Van der Waals interactions in complex materials: Beyond the pairwise approximation

Despite the well-known fact that van der Waals (vdW) interactions are many-body in nature and the polarizability is a non-local function, popular vdW-DF [1] and DFT+vdW [2] methods are based on (semi)-local approximations for the polarizability and only model the pairwise part of vdW interactions. Here we show how to go beyond the pairwise (semi)-local approximation to vdW interactions by coupling the recently developed TS scheme [2] with the Fluctuating-Coupled-Dipole Model (CFDM) [3]. The TS scheme provides parameter-free input atomic polarizability distributions and the CFDM allows to model both polarizing and depolarizing local fields, and captures the many-body nature of vdW interactions. Results are presented for small and medium-size molecules, as well as solids. We find that the many-body screening plays a major role in modifying the polarizability of large systems. Our results for vdW coefficients in semiconductor clusters and solids are in excellent agreement with TDDFT calculations. [1] M. Dion \textit{et al.}, Phys. Rev. Lett., \textbf{92}, 246401 (2004); [2] A. Tkatchenko and M. Scheffler, Phys. Rev. Lett., \textbf{102}, 073005 (2009); [3] M. W. Cole \textit{et al.}, Mol. Simul. \textbf{35}, 849 (2009).