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/<div id=":tc" class="ii gt">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>Sincerely Yours<br>Masoud Nahali<br>SUT<br><br>
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