Atom the nucleus defines to what chemical element the atom belongs: for example, all copper atoms contain 29 protons. The number of neutrons defines the isotope of the element. The number of electrons influences the magnetic properties of an atom. Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules. The ability of atoms to associate and dissociate is responsible for most of the physical changes observed in nature and is the subject of the discipline of chemistry. The idea that matter is made up of discrete units is a very old
Embedded atom model a simulation, the potential energy of an atom, formula_1, is given by where formula_3 is the distance between atoms formula_1 and formula_5, formula_6 is a pair-wise potential function, formula_7 is the contribution to the electron charge density from atom formula_5 of type formula_9 at the location of atom formula_1, and formula_11 is an embedding function that represents the energy required to place atom formula_1 of type formula_13 into the electron cloud. Since the electron cloud density is a summation over many atoms, usually limited by a cutoff radius, the EAM potential is a multibody potential. For a single element system