DFTB basis set

[jalmeida]

Dear,

Please, is it possible set different basis set for different atoms in DFTB scheme? I have a system cluster-molecule-cluster, and I want to keep the symmetry closer to fcc bulk structure. I used the Wulff constructor and I want to optimise with clusters of different sizes. I suppose that for ~20 Au atoms the LCAOCalculator will be nice. However, more than 100 atoms for each cluster, I suppose it is better use DFTB. The gold is coordinate with sulphur and my molecule contains C, N , H and Fe. Seeing the AtomicData page on documentation, I believe that could be good use the basis set auorg-1-1 for the Au, mio-1-1 for H,C,N and S, and trans3d-0-1 for Fe. However, how can I do this?

[Anders Blom]

This is not possible because unlike DFT, the DFTB basis sets are not just for the atoms themselves, but also contain pairwise interactions. So, all elements must be contained in the same parameter set, which obviously is a strong limitation on the applicability and transferability of DFTB.

If your goal is to run "quick-and-dirty" and somewhat approximate calculations, then I would go with the SingleZetaPolarized basis set in QuantumATK's LCAO-DFT model. It will be slower than DFTB  but orders of magnitude faster than plane waves, and also a lot faster than our default LCAO PseudoDojo basis sets.

[jalmeida]

Thank you very much!