  The effective mass is one of the main factors determining the Seebeck
coefficient and electronic conductivity. Nb-doping increases the effective mass
because of two reasons, lattice constants increase and electronic effects. In
this ab-initio study the effective mass is estimated from the curvature of
electronic bands and it could be clarified that the deformation of SrTiO3
crystals has a significant influence on bandgap and effective DOS and band
mass, which are both in excellent agreement to experimental data. However, the
electronic effect due to the e2g- band flattening near the Gamma-point due to
Nb-doping up to 0.2 at% is the main factor for the increase of effective mass.
Doping of La shows a linear decrease of the effective mass; this is explained
by the different surrounding of A- and B-site. Substitution of other elements
like Ba on the A-site and V on the B-site in SrTiO3 were also found to increase
the effective mass.
