Revisiting the definition of ferroelectric negative capacitance based on Gibbs free energy

The applicability of the Gibbs free energy landscape to the definition and understanding of negative capacitance in a ferroelectric capacitor is investigated. We find that the Gibbs free energy cannot define the transient negative capacitance. In order to define the negative capacitance, we suggest returning to the original definition of capacitance, which is the second-order derivative of electrostatic force work with respect to polarization.