Serious convergence problem (Au and CeO2 mixed system)

[Yong Li]

Dear Marcella,

thank you for you reply!

"The combination of functional, DFT+U, basis-sets and potentials might not 
be optimal.
According to our last experience with CeO2, to get a good description of 
the electronic structure we needed a small core Ce element, with 30 valence 
electrons. "

Does CP2K provide other basis set and small core potential ? I don't think 
so, do you create potential and basis set yourself? 
This system is Gold supported CeO2 cluster, the band gap of this whole 
system is pretty small, so I don't know if it is necessary to add U value.

"Have you already tried the following things?
- reduce the mixing coefficient alpha
- increase the smearing temperature
- use a different extrapolation method, e.g., prev_wf
- tighten the eps_default"

I try to increase and reduce mixing value of alpha, it doesn't help, also 
try to increase smearing temperature, and many other keywords. 
I didn't try other extrapolation method, I will try it.
At beginning the EPS_SCF is 1.0E-6, I just loose it when SCF does't 
converge. For MD simulation, the geometries diverge too much, this is main 
reason that SCF doesn't converge. I hope there is something can improve it.

All the best,
Yong



On Tuesday, March 29, 2016 at 9:41:54 PM UTC+8, Marcella Iannuzzi wrote:
>
> Dear Yong Li,
>
> your system is not the easiest to treat with DFT. 
> I am not too much surprised that you encounter convergence problems. 
> The combination of functional, DFT+U, basis-sets and potentials might not 
> be optimal.
> According to our last experience with CeO2, to get a good description of 
> the electronic structure we needed a small core Ce element, with 30 valence 
> electrons. 
>
> Have you already tried the following things?
> - reduce the mixing coefficient alpha
> - increase the smearing temperature
> - use a different extrapolation method, e.g., prev_wf
> - tighten the eps_default
>
> Kind regards
> Marcella
>
>
> On Saturday, March 26, 2016 at 6:40:18 PM UTC+1, Yong Li wrote:
>>
>> Dear Sir/Madam,
>>
>> I was running a large AIMD simulation (about 5200 basis functions) for Au 
>> surface supported CeO2 cluster ( (Au(111) surface has180 Au atoms, and Ce
>> 10O20 cluster). 
>>
>> At the beginning, simulation goes well, then it has a very serious 
>> convergence problems at around step number of 350. it can't get converged 
>> no matter what I do to the SCF control. 
>>
>> Even if I make it converged coincidentally, but it will not converge 
>> after considering Kinetic energy and temperature.
>>
>> I tried every method I can find， but I can‘t figure it out.
>>
>> I am depressed and frustrated now, hope someone could help me out with 
>> it.  Any suggestions are appreciated!!
>>
>> The input output file were enclosed in attachment, part of input file is 
>> as follows
>>
>>      
>>
>>      MULTIPLICITY  1
>>      PLUS_U_METHOD  MULLIKEN_CHARGES
>>      &SCF
>>        MAX_SCF  100
>>        EPS_SCF     7.0E-05
>>        CHOLESKY  INVERSE
>>        SCF_GUESS  ATOMIC
>>        ADDED_MOS  400
>>        &DIAGONALIZATION  T
>>          ALGORITHM  STANDARD
>>        &END DIAGONALIZATION
>>        &OUTER_SCF  T
>>          EPS_SCF     8.0000000000000001E-05
>>          MAX_SCF  5
>>        &END OUTER_SCF
>>        &SMEAR  T
>>     #     METHOD  ENERGY_WINDOW
>>          METHOD  FERMI_DIRAC
>>          ELECTRONIC_TEMPERATURE     3.0000000000000000E+02
>>        &END SMEAR
>>        &MIXING  T
>>          METHOD  BROYDEN_MIXING
>>          ALPHA     0.1
>>          BETA      1.5
>>          NBUFFER  8
>>        &END MIXING
>>        &PRINT
>>          &RESTART  SILENT
>>            FILENAME =RESTART.wfn
>>            &EACH
>>              MD  5
>>            &END EACH
>>          &END RESTART
>>        &END PRINT
>>      &END SCF
>>      &QS
>>        EPS_DEFAULT     1.0000000000000000E-11
>>        EPS_PGF_ORB     1.0000000000000001E-05
>>        EXTRAPOLATION  ASPC
>>        EXTRAPOLATION_ORDER  3
>>      &END QS
>>      &MGRID
>>        CUTOFF     5.0000000000000000E+02
>>      &END MGRID
>>      &XC
>>        DENSITY_CUTOFF     1.0000000000000000E-10
>>        GRADIENT_CUTOFF     1.0000000000000000E-10
>>        TAU_CUTOFF     1.0000000000000000E-10
>>        &XC_GRID
>>          XC_SMOOTH_RHO  NN10
>>          XC_DERIV  SPLINE2_SMOOTH
>>        &END XC_GRID
>>        &XC_FUNCTIONAL  NO_SHORTCUT
>>          &PBE  T
>>          &END PBE
>>        &END XC_FUNCTIONAL
>>      &END XC
>>      &PRINT
>>        &MULLIKEN  SILENT
>>          FILENAME =md.mulliken
>>          &EACH
>>            MD  5
>>          &END EACH
>>        &END MULLIKEN
>>      &END PRINT
>>    &END DFT
>>    &SUBSYS
>>
>>
>>
>>
>>
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