  The magnetic and electronic properties of strontium titanate with different
carbon dopant configurations are explored using first-principles calculations
with a generalized gradient approximation (GGA) and the GGA+U approach. Our
results show that the structural stability, electronic properties and magnetic
properties of C-doped SrTiO3 strongly depend on the distance between carbon
dopants. In both GGA and GGA+U calculations, the doping structure is mostly
stable with a nonmagnetic feature when the carbon dopants are nearest
neighbors, which can be ascribed to the formation of a C-C dimer pair
accompanied by stronger C-C and weaker C-Ti hybridizations as the C-C distance
becomes smaller. As the C-C distance increases, C-doped SrTiO3 changes from an
n-type nonmagnetic metal to ferromagnetic/antiferromagnetic half-metal and to
an antiferromagnetic/ferromagnetic semiconductor in GGA calculations, while it
changes from a nonmagnetic semiconductor to ferromagnetic half-metal and to an
antiferromagnetic semiconductor using the GGA+U method. Our work demonstrates
the possibility of tailoring the magnetic and electronic properties of C-doped
SrTiO3, which might provide some guidance to extend the applications of
strontium titanate as a magnetic or optoelectronic material.
