The DFTD3 method of Grimme et al. [136,137] is supported to include a vdW interaction with default parameters for the GGAPBE functional. The following keywords are relevant for the DFTD3 method.
scf.dftD on # onoff, default=off version.dftD 3 # 23, default=2 DFTD3.damp bj # zerobj, default=bj DFTD.Unit AU # AngAU 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 DFTD2 or DFTD3 calculation, turn on 'scf.dftD'. For DFTD2 use version.dftD=2 and for DFTD3 version.dftD=3. The DFTD3 implemented here supports both zero and BeckeJohnson (BJ) damping functions [137]. 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 caxes 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 DFTD2 method by
<DFTD.periodicity 1 1 2 1 3 1 4 1 .... DFTD.periodicity>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 nonperiodic for the corresponding atom. By considering the periodicity or nonperiodicity of each atom, the interaction is automatically cut when they are nonperiodic.
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=0.751.0 (for DFTD2DFTD3) DFTD.scale8 0.7875 # default=0.7220.7875 (for PBE with zerobj 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 [136] is given by 'DFTD.scale6' and 'DFTD.scale8'. The global scaling parameters are functional and dampingfunction dependent. The parameter 'sr6' of Eq. (6) in [136] needs to be set when using the zero damping function while the parameters 'a1' and 'a2' of Eq. (6) in [137] need to be set when choosing BJ damping.
As an example for the DFTD3 calculation, the interaction energy between two benzene molecules in a parallel structure with symmetry is shown as a function of the interdistance in Fig. 60. All the input files for the calculations can be found in a directory 'work/DFTD3/', and they are
DimerBen10.0.dat DimerBen3.88.dat DimerBen4.5.dat MonoBen1.dat DimerBen3.3.dat DimerBen3.89.dat DimerBen5.0.dat MonoBen2.dat DimerBen3.4.dat DimerBen3.8.dat DimerBen6.0.dat MonoBen.dat DimerBen3.6.dat DimerBen3.9.dat DimerBen7.0.dat DimerBen3.86.dat DimerBen4.0.dat DimerBen8.0.dat DimerBen3.87.dat DimerBen4.2.dat DimerBen9.0.datAfter optimizing the monomer using 'MonoBen.dat', the total energy of dimer in a variety of interdistance was calculated using 'DimerBen#.dat' (#=3.39.0), 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 'MonoBen1.dat' and 'MonoBen2.dat'. The optimum interdistance is found to be 3.87 Å, which is well compared with a reported value (3.89 Å) computed with density fitted local secondorder MøllerPlesset perturbation theory (DFLMP2) [138]. The counterpoise corrected interaction energy is 1.73 kcal/mol being in good agreement with a reported value (1.7 kcal/mol) [138], while the basis set superposition error is found to be large.
