Capacitance of metallic and semiconducting nanowires examined by first-principles calculations

The capacitance of Al and P-doped Si nanowires a few nanometers in diameter are examined by first-principles calculations. During charging, the metallic nanowire expels the charge to its surface, and its capacitance stays relatively constant. For the semiconducting nanowire, depletion of conduction electrons can lead to an increase in the work function, which results in a drop in the capacitance when charged beyond a threshold. This study is made possible by developing a formalism for total energy calculations of charged periodic systems with a specific electrostatic boundary condition.