[Pw_forum] vc-relax time
Masoud Nahali
masoudnahali at live.com
Tue Jul 13 15:41:00 CEST 2010
Dear Gabriele and pwscf users
Perfectly I am sure that the positions of atoms is exactly correct. Note
that the input is belong to a (1*1) slab
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:
C 0.000352513 0.001055549 0.000000000
C 2.459305478 0.000933657 -0.008798962
C -1.229191611 2.130502759 -0.008802160
C 1.229819481 2.130516670 -0.008801637
C 0.000327447 1.420695799 -0.007291549
C -1.229173562 3.550193436 -0.007292113
C 2.459296954 1.420621766 -0.009715082
C 1.229852979 3.550208684 -0.007292392
C 0.000507119 0.000488868 3.187515573
C 2.459486429 0.000491165 3.187352189
C -1.228985445 2.130026298 3.187352283
C 1.229997454 2.130026366 3.187352273
C 1.229970852 0.710263879 3.187439366
C 0.000476982 2.839800509 3.187332530
C 3.688943914 0.710263968 3.187439418
C 2.459456202 2.839797012 3.187439363
C 0.000212609 0.000545761 6.403453823
C 2.459191836 0.000545600 6.403451859
C -1.229278051 2.130084159 6.403451942
C 1.229700861 2.130084205 6.403451921
C 0.000121431 1.420208410 6.403892505
C -1.229369239 3.549746424 6.403892711
C 2.459100653 1.420208253 6.403888354
C 1.229609673 3.549746469 6.403892772
a = 4.9178,
b = 4.9178,
c = 16.4112, 10 angstrom vacuum
Also, see the "As.vcs00.in" example in the "VCSexample" folder of quantum
espresso 4.2. In this example a vc-relax calculation
has been performed using the max_seconds and dt keyboard.
Many Thanks
I hope one helps these problems mentioned below.
>Are you completely sure? You can find as an attachment a picture (from
>xcrysden) of the central graphene layer according to the positions given
>in your input. You can now judge if it looks like a honeycomb lattice.
> 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?
>Please spend some time reading Doc/INPUT_PW to understand the meaning of
>the _keywords_. dt is used only for molecular dynamics runs, not
>relaxations, while max_seconds has nothing to do with how fast your job
>is completed.
> > Dear Gabriele Sclauzero and pwscf Users
>
> > 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?
> >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.
>
> -------------------------------------------------------------------------
>
> > Dear Masoud,
> >
> > 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.
> >
> > 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.
> >
> > 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.
> > 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).
> >
> > HTH
> >
>
> ------------------------------------------------------------------------------------------------
> Dear Quantum Espresso Users
> >
> > 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.
> >
> > input file:
> >
> > CONTROL
> > calculation = "vc-relax",
> > pseudo_dir = "/home/koa/soft/qe4.2/
> > espresso-4.2/pseudo",
> > outdir = "/home/koa/tmp",
> > etot_conv_thr= 1.0D-4,
> > forc_conv_thr= 1.0D-3,
> > dt=80,
> > /
> > &SYSTEM
> > ibrav = 4,
> > a = 2.4579,
> > b = 2.4579,
> > c = 16.3069,
> > cosab = -0.5,
> > cosac = 1.0,
> > cosbc = 1.0,
> > nat = 6,
> > ntyp = 1,
> > ecutwfc = 40.D0,
> > ecutrho = 480.D0,
> > occupations = 'smearing'
> > smearing ='mp',
> > degauss = 0.03,
> > nspin = 2,
> > starting_magnetization(1)= 0.003,
> > london=.true.,
> > /
> > &ELECTRONS
> > conv_thr = 1.D-6,
> > mixing_beta = 0.7D0,
> > diagonalization = "david",
> > /
> > &IONS
> > ion_dynamics="cg"
> > /
> > &CELL
> > cell_dynamics = 'damp-w',
> > press = 0.0,
> > /
> > ATOMIC_SPECIES
> > C 12.0107 C.pbe-rrkjus.UPF
> > ATOMIC_POSITIONS {angstrom}
> > C 0.00000000 0.00000000 0.00000000 1 1 0
> > C 0.00000000 1.41908472 0.00000000
> > C 0.00000000 0.00000000 3.15347111
> > C 11.22896342 0.70954236 3.15347111
> > C 0.00000000 0.00000000 6.30694222
> > C 0.00000000 1.41908472 6.30694222
> > K_POINTS {automatic}
> > 4 4 1 1 1 1
> >
>
>
>
>
>
>
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