In top international Chemistry publications, I observed few are using LANL2DZ for both the metal and other atoms, few are using 6-311g type basis set for both the metal and other atoms and few are using LANL2DZ for metal only and 6-311g type basis set for other atoms except metal. Which one is appropriate and why? I guess the last one....
LANL2DZ is a double zeta basis set, i.e. it doesn't include any polarization functions, but it does have relativistic effects through the use of pseudopotentials. The 6-31G basis is non-relativistic, and very small as well.
You don't need to mix basis sets to get good results. E.g. the Karlsruhe def2 basis sets are available for all the periodic table, contain relativistic effects and the split valence sets are quite affordable, so instead of using lanl2dz + 6-31g* you can just use def2-sv(p).
In general - the larger the basis set, the higher chance to get more accurate results (Article Basis set effects on relative energies and HOMO–LUMO energy ...
). In this particular case I wouldn't use LANL2DZ for all atoms, as it's not that accurate and 6-311g is probably not available for most transition metals. 6-311G** + LANL2DZ on metal seems like a good idea.
Hello Suvendu,
I recommend to use B3LYP method with LanL2Dz for metals and 6-31++G(d,p) (or the smaller 6-31G(d) basis set if you have a large system) for other elements. B3LYP and B3LYP-D3 are known to give HOMO-LUMO gabs for organic molecules that are in a good agreement with experimental values.
lanl2dz is used for atoms that have more than 36 electrons because bases like 6-31G ....... can not describe them
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