Basis Set

When to use which Basis Set

There is no final answer to this question. It is a matter of the level of sophistication you want to have in your model and therefore in your results. If you employ a less sophisticated basis set you will have a result more quickly, but at lower accuracy. Generally speaking the selection of basis set can be separated in 3 different steps:

  1. Do I want high precision or am I still testing/changing things? If High precision is required go for TZVP or 6-311G basis sets. Else start with something cheaper, like def2-SVP or jorge-DZP
  2. Do I need/want relativistic calculations? Yes: jorrge-X-DKH or x2c-familiy basis sets. Else the jorge basis ets without -DKH suffix and all other basis sets work. Keep in mind that only up to Kr is defined in the non-jorge basis sets.
  3. Is my system anionic? If you grow things you might have a resulting calculation which is negatively charged. This system will msot likely require diffuse basis functions (unless you can compensate using a solvation model). In this case e.g. def2-TZVPD and def2-TZVPPD and 6-311++G basis sets have the diffuse functions you are looking for.