ICDD Technical Committee Minutes

Electron Diffraction Subcommittee
Steamboat Springs, CO
Twilight Room
Sunday, 29 July 2001
Chairman: Alwyn Eades

Minutes from the March 2001 Meeting
The minutes were approved.

Board of Directors Liaison Report
R. Goehner (BoD Liaison) reported that the funding for the subcommittee meeting at Steamboat Springs and the Microscopy & Microanalysis (M&M) meeting will be provided by the Technical Committee. He also stated that the sales numbers for electron diffraction companies selling ICDD products are good. However, the manufacturers are a bit nervous about our new product, the PDF-4, which is understandable.

Update on the Joint MAS DXC Symposium
Although there is mutual interest in holding a joint symposium, there is also a serious conflict in dates. A planned joint meeting for 2003 will not be held. There was a mistake in the dates for the M and M meeting and the correct date is not compatible with a joint meeting. The Denver X-ray Conference Organizing Committee will discuss possibilities at its meeting later this week. It seems that both conferences are held the same week nearly every year. This year they are a week apart, but that is unusual. One person guessed that the additional attendance at a joint meeting might be two to three hundred above the normal Denver numbers.

Report on the Possibility of a Database on Bonding Electron Densities
The question is: should the PDF incorporate electron-bonding data. It was agreed that, if this data is to be incorporated into any database, that PDF is the most appropriate. The number of data sets and the market are currently quite small. However, it would take some time to get things going and A. Eades expressed the view that now would be a good time to start. J. Kaduk asked what information would be included. How would the requirements differ from the existing PDF entries?
Headquarters is planning to store Fobs and Fcalc (if they are supplied) in the near future.

It was suggested that a task group be formed of electron diffraction people together with XRD people to define what is needed. The determination of bonding electron densities by electron diffraction is new and the even though there is a low number of data sets, the data is very accurate. The idea would be to define a format for the data that would serve to make comparisons directly between data obtained by all techniques. This could be a useful research validation tool. E-mail exchanges over the next several months should take place to help get a feel for what direction this subcommittee should proceed.

Discussion of Things Electron Diffractionists Would Wish for from the Relational Database
No new items were presented on the electron diffraction wish list. The existing list was summarized:

  •  Include, in the list of d's and I's, entries that would be outside the normal angular range for XRD.
  •  Split out degeneracies - give separate intensity values for overlapping hkl's
  •  Provide a flag to indicate a "standard pattern" where several cards refer to what is essentially the same structure
  •  Provide the means of simulating electron diffraction patterns from the data.

Headquarters is well aware of all of these points and all are being addressed. J. Faber asked for help with the last item on the list. He would like to see a study group formed to give the equations or algorithms needed. In using electron diffraction most people aren't concerned with precision, but it was felt that since we are putting a database together today, the needs of the future should be kept in mind.

Meeting adjourned.