Re: [Ifeffit] Ifeffit Digest, Vol 104, Issue 9

For the first shell, I used cubic phase as my starting model and that gave a pretty good fit. However, when I take wurtzite phase as my starting model and vary two bond lengths (both Zn-S, with the axial bond longer by only 0.004 Ang) independently, my delr and ss go crazy. I think that as the first two S subshells are so close to each other, my data can't identify them (delr and ss) independently. So I defined their delr and ss to be same and the results match pretty well with the cubic phase. The r-factor and reduced-chi square with the two models are very similar.Thanks a lot ! On Sun, Oct 9, 2011 at 10:30 PM, wrote:

Send Ifeffit mailing list submissions to ifeffit@millenia.cars.aps.anl.gov

To subscribe or unsubscribe via the World Wide Web, visit http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit or, via email, send a message with subject or body 'help' to ifeffit-request@millenia.cars.aps.anl.gov

You can reach the person managing the list at ifeffit-owner@millenia.cars.aps.anl.gov

When replying, please edit your Subject line so it is more specific than "Re: Contents of Ifeffit digest..."

Today's Topics:

1. lifetime broadening of pre-edge peaks? (Matthew Marcus) 2. Re: Zinc Sulfide fitting (JeongEunSuk)

----------------------------------------------------------------------

Message: 1 Date: Sat, 08 Oct 2011 14:36:56 -0700 From: Matthew Marcus To: XAFS Analysis using Ifeffit Subject: [Ifeffit] lifetime broadening of pre-edge peaks? Message-ID: <4E90C278.3060602@lbl.gov> Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Is the core-hole lifetime broadening of pre-edge XANES peaks the same as at the main edge? I'm looking into issues of de-noising of XANES epsctra, so need to figure out how narrow real features can be. mam

------------------------------

Message: 2 Date: Sun, 9 Oct 2011 07:06:52 +0900 From: JeongEunSuk To: ifeffit Subject: Re: [Ifeffit] Zinc Sulfide fitting Message-ID: Content-Type: text/plain; charset="ks_c_5601-1987"

hello

Two phase can be mixed in ZnS. You need to check r-factor and reduced-chi squrare with two model. If you want to fit only first shell, I suggest. first use cubic zinc-blende model in FEFF, and check goodness of fit. second, fix the bond length of 3 bonding length and change the bond length of a rest. when you use my suggestion, the variables in Artemis is delrS1(changable), sigmaS1(changable), others(fix)

Date: Thu, 6 Oct 2011 13:32:24 +0530 From: soham.chem@gmail.com To: ifeffit@millenia.cars.aps.anl.gov Subject: [Ifeffit] Zinc Sulfide fitting

Dear Ifeffit Community,

Zinc Sulfide exists largely in two phases, either the cubic zinc-blende (F-43m) phase, or the hexagonal wurtzite (P63cm) phase.

The details of the NN distances are as follows :- 1. For cubic phase, the NN distances (Zinc to Sulfur bond lengths) are 2.3028 Angstroms each, 4 such bonds exist in a tetrahedral arrangement; 2. For hexagonal phase, there are 2 different NN distances (Zinc to Sulfur bond lengths) 3 bonds having the length 2.3421 Angstroms each, and 1 axially elongated bond of length 2.3465 Angstroms. So they differ only by 0.0044 Angstroms !

I am performing a first shell fit to Zinc Sulfide which exists in the wurtzite phase (hexagonal_P63cm). However, I could fit it quite well taking the cubic phase (Zinc blende_F-43m) as my starting model. The only thing is that since bond distances are higher in a hexagonal phase than the cubic phase, I end up with a considerable delr as I underestimated my starting bond length value. Taking a wurtzite model involves defining two different bond lengths (which differ only by 0.0044 Angstroms !), paths 1 and 2 in the FEFF, whose sigma^2 values are quite similar. This gives unusually large delr values and high sigma^2 for the longer axial bond, which looks suspicious !

Do I really need to define the two bond distances separately of so close values? Or taking a cubic phase will be sufficient? Please find the attached project file (artemis.apj) where I have tried out some simulations with both cubic and hexagonal models.

Here are a few details you asked for :-

The sample is a thin layer, it's pretty homogeneous and had no pinholes during measurements. The fit details are :- k_min = 2, k_max = 14 R_min = 1, R_max = 3 The potential is self consistent in these calculations Fitting was performed in the R-space

Best regards, Soham.

_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit