The DFT-D3 method of Grimme et al. [92,93] is supported to include a vdW
interaction with default parameters for the GGA-PBE functional. The following keywords
are relevant for the DFT-D3 method.
scf.dftD on # on|off, default=off
version.dftD 3 # 2|3, default=2
DFTD3.damp bj # zero|bj, default=bj
DFTD.Unit AU # Ang|AU
DFTD.rcut_dftD 100.0 # default=100 (DFTD.Unit)
DFTD.cncut_dftD 40 # default=40 (DFTD.Unit)
DFTD.IntDirection 1 1 1 # default=1 1 1 (1:on 0:off)
When you include the DFT-D2 or DFT-D3 calculation, turn on 'scf.dftD'.
For DFT-D2 use version.dftD=2 and for DFT-D3 version.dftD=3. The DFT-D3
implemented here supports both zero and Becke-Johnson (BJ) damping
functions . The cutoff radius for the interaction is given
by 'DFTD.rcut_dftD' and for the coordination number calculation 'DFTD.cncut_dftD'.
The units are given by 'DFTD.Unit' and the suggested defaults for
both cutoff values are in AU. Also, the interaction for image atoms
can be cut along the a-, b-, and c-axes by 'DFTD.IntDirection', where
1 means that the interaction is included, and 0 not. Also, the periodicity
for each atom can be controlled as in the case of the DFT-D2 method by
where the first column is a serial number which is the same as in
the 'Atoms.SpeciesAndCoordinates', and the second column is a flag
which means that 1 is periodic, and 0 is non-periodic for the corresponding
atom. By considering the periodicity or non-periodicity of each atom,
the interaction is automatically cut when they are non-periodic.
The main modifications are placed at only two routines: DFTD3vdW_init.c
and Calc_EdftD() of Total_Energy.c. In DFTD3vdW_init.c, you can
easily change the parameters for the vdW correction, and in Calc_EdftD3()
of Total_Energy.c you can confirm how they are calculated.
Parameters for other functionals may be set through the following keywords
DFTD.scale6 1 # default=0.75|1.0 (for DFT-D2|DFT-D3)
DFTD.scale8 0.7875 # default=0.722|0.7875 (for PBE with zero|bj damping)
DFTD.sr6 1.217 # default=1.217 (for PBE)
DFTD.a1 0.4289 # default=0.4289 (for PBE)
DFTD.a2 4.4407 # default=4.4407 (for PBE)
The '' and '' global scaling value of Eq. (3) in Grimme's
paper  is given by 'DFTD.scale6' and 'DFTD.scale8'.
The global scaling parameters are functional and damping-function dependent.
The parameter 'sr6' of Eq. (6) in  needs to be set when using
the zero damping function while the parameters 'a1' and 'a2' of Eq.
(6) in  need to be set when choosing BJ damping.
As an example for the DFT-D3 calculation, the interaction energy between
two benzene molecules in a parallel structure with symmetry is shown
as a function of the inter-distance in Fig. 49.
All the input files for the calculations can be found in a directory 'work/DFT-D3/',
and they are
Dimer-Ben-10.0.dat Dimer-Ben-3.88.dat Dimer-Ben-4.5.dat Mono-Ben-1.dat
Dimer-Ben-3.3.dat Dimer-Ben-3.89.dat Dimer-Ben-5.0.dat Mono-Ben-2.dat
Dimer-Ben-3.4.dat Dimer-Ben-3.8.dat Dimer-Ben-6.0.dat Mono-Ben.dat
Dimer-Ben-3.6.dat Dimer-Ben-3.9.dat Dimer-Ben-7.0.dat
Dimer-Ben-3.86.dat Dimer-Ben-4.0.dat Dimer-Ben-8.0.dat
Dimer-Ben-3.87.dat Dimer-Ben-4.2.dat Dimer-Ben-9.0.dat
After optimizing the monomer using 'Mono-Ben.dat', the total energy of dimer in
a variety of inter-distance was calculated using 'Dimer-Ben-#.dat' (#=3.3-9.0),
where the structure of the benzene molecule is the same as the structure of monomer
obtained by the first calculation. The monomer calculations with a counterpoise
correction were performed by 'Mono-Ben-1.dat' and 'Mono-Ben-2.dat'.
The optimum inter-distance is found to be 3.87 Å, which is well compared with
a reported value (3.89 Å) computed with density fitted local second-order Møller–Plesset
perturbation theory (DF-LMP2) . The counterpoise corrected interaction energy
is 1.73 kcal/mol being in good agreement with a reported value (1.7 kcal/mol) ,
while the basis set superposition error is found to be large.
The interaction energy of between two benzene molecules in a parallel structure with symmetry.
The counterpoise corrected interaction energy is shown by the triangle.
All the input files for the calculations can be found in a directory 'work/DFT-D3/.