Relativistic effects are treated with the accurate and efficient ZORA approach [17-18], controlled by the Relativistic keyword. Relativistic effects are negligible for light atoms, but grow to dramatic changes for heavy elements. A rule of thumb is: Relativistic effects are quite small at row 4, but very large at row 6 (and later).
Includes a relativistic correction in the Hamiltonian.
Relativistic {level}
Level {None | ZORA | ZORA Spin}
NONE: no relativistic effects
ZORA: scalar relativistic ZORA. This option comes at very little cost, and is advised when you want to compare to experimental results.
ZORA Spin: Spin-orbit coupled ZORA. This is the best level of theory, but it is much more (4-8 times) expensive than a normal calculations. Spin-orbit effects are generally quite small, unless there are very heavy atoms in your system, especially with p valence electrons (like Pb).
