[CP2K:6359] Re: Electronic structure of CeO2 greatly depends on initial guess of wave function in OT method

Lei Li leili... at gmail.com
Tue Apr 7 21:22:38 CEST 2015


Dear Matt,

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 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 <MattWa... 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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