Instument parameter file
Hi! I am trying to refine some XRD data using GSAS and looking for an instrument parameter file for the Rigaku Dmax 2000 x-ray diffractometer. Can anyone help? Thanks Donna
Introduction
Hi! Just thought i'd quickly introduce myself as I am a new member. Currently a postdoc researcher in layered oxide materials. Donna
RE: Donna Arnold
I don't know the answer to Donna's question but would be interested in learning how one creates an instrument parameter file for a specific diffractometer if anyone cares to explain or point me in the direction of information describing this. Many thanks to Brian Toby for his space group explanation and suggestion of additional resources. Nichole Wonderling Penn State University Materials Research Institute 159 Materials Research Laboratory University Park, PA. 16802 814-863-1369
RE: Donna Arnold
A search in the Rietveld archives brings up a wealth of information: http://pcb4122.univ-lemans.fr/cgi-bin/searchrietveld.pl?Range=AllForma t=StandardTerms=instrument+parameter+file (old archive) http://www.mail-archive.com/cgi-bin/htsearch?method=andformat=shortco nfig=rietveld_l_ill_frrestrict=exclude=words=instrument+parameter+fil e (new archive) The entries in the parameter file are also explained in the GSAS manual (somewhere in the back). Best regards, Jens -Original Message- From: Nichole Wonderling [mailto:[EMAIL PROTECTED] Sent: 18. marts 2004 13:27 To: Rietveld List Subject: RE: Donna Arnold I don't know the answer to Donna's question but would be interested in learning how one creates an instrument parameter file for a specific diffractometer if anyone cares to explain or point me in the direction of information describing this. Many thanks to Brian Toby for his space group explanation and suggestion of additional resources. Nichole Wonderling Penn State University Materials Research Institute 159 Materials Research Laboratory University Park, PA. 16802 814-863-1369
Instument parameter file
Donna (and anyone else who wonders about this), In gsas\examples there is an iparm file (inst_xry.prm) that can be used for most any Bragg-Brentano powder diffractometer. These instruments all perform more or less equally independent of manufacturer with respect to the things of interest for Rietveld refinement. If after doing a calibration with some sharp standard material you think you ought to change some of the default parameters the following records in the iparm file might be changed. INS 1 IRAD 3 This record determines the choice of standard wavelength for selecting f' and f for each atom type to be used in structure factor calculations. IRAD=3 is for CuKa radiation. INS 1 ICONS 1.540500 1.544300 0.0 0 0.70 0.5 This record contains the Ka1 and Ka2 wavelengths, zero point, polarization Ka2/Ka1 ratio. If just using CuKa you may only need to change the polarization coefficient (0.7 in this example). It can be refined for a standard with reasonably known atom thermal motion parameters and a wide 2-theta scan. Align your diffractometer so ZERO=0; any peak offsets you may see are due to sample displacement not zero offset. INS 1PRCF1 26 0.01 INS 1PRCF11 2.00E+00 -2.00E+00 5.00E+00 0.10E+01 INS 1PRCF12 0.10E+01 0.00E+00 These records select the default profile function and values. The GU, GV and GW values are typical for most Bragg-Brentano diffractometers. Your sample will probably broaden the lines (LX, LY, etc.) so much that any attempt to vary the Gaussian coefficients will yield nonsense. Look in the GSAS Manual for details of the formats of these records and do the examples before you start on your own stuff. Bob Von Dreele -Original Message- From: Donna Arnold [mailto:[EMAIL PROTECTED] Sent: Thu 3/18/2004 4:32 AM To: [EMAIL PROTECTED] Hi! I am trying to refine some XRD data using GSAS and looking for an instrument parameter file for the Rigaku Dmax 2000 x-ray diffractometer. Can anyone help? Thanks Donna
Re: Instument parameter file
Your sample will probably broaden the lines (LX, LY, etc.) so much that
any attempt to vary the Gaussian
coefficients will yield nonsense.
Just some remark (of course, I am not a great specialist):
At least to my experience, there is always some Gaussian broadening from
the sample as well, and (again it is my humble opinion only) at least U is
better to allow to be refined.
For example, Rietan manual states the problem in the following way:
{
U, V, and W tend to be highly correlated, with a result that various
combinations of quite different values can lead to essentially the
same variance, sigma^2.These three parameters, therefore, do not
converge in a stable manner when refined simultaneously (Prince,
1993). In particular, refining P in addition to U, V, and W almost
certainly affords a singular (non-positive definite) coefficient matrix.
Of the four profile-shape parameters in Eq. (5), V and W depend not on
specimens but only on instruments (Young Desai, 1989). Then, these two
instrumental parameters may well be fixed at values obtained by the
Rietveld refinement of a well-crystallized sample where profile broadening
is negligible, i.e., P = 0 .
}
Sincerely, Maxim.
__
Maxim V. Lobanov
Department of Chemistry
Rutgers University
610 Taylor Rd
Piscataway, NJ 08854
Phone: (732) 445-3811
Subscribing Unsubscribing to the Rietveld list
At 17:07 18/03/2004, Brian H. Toby wrote: Please remove me from the mailing list-thank you I seem to provoke the above response every time I post to the list... Perhaps :-) But you don't see the requests I have from new people wanting to join, which seem to increase whenever there is some controversy being discussed :-) Seriously people, if you want to change your email address or otherwise unsubscribe/subscribe, obtain help with the list, send a message to the administrator (me) etc, just click on the appropriate links in the headers of any message (reproduced below for the archive). List-Help: mailto:[EMAIL PROTECTED] List-Subscribe: mailto:[EMAIL PROTECTED] List-Unsubscribe: mailto:[EMAIL PROTECTED] List-Post: mailto:[EMAIL PROTECTED] List-Owner: mailto:[EMAIL PROTECTED] Alan. Dr Alan W. Hewat, Diffraction Group Leader. Institut Laue-Langevin, BP 156X Grenoble FRANCE 38042 fax (33)4.76.20.76.48 tel (33)4.76.20.72.13 (or .26 Mme Guillermet) [EMAIL PROTECTED] http://www.ill.fr/dif/AlanHewat.htm ___
Note to software designers
Maxim V. Lobanov wrote: U, V, and W tend to be highly correlated, with a result that various combinations of quite different values can lead to essentially the same variance, sigma^2.These three parameters, therefore, do not converge in a stable manner when refined simultaneously (Prince, 1993). As Ted Prince also pointed out, if the Cagliotti equation is given an origin shift, e.g. U tan2(theta-theta0) + V tan(theta-theta0) + W where theta0 is fixed at 1/2 the monochromator off-angle, the correlation in these parameters is greatly reduced. Brian Brian H. Toby, Ph.D.Leader, Crystallography Team [EMAIL PROTECTED] NIST Center for Neutron Research, Stop 8562 voice: 301-975-4297 National Institute of Standards Technology FAX: 301-921-9847Gaithersburg, MD 20899-8562 http://www.ncnr.nist.gov/xtal
Re: Instument parameter file
U, V, and W tend to be highly correlated The correlation between U,V,W is the result of a resolution curve that doesn't have a well defined minimum. If you differentiate the Caglioti equation for the FWHM: FWHM**2=U.tan**2(theta)+V.tan(theta)+W you obtain the condition for the minimum as 2U.tan(theta) + V = 0 so you can constrain V = -2U.tan(theta) Theta can be assumed to be about half the monochromator take-off angle (2thetaM) for a conventional neutron diffractometer eg for 2thetaM=90 you can just approximate: V=-2U (This was known from the time of Rietveld...) Alan Hewat, ILL Grenoble, FRANCE [EMAIL PROTECTED] fax (33) 4.76.20.76.48 (33) 4.76.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/AlanHewat.htm ___
Re: Instument parameter file
Theoretically U,V,W should not be refined at all as they describe instrumental
broadening, and this is exactly what I do
(usually). After diffractometer alignment, a good quality pattern in whole possible
angular range has to be collected from Rietveld
standard which currently is LaB6. From these data it is possible to calculated UVW
assuming high quality (e.g. step size 0.01 deg.
2theta or less, 5-10 sec/point, etc.).
These UVW could be used w/o refinement in any other experiment obtained at the same
diffractometer settings and alignment. Thus
separate instrumental files have to be created for each diffractometer configuration
used (e.g. different slits).
Peter Zavalij
Dr. Peter Y. Zavalij
University Crystallographer
Institute for Materials Research
and Chemistry Department
Binghamton University, SUNY, Vestal Pkwy, East
Binghamton, NY 13902-6000, USA
Tel: (607)777-4298Fax: (607)777-4623
E-mail:[EMAIL PROTECTED]
http://materials.binghamton.edu/zavalij
-Original Message-
From: Maxim V. Lobanov [mailto:[EMAIL PROTECTED]
Sent: Thursday, March 18, 2004 10:50 AM
To: [EMAIL PROTECTED]
Your sample will probably broaden the lines (LX, LY, etc.) so much that
any attempt to vary the Gaussian
coefficients will yield nonsense.
Just some remark (of course, I am not a great specialist):
At least to my experience, there is always some Gaussian broadening from
the sample as well, and (again it is my humble opinion only) at least U is
better to allow to be refined.
For example, Rietan manual states the problem in the following way:
{
U, V, and W tend to be highly correlated, with a result that various
combinations of quite different values can lead to essentially the
same variance, sigma^2.These three parameters, therefore, do not
converge in a stable manner when refined simultaneously (Prince,
1993). In particular, refining P in addition to U, V, and W almost
certainly affords a singular (non-positive definite) coefficient matrix.
Of the four profile-shape parameters in Eq. (5), V and W depend not on
specimens but only on instruments (Young Desai, 1989). Then, these two
instrumental parameters may well be fixed at values obtained by the
Rietveld refinement of a well-crystallized sample where profile broadening
is negligible, i.e., P = 0 .
}
Sincerely, Maxim.
__
Maxim V. Lobanov
Department of Chemistry
Rutgers University
610 Taylor Rd
Piscataway, NJ 08854
Phone: (732) 445-3811
Re: Rietveld question - EXPGUI
I am going to give up my 'lurker' status on this mailing list to switch this thread to a more philosophical vein. In the past generation, many good crystallographers have also been good programmers. I suspect it was easier to learn programming than it was to teach crystallography to a programmer. As a result, the current set of codes are very sophisticated and powerful. The question that I wish to discuss is the following: What happens in the future? When Bob Von Dreele and Brian Toby, to name two, join Al Larson in retirement, (and Al finally stops working) what happens then? As was made abundantly clear in the message that started this thread, if the program doesn't complain about garbage, then the input MUST be gospel. I recently got an E-mail from someone stating that there was a definite bug in my crystal-structure drawing program DRAWxtl. The evidence for this 'bug' was a V-V bond distance of 0.3 Angstom. Of course, the problem was a discrepancy between the structural coordinates and the space group. As I no longer have access to a scientific library, I could only suggest how to resolve the problem. It is even possible that the published result is the source of the problem. In any case, I have not heard back. I will be very interested in your responses. Is my prediction of coming disaster too pessimistic? Probably. After all, the late Jose Donnay of Johns Hopkins University always claimed that crystallography was ruined by the invention of the computer. I never learned to what extent his opinion was effected by the conflicts I had with his wife. Cheers, Larry Finger, Crystallographer (retired)
Re: Instument parameter file
Theoretically U,V,W should not be refined at all as they describe instrumental broadening This is true only when there is no Gaussian strain present. Brian
