How to specify the magnetic moment of each atom?

[stclair]

Dear CP2K user,

    I am working on CeO2 (111) surface with oxygen vacancy. Based on the previous studies, two extra electrons should locate on two next-nearest Ce atoms (as shown in the attached pictures). But my calculation converges to a different electronic configuration where the extra electrons locate on the Ce atoms closest to vacancy. Is there any keywords I can use to specify the magnetic moment for the atoms? Some keywords are similar to MAGMOM in VASP?

   Thanks in advance.

Best,

Lei

[Matt W]

Hi,

you can get what you are after by using the broken symmetry (&BS) keyword within the &KIND block. It is a bit fiddly to use, but can be used to specify the atomic guess used to generate the initial density matrix. The are some threads in the forum and some stuff online if you look for it.

But, my preferred way of _trying_ to localize the spins is to use the &CORE_CORRECTION keyword, again in the &KIND section. So in this case pick the two Ce that you want to localize the electrons onto and make them a new kind in your geometry file (Ce3 or something). Then in &KIND Ce3 add &CORE_CORRECTION 0.5 or 1.0.  This increases the effective nuclear charge of these atoms and makes it very likely the electrons will localize on them. You can then do a rough geometry relaxation to get the lattice distortion that might stabilize the localized electrons. Then you can restart but setting the &CORE_CORRECTION back to 0.0. If you are using an appropriate density functional then you have a decent chance of getting the localization you want. For the O vac in CeO2 you can just run a triplet calculation with the modified core charge on a couple of Ce and you should get what you want without bothering with the broken symmetry guess.

Matt

[stclair]

Hi, Matt,

Thanks great for your helpful reply. I will give a try with 'CORE_CORRECTION.

For the broken symmetry, I have tried it by setting the initial guess of the Ce atom as Ce3+ (only for the Ce atoms I want to localize the electrons). I attached the 'KIND' section for these Ce atoms. But I got the following error message:

 *************************************************************************

 *** 15:35:59 ERRORL2 in qs_subsys_methods:num_ao_el_per_molecule ::   ***

 *** SECOND SPIN CONFIG IS IGNORED WHEN MOLECULAR STATES ARE ASSIGNED! ***

 *************************************************************************

I checked the source file from http://cp2k.web.psi.ch/doxygen/trunk/de/d42/qs__subsys__methods_8f90_source.html. It seems due to the different initial guess for Alpha and beta and only Alpha will be used for calculation. Is that correct?

Could you help check if there is anything wrong in my setting?

The basis set for Ce I am using is from a recent paper: JPCC, 2013, 117, 23082.

Thanks great!

Best,

Lei

[S Ling]

For the warning message, you might ignore it if your calculation can proceed. There was a recent post by Prof Juerg Hutter on that, just search "ERRORL2 in qs_subsys_methods:num_ao_el_per_molecule" in the forum and you should be able to find the post.

SL

[stclair]

Got it. Thanks great!

On Thursday, February 26, 2015 at 11:51:15 AM UTC-6, S Ling wrote:

For the warning message, you might neglect it if your calculation can proceed. There was a recent post by Prof Juerg Hutter on that, just search "ERRORL2 in qs_subsys_methods:num_ao_el_per_molecule" in the forum and you should be able to find the post.

SL

On Thursday, February 26, 2015 at 4:55:18 PM UTC, stclair wrote: