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Selfconsistent screening in TkatchenkoScheffler method
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 frequencydependent screened polarizabilities
are obtained
by solving the selfconsistent screening equation:

(6.104) 
where is the dipoledipole interaction tensor
and
is the effective frequencydependent polarizability, approximated by

(6.105) 
with the characteristic mean excitation frequency
.
The dispersion coefficients are computed
from the CasimirPolder integral:

(6.106) 
The van der Waals radii of atoms are obtained by rescaling
the radii computed using DFTTS:

(6.107) 
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 DFTTS method (see sec. 6.77.3),
the following optional parameters can be userdefined:
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 rescale parameter  yes no 
Details of implementation of the TS+SCS method in VASP and the performance
tests made on various crystalline systems are presented in Phys. Rev. B. 87, 064110 (2013).
IMPORTANT NOTES:
 this method requires the use of POTCAR files from the
PAW dataset version 52 or later
 this method is incompatible with the setting ADDGRID=.TRUE.
 this type of calculation may be timeconsuming for large systems.
Note that the SCS contribution to gradients and stress tensor is only modest
(but nonnegligible) in many cases.
In the initial stages of relaxation of large systems, or if
only energy is of interest,
the calculation can be accelerated
by setting LSCSGRAD=.FALSE.
 the default value of the parameter VDW_SR (which is, in general, different from
that used in the unscreened DFTTS method) is
available only for the PBE functional. If functional other than PBE is used,
the value of VDW_SR must be specified in INCAR.
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N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at