$DFTBSK group                (required if GBASIS=DFTB)
 
This group is required for all DFTB calculations
unless PARAM is specified in $DFTB. $DFTBSK is much more
general than PARAM. It defines the file names for Slater-Koster
parameters describing pairwise interactions for each pair of
species (see $DFTB for the introduction).
 
The group is free-formatted, and consists of N*N lines,
where N is the number of species.  Each line has the
format:
  species-i species-j i-j parameter-file-name
Note that (species-i species-j) is different from (species-
j species-i), and both must be given!  For example,
   C O /home/user/DFTB/mio-0-1/C-O.skf
which defines carbon-oxygen parameters to be in that file.
Naturally, this file must be readable on the computer where
calculations are actually run.
 
The names of species should be the same as in $DATA
(for FMO, in $FMOXYZ).  In FMO-DFTB calculations, these
names must be atomic symbols (H, He, ...), otherwise names
may be used (hydrogen, helium, ...) truncated to 8 symbols.
The names may include numbers, as in (H.1).
 
Slater-Koster parameters are available from
          http://www.dftb.org/
(for free) and from some other sources. There are many
different parameter sets, for instance, the above example
uses the "mio-0-1" set. Follow the requirements on proper
citations when using these parameters.