Dear Habibi, > I have been trying to use pp.x on a Cr(001) slab, and I would like to > calculate PDOS in a box above de surface. I guess you are referring to projwfc.x rather than pp.x
> As a matter of fact, I would like to see the decrease of the > wavefunctions in the vacuum, by analysing the PDOS in boxes at different > heights. Maybe you could be more interested in using indeed pp.x to extract the DOS as a function of position. To make the distinction clear (?): 1) the local DOS is a function of position and energy, say D(r,E); 2) projwfc.x allows to compute and plot *as a function of E*, the integral of D in a specified volume (box) 3) pp.x allows to compute and plot *as a function of r*, the integral of D in a specified energy window (see plot_num=10) It seems to me that this last point is what you are interested in. You have to choose your energy window. Alternatively, pick up just one wavefunction (plot_num=7). > After a calculation on small boxes, I would like to have, now, an > average type box, on the whole surface, so let's say a pavement-like > box. > > After a pp.x regular PDOS calculation, I have noticed that the > segmentation along x and y direction is 30, I thought that regarding > this information, I could take a box with a width of 30 on x and y > direction for another pp.x calculation with the boxes to get the big box > I need. If your FFT grid contains 30 points, you can select the full cell (in that direction) by putting irmin=1 and irmax=30. See example16. (irmin=0, from your input, is equivalent to 30; the first and last points you specify are INCLUDED). > Hence, pp.x generates a .xsf file for visualizing the boxes. When I > would calculate it with a small box (width=2 on x and y directions, ie > irmin(1)=1, irmax(1)=3 in the pp.x input file), I could see the box with > xcrysden. However, using the big values (30) for my boxes boundaries, I > cannot visualize them. But I still get a result about ldos in the boxes. The box is visualized as xsf files with 3D datagrids, valued 1.0 inside the box volume and 0 outside (visualize them as isosurfaces with isovalue 0.5). If the box is as large as the unit cell, all values are =1.0 and no isosurface=0.5 can be shown. There's no box boundary, in a periodic world. > My questions are the following : how can I be sure that the ldos > calculation are actually done within my big boxes boundaries? Is it > correct to use that big segmentation in the first place? Try a few tests to practice: compute the LDOS in the full cell; compute it in two halves; ... Notice that augmentation charge contribution is not included, so you should use norm-conserving pseudopotentials if you want to compare this to the full DOS. Hope this helps, Guido Fratesi -- Guido Fratesi Dipartimento di Scienza dei Materiali Universita` degli Studi di Milano-Bicocca
