The idea to get an accurate description of van der Waals complexes by density functional theory by including empirical corrections by Grimme [211] was implemented in ADF by J.M. Ducere from the group of Prof. L. Cavallo [215]. Please contact this group for more details on this functionality.
This is an expert option. As input one needs certain atomic parameters and (for a given basis set and functional optimized) parameters for a damping function. At the moment only for a few atoms atomic parameters can be found in the file $ADFRESOURCES/MMDispersion/disp-param. Only for the PBE functional with a DZP or TZP basis set parameters are optimized for the damping function. This optimization was done with respect to MP2 theoretical data. The parameters from Grimme's paper can also be used.
MMDispersion
{FILE_NAME filename}
{DAMPING damping}
{DAMP_PARAM damp_param {a b c}}
{COMBI combi}
{DISPALL}
{NODEFAULT}
{ATOMTYPE
attype c6 pol rad
SUBEND}
End
FILE_NAME filename
Optional. The filename (full path) from which are read the C6 parameters, polarizabilities and radii. The file is expected to have the following structure:
attype c6 pol rad
The attype must exactly match the atom-type name present in the ATOMS key-block (case-sensitive), for being recognized; c6, pol, and rad are in atomic units (hartree and bohr). A "---" sequence indicates the end of the read part. Even if the sqrt option is chosen for COMBI, a polarizability is needed. If the environment variable ADFRESOURCES is set, the default value for filename is $ADFRESOURCES/MMDispersion/disp-param.
DAMPING damping
Optional. Defines the kind of damping function to be used, damping can be one of:
sigm: sigmoid (default)
fermi: Fermi-like function (Grimme [211])
DAMP_PARAM damp_param {a b c}
Optional. Defines which parameters of the damping function should be used, damp_param can be one of:
tz: parameters optimized for PBE/TZP (default)
dz: parameters optimized for PBE/DZP
grimme: parameters from Grimme paper
cust a b c: parameters are a, b and c
COMBI combi
Optional. Defines the kind of combination rule to be used, combi can be one of:
s-k: Slater-Kirkwood combination rule (default)[214]
sqrt: square-root combination rule
DISPALL
Optional. If present, all atom-pairs are considered, else, only contributions from different fragments (different indexes, see below) are considered. DISPALL is NOT the default.
NODEFAULT
Optional. By default, if there is no match for a given atom-type, ADF looks in the parameter file specified in FILENAME for atomic default parameters (Grimme's ones). NODEFAULT switches off this check. Example: suppose the atom-type is H.text. By default if there is no match for H.text, but there is a match for H, parameters for H will be used. If NODEFAULT is set, and there is no match for H.text an error message is printed and ADF will stop.
ATOMTYPE
Optional. For input supplied c6, polarizability and radius paramaters of atom-types; attype must exactly match an atom-type name present in the ATOMS block for being recognized; c6, pol and rad are in a.u.
Atom-types and fragment-indexes are specified in the ATOMS keyblock:
ATOMS atom-type x y z FD=n ... END
FD is the index of the fragment. FD=0 switch off the calculation for the atom. If DISPALL is present in the input, non-zero values of FD only have an analytical role. If DISPALL is not present, the contributions are calculated between atoms of different non-zero values of FD. By default, FD=1 for all atoms.
