[Pw_forum] relaxation and TS
Masoud Nahali
masoudnahali at live.com
Thu Sep 30 15:49:49 CEST 2010
Dear Prof. Stefano Baroni and Vega Lew
Many many thanks for your detailed answers and helpful comments. This is
scf energy of each relaxation steps :
-411.0652023864
-411.1576447124
-411.1877929276
-411.1989785058
-411.1027361193**
-411.2006610355
-411.2078087316
-411.2087637085
-411.2094335080
-411.2112728535
-411.2137042660
-411.2145098860
-411.2163180058
-411.2200044391
-411.2186337506**
-411.2238781353
-411.2272606876
-411.2335499997
-411.2410057850
-411.2486666714
-411.2432716037**
-411.2545344840
-411.2632404207
-411.2686094326
-411.2697596541
-411.2688830229**
-411.2723156669
-411.2728025269
-411.2731592912
-411.2735337540
-411.2741229900
-411.2749931725
-411.2755105410
-411.2761617487
-411.2768678588
-411.2772028256
-411.2775503379
-411.2785154793
-411.2823072885
-411.2298751795**
-411.2825004743
-411.2845206434
-411.2875009929
-411.2801470356**
-411.2954982819
-411.3096061836
-411.3466223605
-411.367570164
-411.3724319076
-411.3795692495
-411.3812435563
-411.3823959522
-411.3829995766
-411.3833540501
-411.3835954004
-411.3839027669
-411.3841960285
-411.3843908495
-411.3844986818
-411.3845647753
-411.3846244537
-411.3846644112
-411.3846945470
-411.3847346519
-411.3848191008
-411.3848652595
-411.3849367730
-411.3849811533
-411.3851262954
-411.3534987061**
-411.3850020755
-411.3851753523
-411.3852665074
-411.3853358233
-411.3855056618
-411.3858383834
-411.3860833880
-411.3866016967
-411.3874393558
-411.3878819548
-411.3881741927
-411.3884732905
-411.3886017423
-411.3886998952
-411.3887918295
-411.3888586159
-411.3888992755
-411.3889304888
-411.3889622530
-411.3889906826
-411.3890146960
-411.3890447538
-411.3890806506
-411.3891138607
-411.3891306978
-411.3891510321
-411.3891853920
-411.3892253795
-411.3892680354
-411.3893152439
-411.3893766070
-411.3894890010
-411.3895516220
-411.3896539375
-411.3896995617
-411.3897936720
-411.3898406152
-411.3898796419
-411.3899004418
** shows the step in which the energy rises. I don't think that these
points indicate a TS or something like that since one may see such points
through any optimization procedure; am I correct ?
Also, here is the input :
&CONTROL
calculation = "relax",
pseudo_dir = "/home/soft/qe4.2/espresso-4.2/pseudo",
outdir = "/home/AB/tmp",
restart_mode = 'from_scratch'
etot_conv_thr= 1.0D-4,
forc_conv_thr= 1.0D-3,
nstep=120
/
&SYSTEM
ibrav = 4,
a = 4.864990484,
b = 4.864990484,
c = 16.418933296,
cosab = -0.5,
cosac = 1.0,
cosbc = 1.0,
nat = 26,
ntyp = 3,
ecutwfc = 40.D0,
ecutrho = 480.D0,
occupations = 'smearing'
smearing ='mp',
degauss = 0.03,
nspin = 2,
starting_magnetization(1)= 0.01,
starting_magnetization(2)= 0.01,
starting_magnetization(3)= 0.01,
london=.true.,
nosym=.true.
/
&ELECTRONS
conv_thr = 1.D-6,
mixing_beta = 0.7D0,
diagonalization = "david",
/
&IONS
ion_dynamics="bfgs"
/
ATOMIC_SPECIES
C 12.0107 C.pbe-rrkjus.UPF
Ni 58.69 Ni.pbe-nd-rrkjus.UPF
O 15.9994 O.pbe-rrkjus.UPF
ATOMIC_POSITIONS {angstrom}
C 0.000000000 0.000000000 0.000000000 0 0 0
C 2.461165257 -0.001796837 0.002770193
C -1.232804188 2.130698110 0.002678921
C 1.230011567 2.131364695 0.003376901
C -0.003333507 1.422214727 0.001510708
C -1.234100323 3.553382228 0.001755289
C 2.458567713 1.421054385 0.003703007
C 1.228614904 3.554143930 0.002513562
C -0.235163108 0.160826352 3.247131267
C 2.244119337 0.161060766 3.248352597
C -1.457317029 2.298122349 3.233987380
C 1.004488573 2.308122685 3.246477338
C 1.003490453 0.877294779 3.260744638
C -0.228726740 3.007907781 3.234369538
C 3.466400555 0.879138405 3.235278922
C 2.237111888 3.008093688 3.233133671
C 1.014869884 -0.620629524 6.400327421
C 3.476740887 -0.544001537 6.494151711
C -0.280354238 1.625208172 6.378065136
C 2.312052832 1.626645989 6.400900301
Ni 1.023326058 0.872911705 5.337347244
O 1.023326000 0.872911000 8.700000000
O 2.012052000 1.326645000 8.700000000
C -0.206008752 3.013580161 6.506783380
C 3.478548719 0.866737695 6.505990211
C 2.235793764 3.015530163 6.513155404
K_POINTS {automatic}
4 4 1 1 1 1
*-----------------*
*Masoud Nahali*
*PhD Student of Physical Chemistry
Sharif University of Technology
*
Stefano Baroni wrote :
>
> On Sep 29, 2010, at 5:32 PM, vega lew wrote:
>
> > Through the relaxation of a oxygen molecule on a surface by QE4.2, it
> dissociated and adsorbed on the surface. The scf energy of each step has
> decreased in compared with the previous step until the relaxation completed.
> Now, can one say that there is not any TS for O2 dissociation here ?
> >
> >> Probably not. The potential energy surface might be not very corrugated
> and the energy barrier for the dissociation might be not very large, so that
> the dissociation of O2 could happen in a relax calculation. I think there
> might be a very minute TS in the dissociation process.
>
> here, I beg to differ. If a state, say B, can be reached from another
> state, say A, following a path along which the energy always decreases, this
> means *by definition* that there is *no* energy barrier between A and B. I
> admit that if the energy barrier is so "minute" as to be smaller that the
> numerical accuracy of the minimization algorithm, it can escape proper
> detection. (notice that this can be said of most, if not all, numerical
> computations of any quantity)
>
> >
> > Or is the reaction spontaneous ?
>
> It is spontaneous
>
> >> If the total energy of system goes down continuously and the adsorption
> energy of dissociated state is lower than the one of molecular state, you
> could say the reaction is favorable. Whether it is spontaneous, it is depend
> on how large of the energy barrier.
>
> in the reported conditions, the energy barrier is zero
>
> >> If there was a TS in this procedure (dissociation and adsorption of O2)
> would the optimization algorithm of QE4.2 stop the work or continue ?
>
> In the presence of an energy barrier, the system would stay stuck in the
> starting configuration
>
> Stefano
>
> > If there is only one bond broken in the process you considered, you could
> try constrained optimization technique. For you information, please refer to
> B.Hammer (Hammer, B.; Jacobsen, K. W.; Norskov, J. K. Phys. Rev. Lett. 1992,
> 69, 1971) or PJ Hu's work. (Alavi, A.; Hu, P.; Deutsch, T.; Silvestrelli, P.
> L.; Hutter, J. Phys. Rev. Lett. 1998, 80, 3650). Or recent developed method
> by ZP Liu (J. Chem. Theory Comput. 2010, 6, 1136?1144 )
>
> If I have not misunderstood some important point, no constrained
> minimization or other advanced techniques are needed here.
>
> Stefano B
>
>
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