[Pw_forum] Re: convergence NOT achieved, stopping

[stewart at cnf.cornell.edu]

Hi You Lin, 

   I would suggest increasing degauss to at least 0.02.  This could help 
with convergence.  In addition, it may help to increase the number of 
k-points used in your calculation.  However, interfaces between oxides and 
metals can be very tricky due to the formation of a Schottky barrier.  
Another approach to consider would be to make a superlattice of Nickle and 
Alumina.  The convergence may improve in this case and it you have enough 
layers, it should provide some insight into interface properties. 

Best regards, 

Derek 


You Lin writes: 

> Dear pwscf developers or users: 
> 
> I tried pwscf on an interface between Nickle and Alumina.
> The self-consistent calculation cannot finish with the following error: 
> 
> convergence NOT achieved, stopping 
> 
> I found this in the manual:
> --
> Self-consistency is slow or does not converge. 
> 
> [...] If the highest occupied and lowest unoccupied state(s) keep 
> exchanging place during self-consistency, forget about reaching 
> convergence. A typical sign of such behavior is that the self-consistency
> error goes down, down, down, than all of a sudden up again, and so on.
> Usually one can solve the problem by adding a few empty bands and a
> broadening.
> --  
> 
> So I tried to manually assign more empty bands and degauss=0.0002.
> I still get oscillations in total energy. The last a few total energies 
> are listed below: 
> 
>      total energy              = -2803.40138682 ryd
>      total energy              = -2830.79824814 ryd
>      total energy              = -2819.95336489 ryd
>      total energy              = -2846.17498280 ryd
>      total energy              = -2838.30750908 ryd
>      total energy              = -2816.89515320 ryd
>      total energy              = -2844.65794627 ryd
>      total energy              = -2851.17678186 ryd
>      total energy              = -2857.26598638 ryd
>      total energy              = -2851.22021650 ryd
>      total energy              = -2803.07516948 ryd
>      total energy              = -2831.39193734 ryd
>      total energy              = -2819.19178874 ryd
>      total energy              = -2846.04973420 ryd
>      total energy              = -2836.37911313 ryd
>      total energy              = -2817.70612317 ryd
>      total energy              = -2842.03435570 ryd
>      total energy              = -2850.49039020 ryd
>      total energy              = -2857.53771242 ryd
>      total energy              = -2851.23397342 ryd
>      total energy              = -2800.87394328 ryd
>      total energy              = -2831.32149373 ryd
>      total energy              = -2819.05136878 ryd 
> 
> Looks like the problem still exists. I didn't finish this calculation 
> since it doesn't seem to converge anyway.
> Is there solution out of this problem? 
> 
> More info:
> I'm using espresso 3.0 running both in series and in parallel.
> My input file is:
> -- Start of input --
>  &control
>     calculation='relax'
>     restart_mode='from_scratch',
>     pseudo_dir = '/homes/r40/ylin/Del/Run/pwscf/espresso-3.0/pseudo/',
>     outdir='/scratch1/ylin/tmp/3.0/'
>     prefix='al2o3'
>     tprnfor = .true., nstep=20, dt=100.
>     tstress = .true., verbosity='high'
>  /
>  &system
>     ibrav=0, celldm(1) =9.4176391165, nat=46, ntyp=3, nbnd=230,
>     ecutwfc = 26, ecutrho = 288.0, nspin = 2,  
> starting_magnetization(1)=0.7,
>     occupations='smearing', smearing='methfessel-paxton', degauss=0.0002
>  /
>  &electrons
>     diagonalization='david'
>     conv_thr = 1.0e-2, electron_maxstep=200
>     mixing_beta = 0.7
>  /
>  &ions
>     upscale=10
>  /
> ATOMIC_SPECIES
>  Ni 58.69 Ni.pbe-nd-rrkjus.UPF
>  Al  26.98 Al.pbe-n-van_ak.UPF
>  O 16.00  O.pbe-rrkjus.UPF
> ATOMIC_POSITIONS {crystal}
>  Ni          0.000000000          0.000000000          0.000000000
>  Ni         -0.000000000         -0.000000000          0.247992113
>  Ni         -0.000000000         -0.000000000          0.495984226
>  Ni          0.000000000          0.500000000          0.000000000
> ....
>   O         -0.000002801         -0.695543049          0.704618081
>   O         -0.028885007         -0.333327809          0.617873620
>   O          0.362212748         -1.028876505          0.617873591
>   O          0.666663767         -0.637778737          0.617873627
>  Al          0.333330268         -0.666660823          0.737258713
>  Al          0.333330525         -0.666661167          0.845466117
> CELL_PARAMETERS
>           1.0000000000          0.0000000000         0.0000000000
>           0.5000000000          0.8660254038         0.0000000000
>           0.0000000000          0.0000000000         4.9386941745
> K_POINTS automatic
>  4 4 1  0 0000 0000
> -- End of input -- 
> 
> Thanks in advance. 
> 
> ________________________________________ 
> 
> You Lin 
> 
> Department of Physics
> University of South Florida
> 4202 East Fowler Avenue
> Tampa, FL 33620
> ________________________________________ 
> 
> Tel: (813)396-9220 [Office] 
> 
> Homepage: http://shell.cas.usf.edu/~ylin
> ________________________________________ 
> 
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################################
Derek Stewart, Ph. D.
Scientific Computation Associate
250 Duffield Hall
Cornell Nanoscale Facility (CNF)
Ithaca, NY 14853
stewart (at) cnf.cornell.edu
(607) 255-2856