Sadhukhan and Tkatchenko Reply:

investigated the interaction between a pair of 3D Drude oscillators (charge-separated, overall-neutral quantum harmonic oscillators), coupled by a Coulomb potential in reduced spatial dimensions, utilizing a novel perturbation expansion based on Ref. [2] and correlated dipolar oscillator states. The coupled oscillator Hamiltonian models the instantaneous, quantum-mechanical electronic fluctuations (not the permanent deformations of the electron density), therefore being a model for electron correlation via the adiabatic connection fluctuation-dissipation theorem [3]. We have shown that as a result the repulsive interaction between van der Waals (vdW) dimers arises from dynamic electron correlation effects in confined environments and can only be realized when going beyond the widely used dipole coupling between the oscillators. Our results do not require any permanent multipole moments. In the preceding Comment [4], Podeszwa and Jansen (PJ) criticize our interpretation of the repulsive interaction as “rather the interaction between the static quadrupole moments of 1D, 2D, and anisotropic 3D QHOs”, claiming our result involves only one oscillator’s parameters and postulated that the expression will contain the product of two independent oscillator’s parameters. Here, we show that their classical interpretation disagrees with our full quantum-mechanical treatment of two dissimilar Coulombcoupled oscillators, proving that the repulsive interaction arises from electronic correlations. We generalize our expression [1] for two 1D oscillators with different charges (qA=B), masses (mA=B), and frequencies (ωA=B). Diagonalization of the dipole-coupled potential matrix in coordinates ζA=B 1⁄4 ffiffiffiffiffiffiffiffiffiffi mA=B p x1=2 (see Supplemental Material of Ref. [1]) yields the frequencies of two uncoupled oscillators as