pseudopotentials

• 2.1 Where can I find pseudopotentials for atom X?
• 2.2 There are so many pseudopotentials, which ones should I use?
• 2.3 Can I mix USPP/NCPP/PAW ?
• 2.4 My total energy depends upon the pseudopotential!
• 2.5 Where can I find pseudopotentials for rare-earth X?
• 2.6 Is there a converter from format XYZ to UPF, or vice versa?
• 2.7 Where can I find pseudopotentiaIs for hybrid/nonlocal functionals?

A proper choice of pseudopotentials is a pre-requisite for any successful calculation. You should always test pseudopotentials on simple systems before trusting them!

2.1 WHERE CAN I FIND PSEUDOPOTENTIALS FOR ATOM X?

See the pseudopotential page on this web site. There you can find several tables, pointers to other tables, indications on what to do if you do not find the pseudopotential(s) you need. In case you inquire for a pseudopotential on the mailing list, please specify which kind of pseudopotential you need (norm-conserving, ultrasoft, PAW, full- or scalar-relativistic, for which XC functional, and, for many elements, with how many electrons in valence).

2.2 THERE ARE SO MANY PSEUDOPOTENTIALS, WHICH ONE SHOULD I CHOOSE?

Those that fit your needs in terms of transferability and computational efficiency, for the calculations you want to perform. Choosing good pseudopotentials is an important part of an electronic-structure calculation. Are you sure you really like somebody else do this for you? Please have a look at the various links and resources of the pseudopotential page.

2.3 CAN I MIX USPP/NCPP/PAW ?

Yes, you can (when possible, of course: a few kinds of calculations are not available with USPP, a few more are not for PAW). A small restrictions exists in cp.x, expecting atoms with USPP listed before those with NCPP, which in turn are expected before local PP’s (if any). A further restriction, that can be overridden, is that all PP’s should be generated with the same XC. Otherwise, you can mix and match. Note that it is the hardest atom that determines the cutoff.

2.4 MY TOTAL ENERGY DEPENDS UPON THE PSEUDOPOTENTIAL!

That’s correct: absolute energies depend upon the kind of pseudopotential(s) used. Only energy differences are physically relevant. Differences in absolute energies may be especially large if you compare pseudopotentials with different number of electrons.

2.5 WHERE CAN I FIND PSEUDOPOTENTIALS FOR RARE-EARTH X?

Please consider first if DFT is suitable for your system! In many cases, it isn’t (at least “plain” DFT: GGA and the like). If you are still convinced that it is, see above.

2.6 IS THERE A CONVERTER FROM FORMAT XYZ TO UPF, OR VICE VERSA?

What is available (no warranty) is in directory upftools/. You are most welcome to contribute a new converter.

2.7 WHERE CAN I FIND PSEUDOPOTENTIAIS FOR HYBRID/NONLOCAL FUNCTIONALS?

Short answer: nowhere, for the time being. Use pseudopotentials for the non-hybrid functional that is closer to the hybrid you like: PBE for PBE0 and HSE, BLYP for B3LYP. Same for nonlocal (e.g. vdw-DF) functionals: use pseudopotentials generated for the closest GGA functional.