[Pw_forum] "scf" calculation with "PBE0" hybrid functional

[dario rocca]

Dear Narendra,
If you do a PBE calculation with norm-conserving, ultrasoft, and PAW
pseudopotentials very likely you will get very similar results (but it
depends
also on the quality of the pseudopotential, the property under
consideration, etc.).
In the case of PBE0 the type of pseudopotential will have a stronger effect
on the final result.
For purely esthetic reasons, if your previous calculations didn't take too
long you could redo them with norm-conserving pseudopotentials and
confirm that the results are indeed the same.
Otherwise I don't see anything wrong in comparing, for example, a gap
obtained at PBE level with US pseudos and a gap obtained at PBE0
level with NC pseudos.
Best,
Dario



On Fri, Aug 5, 2016 at 3:44 PM, Narendranath Ghosh <ghosh.naren13 at gmail.com>
wrote:

> Dear Dario
>
> Thank you very much  for your support.It works well and some of the jobs
> have been finished successfully.
>
> But one thing in my mind. In my whole calculations , I used PBE with
> ultrasoft pseudopotentials. But to do "scf" calculations with  PBE0 "hybrid"
> functional I have to use "Norm conserving pseudopotential". So how can I
> compare these two results.
>
> Please suggest any idea.....
>
> Thank you again
>
> *Narendra Nath Ghosh*
>
> *Research Associate*
>
> *University of Gour Banga*
>
> *Department of Computational Physics *
>
> *Malda-732102*
>
> *India*
>
>
> On Thu, Aug 4, 2016 at 2:17 AM, dario rocca <roccad at gmail.com> wrote:
>
>> Dear Narendranath,
>> Your calculation has reached convergence if you read the message "EXX
>> self-consistency reached".
>> You can learn some details about the scf procedure with hybrid
>> functionals in PW/examples/EXX_example.
>> PBE0 and hybrid functional calculations are in general very expensive. I
>> would suggest you run an example to see what to expect.
>> You might also try to perform a calculation on your system with minimal
>> computational parameters (very small cut-off, few/one k-points) just to see
>> that your run can indeed terminate smoothly. Then I would look for a set of
>> parameters which are a good compromise between computational time and the
>> accuracy you need.
>> You might also try to modify the parameter ecutfock to gain some speed.
>> For sure a hybrid functional calculation on a CNT+Fullerene system might
>> be rather challenging.
>> Best,
>> Dario
>>
>> On Wed, Aug 3, 2016 at 11:16 AM, Narendranath Ghosh <
>> ghosh.naren13 at gmail.com> wrote:
>>
>>> Dear all
>>>
>>>                    After optimizing a system "CNT+Fullerene" with "PBE"
>>> I am trying to calculate "scf" calculation with "PBE0" hybrid functional
>>> using  NC Pseudopotential.
>>>
>>> In output file I found "*convergence has been achieved in  15
>>> iterations" *But the job was not finished even after more than one
>>> week. I could not find any mistake in my input.
>>>
>>>
>>> Please suggest any idea.
>>>
>>>
>>>
>>>
>>>
>>>
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>>
>>
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