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Re^5: SCF Convergence Problem in modelling Ag cluster

Davide Vanossi
vanossi.davide@unimore.it

Dear Alex,
         thank you very much for your kind reply.
Actually I know very well the need to perform an MCSCF description for Co isolated atom. But how can I obtain, for my cluster (Ag37Co), an acceptable (converged) initial guess for using it in the next MCSCF calculation? Using fshift=0.15-0.2 didn’t help a lot.
Thank you again.
Have a nice day

  Davide

On Sun Nov 6 '11 11:41pm, Alex Granovsky wrote
----------------------------------------------
>Dear Davide,

>actually, Firefly' DFT code has problems converging just an isolated
>Co atom with e.g., mult=4. The reason is very simple. As Sanya has already
>mentioned, this state actually requires MCSCF for correct description.
>Indeed, there are both empty and occupied degenerated d orbitals so SCF oscillates
>between solutions having different occupation numbers for different
>orbitals. Increasing $scf fshift to say 0.15 or so helps. Nevertheless,
>one should generally realize that DFT can be inadequate and that
>there exist multiple (quasi)degenerated solutions of KS equations for this system.
>
>
>As to system with Co near Ag cluster, my guess is that as Co is far
>away the cluster, the convergence problems are caused by the same
>reason. Try to move Co atom closer to the surface.

>Best regards,
>Alex
>
>
>
>On Fri Nov 4 '11 2:04pm, Davide Vanossi wrote
>---------------------------------------------
>>Dear Amir,
>>         I’m absolutely agree with you and, in fact,  I tried the lanl2dz from the beginning; unfortunately this introduced, on my system, a quasi linear dependence on the basis set which is not a good companion “to cure” the SCF convergence problem. For the moment I have “solved” the problem using another quantum chemistry package (NWChem) which permits to obtain a feasible SCF convergence even for the singlet multiplicity case.
>>Thank you very much for your interest.
>>Have a nice day.

>>    Davide
>>
>>
>>On Fri Oct 28 '11 11:56am, Amir Nasser Shamkhali wrote
>>------------------------------------------------------
>>>Dear Davide
>>>I think that relativistic effects can be important for Ag atom. So, it's better to perform calculations with an ECP basis set which has been included relativistic effects (spin-orbit coupling) such as LANL2DZ and etc. Also these basis sets reduces the cpu time and memory considerably. You can download them form this site:
>>>https://bse.pnl.gov/bse/portal
>>>Please note that spin-orbit coupling reduces spin multiplicity and do not use high spin cases. The 2S+1=3 or 5 or 7 is sufficient.

>>>Best wishes

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