Dear Nicola, Many thanks for the prompt reply.
> first question - would mp work? This we haven't tried. Since mv and mp give very similar numerical results for a given smearing width I guess I thought I should try something a bit different, i.e. gauss. > In terms of "structure" of the smearing function, gaussian is > the smoothest, then mv, then mp. So if there were an intrinsic problem > with states at the fermi energy, it should be even more apparent in > mp . I see. I'll surely take a look at mp then. > As a general comment, the role of smearing is to help improve the > accuracy of k-point sampling - and so the 0.01-.02 you are using > is exactly in the right ball park. Sure. Actually using a larger kpoint set sometimes helps but it gets a bit tricky because if you've run a number of calculations with a smaller kpoint set (say for a publication), then you want to stick to that. So sometimes we actually try with a larger set and then once (if) we see convergence revert back to the one we want. This only works about half the time though. Our g-Al2O3 + precious metal atom calculations were particularly notorious so we got to try this close to about 20-30 times. > A side effect (a positive one) for smearing is to help convergence > in iterative algorithms (as in PWSCF) - for that side effect, > 0.01-0.02 is actually small, and so the more "structure" of > mv or mp could hamper the iterative convergence. So you could try > converging first with a larger smearing (.04 to .08), and then restart > with the "right" one. I'd be somewhat surprised to see much difference > between gaussian/mp/mp for say 0.07 Ry ~ 1 eV of smearing. Of > course, such a large smearing shoudl be used only to help > get convergence, and then reduced. Oh, wow. We haven't done that since I'm a bit scared of large smearings but this is a great suggestion. We do make use of a similar trick though, namely going back and forth between an initial gauss shot followed by mv but I'm afraid this works even less than half the time. But I will definitely give this a shot and report back the result. Many thanks once again. Best wishes, Hande -- Hande Toffoli Department of Physics Office 439 Middle East Technical University Ankara 06531, Turkey Tel : +90 312 210 3264 http://www.physics.metu.edu.tr/~hande
