DFT-D tab

The DFT-D tab allows you to prepare customized parameters for van der Waals dispersion corrections. This can involve the definition of DFT-D corrections for exchange functionals that are not usually supported, the definition of support for additional elements, or changing existing parameters.

Use custom DFT-D parameters: Specify whether to use custom DFT-D parameters. When selected, you can choose the van der Waals scheme to use from the list, options are:

TS (default)
Grimme
OBS
MBD*

The option selected automatically updates the Use method for DFT-D correction option on the Setup tab of the CASTEP Calculation dialog.

The schemes that rely on calculated electron densities, namely TS and MBD*, may not work well in calculations with small unit cells, where the diameter of van der Waals spheres is comparable to the lattice parameters. The MBD* scheme is particularly sensitive to such situations. In such cases, the CASTEP output file contains a warning explaining the problem. The MBD* scheme can also fail if the geometry is far from equilibrium, in which case it is useful to perform a preliminary geometry optimization with the TS scheme. The main area of application of the MBD* scheme is molecular crystals, so it may experience problems with highly ionic systems.

This table allows you to edit the dispersion correction parameters for each of the atomic species. The type and number of parameters depend on the DFT-D scheme selected. Refer to the original literature for the meaning and usage of each parameter.

The units for all parameters are in eV for energies and in Å for lengths. The available columns are:

Atom: Denotes the element to edit.

C6 (eV Å⁶): Available for TS, MBD*, and Grimme schemes.

R0 (Å): Available for TS, MBD*, and Grimme schemes.

alpha (Å³): Available for TS, MBD*, and OBS schemes.

I (eV): Available for the OBS scheme.

Rvdw (Å): Available for the OBS scheme.

The Atomic parameters table only lists the elements in the active document.

Each scheme includes a radius (R0 for TS and Grimme, Rvdw for OBS) that must be non-zero for each of the active elements.

Scheme parameters are dimensionless numbers that define the functional form of each scheme.

Refer to the original literature for the meaning and usage of each parameter.

Depending on the van der Waals scheme selected for the custom DFT-D parameters setting, the Scheme parameters that you can specify are:

TS: sR, d
Grimme: s6, d
OBS: lambda, n
MBD*: sR

The default values for these parameters depend on the exchange correlation functional selected on the Setup tab of the CASTEP Calculation dialog.

Both scheme parameters must be non-zero for the calculations to start and for Materials Studio to write to the input files.

Reset All: Restores the default settings for each element in the grid.

Access methods

Menu	Modules \| CASTEP \| Calculation \| Electronic \| More... \| DFT-D
Toolbar	\| Calculation \| Electronic \| More... \| DFT-D

DFT-D tab

Atomic parameters

Scheme parameters

See Also: