DFT-D4

DFT-D4 is an external package maintained by the Grimme group that can be linked to VASP. Read the documentation for more information about this package. DFT-D4 adds van-der-Waals (vdW) interactions to DFT because they are not included in most exchange-correlation functionals. It approximates the vdW interactions considering only the structure of the system which allows for a fast computation. Since every functional has different interactions between atoms, DFT-D4 tailors its adjustable parameters to the functional.

Usage

In most cases, it is sufficient to set IVDW=13 in the INCAR file if VASP was compiled and linked to DFT-D4. Internally, VASP passes the name of the used exchange-correlation functional to DFT-D4. Based on this, DFT-D4 internally maps the name of functionals to optimized settings for the adjustable parameters. VASP uses these parameters to compute the DFT-D4 energies, forces, and stresses in every ionic step and adds them to the corresponding DFT terms. As a result, you can relax structures or run MD simulations with an approximate treatment of vdW interactions.

Warning: Below, we explain how to tweak the parameters of DFT-D4. Typically, you should not modify them unless you have a very good reason, e.g., because the interface is not implemented for the exchange-correlation functional you use.

VASP allows setting the following tags in the INCAR file to change the strength of the vdW interaction.

• VDW_S6, VDW_S8 determine the strength of the dipole-dipole and dipole-quadrupole interaction.
• VDW_A1, VDW_A2 are scaling constants in the Becke-Johnson damping.

For more information regarding these parameters, please refer to the DFT-D4 paper.

Related tags and articles

IVDW, VDW_S6, VDW_S8, VDW_A1, VDW_A2, DFT-D3, Linking to DFT-D4