Using MPA, the total charge is partitioned into four favorable orbitals: 3s, 3p x , 3p y , and 3p z . For a phosphorene layer with N atoms, we have N s orbitals and 3N p orbitals. When zero strain is applied and the system is relaxed, each atom has a charge of 5.0, or the number of valence electrons that may freely distribute throughout the system. Given that no charge leaves the system, the total charge of the system (χ) can be expressed with the following equation,