<div> Dear Gabriele Sclauzero and pwscf Users</div>
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<div> Many thanks for your attentions. The cell dimension and the positions of the atoms are exactly correct. Yes, indeed the high ecutrho is important for ultrasoft pseudopotentials. About the rippling : It was my mistake in selecting a wrong pseudopotential which has a hole. Nicola had explained it before and accordingly I solved it. The graphite surface is not ripple. When I use the "max_second=6000 and dt=150" the job completes very fast as the example of pwscf. Is the using of such keyboards plausible?</div>
<div> As I mentioned before I had used the optimized cell parameters of (1*1 slab) for vc-relaxing the (2*2 slab) and I expected to see the results very soon but the calculation was time consuming while there was only a very very bit change of the cell dimensions during this 16 hours. There is only 1-3 iterations per each step in the output file and each of them was time consuming. The job was completed after about 50 steps. </div>
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<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Dear Masoud,<br><br> first I would suggest you to use bfgs as the algorithm for both ions and cell dynamics. Excepted particular cases, it should reach the minimum much faster.<br>
<br>Also, why do you specify the cell with such an unusual way. You simply need celldm(1) and celldm(3) with ibrav=4 if you want to describe an hexagonal lattice. Other suggestions: your ecutrho looks really large to me, do you really need it. On the other hand, degauss might be too large to describe a spin-polarized system.<br>
<br>Then, are you sure that you have built correctly your supercell? It looks like there are some C-C bonds much shorter that others in the central 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 some kind of surface-reconstruction may appear, since you leave more freedom to atoms to rearrange in structures with larger periodicity. I don't think this is the case for graphite, but you may find some ripples (as you mentioned in your earlier emails, if I am not wrong) if the C-C bonds are at a distance shorter than the theoretical equilibrium distance (I guess).<br>
<br>HTH<br></blockquote>
<div>------------------------------------------------------------------------------------------------<br> Dear Quantum Espresso Users<br>><br>> I vc-relaxed a (1*1) slab of graphite surface with 3 layers; It takes 20 minutes with parallel running by 4 CPUs. Then I used the exact optimized cell parameters (obtained from vc-relaxed calculation) to make a (2*2) slab of graphite with 3 layers and I expected to see the results in a few minutes. But amazingly it took 17 hours to complete. 48 steps were done in the calculation for vc-relaxing the cell which have the parameters that had been optimized before. The cell parameters only change a very bit in the current vc-relaxing the (2*2) slab. I appreciate if one explain the physical procedure of vc-relaxing and the reason of the time needed for the 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></div>
<div> Sincerely Yours<br> Masoud Nahali<br> SUT<br><br></div></div>