[QE-users] scf not converge in neb.x caluculation

Giuseppe Mattioli giuseppe.mattioli at ism.cnr.it
Thu Mar 21 11:00:32 CET 2019


Dear Liang Xiongyi

There are a lot of things you can try, but neb.x can be somewhat whimsical...

1) You can change the total number of images. This will change the  
starting points and might ensure a smoother convergence.

2)  path_thr          = 0.05D0
This does not help convergence, but it is a bit tight in my  
experience. 0.1 is generally tight enough (in reasonably complex  
systems) to provide meaningful results.

3)   degauss = 0.005
This is very tight and can hinder convergence. You should try to use  
0.01~0.02 (check how much it affects total energies of images by  
looking at the -TS contribution in the PW.out files)

4)  mixing_beta=0.7d0
You can lower this even down to 0.01 (but 0.1 is generally a good  
value for not extremely stubborn convergence).

5) you are using a default electron_maxstep=100 value. You can raise  
this value, or you can raise (a littele bit) conv_thr. You may also  
carefully use scf_must_converge=.false., specially if scf cycles dance  
close to convergence and you want to force the system to step across a  
problematic atomic configuration.

6) K_POINTS {automatic}
    5 5 1 0 0 0

This might be too much for calculation of barriers in a quite large  
supercell having no symmetry. For example, I would check if the total  
energy difference between the converged final and initial images was  
(almost) constant by using K_POINTS {gamma}. If this was true, then I  
would calculate the whole path by using gamma_only tricks, which  
should also provide better convergence for the system.

HTH
Giuseppe

LEUNG Clarence <liangxy123 at hotmail.com> ha scritto:

> Dear QE users,
>
> I want to calculate the mobility of  metal atom on surface bu neb.x.  
> However, the image 9 is very difficult to converge. Could you please  
> give me some advice.  The input file as follows:
>
> Thanks.
> LIANG XIongyi
> City University of Hong Kong
>
> BEGIN
> BEGIN_PATH_INPUT
> &PATH
>   restart_mode      = 'from_scratch'
>   string_method     = 'neb',
>   nstep_path        = 30,
>   ds                = 1.D0,
>   opt_scheme        = "broyden",
>   num_of_images     = 10,
>   k_max             = 0.3D0,
>   k_min             = 0.2D0,
>   path_thr          = 0.05D0,
>
> /
> END_PATH_INPUT
>
> BEGIN_ENGINE_INPUT
> &CONTROL
>   prefix='av-y',
>   outdir='/home/qeuser/Clarence/phosphorene/v/d3/av/neb',
>   pseudo_dir='/home/qeuser/SSSP_acc_PBE' ,
>   verbosity='low',
>   etot_conv_thr = 1.0D-5 ,
>   forc_conv_thr = 6.0D-4 ,
>   nstep = 200 ,
>   wf_collect = .true. ,
>   verbosity='low',
> /
> &SYSTEM
>   ibrav=8,
>   celldm(1)=25.0298004651d0, celldm(2)=1.3810663486d0,  
> celldm(3)=1.8874762178d0,
>   nat=65,
>   ntyp=2,
>   ecutwfc=50,
>   ecutrho=500,
>   input_dft='PBE',
>   occupations='smearing',
>   smearing = 'gaussian' ,
>   degauss = 0.005 ,
>   nspin = 2 ,
>   starting_magnetization(1) = 0.5 ,
>   vdw_corr = 'DFT-D3' ,
> /
>
> &ELECTRONS
>   conv_thr=1d-06,
>   mixing_beta=0.7d0,
>   mixing_mode ='local-TF',
>   electron_maxstep = 1000 ,
> /
> &IONS
> /
>
> ATOMIC_SPECIES
>   P 30.973800d0 P.pbe-n-rrkjus_psl.1.0.0.UPF
>   V 50.941500d0 V_pbe_v1.uspp.F.UPF
>
> K_POINTS {automatic}
>   5 5 1 0 0 0
>
> BEGIN_POSITIONS
> FIRST_IMAGE
> ATOMIC_POSITIONS {crystal}
> P        0.062364056   0.146835680   0.461004179
> P        0.187979850   0.227571721   0.458486567
> P        0.187359072   0.023967396   0.547448145
> P        0.062390271   0.105486489   0.546314111
> P        0.062391562   0.397230966   0.452233415
> P        0.187453676   0.479039381   0.452606421
> P        0.189364962   0.278117380   0.541172586
> P        0.062407749   0.357692419   0.537875656
> P        0.062401956   0.644403307   0.461059945
> P        0.188082333   0.725080248   0.462700469
> P        0.188395810   0.514757114   0.539192335
> P        0.062460702   0.595965919   0.543895751
> P        0.062381001   0.895525242   0.463867650
> P        0.186790459   0.977279845   0.463560403
> P        0.187798718   0.768448197   0.547468271
> P        0.062423049   0.849704828   0.548098847
> P        0.312659868   0.146168383   0.460453461
> P        0.437781276   0.227744221   0.458426404
> P        0.437455901   0.023776880   0.547310817
> P        0.312549613   0.105320407   0.545904997
> P        0.312139598   0.397030501   0.450854221
> P        0.438074098   0.477737365   0.445066729
> P        0.439912044   0.279485733   0.540862256
> P        0.314542445   0.359645859   0.537231792
> P        0.314544837   0.644905805   0.460878636
> P        0.434594009   0.730077067   0.459781958
> P        0.448827043   0.514927416   0.532500900
> P        0.317525398   0.592780735   0.543968174
> P        0.311728367   0.896097058   0.463720553
> P        0.436893865   0.977260819   0.463347579
> P        0.437860024   0.769032959   0.545891816
> P        0.312518709   0.850247622   0.547849195
> P        0.562393332   0.146370379   0.460376779
> P        0.686969347   0.227774704   0.458451805
> P        0.687291897   0.023755188   0.547362489
> P        0.562382204   0.105350763   0.545849427
> P        0.562473269   0.396448431   0.443507308
> P        0.686748477   0.477847993   0.445052781
> P        0.684946773   0.279498604   0.540893439
> P        0.562452036   0.365431435   0.533574680
> P        0.562388294   0.651473527   0.453514755
> P        0.690184909   0.730079028   0.459780328
> P        0.676015132   0.514980165   0.532495771
> P        0.562386005   0.604919173   0.537701074
> P        0.562374845   0.896356486   0.463525401
> P        0.687848329   0.977264329   0.463389247
> P        0.686894465   0.769048044   0.545881597
> P        0.562366018   0.850830890   0.547709669
> P        0.812039406   0.146172639   0.460500457
> P        0.936731753   0.227556339   0.458506445
> P        0.937413894   0.023975028   0.547450256
> P        0.812195810   0.105311249   0.545951465
> P        0.812689390   0.397151038   0.450847120
> P        0.937418545   0.479112680   0.452648391
> P        0.935397084   0.278168840   0.541173905
> P        0.810251826   0.359711909   0.537223718
> P        0.810287195   0.644943491   0.460914925
> P        0.936753166   0.725104783   0.462754832
> P        0.936455552   0.514807673   0.539237217
> P        0.807300389   0.592829495   0.544001475
> P        0.813022989   0.896104987   0.463696223
> P        0.937973444   0.977284048   0.463557949
> P        0.937000660   0.768483060   0.547514207
> P        0.812240625   0.850260753   0.547823269
> V        0.562457425   0.460038104   0.589861636
> LAST_IMAGE
> ATOMIC_POSITIONS {crystal}
> P        0.062445615   0.146456673   0.451477017
> P        0.187505780   0.228300342   0.450996126
> P        0.189411819   0.029049537   0.541552681
> P        0.062449177   0.108536309   0.537537957
> P        0.062447760   0.395196377   0.458733376
> P        0.188131570   0.475920562   0.460828460
> P        0.188374349   0.265401889   0.537271427
> P        0.062442541   0.346561452   0.541532408
> P        0.062445852   0.646720019   0.463330906
> P        0.186881361   0.728456886   0.463846544
> P        0.187786345   0.518231310   0.545890007
> P        0.062453053   0.599463807   0.547113520
> P        0.062449884   0.896772437   0.462088203
> P        0.188068030   0.977403357   0.459227449
> P        0.187407760   0.773919686   0.548121428
> P        0.062451045   0.855509144   0.547403030
> P        0.312157931   0.146197729   0.450100263
> P        0.437962144   0.226895792   0.443334809
> P        0.439781032   0.030364618   0.541401226
> P        0.314537903   0.110579019   0.536930990
> P        0.314516246   0.395673292   0.458770827
> P        0.434514870   0.480945643   0.457958047
> P        0.448849945   0.265612968   0.530384087
> P        0.317545829   0.343415876   0.541814557
> P        0.311882120   0.647337595   0.463336957
> P        0.437025970   0.728486497   0.463886605
> P        0.437893522   0.518734801   0.544383856
> P        0.312565523   0.599936087   0.546984686
> P        0.312792214   0.896123190   0.461534507
> P        0.437703418   0.977802230   0.459342638
> P        0.437537090   0.773854879   0.548208275
> P        0.312529860   0.855396994   0.547005515
> P        0.562445549   0.145582412   0.442645546
> P        0.686938850   0.226884972   0.443352934
> P        0.685108766   0.030376879   0.541401741
> P        0.562439931   0.116211878   0.533161816
> P        0.562454842   0.402446010   0.451051275
> P        0.690383198   0.480958602   0.457954855
> P        0.676029527   0.265601905   0.530394460
> P        0.562442494   0.355543724   0.535081296
> P        0.562448326   0.647583315   0.463280787
> P        0.687873726   0.728484011   0.463890075
> P        0.687007439   0.518737405   0.544382783
> P        0.562448794   0.600455024   0.546972980
> P        0.562448881   0.896623478   0.461579252
> P        0.687191466   0.977803753   0.459347311
> P        0.687350603   0.773851566   0.548211631
> P        0.562445632   0.855549232   0.547048125
> P        0.812742443   0.146187679   0.450102692
> P        0.937382360   0.228298381   0.450991288
> P        0.935497478   0.029039399   0.541554721
> P        0.810375354   0.110570352   0.536929886
> P        0.810378355   0.395682293   0.458771630
> P        0.936769992   0.475925052   0.460830172
> P        0.936505251   0.265408800   0.537265660
> P        0.807335019   0.343422437   0.541813266
> P        0.813017687   0.647336128   0.463349568
> P        0.938011871   0.728458147   0.463853218
> P        0.937122704   0.518229776   0.545892176
> P        0.812342101   0.599934329   0.546995984
> P        0.812096929   0.896122158   0.461548112
> P        0.936825737   0.977397364   0.459230552
> P        0.937491966   0.773921441   0.548127880
> P        0.812360758   0.855393535   0.547018412
> V        0.562433776   0.211933054   0.588349784
> END_POSITIONS
> END_ENGINE_INPUT
> END



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>



More information about the users mailing list