[CP2K:6362] Re: Electronic structure of CeO2 greatly depends on initial guess of wave function in OT method

[Lei Li]

Thanks great, Matt!

I will continue work on the calibration and see which method is most
suitable in my case.


Best,

On Tue, Apr 7, 2015 at 2:50 PM, Matt W <MattWa... at gmail.com> wrote:

> Hi again,
>
>
>> Thanks for your great suggestion.
>>
>> Core correction indeed can help localize electron density correctly. But
>> next step I will run molecular dynamics simulation with adsorbed molecules.
>> In that case, I will not be able to use the core correction.
>>
>>
>
>> So question is: if the electronic properties can be correctly predicted
>> by restarting from the wavefunction obtained from the calculation with core
>> correction, are the parameters (basis set, potential, U value, etc.) good
>> enough to be used in MD simulation?
>>
>>
> sorry can't answer that. This would allow you to systematically get
> different solutions and compare them. To be clear, I only suggest this
> "hack" with the core correction to get an initial guess - then you remove
> it. At that point, when the correction is removed, you get what your
> density functional gives you.
>
> For MD you need to decide a starting point - then what wants to happen ->
> happens, if you see what I mean, e.g.
> http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.146405
>
> Whether the basis sets/pseudopotentials/density functional you are using
> are good enough to describe what you want ...you need to decide.
>
> Matt
>
> Sorry for so many questions since I don't want to start a big project with
>> some unknown questions.
>>
>> Thanks great!
>>
>> On Tue, Apr 7, 2015 at 12:10 PM, Matt W <Matt... at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> you should check in the atomic output at the beginning of the run
>>> whether the changes to the atomic states have worked as you want - it shows
>>> the orbital occupations of both spin channels for each atomic kind. Also,
>>> because of .. well it is a feature .. the changes in electron number will
>>> be divided by two (there is a post from Marcella about this somewhere).
>>>
>>> I'd still go with what I suggested a while back - add a CORE_CORRECTION
>>> to your desired Ce3+ to make the electrons localize, then restart with that
>>> wavefunction without the extra core charge.
>>>
>>> Run in a triplet (or maximum multiplicity for all aligned Ce3+) state -
>>> there should be no noticable exchange interaction between pairs of Ce3+, if
>>> you get splittings between singlet/triplet spin states etc then something
>>> is wrong. Running in max spin state automatically breaks some symmetry and
>>> makes it easier to get a proper solution.
>>>
>>> Matt
>>>
>>>
>>> On Tuesday, April 7, 2015 at 6:00:17 PM UTC+2, stclair wrote:
>>>
>>>> Hi, Florian,
>>>>
>>>> Thanks great for your suggestion.
>>>>
>>>> I have tried broken symmetry for Ce with 'scf_guess' set as 'atomic'.
>>>> But the situation is same to what I got from calculation without Ce (total
>>>> energy ~0.86 eV higher than the restart situation)
>>>> Here are the parameters I used. Could you check if they look good?
>>>> First time to use broken symmetry. Also, I will try to add it for O.
>>>> For two Ce atoms next-nearby the oxygen vacancy, I tried the following
>>>> setting to make it Ce3+.
>>>>        &BS
>>>>          &ALPHA
>>>>            NEL -2   -1  1
>>>>            L    0   2   3
>>>>            N    6   5   4
>>>>          &END
>>>>          &BETA
>>>>            NEL -2  -1   -1
>>>>            L    0   2   3
>>>>            N    6   5   4
>>>>          &END
>>>>        &END
>>>> But for other Ce atoms, I used the following setting to make it Ce4+.
>>>>        &BS
>>>>          &ALPHA
>>>>            NEL -2   -1  -1
>>>>            L    0   2   3
>>>>            N    6   5   4
>>>>          &END
>>>>          &BETA
>>>>            NEL -2  -1   -1
>>>>            L    0   2   3
>>>>            N    6   5   4
>>>>          &END
>>>>        &END
>>>>
>>>> Thanks!
>>>>
>>>> Best.
>>>>
>>>>
>>>> On Tue, Apr 7, 2015 at 12:37 AM, Florian Schiffmann <
>>>> flos... at gmail.com> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> that makes it more clear. As I am not 100% sure what is going on I
>>>>> will have to do some guesswork.
>>>>>
>>>>> From your input you run an unrestricted calculation. In the atomic
>>>>> guess, CP2K still uses the restricted atomic orbitals as initial guess for
>>>>> both alpha and beta. This might lead to a situation where you have 0.5 of
>>>>> an electron initially sitting in the orbital affected by the U correction.
>>>>> As far as I remember te U correction is symmetric at this point and it
>>>>> might be arbitrary whether the orbital gets further filled or emptied due
>>>>> to the penalty function (therefore there is some arbitraryness in your
>>>>> result). I think this is somewhat general that the U term can lock you in a
>>>>> given state depending on your initial guess.
>>>>>
>>>>> Could you try to use a broken symmetry guess in your calculation where
>>>>> you initialize O as 2-  and Ce as 4+ and see how the energy is affected?
>>>>> For O this chould look like
>>>>> &BS
>>>>> &ALPHA
>>>>>    L 1
>>>>>    N 2
>>>>>    NEL 2
>>>>> &END
>>>>>  &BETA
>>>>>    L 1
>>>>>    N 2
>>>>>    NEL 2
>>>>> &END
>>>>> &END
>>>>>
>>>>> For Ce it is a bit more complicated. simply remeber, that cp2k puts a
>>>>> closed shell wfn in alpha and beta. Therefore NEL in this case is 2 as the
>>>>> closed shell representation of a 2p3 is a 2p6 wfn.
>>>>>
>>>>> Hope that helps
>>>>>
>>>>> Flo
>>>>>
>>>>> --
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>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Best,
>>>> Lei
>>>>
>>>> University of Nebraska - Lincoln,
>>>> Department of Chemistry,
>>>> 536 Hamilton Hall.
>>>> Lincoln, NE 68588
>>>> Phone: 402-853-8119
>>>>
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>>
>>
>>
>> --
>> Best,
>> Lei
>>
>> University of Nebraska - Lincoln,
>> Department of Chemistry,
>> 536 Hamilton Hall.
>> Lincoln, NE 68588
>> Phone: 402-853-8119
>>
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-- 
Best,
Lei

University of Nebraska - Lincoln,
Department of Chemistry,
536 Hamilton Hall.
Lincoln, NE 68588
Phone: 402-853-8119
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