Re: About zero counts etc.

Hello Joerg, > -Having measured n counts, the estimated value is n+1 You might have a hard time convincing me on that one. > -Having measured n counts, the esd is also sqrt(n+1)! If n is zero then spending more time on the data collection might be better than more time on the analysis. > Thing

Re: Strange peaks from grainy Si (data re-attached)

Congwu, If you can move the detector the radius of the silicon rings will change according to the distance and Bragg angles. Moving the sample might be easier for the same check. Does your spurious ring move so that you can trace it back to a point inside the sample? Could it come from the collima

Re: Negative Biso from neutron data

Quoting Alan Hewat <[EMAIL PROTECTED]>: > > There were discussions about the factors that may cause negative atomic > > displacement parameters for XRD data. What about neuton data and how to > > solve the problem (time-of-flight data in this case) ? > > Negative temperature factors Biso mean tha

Re: Negative Uiso in GSAS

I can't resist adding one more to Mike's excellent list: 5. When peaks overlap strongly it becomes difficult to determine the background level. Negative Uiso is a consequence of the background refining to a value which is too low, especially where the peaks are most dense in the pattern (short

Re: [sdpd] Re: Are restraints as good as observations ?

On 31/07/2013 03:07, Leonid Solovyov wrote: ... There is a widely scattered belief that restraints always improve not only the restrained values, but also the “unrestrained” part of structure such as intermolecular distances, orientations, planarity etc. Apart from your word "always", I certai

Re: [sdpd] Re: Are restraints as good as observations ?

On 31/07/2013 17:25, Leonid Solovyov wrote: One can make everything "OK" simply by choosing an "appropriate" weight of restraints. The uncertainty in the restraint's weight appropriateness makes every restrained refinement a "know how". Likelihood and/or the free R-factor offer routes to choose

Re: [sdpd] Re: Are restraints as good as observations ?

On 31/07/2013 20:19, Brian Toby wrote: To perform R-free with powder data, one must excise multiple complete peaks from the pattern, say a few sections making up 10-20% of pattern. Hi Brian, It is not so bad, you only need to throw in some peak intensities as variables (a partial Pawley). You

Re: Delta ferrite by xrd

On 08/08/2013 18:04, led15 wrote: Is possible confirm the presence of delta ferrite in steel by xrd. Yes: http://dx.doi.org/10.1007/s11661-010-0371-7 ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the su

Re: rocking curve

With a 2D detector you see spots for "grains" and smooth peaks for "texture". You can also observe a collection of grains which exhibit texture giving a non uniform spot density. Usually by "grains" people expect randomised changes in intensity with small orientation changes. For "texture" ther

Re: X-ray diffraction laboratory manager position

Did I click on the right link? The second point says: "Develop new experimental approaches and measurement routines as required by a growing user base." It doesn't sound so bad, unless the candidate can't think of any novel experimental techniques to invent. Jon On 05/12/2013 19:02, Cline,

Re: Dollase Paper

On 21/03/2014 10:59, Norberto Masciocchi wrote: ... > So, the question is: > Is there any way do get around this problem (without resorting to > spherical hamonics or to grind the specimen in a WC, SiC or BN mill)? High energy X-rays or neutrons in transmission geometry would seem to help? Best

Re: Stacking faults and antiphase boundary

On 06/04/2014 08:06, Leonid Solovyov wrote: The faulting model in DDM gives nearly perfect agreement with the experiment: http://sites.google.com/site/ddmsuite/home/Copper-DDM.png It looks a little bit reminiscent of this pattern for ice: http://www.science24.com/paper/15441 ...but the litt

Re: Polarization factor por Ge (111) monochromator

Jools, To get the value more directly I think you can also measure the scattering at two theta of 90 degrees in the horizontal versus vertical plane. We did this last week at the synchrotron in the course of making some detector correction files and there was a nice hole in the diffraction pa

Re: Thermal factor for magnetic phase?

Dear Jae-Ho The thermal parameters of the magnetic moments are identical to the thermal parameters of the nuclei which they are attached to (along with the x,y,z positions and occupancies). Normally they will refine much better from the nuclear intensities which should extend to higher Q. Be

Re: Statistics on semi-quantitative XRD data

Dear James, I'm not sure these are quite what you are after, but I'm suggesting them anyway. There were several papers from Gordon Barr about non-parametric methods: SNAP-1D: a computer program for qualitative and quantitative powder diffraction pattern analysis using the full pattern profi

Re: Intensity issue with synchrotron data

On 15/01/2015 12:15, Norberto Masciocchi wrote: Il 15/01/2015 11:46, Fauth Francois ha scritto: 1- the data format of the input file your are using for your refinement does not allow counts more than 10^6, This is typically the case with GSAS input file format Here at ALBA, as you suggeste

Re: regress in crystallographic good practices and knowledge

Dear Kurt, You can peaksearch the images with any number of packages and then look at the extracted spot positions. The stuff we wrote lives at http://sourceforge.net/projects/fable/ and it is normally used to fit grain-by-grain strain tensors. If you can isolate the spots you do indeed get a l

3D powder averaging...

On 2015-05-10 17:36, Alan Hewat wrote: Jon... nicely illustrated... by posting an interesting link... Thanks! Obviously I think these serial methods are a fantastic opportunity for this community. An IUCrJ commentary by me is here: "Serial crystallography for the masses": http://journals.iu

Re: Powder Diffraction Discussion Group on Facebook

Thanks Davide for this useful initiative, I have joined. I don't doubt the value of the Rietveld list but pictures are also useful. It was recently bought to my attention that funding may be related to "public perceptions" of research and for this reason we should pay attention to things like

bookmarks: Re: Powder Diffraction Discussion Group on Facebook

> > Powder Diffraction Discussion Group on facebook > > http://www.facebook.com/groups/1087352967946225/ So from what I gather we have: http://www.xrayforum.co.uk http://www.reddit.com/r/crystallography http://www.researchgate.net/topic/x-ray_diffraction There are many other places where c

Re: Anomalous scattering factor and Dispersion coefficients

Dear Xiaodong, Jeremy, Isn't it equation 3 here? http://www.nist.gov/srd/upload/jpcrd488.pdf f1/f2 are "dispersion" numbers and f'/f" are the "anomalous" ones. The relativisitic correction number for iron then shows up on page 221. Best, Jon === On 11/06/2015 17:27, Jeremy Karl Cockcroft

Re: source of diamond powder for internal standard

Hello In the reference below they say they purchased 2-4 micron grain size from Nilaco (perhaps it was: http://nilaco.jp/en/order.php?DIR=CHEMI&MENU=15&CODE=&FROM=14&ITEM1=Diamond_Powder&ITEM2=Powder). /J. Synchrotron Rad./(2014).*21*, 119-126[doi:10.1107/S1600577513028269

Re: TOPAS Macro Language (peak shape broadening macros)

Hi Alan, In the limiting case of orienting all crystals in 3D you get a mosaic single crystal (e.g. [1], or using an XFEL to measure 1 at a time). Then the refined the crystal structure has somewhat better accuracy than with a 1D Rietveld fit. Perhaps not the most popular idea for this mailing

Re: R: Re: synchrotron beamline info

ESRF, see: Sørensen, H. O., Schmidt, S., Wright, J. P., Vaughan, G. B. M., Techert, S., Garman, E. F., Oddershede, J., Davaasambuu, J., Paithankar, K. S., Gundlach, C. & Poulsen, H. F. (2012). Z. Kristallogr. 227, 63–78. http://dx.doi.org/10.1524/zkri.2012.1438 This approach might be usefu

Re: structure solution terminology

On 16/12/2015 23:05, Lubomir Smrcok wrote: shuffles atoms or molecules around a cell and compares experimental and calculated patterns ? It could be well used also for single crystal data, I know, but it is not routinely done (yet ?). In protein crystallography one says "molecular replacement"

3D whole pattern fits for SFX data

3D whole pattern fitting has arrived: http://dx.doi.org/10.1107/S2052252516001238 ... and the samples are powders! ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietv

Something to read...

Probably of interest to several readers here, a new paper on methodology: "Use of Bayesian Inference in Crystallographic Structure Refinement via Full Diffraction Profile Analysis" Chris M. Fancher, Zhen Han, Igor Levin, Katharine Page, Brian J. Reich, Ralph C. Smith, Alyson G. Wilson & Jacob

Re: Asymmetry peak shape difference between (pellet/powder)

Hello, In the photo, the pellet is black and the powder is white. Why is that? Best Jon On December 8, 2017 3:35:20 PM GMT+01:00, "François Goutenoire" wrote: >Dear Rietveld users, > >We observe an unusual asymmetric peak shape on pellet and not when the >sample has been crushed in powder. >

Re: Literature on Rietveld limitations in nano materials

Hello, I think it would be nice if I could cite some critical discussion, or There are a couple of comments in the current issue of J.Appl.Cryst that might be interesting for you: https://doi.org/10.1107/S1600576719006575 Best, Jon

Re: Software re-binned PD data

If this rule is broken, such as the mode in FIT2D that smooths patterns by pixel-splitting) then one introduces correlation between points in the pattern Hi Brian, your comment has triggered me it seems :-) For SAXS and PDF it could be better to under-sample the data (see end), but for profi

Postdoc openings at ESRF

Dear Friends and colleagues, The ESRF is currently recruiting postdoctoral fellows for various beamlines to coincide with the upgrade to the EBS light source. Details can be found at: https://esrf.gestmax.eu/ https://www.youtube.com/watch?v=btZlcuLDY5U It is unusual for there to be so many

Re: GSAS-II - indexing TOF data

Hi Alex I think conograph does well for tof. Best Jon On April 13, 2020 8:24:55 PM GMT+02:00, Alexandros Lappas wrote: >Dear colleagues, > > > >We are working on some neutron time-of-flight (TOF) data and attempt to >index them within GSAS-II. > > > >As the low-angle detector banks contain i

Re: Computing code for hkl generation

Dear Martin, In addition to the other replies: I am currently looking for a Python xfab does this, see: https://github.com/FABLE-3DXRD/xfab/blob/fd3015dbd4145daf6a471765887c3aa139eb8bab/xfab/tools.py#L1039 or C/C++ module sginfo (https://github.com/rwgk/sginfo) offers a "simple_hkllist

Re: NIST SRM656 Analysis

Maybe a silly question: are you assuming you have the data on an absolute scale in order to do these calculations? Do things like surface roughness somehow not matter? Best Jon On 13/04/2022 11:56, Matthew Rowles wrote: Thanks Tony When I add the absorption edge correction to the silicon

Re: scattering factor for O2- ?

Hi Matthew, About the form factors : there is an active community doing "Quantum Crystallography" or charge density analysis with the IUCr. Some of them have been running a nice series of online lectures recently: https://qcrwebinar.chem.uw.edu.pl/ You can find many experts there, and there

FPSM : (was Re: [EXT] [External] Re: Step-like basline)

Hi Luca, Thanks for sharing the links to your method - I hope we can try it the next time we get stuck on identification. It is a shame to hear you were delayed for so long by J.Appl.Cryst. Did they ask you to cite some work from the Glasgow group as the commercial competitor? I have in min

Re: Misconduct

On 17/01/2024 09:40, Reinhard Kleeberg wrote: > "Automated mineralogy" Dear Colleagues, It sounds like there crisis for this community? I didn't see anyone mention the AI story that was also in the news: https://www.chemistryworld.com/news/new-analysis-raises-doubts-over-autonomous-labs-mater

Re: Rietveld ESD calc fortran code typo?

Dear Matthew That fortran snippet was corrected in Appendix 1 of Andreev's paper here: https://doi.org/10.1107/S002188989300891X It is a shame that implicit none was not part of fortran 77. The google search resul leading me to that was: https://www.researchgate.net/publication/359342753_Pro

Re: OMIT-map

It should be slightly different (https://doi.org/10.1107/S0021889887012755), see slide 9 here: https://brockhouse.lightsource.ca/media/uploads/xrd-school-2024/introduction_to_gsas-ii.pdf The calculation appears to be here: https://github.com/AdvancedPhotonSource/GSAS-II/blob/0b735da79488087ee5bc

Re: Comments on "Importance of matching software with hardware"

hed up into some spikes. Horses for courses... shouldn't a fit show information which all has approximately equal weighting in the minimisation algorithm? In the same way that difference/esd is often more illuminating than just a plain difference curve. Jon Wri

Re: Graphics

ld try MI/X. The URL to download MI/X from MicroImages' is http://www.microimages.com/ in the "Free Downloads" section. Hope this helps, Jon Wright On Tue, 30 Mar 1999, Hongwu Xu wrote: > Hi, Everyone, > > We have some neutron diffraction data collected and stored in t

Re: Errors in Rietveld refinement

r intensity or position. This fix says that the systematic problems are really just random noise and effectively increases the weights on the y_obs accordingly, giving larger esd's. Hope this helps, Jon Wright PS: See also GSAS/fullprof manuals and "Rietveld refinement guidelines"

Re: Combined neutron/x-ray refinements

lable as a beta version. It appears you can assign the statistical weight to each pattern, and in the example x-rays and neutrons are weighted equally. I'm wondering what the best choice is. Each observation comes with a statistical weight from the experiment? Isn'

Re: data format for GSAS using ISIS Polaris

Renyang, Your best bet is to log into isis and read the data back into genie, then write it out using gsasgen. Something like the following will read your data in (check with the instrument scientist, it depends on you login.com file as to which commands you need and what works) : >> lo w1 myfil

Combined neutron/x-ray refinements

oday. Incidentally does anyone have an example of a refinement where parameters are degraded by the combined fit *and* they agree with each other when two separate fits are carried out. Jon Wright PhD Student, Chemistry Dept, Cambridge Uni, UK. On 25 May 1999, Andrew Wills wrote: > Alan,

RE: Combined neutron/x-ray refinements

ing combined fits anyway? Apologies to the list if I am displaying my ignorance, sometimes it's the quickest way to learn. Jon Wright PS: Sorry to pick at your comments Paolo, it's a shame I'm not at RAL at the moment. Could have discussed it out over a coffee...

RE: Combined neutron/x-ray refinements

a neutron expert might look on this as an systematic error in the x-ray model :) Maybe not if one looks on the x-ray refinement as fitting of the electron density function, rather than the nuclear positions. For bonding studies it is the differences which are of interest! Jon Wright. PS: Any offers

Re: RIET: Are Spherical Harmonics for Preferred OrientationCorrection Evil?

On Thu, 16 Sep 1999, Dr.Joerg Bergmann wrote: > (high systematic error, bad difference plot, but low e.s.d.'s) > (low systematic error, good difference plot, but high e.s.d.'s). Apologies for diving off onto the general case, but does this make sense? You improve your model and the quality of y

Re:

There are two programs which spring to mind. GSAS and Fullprof both allow you to simulate neutron data. GSAS only does commensuate magnetic structures. See www.ccp14.ac.uk for link to the programs. Jon Dept. of

Re: RIET: TOF Neutron Web based programming resources?

Lachlan, You can get hold of the freely available CCSL code from your site and compile programs tf112m etc for doing TOF neutron Reitveld fits with magnetism too! Compiles with the free g77 compiler after some minor changes. All code is there, I have compiled and run it on a PC and presented the

Re: Bond length and angle ESDs

> On Thu, 23 Sep 1999, Ed Cussen wrote: > > We're forced to use CCSL for the superior peak shape description and > > so simply changing refinement program is not an option. I'm sure > > that this problem must have been encountered before and I'm suprised that > > there's not a 'standard' solutio

RE: As sent to the neutron mailing list

> ... not at all for magnetism, ... Ahem, magnetism - resolution is very useful, in certain (rare) cases. I guess that magnetic structures are not Armel's primary interest but in at least one case resolution was essential. (FeAsO4 from IRIS (TOF neutron) dataset, J.Phys:Condens.Matter 11 (1999) 1

Non standard space group settings.

generators. Is this possible with fullprof or would I run out of matrices there too? Thanks for any hints, Jon Wright -- >From international tables Fd-3m has a subgroup F 1 -3 2/m, which is a non standard setting of R-3m. I get the following output from expedt: Enter space group symbol

Cell constraints question

st squares matrix rather than the real space unit cell parameters? I haven't picked up yet on why the derivatives cannot be converted from w.r.t A* etc to w.r.t a etc. Is it just a time saving? Thanks Jon Wright

Re: Understatement of the year..so far

On Fri, 7 Jan 2000, Armel Le Bail wrote: > 15mn for checking a crystallography set is about my > performance too. Just out of interest, how long does it take people to pick up the error in entry number 17280, attached below. It's just a cell transformation from the cubic spinel [a->(a+b)/2, b->

Re: Understatement of the year..so far

On Mon, 10 Jan 2000, Armel Le Bail wrote: > The number of papers published in crystallography which > have incorrect space group or cell choice are quite numerous. > Databases should show exactly the same number (5-10% > or even more ??). But isn't one of the values of a database that it should

Re: Understatement of the year..so far

On Mon, 10 Jan 2000, Jaime Alamo wrote: > >PS: Has anyone found the error in that Fe3O4 entry yet? > > I think, It lacks the sqrt symbol, so ... > > [a->(a+b)/sqrt(2), b->(a-b)/sqrt(2)), c->2c] > > Also, it yields a negative setting that is less important. ?? I'm thinking of vector a b c,

Re: Absorption GSAS and TOF Instruments

me out right when absorbtion is taken into account. So absorbtion is only a problem when the peaks disappear. Hope this helps, Jon Wright PS: Can anyone tell me if sigma_abs goes as 1/v for Gd? Dept. of Chem

Re: Asymmetry

Asymmetry is discussed in: J.Appl.Cryst (1984) 17, p.47 - van Laar & Yelon (+ ref's therein) The above method is implemented in: J.Appl.Cryst (1994) 27, p.892 - Finger, Cox & Jephcoat. and source code for this peakshape is available. (They also talk about secondary monochromators). Hope th

Fitting lorentzian tails in GSAS

e (with an low angle asymmetry correction) would be also be appreciated. Thanks in advance, Jon Wright Dept. of Chemistry, Lensfield Road, Cambridge, CB2 1EW Phone-Office 01223 (3)36396; Lab 01223 (3)36305; Home 01223 462024

Re: GSAS and CYCLIC refeinements ?

Alex, There's something below which might help you. You'd need to set up a refinement with a .exp file and a .raw file with the same root name (eg fit.raw and fit.exp). The batch file then takes two arguments, the data file name (eg run1.raw) and the root of name of the .exp file (eg. fit for fit

Getting background subtracted r-factors from GSAS?

Hi all, Does anyone know if there is a quick way of getting at a background subtracted r-factor within GSAS? (Without wishing to start a discussion about why I might want one) Thus far the only idea I've had is to calculate it by hand from hstdump, but that appears to be listing the background as

Re: Lp correction in GSAS

being applied to data before presenting it for refinement, which sounds ugly. Fullprof has a flag for transmission geometry, hence my question. Thanks in advance, Jon Wright PS : If someone could refer me to simple derivatio

Re: Powplot problems with NT

On Tue, 8 Aug 2000, Brian H. Toby wrote: > Brian Mitchell wrote: > > > > I have recently installed Windows NT on my laptop and find that the GSAS > > graphics plot takes an excessive amount of time to appear. I did not have > > this problem with Win 98. > > > > Any help/advice appreciated. > >

RE: Riet_L: Scale factor in Rietveld (with a question for Bob and Juan)

Paolo, On Fri, 15 Sep 2000, Radaelli, PG (Paolo) wrote: . > Finally, here is a question for Bob and Juan. To me, it would be much more > natural to remove Vo from the scale factor, that is to redefine a new S' so > that > > Y=S'*L*A*E*|F|^2/Vo^2 and S'=K*Ltot*f > > This way, the scale fa

Re: Neutron diffraction with boron

Armel wrote: >>And yes, the measurements have been done. >I would not call Science giving the MgB2 atomic >coordinates, already known. Was this meant to be serious? Checking for any subtle structural changes around Tc would be (has been?) a worthwhile investigation. Something easily worthy of t

Re: new GSAS

Bob, Ask and it shall appear! I'm very impressed by your speedy creation of the new GSAS windows version. I've not found any of these zero length files yet, so maybe that's platform specific? No file named expedt has turned up anywhere on my hard disks. Thinking back I remember there used to be a

Re: Neutron diffraction with boron

At 04:48 PM 3/29/01 +0200, you wrote: > >>You really think that MgB2 will give more ? Maybe... just routine to do so. > >Armel, it was you who asked if boron was possible with neutrons, and when >you are told that it is, you say that anyway it is borin' (excuse the pun :-) I hadn't realised ther

Update to PRODD rietveld software

number of undesirable features probably remain, so all feedback is welcome. Source code is available from me or Bruce Forsyth. Jon Wright ([EMAIL PROTECTED])

Re: Hamilton's test

to the confusion. Cheers, Jon Wright

Re: Resolution in powder diffraction

Brian H. Toby wrote: > ... Besides, Q > is the Fourier conjugate of x (the coordinates); d-spaces have no > physical significance. D-spaces can mislead a novice into correlating > reciprocal space distances with real space distances. D-spacings are distances between lattice planes and provide m

RE: One GSAS question.

Better to work with a single phase and use the red and black symmetry operators, in my opinion. You might have to lower the symmetry for some magnetic structures and add contraints on the positions accordingly, but this saves a lot of headaches, even if it creates a few by making you think about t

Re: rietveld program (fwd)

At 05:51 PM 7/3/01 +0200, Luca Lutterotti wrote: > - only one type of peak is inside the program but the asymmetry is > handled in a much better way than in other programs (is a real > convolution as it should be) so I never found a pattern that I was not > able to fit very well with my functi

Re: x-ray scattering factors values for B-1

Asking purely as someone who once studied chemistry and has a selective memory about boron; what is the compound you're looking at? I remember things like (BH4)- and hearing about Wade's rules, but not isolated B- anions. Isn't boron even less electronegative than carbon? Could you get away with n

Re: Bragg R and GSAS

In comparing refinements with different powder datasets there is no "number of observations" in common usage and no 10:1 rule of thumb. Broadly, this means "crappy" data with a chemically unreasonable model can sometimes give much better figures of merit than a good structure with "good" data.

Re: Is it really preferred orientation problem?

> Like Rp, Rwp, Chi2, RB are respectively from 3.96, 5.33, 2.68, 5.80 > to 3.35, 4.42, 1.85, 3.07. This should pass a test of statistical significance. That does not mean it really is preferred orientation, but if it is not preferred orientation, then you

Re: CIF to powder pattern

With all the file converters floating around, what are the chances that we are going to proliferate files with corrupted formats? I have gotten some files already that were supposed to be "GSAS files" but didn't have 80 columns, had blank lines, etc., and I assume they were made by file converter

Re: Magnetic Form Factor of Ru+4

Ozhan Unverdi wrote: Could someone give me the magnetic scattering factors of Ru+4 please? www.google.com searching for "Ru4+ magnetic form factor" gives 17 results. One of them is Sidis et al, "Evidence for Incommensurate Spin Fluctuations in Sr2RuO4", Phys. Rev. Lett (1999) 83, 3320. In

Re: Is it really preferred orientation problem?

zhijian fan wrote: *> Like Rp, Rwp, Chi2, RB are respectively from 3.96, 5.33, 2.68, 5.80 > to 3.35, 4.42, 1.85, 3.07. This should pass a test of statistical significance. * I made a hypothesis testing. H0: It needs not PO correction. The model with PO correction: G1=sum[wi

Choosing origins

I am amazed by the flow of miss information that flows on this list whenever an apparent problem with a space group comes up. I asked a related question on sci.techniques.xtallography a few weeks ago, but have yet to hear anything, misinformation or otherwise. If anyone here can give me some

Re: Choosing origins

Bill, Thanks! Exactly what I was after and I'd never have guessed it from the title... Jon On Wed, 31 Mar 2004, David, WIF (Bill) wrote: > Hi Jon, > > A lot of what you'll need is in the back of the International Tables Vol. A > in Chapter 15 which goes under the snappy title of "Euclidean

Re: GSAS informations

Nicolae Popa wrote: the condition to not violate some elementary principles, in particular, here, the invariance to symmetry. Dear Prof Popa, I had been meaning to implement the quartic form for peak width in a refinement program for some time, but did not figure out how to generate the const

Re: GSAS informations

Not violating symmetry restrictions you may either have the sphere with the terms 11=22=33 and 12=13=23=0 or something else allowing the 12=13=23 terms to be equal but different from 0. These two possibilities are all you can do in cubic symmetry with h,k,l permutable. If I am not wrong. The (111)

Re: GSAS informations

>... to answer to your (too) long questions. May be later, OK? Going back to this quartics versus ellipsoids peak broadening stuff, maybe I can summarise: Why should the distribution of lattice parameters (=strain) in a sample match the crystallographic symmetry? If the sample has random, isolat

Re: fundamental parameters approach

Is the fundamental parameter approach better than mathematical approach used in most of the Rietveld refinement programs? Perhaps someone is about to explain the difference is between "fundamental parameters" and anything else? I used to think it might mean convoluting something which was actu

Re: gnuplot, powder pattern

Freidrich, Assuming you can use gsas2cif (or reflist or something) plus a text editor to get an ascii file containing a column of peak positions then in gnuplot I use: top=0 bottom=-100 set bar 0.0 plot "hklfile.dat" u (n):(bottom):(bottom):(top):(top) with financebars where n is the column in y

Re: Rietveld refinement and PDF refinement ?

Well, that is an old chestnut that Cooper and Rollet used to oppose to Rietveld refinement. I think Rollet eventually agreed that Rietveld was the better method. Has Bill really gone back on that ? The difference between the two approaches are just an interchange of the order of summations wit

Re: Rietveld refinement and PDF refinement ?

Bob, This exactly what is needed when the sample is a mixture of amorphous and crystalline components. But what happens when the material is a single crystalline phase with some coherent defects? Don't the defect <-> average structure correlations start to dominate, and separating components is

Re: Magnetic Visualisation in GSAS

vrstplot, which is part of the GSAS package certainly used to plot the magnetic moments into a VRML file. You can view this with various tools, many of which are windows based, and they should allow you to fly around the structure as a 3D object. It also plots fourier maps in 3D. Good luck, Jon

Re: TOPAS-Academic

Alan, The "planned plugin architecture" sounds interesting. How concrete are the plans? I'm interested in auto-generation of restraints for proteins and fourier mapping at the moment... Regards, Jon alan coelho wrote: Dear all, An academic version of BRUKER-AXS TOPAS is now available to degree-g

Re:

Alberto, Check you have the right polarisation correction. Synchrotron ~ 1, laboratory typically 0.5 with no mono... HTH, Jon Alberto Martinelli wrote: Dear all, I've got a problem with the Rietveld refinements of synchrotron data. I'm using Fullprof and the problem is that the overall B, and t

Re: Google Scholar

Alan wrote: BTW, Google.com ranks ILL WWW pages 3rd worldwide, in both Condensed Matter and Crystallography, ahead of IUCr. To see what this means in practice, try a Google search on inorganic structure :-) http://rankwhere.com/google-page-rank.php?url=www.ill.fr www.ill.fr has Google PageRank 7

Re: How to output correlation matrix in GSAS

Least matrix is in the .CMT, according to the manual. Alter the printing options in expedt to get it to print correlations on the normal list file. HTH, Jon On Tue, 30 Nov 2004, Sang-Heon Shim wrote: > Dear Experts, > > This might be an FAQ. Where (in which file) can I find correlation > ma

Rwp versus R(F^2)

Hello everyone, Has anyone else noticed that sometimes when comparing two models Rwp is better for one and R(F^2) is better for the other? The case I am looking at is spacegroups P3 versus P-3, with the non-centrosymmetric structure having more degrees of freedom and therefore very slightly bett

Re: K alpha-2 stripping

Gerard, If you "strip" the K-alpha-2 using a monochromator, then you might get better data. If you don't have that option, then fitting the data as they come is probably a better approach, as you don't run the risk of introducing artifacts. Jon Gerard, Garcia S wrote: Dear everybody, How impo

Re: Change format

Brian Toby wrote: If the numbers are real values then they are not counts. They may be counts per second or something else. One needs to have uncertainty estimates for these intensities before one can do a meaningful Rietveld refinement (with any code). Following the above procedure, by multipl

Re: Questions about the asymmetry correction

Xianqin, How did you calibrate the sample detector distance? For reliable absolute cell parameters it is very difficult to get good data with an area detector. One approach is to mix a standard material into the sample. As a gross approximation for small angles (in radians): sin(theta) ~ theta

Re: Level of Preferred Orientation

Dear Bhuv > pattern and I have corrected possible graininess with spherical [...] > The data I have collected is on a image plate (only one frame). Not sure I understand? If you have a 2D image showing powder rings then you should have some very good ideas about the level of granularity or textur

Re: Mean vs. Median to reduce bias in grainy intensities (was Re:

Alex, While I can understand the general rationale for the idea (minimize the weight of the very strong reflections to the final integrated intensity for the reflection), could you expand further on your level of success and any analysis you have carried out on this plan? The massive random spike

RE: Mean vs. Median to reduce bias in grainy intensities (was

> Of course, both are eventually linked, so the manner in which applying a > median filter to the 2-D image prior to producing a histogram affects > the whole procedure is what I was wondering about. Make a radial transform ("cake") BEFORE you apply any filters. > According to Jon's > comments,

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