[TCOD] What structures do we accept to TCOD?

[Stefaan Cottenier]

 >> 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.

People who compute from DFT spectroscopic spectra often just take the 
experimental cif and do their computational spectroscopy on that one. 
Although these are legitimate DFT calculations, there is nothing in them 
that is useful for a structural database as TCOD.

Everbody is biased by his/her background. So am I. I have often 
calculated hyperfine properties of solids. They can sensitively depend 
on the atomic positions, but usually do not depend very much on small 
variations of the cell shape. And as one needs a LAPW code for accurate 
hyperfine properties -- a type of method in which cell shape 
optimizations are very tedious due to the lack of a stress tensor -- the 
standard procedure in that field is to take the experimental cell shape 
yet DFT-optimized atomic positions. Having such data included in TCOD 
looks meaningful to me, provided one is aware that the cell parameters 
are taken from experiment. Which is why this should probably be level-0 
info.

Furthermore, as atomic positions are harder to get from experiment than 
the cell parameters, I can imagine also refinement people would want to 
contribute calculations with experimental cell parameters and 
DFT-optimized positions.

Obviously, a fully DFT-optimized crystal (cell parameters and positions) 
is the most useful type of entries.

Stefaan