Unrestricted and Spin-Orbit Coupling

In the case of Spin-Orbit coupling there are two ways to do spin-polarized calculations, either using the collinear approximation or the noncollinear approximation [101, 102]. Using the unrestricted feature in order to assign different numbers of electrons to a and b spin, respectively, cannot be applied as such, if one includes Spin-Orbit coupling, since the electrons are not directly associated with spin-α and spin-β. For the collinear and noncollinear approximation one should use symmetry NOSYM, and each level can allocate 1 electron. Note that with the key CHARGE one should only specify one value, namely the total charge. One should not specify the spin-polarization.

COLLINEAR

This key is only relevant in the case of Spin-Orbit coupling. The key has no argument. See also the key noncollinear.

In the collinear approximation in each point in space the spin-polarization has the same direction (default is in the direction of the z-axis). Kramer's symmetry does not have to be satisfied. Symmetry used in the calculation should be NOSYM. The default direction of the spin-polarization can be overruled using the key SOUX (this key has no argument) for spin-polarization only in the direction of the x-axis, and the key SOUY (this key has no argument) for spin-polarization only in the direction of the y-axis. Both keys SOUX and SOUY are only relevant in the case of Spin-Orbit coupling in combination with the key collinear.

NONCOLLINEAR

This key is only relevant in the case of Spin-Orbit coupling. The key has no argument. See also the key collinear.

In the noncollinear approximation in each point in space the spin-polarization can have a different direction. Kramer's symmetry does not have to be satisfied. Symmetry used in the calculation should be NOSYM.