Electrical analogy between a capacitor and the condensed linear response function

In this work, we explore a novel analogy between the classical capacitor from electrostatics and the linear response function within the framework of conceptual density functional theory (CDFT). Parallels are drawn between the electrostatic behavior of capacitors and the chemical reactivity described by the linear response function, a key descriptor in CDFT. This analogy is illustrated on molecular systems ranging from diatomics to four-atom molecules, and generalized to larger systems. We further show how this relationship extends to other chemical descriptors, offering new physical interpretations. The results demonstrate that this capacitor analogy provides fresh insights into chemical reactivity and enriches the conceptual framework of theoretical chemistry.

All calculations were performed using the ADF package. Molecules were optimized in the gas phase at the PBE0/TZP level, including scalar relativistic effects, with convergence verified by positive vibrational frequencies. Conceptual DFT descriptors, including the condensed linear response function, were obtained using the standard implementation in ADF. An in-house Python program was developed to extract and visualize condensed linear response data, perform diagonalizations, and generate graphical representations of eigenmodes.