[CP2K:6353] Re: Electronic structure of CeO2 greatly depends on initial guess of wave function in OT method

[Matt W]

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 
> <javascript:>> 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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