Hydrogen atom Hydrogen atom A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force. Atomic hydrogen constitutes about 75% of the baryonic mass of the universe. In everyday life on Earth, isolated hydrogen atoms (called "atomic hydrogen") are extremely rare. Instead, hydrogen tends to combine with other atoms in compounds, or with itself to form ordinary (diatomic) hydrogen gas, H. "Atomic hydrogen" and "hydrogen atom" in ordinary English use have overlapping, yet distinct, meanings. For example, a
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