Methodological Components: Final Remarks.
The main message of this second section can be summarized as follows.
- Always follow recommendations from experts in the field when choosing
any combination of functional and basis set.
- Avoid picking a functional/basis set only because they are popular.
- The best way to pick a functional is to compare the chemical problem
under consideration with similar problems collected in databases of
high-level computational data. Databases can also give an indication
on the expected accuracy of the results (i.e. estimate the error bars
associated with a calculation).
- Basis sets are responsible for two types of errors – BSIE and BSSE.
Both errors can be alleviated by choosing a suitably large basis set,
and in some specific situation by using appropriate techniques.
- Do not use B3LYP/6-31G* blindly. It cannot be universally trusted.