Molecular solids may consist of single atoms, diatomic, and/or polyatomic molecules. Ions can be metals, non-metals or polyatomic ions. For example, calcium carbonate consists of the monatomic ion Ca and the polyatomic ion CO. See polyatomic ion for a list of possible ions. The ammonium cation is a positively charged polyatomic ion with the chemical formula . The following tables give additional examples of commonly encountered polyatomic ions. It is a polyatomic anion with the chemical formula . Lewis structures for polyatomic ions may be drawn by the same method. There are two "rules" that can be used for learning the nomenclature of polyatomic anions. Other polyatomic bismuth cations are also known, such as Bi, found in . It atomizes the sample and creates atomic and small polyatomic ions, which are then detected. In polyatomic molecules, different vibrational and rotational energy levels are also involved. But in polyatomic molecules the number of independent mutual distances of nuclei are more. The ligand may be atomic or polyatomic. The first polyatomic calculations using Gaussian orbitals were performed in the late 1950s.