Re: [Ifeffit] Recommendations for DFT/computational chemistry software?

Please correct me if I'm wrong, but I get the impression that if you don't know exactly what you're doing, these programs will cheerfully return wrong answers. There seem to be many parameters and choices to be made. I once looked at Quantum Espresso but gave up when I saw that the script for doing MD on a single water molecule ran for over a page of incomprehensible code. I didn't see anything that looked like a step-by-step tutorial or manual. Gaussian with the Gaussview UI is simple enough for an experimentalist like me to use; are there better packages out there which are as well? I also get the impression that you need some pretty hefty compute power. A Linux system is probably to be preferred over Windows. One of these days I should learn Python, not just for this stuff. mam On 8/16/2013 7:27 AM, Paul Fons wrote:

Hi Scott, I have been dabbling in DFT for a while. There are many free packages around, but if you would like to model XAFS as well, I would suggest an all electron code for accuracy (such as Wien2K). For general purposes, I am also using VASP and CASTEP. The former uses projector augmented waves and the other ultrasoft pseudopotentials. VASP is fast and scalable to the largest machines and is designed from the ground up for quantum molecular dynamics. Both VASP and CASTEP use pseudopotentials whereas Wien2K uses a linearized augmented plane wave basis (read as radial wavefunctions and Ylms in a sphere about each atom and plane waves between spheres with boundary condition matching at the surface of the spheres. This way it is possible to model even the 1s electrons for heavier atoms and yes it does affect valence electron wavefunctions via orthogonality. All of these approaches are single particle DFT approaches, but it should be good enough for a start, if you want to go beyond these, with solutions of the Bethe-Saltpeter equation (electron and a hole) things get complicated and expensive (in terms of computer time) very quickly.

If you are interested in free software I would suggest gpaw, quantum espresso, and abinit. I would also suggest learning the atomic simulation environment in which you can program multiple codes in python (and even solve for maximally localized Wannier functions in a few lines of code!) (Atomic Simulation Environment — ASE 3.8.0.3329 documentation https://www.google.co.jp/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CC8QFjAA&url=https://wiki.fysik.dtu.dk/ase/&ei=WDYOUs2vBsaHkwX3h4H4Cg&usg=AFQjCNGJtTBmzvPVE0wgaKpLivT6K59Whw&bvm=bv.50768961,d.dGI).

What exactly are you trying to do? If you are looking for a non-spherical approximation for EXAFS beyond feff8's spheres, you might try FNDMES by Joly as well.

Cheers, Paul

On Aug 12, 2013, at 10:30 PM, Scott Calvin mailto:scalvin@sarahlawrence.edu> wrote:

...

Hi all,

I know many of you use DFT calculations to help model EXAFS data for molecular compounds. Do you have recommendations for good computational chemistry packages, commercial or otherwise, to use for that purpose?

--Scott Calvin Sarah Lawrence College _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov mailto:Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

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