Serious convergence problem (Au and CeO2 mixed system)

[Matt W]

Hi,

When Marcella says "not the easiest to treat with DFT", I think she means 
'an absolute nightmare to treat with DFT':)

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.
>
> You'll need a very small timestep for MD too. The electronic structure is 
unstable, with multiple solutions (polarons jumping onto the CeO2 from the 
metal) so if you aren't very careful you'll lose your solution. This occurs 
with any DFT code, should be papers from Michaelides for instance where I 
think they used 0.1 fs with a popular plane-wave code.

Matt
 

> 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 Ce10O20 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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