[TCOD] What structures do we accept to TCOD?

[Björkman Torbjörn]

---
Torbjörn Björkman, PhD
COMP, Aalto University School of Science
Espoo, Finland


>> My point is: the task of comparing experiment and theory (i.e.
>> comparing COD and TCOD) is a research task in its own right.
>
> To my knowledge, theoricians are aware about the low quality of the
> cell parameters derived from their DFT optimizations to the point that
> they prefer to fix them to the experimental values when available.

I would agree with Stefaan that this is a problem we largely know how to deal with, if all you want is lattice constants for a single compound. But in practice there are often associated complications, such as the need to simultaneously describing two different structures at an interface, and then you often need to weigh a lot of different factors together to get the best approximation to the whole problem. It is fairly common that this balance in the end produces the solution "just fix the lattice constant to their experimental values", since that is typically good enough and well controlled and easily reproducible. 


> This triggered another thought: isn't the information whether only
> positions were optimized and/or whether the full cell shape was
> optimized as well level-0 information? If we see only the cif without
> this information, then there is not much that can be concluded about
> such an entry. And as a corollary: doesn't that imply that there is no
> place in TCOD for DFT calculations that start from the experimental cif
> without any subsequent optimization? What do others think?

Hmm... actually, it never even occured to me that someone might want to submit an only partially optimized structure. I guess that means that I think that there is no place for such calculations in TCOD. It seems very difficult to estimate the practical value of such a calculation and I can't see myself being very interested in the outcome. But there may be folks out there with a different viewpoint, I can guess that there could be a use for calculations like that for things like molecular crystals, where the molecules are easy and their weak interaction (which will determine the cell shape) is hard, whereas experimentally the cell shape is easier (I guess, but correct me if I'm wrong). Anyway my instinctive vote is No.

Cheers,
Torbjörn


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