How to use

The keyword $soghf enforces the two-component calculations. Keywords for specification of the method of calculation are the same as for the one-component case ($dft and $rij for pure density functional calculations within the RI-J-approximation, $rij and $rik for Hartree-Fock with the RI-approximation for Coulomb and exchange operators, and all three keywords for Hybrid-DFT). The DIIS scheme for complex Fock operators can be activated by inserting $gdiis in the control-file. For closed-shell species a Kramers invariant density functional formalism (only pure density functionals) can be switched on with the keyword $kramers. These keywords have to be inserted into the control-file manually.

As start wavefunctions Hückel-, UHF- or RHF-wavefunctions may be used. The two-component formalism does not support the point group symmetries, start wave functions may be transformed to C1 symmetry by define or the script 'uhfuse'.

For spin-orbit treatments two-component ECPs (suffix -2c) are required, the use of extended basis sets accounting for the spatial splitting of inner p-shells (also suffix -2c) is recommended (see [62]). ECPs and basis sets def2-XVP-2c (X=S ,TZ ,QZ ) are available for Ag - I, Au - At, they can be selected within the define session. RI-J and RI-JK auxiliary basis sets of def2-type are of sufficient flexibility for two-component treatments; they are the same with and without suffix -2c.

The two-component formalism may be most easily prepared and applied in the following way:

• run define: choose C1-symmetry; select ECPs and basis sets with suffices -2c for the respective elements. The corrresponding auxiliary basis sets are provided automatically.
• insert $soghf in the control file (as well as further desired keywords).
• For open-shell molecules it is often helpful to increase the value for $scforbitalshift closedshell; a value of ca. 1.0 may serve as a rough recommendation.
• start the two-component calculation with ridft
• At the end of the SCF procedure real and imaginary parts of spinors are written to files spinor.r and spinor.i, eigenvalues and spinor occupations are collected in the file EIGS, the total energy is added to data group $energy. The data groups $closed shells ($alpha shells and $beta shells for open shell cases) are no longer significant, but nevertheless kept in the control-file; additionally the spinor occupations are diposited in data group $spinor.