CCL: Why on increasing the SCF maxiter, the undesired modes vanish?



Sumangla,

Then, why frequency calculation is showing SCF convergence error?

By default, ORCA operates with looser convergence tolerances during the geometry optimization, and then performs a final SCF calculation at the optimized geometry before moving on.  For example, here are the SCF settings for one of my calculations in ORCA 4.2.1, from a step within the geometry optimization (note that I've manually fixed the BFCut and WCut values here):

-------------------
DFT GRID GENERATION
-------------------

General Integration Accuracy     IntAcc      ...  4.670
Radial Grid Type                 RadialGrid  ... Gauss-Chebyshev
Angular Grid (max. acc.)         AngularGrid ... Lebedev-302
Angular grid pruning method      GridPruning ... 3 (G Style)
Weight generation scheme         WeightScheme... Becke
Basis function cutoff            BFCut       ...    1.0000e-12
Integration weight cutoff        WCut        ...    1.0000e-14
Grids for H and He will be reduced by one unit


Here are the SCF settings for the final SCF at the optimized geometry:

Setting up the final grid:

General Integration Accuracy     IntAcc      ...  5.010
Radial Grid Type                 RadialGrid  ... Gauss-Chebyshev
Angular Grid (max. acc.)         AngularGrid ... Lebedev-434
Angular grid pruning method      GridPruning ... 3 (G Style)
Weight generation scheme         WeightScheme... Becke
Basis function cutoff            BFCut       ...    1.0000e-12
Integration weight cutoff        WCut        ...    1.0000e-14
Grids for H and He will be reduced by one unit

 As you can see, both IntAcc and AngularGrid are increased for the final SCF. Most likely, your system is just large/challenging enough that it doesn't quite converge with the larger grid, without increasing MaxIter.

-------------------------------

Can we restart the frequency calculation from the point it got stopped?

Yes! Just include Restart True in the %freq ... end block syntax:

%freq Restart True end

You will have to make sure all of the temporary *.hess files from the aborted run are in the working directory for the restarted run.


-Brian


On Mon, Nov 22, 2021 at 2:46 AM Sumangla Arora arorasumangla:+:http://gmail.com">gmail.com <owner-chemistry~!~ccl.net> wrote:
Thanks to All.
Tatiana, Orca printed the warning as Ulrike also mentioned. Yes, Mariusz you are right, I have increased SCF-maxiter.
In addition, I want to ask one more thing if the structure got optimized at the given SCF maxiter without any error. Then, why frequency calculation is showing SCF convergence error? 
Christoph, as per your suggestion, I will use the ORCA 5.0.
I have one more query. Can we restart the frequency calculation from the point it got stopped?

Thanks
Sumangla


On Sat, Nov 20, 2021 at 7:01 AM Christoph Riplinger christoph.riplinger-,-gmail.com <owner-chemistry#%#ccl.net> wrote:

Sent to CCL by: Christoph Riplinger [christoph.riplinger-,-gmail.com]
Thanks!

A meaningful warning was printed by ORCA, but fully agreed, the
calculation should have stopped. We'll change that for the next ORCA
(bugfix) release.

^_^Sumangla: The newest ORCA 5 version has a super-robust default SCF
converger, thus not-converging SCFs should (almost) not occur any more.
I suggest to update to that if you haven't done so yet.

Best wishes,

Christoph


On 19.11.21 11:13, Mariusz Radoń mariusz.radon*_*uj.edu.pl wrote:
> Sent to CCL by: =?utf-8?B?TWFyaXVzeiBSYWRvxYQ=?= [mariusz.radon(-)uj.edu.pl]
>
>
>> On 19 Nov 2021, at 00:54, Tatiana Korona tania=-=tiger.chem.uw.edu.pl <owner-chemistry~!~ccl.net> wrote:
>>
>> Mariusz, it is interesting, however, why the program does not stop after nonconverged SCF. I do not use Orca, but shouldn't it produce at least a warning?
>> Best wishes,
>> Tatiana
> Dear Tatiana and Sumangla:
>
> Yes, indeed, it should. It had no chance to see the output file, but Sumangla mentioned there was an “error termination in SCF” in the output,... so this is a kind of warning which should not be ignored.
>
> As Benjamin suggested, it may be worth to report this issue to the Orca forum (with attached input and output files) - so that the developers can analyze it and react properly to either increase the verbosity of the warning / error message or entirely stop the property calculations in the case of  error termination in SCF.
>
> Best wishes,
> Mariusz
>
>> On Wed, 17 Nov 2021, Mariusz Rado�~D mariusz.radon++http://uj.edu.pl" rel="noreferrer" target="_blank">uj.edu.pl wrote:
>>
>>> Sent to CCL by: =?utf-8?B?TWFyaXVzeiBSYWRvxYQ=?= [mariusz.radon-#-uj.edu.pl]
>>>
>>>
>>>> On 17 Nov 2021, at 07:15, SUMANGLA ARORA arorasumangla[#]http://gmail.com" rel="noreferrer" target="_blank">gmail.com <owner-chemistry/./ccl.net> wrote:
>>>>
>>>>
>>>> Sent to CCL by: "SUMANGLA  ARORA" [arorasumangla~~gmail.com]
>>>> Dear All,
>>>> I am using Orca for calculations. I am getting too many imaginary modes in
>>>> transition state when running numfreq with lower SCF maxiter  (error
>>>> termination in SCF). However, when I increase SCF maxiter, I am getting only
>>>> one imaginary mode.
>>>> Can you please explain why on increasing the SCF maxiter, the undesired modes
>>>> vanish?
>>>>
>>>>
>>>> Thanks
>>>> Sumangla
>>>>
>>> Dear Sumangla:
>>>
>>> You already answered your question: this is because with the lower SCF maxiter you are not able to converge the SCF (you mentioned error termination in SCF). If the SCF procedure is not properly converged, the “frequencies” (and all other properties) obtained afterwards are rubbish... they are totally unreliable and you should not give them any physical significance.
>>>
>>> Best wishes,
>>> Mariusz
>>>
>>>
>>>
>>>
>>> --
>>> Mariusz Radon, Ph.D., D.Sc.
>>> Assistant Professor
>>> Faculty of Chemistry, Jagiellonian University
>>>
>>> Address: Gronostajowa 2, 30-387 Krakow, Poland
>>> Room C1-06, Phone: 48-12-686-24-89
>>> E-mail: mradon/./chemia.uj.edu.pl (mariusz.radon/./uj.edu.pl)
>>> Web: https://tungsten.ch.uj.edu.pl/~mradon
>>> ORCID: https://orcid.org/0000-0002-1901-8521>
>>>
>> Dr. Tatiana Korona http://tiger.chem.uw.edu.pl/staff/tania/tania.html
>> Quantum Chemistry Laboratory, University of Warsaw, Pasteura 1, PL-02-093 Warsaw, POLAND
>
>



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