Re: [Ifeffit] Ifeffit Digest, Vol 117, Issue 24

Hi Joshua, Thank you for your comment. Like you said, I tried FOLP with value from 1 to 1.3 and it didn't change the calculated spectrum much. It's very time-consuming when FOLP reached 1.3, taking more than 3 hours to finish the calculation on my laptop. On using 0.8 for hydrogen, actually I'm going to calculated a sample with lots of Li in it. Do you suggest using a similarly small number of FOLP for Li, in an analogy to H? The other thing I want to ask is the CRITERIA card in Feff9. It seemed that once I asked the program to calculate XANES, the CRITERIA card in the software cannot be checked. It can only be checked if I selected EXAFS calculation mode. Is there any way to solve this? thanks again for all your answers. Enyuan On Mon, Nov 26, 2012 at 5:33 PM, wrote:

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Today's Topics:

1. Re: FOLP card (Joshua Kas) 2. Question on Glitch in FEFF for Ru EXAFS measurements (Dooshaye Moonshiram) 3. Re: Question on Glitch in FEFF for Ru EXAFS measurements (Bruce Ravel) 4. Re: Question on Glitch in FEFF for Ru EXAFS measurements (Bobrik, Michael)

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Message: 1 Date: Mon, 26 Nov 2012 10:56:19 -0800 From: Joshua Kas To: ifeffit@millenia.cars.aps.anl.gov Subject: Re: [Ifeffit] FOLP card Message-ID: < CAHuhYRkW5R6iSLjSc03aNnfVRmX+YWvUiNB4HDF7CDEJLNNSjw@mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1"

Hi Enyuan, I don't really know a rule of thumb for ionic bond v.s. covalent bond, but by default, the FEFF code will automatically choose reasonable muffin tins in most cases, and most of the time it overlaps them by ~15%, i.e. FOLP 1.15. In many cases, the overlap doesn't change the structure in the XANES a lot until you get far from FOLP 1.0. However, there are some special cases. For example, we have found that using FOLP 0.8 for hydrogen atoms seem's to work reasonably well in the XANES. This is because of the short bond lengths of H. In addition, there are cases where one atom is fairly isolated from the others, i.e., cage like structures, where FEFF can't overlap the potentials, and setting FOLP to something smaller than 1.0 is essential to make the code run. I would start by letting the code choose the muffin tins automatically, then change them and see how the results change. If the changes in the XANES are small, you probably don't have to worry about FOLP. Otherwise, this is probably a limitation of the spherical muffin tin potential. The best thing to do in that case, is to compare the DOS (LDOS) with a calculation from a full potential electronic structure code, i.e., WIEN2K, ABINIT, QUANTUM ESPRESSO, etc. This can give you confidence in the FEFF calculation, or lead you to the best values for FOLP. You could also use the FOLP values to get the best comparison to experiment, but in some cases you may be fitting many-body effects, which can lead you to the wrong conclusions about your system. Cheers, Josh Kas

On Mon, Nov 26, 2012 at 7:53 AM, wrote:

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