistry and physics studies the properties of matter at a larger scale (for example, astrochemistry) and the reactions of matter at a larger scale (for example, technical chemistry), but typically, explanations and predictions are related back to the underlying atomic structure, giving more emphasis on the methods for the identification of molecules and their mechanisms of transformation than any other science. Although both physics and chemistry are concerned with matter and its interaction with energy, the two disciplines differ in approach. In physics, it is typical to abstract from the specific type of matter, and to focus on the common properties of many