Dear Gabriele and pwscf users<br><br><br>Perfectly I am sure that the positions of atoms is exactly correct. Note that the input is belong to a (1*1) slab <br>and indeed you could not see a honeycomb ! but It is easy to see a honeycomb when you have a (2*2) slab like this:<br>
<br>C 0.000352513 0.001055549 0.000000000 <br>C 2.459305478 0.000933657 -0.008798962<br>C -1.229191611 2.130502759 -0.008802160<br>C 1.229819481 2.130516670 -0.008801637<br>C 0.000327447 1.420695799 -0.007291549<br>
C -1.229173562 3.550193436 -0.007292113<br>C 2.459296954 1.420621766 -0.009715082<br>C 1.229852979 3.550208684 -0.007292392<br>C 0.000507119 0.000488868 3.187515573<br>C 2.459486429 0.000491165 3.187352189<br>
C -1.228985445 2.130026298 3.187352283<br>C 1.229997454 2.130026366 3.187352273<br>C 1.229970852 0.710263879 3.187439366<br>C 0.000476982 2.839800509 3.187332530<br>C 3.688943914 0.710263968 3.187439418<br>
C 2.459456202 2.839797012 3.187439363<br>C 0.000212609 0.000545761 6.403453823<br>C 2.459191836 0.000545600 6.403451859<br>C -1.229278051 2.130084159 6.403451942<br>C 1.229700861 2.130084205 6.403451921<br>
C 0.000121431 1.420208410 6.403892505<br>C -1.229369239 3.549746424 6.403892711<br>C 2.459100653 1.420208253 6.403888354<br>C 1.229609673 3.549746469 6.403892772<br><br> a = 4.9178,<br>
b = 4.9178,<br> c = 16.4112, 10 angstrom vacuum<br><br><br>Also, see the "<a href="http://As.vcs00.in">As.vcs00.in</a>" example in the "VCSexample" folder of quantum espresso 4.2. In this example a vc-relax calculation <br>
has been performed using the max_seconds and dt keyboard. <br><br>Many Thanks<br><br>
I hope one helps these problems mentioned below.<br><br><br><br><br><br>>Are you completely sure? You can find as an attachment a picture (from<br>
>xcrysden) of the central graphene layer according to the positions given<br>
>in your input. You can now judge if it looks like a honeycomb lattice.<br>
<br>
> Yes, indeed the high ecutrho is important for ultrasoft<br>
> pseudopotentials. About the rippling : It was my mistake in selecting<br>
> a wrong pseudopotential which has a hole. Nicola had explained it<br>
> before and accordingly I solved it. The graphite surface is not<br>
> ripple. When I use the "max_second=6000 and dt=150" the job completes<br>
> very fast as the example of pwscf. Is the using of such keyboards<br>
> plausible?<br>
<br>
>Please spend some time reading Doc/INPUT_PW to understand the meaning of<br>
>the _keywords_. dt is used only for molecular dynamics runs, not<br>
>relaxations, while max_seconds has nothing to do with how fast your job<br>
>is completed.<br><br><div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
> Dear Gabriele Sclauzero and pwscf Users<br>
<br>
> Many thanks for your attentions. The cell dimension and the positions of<br>
>the atoms are exactly correct. Yes, indeed the high ecutrho is important for<br>
>ultrasoft pseudopotentials. About the rippling : It was my mistake in<br>
>selecting a wrong pseudopotential which has a hole. Nicola had explained it<br>
>before and accordingly I solved it. The graphite surface is not ripple. When<br>
>I use the "max_second=6000 and dt=150" the job completes very fast as the<br>
>example of pwscf. Is the using of such keyboards plausible?<br>
>As I mentioned before I had used the optimized cell parameters of (1*1<br>
>slab) for vc-relaxing the (2*2 slab) and I expected to see the results very<br>
>soon but the calculation was time consuming while there was only a very very<br>
>bit change of the cell dimensions during this 16 hours. There is only 1-3<br>
>iterations per each step in the output file and each of them was time<br>
>consuming. The job was completed after about 50 steps.<br>
<br>
-------------------------------------------------------------------------<br>
<br>
> Dear Masoud,<br>
><br>
> first I would suggest you to use bfgs as the algorithm for both ions and<br>
> cell dynamics. Excepted particular cases, it should reach the minimum much<br>
> faster.<br>
><br>
> Also, why do you specify the cell with such an unusual way. You simply need<br>
> celldm(1) and celldm(3) with ibrav=4 if you want to describe an hexagonal<br>
> lattice. Other suggestions: your ecutrho looks really large to me, do you<br>
> really need it. On the other hand, degauss might be too large to describe a<br>
> spin-polarized system.<br>
><br>
> Then, are you sure that you have built correctly your supercell? It looks<br>
> like there are some C-C bonds much shorter that others in the central<br>
> graphene plane (1.2 instead of 1.4 angs). Please check again your structure.<br>
> In general, you can expect that if you relax the atoms in the supercell<br>
> some kind of surface-reconstruction may appear, since you leave more freedom<br>
> to atoms to rearrange in structures with larger periodicity. I don't think<br>
> this is the case for graphite, but you may find some ripples (as you<br>
> mentioned in your earlier emails, if I am not wrong) if the C-C bonds are at<br>
> a distance shorter than the theoretical equilibrium distance (I guess).<br>
><br>
> HTH<br>
><br>
------------------------------------------------------------------------------------------------<br>
Dear Quantum Espresso Users<br>
><br>
> I vc-relaxed a (1*1) slab of graphite surface with 3 layers; It takes 20<br>
minutes with parallel running by 4 CPUs. Then I used the exact optimized<br>
cell parameters (obtained from vc-relaxed calculation) to make a (2*2) slab<br>
of graphite with 3 layers and I expected to see the results in a few<br>
minutes. But amazingly it took 17 hours to complete. 48 steps were done in<br>
the calculation for vc-relaxing the cell which have the parameters that had<br>
been optimized before. The cell parameters only change a very bit in the<br>
current vc-relaxing the (2*2) slab. I appreciate if one explain the physical<br>
procedure of vc-relaxing and the reason of the time needed for the<br>
computation.<br>
><br>
> input file:<br>
><br>
> CONTROL<br>
> calculation = "vc-relax",<br>
> pseudo_dir = "/home/koa/soft/qe4.2/<br>
> espresso-4.2/pseudo",<br>
> outdir = "/home/koa/tmp",<br>
> etot_conv_thr= 1.0D-4,<br>
> forc_conv_thr= 1.0D-3,<br>
> dt=80,<br>
> /<br>
> &SYSTEM<br>
> ibrav = 4,<br>
> a = 2.4579,<br>
> b = 2.4579,<br>
> c = 16.3069,<br>
> cosab = -0.5,<br>
> cosac = 1.0,<br>
> cosbc = 1.0,<br>
> nat = 6,<br>
> ntyp = 1,<br>
> ecutwfc = 40.D0,<br>
> ecutrho = 480.D0,<br>
> occupations = 'smearing'<br>
> smearing ='mp',<br>
> degauss = 0.03,<br>
> nspin = 2,<br>
> starting_magnetization(1)= 0.003,<br>
> london=.true.,<br>
> /<br>
> &ELECTRONS<br>
> conv_thr = 1.D-6,<br>
> mixing_beta = 0.7D0,<br>
> diagonalization = "david",<br>
> /<br>
> &IONS<br>
> ion_dynamics="cg"<br>
> /<br>
> &CELL<br>
> cell_dynamics = 'damp-w',<br>
> press = 0.0,<br>
> /<br>
> ATOMIC_SPECIES<br>
> C 12.0107 C.pbe-rrkjus.UPF<br>
> ATOMIC_POSITIONS {angstrom}<br>
> C 0.00000000 0.00000000 0.00000000 1 1 0<br>
> C 0.00000000 1.41908472 0.00000000<br>
> C 0.00000000 0.00000000 3.15347111<br>
> C 11.22896342 0.70954236 3.15347111<br>
> C 0.00000000 0.00000000 6.30694222<br>
> C 0.00000000 1.41908472 6.30694222<br>
> K_POINTS {automatic}<br>
> 4 4 1 1 1 1<br>
><br>
<br>
<br>
<br>
<br>
<br>
</blockquote><br></div><br>