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I would like to know when we need to apply Van der Waals (vdW) correction in our system. If I am dealing with 2d systems (monolayer or bilayer), then should I need to add IVDW (vdW (dispersion) correction) tag in the VASP input file. What is the role of vdW correction. Also, I would like to know when we are applying SOC in the calculations, can we escape vdW correction at that time.

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    $\begingroup$ I gave my +1 long ago but have you figured this out now? Please update us! Are you still urgently or actively in need of an answer? $\endgroup$ Dec 19, 2023 at 20:23

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Van der Waals (vdW) correction is important in systems where non-local interactions between atoms or molecules play a significant role. It is particularly relevant for materials with layered structures, such as 2D systems (monolayers or bilayers), as these systems often exhibit weak interlayer interactions.

The vdW correction accounts for dispersion forces, which are long-range interactions arising from the fluctuating dipoles of atoms or molecules. These forces are not adequately captured by standard density functional theory (DFT) calculations. You might think that you will not include these forces in a monolayered system, however, weak interlayer interactions can still exist in monolayered systems due to the presence of vdW forces, specifically dispersion forces, that can arise from the fluctuations in electron density and induce temporary dipoles in adjacent atoms or molecules. These temporary dipoles can induce dipole-dipole interactions, resulting in weak attractive forces.

Regarding the inclusion of vdW correction when applying spin-orbit coupling (SOC). The vdW correction and SOC address different physical phenomena. The vdW correction accounts for long-range dispersion interactions, while SOC describes the interaction between the electron's spin and its motion. In most cases, both effects can coexist, and including both in your calculations provides a more comprehensive description of the system.

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