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Dear pwscf users<br><br>answer to the comments:<br>(many thanks for your kind attention and help but I could not solve the problem)<br><br><b>to G. Scluuzero:</b> I have used the experimental C-C distance but then I have vc-relaxed the bulk cell and found the new positions. After vc-relax I have used <br>these coordinates to "relax" the atoms in the cell with vacuum. Also the innermost layer is not graphite-like and is rippled. <br><br><b>to D. C. Andera: </b>this pseudopotential reproduces the experimental cell parameter of the bulk correctly and exactly. the predicted cell parameter in z-direction (c) by the other pseudopotentials is not so exact and sometimes, a difference about 1 angstrom compared to experimental value appears.<br><br><b>to G. Mattioli:</b><br>london=.true. closes the atoms in the different layers to each other in the relax calculation and did not solve the problem.<br><br><b>Now</b> I am trying to relax a 5-layer sample and see the result. but it has not completed yet. really I do not know the surface of graphite is "ripple" in the nature (experimentally) or not? I appreciate your help.<br><br>> On 07/05/2010 08:19 PM, Masoud Nahali wrote:<br>> > Dear Quantum Espresso users<br>> ><br>> > I optimized the graphite bulk and the layers were completely flat. But <br>> > when I try to "relax" the graphite surface (slab 2*2 with 3 monolayer) <br>> > with 10 angstrom vacuum all the layers become extremely ripple!!! I <br>> > can not find the problem. May it related to the number of layers? <br>> > anyhow the number of layers is like the bulk. Your help would be a <br>> > great gift.<br><b>G. Scluuzero:</b><br>> > __<br>> Are you using the experimental or the theoretical value for the in-plane <br>> (graphene) C-C distance? I guess that the PBE value is larger than the <br>> experimental one, so that if you start from the experimental C-C <br>> distance in the graphene layer and let everything relax, then the atoms <br>> would like to go towards the theoretical equilibrium distance and this <br>> may cause the rippled structure.<br>> Secondly, I don't know if you can pretend that the innermost layer is <br>> graphite bulk-like, having only three layers in total.<br><br><b>Dal Corso Andrea :</b><br><br>> Check the pseudopotential. This is a PP with a core hole for special<br>> purposes not for standard simulations.<br><br> <br> <b>Giuseppe Mattioli :</b><br>> Dear Masoud<br>> apart from the pseudo problem issued by Andrea, you could try the keyword<br>> london=.true.<br>> It adds a Van der Waals contribution to total energy and it is likely to <br>> improve the interlayer interactions in your system.<br>> Hope this helps<br>> Giuseppe <br><br><u>input file:</u><br><br>&CONTROL<br>
calculation = "relax",<br> pseudo_dir =
"/home/koa/soft/qe4.2/espresso-4.2/pseudo",<br> outdir =
"/home/koa/tmp",<br> etot_conv_thr= 1.0D-4,<br> forc_conv_thr= 1.0D-3,<br>
nstep=150,<br> /<br>&SYSTEM<br> ibrav = 4,<br> a =
4.9318,<br> b = 4.9318,<br> c = 16.7029,<br>
cosab = -0.5,<br> cosac = 1.0,<br> cosbc = 1.0,<br>
nat = 24,<br> ntyp = 1,<br> ecutwfc = 40.D0,<br>
ecutrho = 400.D0,<br> occupations = 'smearing'<br> smearing ='mp', <br>
degauss = 0.01,<br> nspin = 2,<br> starting_magnetization(1)= 1.0,<br>
/<br>&ELECTRONS<br> conv_thr = 1.D-6,<br> mixing_beta = 0.7D0,<br>
diagonalization = "david",<br>/<br>&IONS<br> ion_dynamics="bfgs"<br>/<br>ATOMIC_SPECIES<br>C
12.0107 C.star1s-pbe-rrkjus.UPF<br>ATOMIC_POSITIONS {angstrom}<br>C
0.000000 0.000000 0.000000<br>C 2.465900 0.000000
0.000000<br>C -1.232950 2.135532 0.000000<br>C 1.232950
2.135532 0.000000<br>C 0.000000 1.423688 0.000000<br>C
-1.232950 3.559220 0.000000<br>C 2.465900 1.423688
0.000000<br>C 1.232950 3.559220 0.000000<br>C 0.000000
0.000000 3.351450<br>C 2.465900 0.000000 3.351450<br>C
-1.232950 2.135532 3.351450<br>C 1.232950 2.135532
3.351450<br>C 1.232950 0.711844 3.351450<br>C 0.000000
2.847376 3.351450<br>C 3.698850 0.711844 3.351450<br>C
2.465900 2.847376 3.351450<br>C 0.000000 0.000000
6.702900<br>C 2.465900 0.000000 6.702900<br>C -1.232950
2.135532 6.702900<br>C 1.232950 2.135532 6.702900<br>C
0.000000 1.423688 6.702900<br>C -1.232950 3.559220
6.702900<br>C 2.465900 1.423688 6.702900<br>C 1.232950
3.559220 6.702900<br>K_POINTS {automatic}<br>4 4 1 1 1 1<br><br><br><u>out
put (optimized positions):</u><br><br>C 0.000000000
-0.000000000 -0.686394528<br>C 2.465900000 -0.003714144
-0.758610095<br>C -1.229733457 2.137389072 -0.758610095<br>C
1.229733457 2.137389072 -0.758610095<br>C 0.000000000
1.427474855 -0.213813075<br>C -1.229670488 3.557326573
-0.213813075<br>C 2.465900000 1.423688000 -0.285079086<br>C
1.229670488 3.557326573 -0.213813075<br>C -0.000000000
0.000000000 3.630366631<br>C 2.465900000 -0.014904710
3.544792504<br>C -1.220042143 2.142984355 3.544792504<br>C
1.220042143 2.142984355 3.544792504<br>C 1.220249305
0.704511250 3.106073641<br>C 0.000000000 2.847376000
3.022325711<br>C 3.711550695 0.704511250 3.106073641<br>C
2.465900000 2.862041499 3.106073641<br>C 0.000000000
0.000000000 7.468882932<br>C 2.465900000 0.008344370
7.466151214<br>C -1.240176436 2.131359815 7.466151214<br>C
1.240176436 2.131359815 7.466151214<br>C 0.000000000
1.414904155 6.963129179<br>C -1.240557033 3.563611923
6.963129179<br>C 2.465900000 1.423688000 6.961528237<br>C
1.240557033 3.563611923 6.963129179<br><br><br><br>Many Thanks<br>Masoud Nahali<br>Sharif
University of Technology<br><br> <br /><hr />Hotmail: Free, trusted and rich email service. <a href='https://signup.live.com/signup.aspx?id=60969' target='_new'>Get it now.</a></body>
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