Hello Stefano, Fantastic response! Thank you very much. I am using such a large super-cell to look at PbS surfaces via slab models. I am hoping that the finer grid works, but if it doesn't I will look into changing the bands.x code. It appears as if the code picks the first point it finds with abs(pro) > 1%; wouldn't it be better for it to find the k-point with the highest value of abs(pro)?
Also, this is probably a novice question, but would I have to recompile all of QE after I make changes to bands.x? Thank you for your response; I'm glad I asked since this has been giving me trouble for some time. -Hank Seeley Chemistry PhD student University of Oregon On 2016/01/13 14:29, stefano de gironcoli wrote: > Hi Hank, > bulk PbS has 2 atom per cell. why do you need 20-30 ? > > bands.x "follows" a band based on the overlap of the wfcs in two > neighboring points.. > it accepts the band on the basis of a rather small overlap threshold > > ... somewhere around line 350 in $espresso_root/PP/src/bands.f90 > pro=cgracsc(nkb,becp%k(:,jbnd),becpold%k(:,idx(ibnd)), & > nhm, ntyp, nh, qq, nat, ityp, ngm, NEW, old, > upf) > ENDIF > ! write(6,'(3i5,f15.10)') ik,idx(ibnd), jbnd, abs(pro) > IF (abs (pro) > 1.d-2 ) THEN > il (idx(ibnd),ik) = jbnd > GOTO 10 > ENDIF > ... > > this is probably ok in most cases when there are few bands to chose > from and only one is the "right one". In your case there are many bands > and maybe there are many not too wrong bands that fulfill the > threshold..:-( > I would try to > 1) uncomment the write statement and see what are the typical > values > of abs(pro) you get. > if everything is fine there should be only one jbnd band for each > idx(ibnd) band that is significantly different from zero (much more > than > 1.d-2 i would expect).. If you have more than one jbnd band that > exceeds > the threshold for a given examined idx(ibnd) then the code may do the > wrong assignment > 2) if this is the origin of the problem i would try to play with > the > threshold to induce the code to make the proper assignment > > using a finer k point grid should also work but I would say that 15 > points in a 20-30 atom cell should already be enough ! > > good luck, > > stefano > > On 13/01/2016 21:52, Henry J Seeley wrote: >> Hello everyone, >> >> I'm using bands.x to assign eigenvalues to specific bands of PbS. I >> have >> fairly large supercells (20-30 atoms), so my bands are dense with lots >> of crossings. When I run bands.x it incorrectly assigns bands >> resulting >> in erratic band diagrams (e.g., bands suddenly jump across the bandgap >> to connect conduction and valence eigenvalues). What are the potential >> causes of this error? >> >> Perhaps I am not sampling my k-points densely enough; I have >> approximately 10-15 points per sampling line. I plan on increasing >> this >> density to 50 kpts per line, and will report back if this solves the >> problem. I am somewhat in a rush to get these results though, so if >> anyone has some insight it would be much appreciated. >> >> Also, assuming there is a solution to this problem, is band.x capable >> of >> sorting a 2D grid of kpoints into bands? I am interesting in >> generating >> contour maps. >> >> Thank you, >> Hank Seeley >> Chemistry PhD student >> University of Oregon >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
