DFT-D4

From VASP Wiki

DFT-D4[1][2][3] is an external package that can be linked to VASP. DFT-D4 adds to the DFT energy expression a term that accounts for the van der Waals (vdW) interactions, which are in principle not included in semilocal and hybrid exchange-correlation functionals. This is an approximation of the atom-pairwise type that depends only on 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. For more information regarding these parameters, please refer to the DFT-D4 paper[1] and websites.[2][3]

Usage

For some of the common exchange-correlation functionals (e.g., PBE, SCAN, or HSE06) it is sufficient to set IVDW=13 in the INCAR file. Internally, VASP passes automatically the name of the functional to DFT-D4. However, for other functionals the DFTD4_XC tag has to be used to specify the functional to DFT-D4 (the names are listed in the file param.f90 of the DFT-D4 source code). Subsequently, DFT-D4 maps the functional name to optimized settings for the adjustable parameters of the vdW interaction. 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.

Important:
  • The API of DFT-D4 has been modified starting with version 4.0.0. The adaptation has been made in VASP.6.6.0. Versions of DFT-D4 with the old API (v3.7.0 and older) can still be compiled with VASP.6.6.0 as explained here.
  • 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:

  • DFTD4_MODEL : dispersion model (available from VASP.6.6.0 onwards).
  • DFTD4_XC : functional name to determine the set of vdW parameters (available from VASP.6.6.0 onwards).
  • VDW_S6 : scaling of the dipole-dipole dispersion.
  • VDW_S8 : scaling of the dipole-quadrupole dispersion.
  • VDW_A1 : scaling of the critical radii in the Becke-Johnson rational damping.
  • VDW_A2 : offset of the critical radii in the Becke-Johnson rational damping.
  • VDW_S9 : scaling of the three-body dispersion energy (available from VASP.6.6.0 onwards).
  • VDW_RADIUS : two-body interaction cutoff (available from VASP.6.6.0 onwards).
  • VDW_CNRADIUS : coordination number cutoff (available from VASP.6.6.0 onwards).

References

  1. ↑ a b E. Caldeweyher, S. Ehlert, A. Hansen, H. Neugebauer, S. Spicher, C. Bannwarth, and S. Grimme, J. Chem. Phys. 150, 154122 (2019).
  2. ↑ a b https://dftd4.readthedocs.io
  3. ↑ a b https://github.com/dftd4

Related tags and articles

IVDW, DFTD4_MODEL, DFTD4_XC, VDW_S6, VDW_S8, VDW_A1, VDW_A2, VDW_S9, VDW_RADIUS, VDW_CNRADIUS, DFT-D3, simple-DFT-D3

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