Performance of Tkatchenko-Scheffler Dispersion Method with Updated van der Waals Radii: Importance for Alkali-Containing Systems

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The Tkatchenko-Scheffler (TS) pairwise method to calculate dispersion interactions is a widely used approach to incorporate missing long-range van der Waals contributions in semilocal and hybrid density functional calculations. Despite numerous refinements of the approach to include many-body terms, the original formulation still remains highly relevant as an efficient and robust method, especially for organic and/or insulating materials. In 2018, Fedorov et al. reported updated van der Waals radii to the seminal work published in 2009. The present work examines the accuracy of the TS method with updated van der Waals radii (abbreviated as TS₂018), coupled with the semilocal Perdew-Burke-Ernzerhof density functional, for structural predictions of semiconducting and insulating materials in comparison to the non-local many-body dispersion method and the original TS method (TS₂009). Special attention is paid to materials containing alkali elements, for which the TS₂009 method exhibits a large overbinding, associated with potentially large errors in predicted atomic structures. We also consider a more narrow reformulation (TSₐlkali) where only the the alkali atoms are corrected, so the method remains otherwise compatible with TS₂009. The binding energy curves of five alkali dimers are used to assess the TS₂009 and the TS₂018 methods in comparison to the random phase approximation. Using 45 inorganic solid compounds with available experimental reference data, as well as three widely studied, Cs-containing halide perovskites, CsPbX₃ (X = Cl, Br, I), we then examine the performance of the TS₂018 and TSₐlkali approaches compared to TS₂009 and the beyond-pairwise, nonlocal many-body dispersion method; the latter found to give good results as well.