On 2014-07-28 11:23, Armel le Bail wrote:
Since it is time to questions, I have one.
DFT-optimized structures are done in a great variety of cases, one being when the refinement quality against experimental data (powder, etc) is poor due to an unfavourable ratio P/D (parameters/Data).
However, I have almost never seen the comparison of the experimental data to the intensities calculated from the optimized atomic coordinates... I have especially in mind a "simple" example, calcium carbonate, vaterite form, for which dozens of optimized models were proposed, without even one comparison to the data...
So the question is : In case of the existence of an experimental dataset, should a comparison observed/calculated be requested (classical R values but with fixed coordinates) ?
I thing that COD/TCOD comparison of the same crystal structure refined against Fobs and optimised with the advanced DFT methods would give an good overview of the correspondence, and that's what I would be very interested in.
I regard this as a win-win-win situation:
a) if both X-ray and DFT agree, we will have greater reassurance that both are correct (within experimental and computational errors);
b) if the disagree, then either:
b') the x-ray structure has problems
or
b'') the DFT computation has problems.
In both cases we can check the data, trace down the problems and (ideally) fix them.
I am currently in Cambridge with Peter Murray-Rust, and we had very interesting conversations with people who actually do similar things, for their own research. The results are very intriguing :). If we could get these people on board we could have valuable contributions, I hope.
Regards, Saulius