Scalar-relativistic effects in solids in the framework of a   Douglas-Kroll transformed Dirac-Coulomb Hamiltonian
  The Douglas-Kroll transformed Dirac-Coulomb Hamiltonian is used to describe scalar-relativistic effects in solids. A Hartree-Fock approximation with periodic boundary conditions makes it feasible to use methods originally developed for atoms and molecules to solve the corresponding equations for crystalline systems. The implementation is realized within the CRYSTAL program. Scalar-relativistic effects in silver compounds of FCC structure such as AgF, AgCl, AgBr and Ag are investigated for the molar formation energy, the lattice parameter, the isothermal bulk modulus and the pressure derivative. 
Norbert J. M. Geipel, Bernd A. Hess