A computationally efficient way to account for electrodynamic response effects, in particular the interaction of atoms with the dynamic electric field due to the surrounding polarizable atoms was proposed by Tkatchenko et al. [130]. In this method, termed TS+SCS, the frequency-dependent screened polarizabilities are obtained by solving the self-consistent screening equation:
(6.104) |
where is the dipole-dipole interaction tensor and is the effective frequency-dependent polarizability, approximated by
with the characteristic mean excitation frequency . The dispersion coefficients are computed from the Casimir-Polder integral:
(6.106) |
The van der Waals radii of atoms are obtained by rescaling the radii computed using DFT-TS:
The dispersion energy is computed using the same equation
as in the original TS method (eq. 6.87) but
with corrected parameters
,
, and
.
The TS+SCS method is invoked by
defining IVDW=220 and LVDWSCS=.TRUE.
In addition to parameters controlling the DFT-TS method (see sec. 6.77.3),
the following optional parameters can be user-defined:
VDW_SR | = 0.97 | scaling factor |
SCSRAD | = 120. | cutoff radius (Å) used in calculation |
LSCSGRAD | = .TRUE..FALSE. | compute SCS contribution to gradients - yesno |
LSCALER0 | = .TRUE..FALSE. | use eq. 6.107 to re-scale parameter - yes no |