[CP2K-user] [CP2K:21292] U parameter benchmarking for Ni(2+)

[Lovro Šarić]

Dear all,

I am currently running calculations to determine the electronic structure 
of a 3d transition metal - containing phosphate and am facing an issue with 
evaluating the correct value for the Hubbard U parameter. 

I am trying to determine the value through a benchmarking method, 
attempting to reproduce the electronic bandgap reported in literature for 
bulk NiO (usually between 3.6 to 4.0 eV is reported). The .xyz file was set 
up in a manner that we handle a spin-polarized system with an equal number 
of UP and DOWN spin states for (A Antiferromagnet), within which there are 
ferromagnetic layers along the {111} direction. 


Firstly the PLUS_U_METHOD section was set to MULLIKEN, which resulted in 
negative DFT+U  energies for any value of U above U=2.0 eV (-0.38 eV for 
U=3.2 eV for instance) , but the overal DFT+U occupancies of the d-orbitals 
were quite reasonable. Nevertheless, I switched to LOWDIN method in an 
attempt to obtain a positive DFT+U energy, which then in turn causes a 
lowering of the bandgap value (2.9 eV HOMO-LUMO gap for U=3.4 eV using 
LOWDIN, compared to e.g 3.3 eV HOMO-LUMO Gap for U=3.2 eV using MULLIKEN).

My question would then be, should I stick to the LOWDIN method and ramp up 
to even higher U values until I reach a bandgap comparable to literature, 
or can the negative DFT+U energy contribution that comes out from the 
MULLIKEN method be ignored as long as the orbital occupancies are of a 
reasonable value?

Thank you in advance for you assistance,

Kind Regards,

Lovro  Šarić 

-- 
You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp2k+unsubscribe at googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/cp2k/99d5fc8d-dd9a-4505-a5a8-c02af8e9109en%40googlegroups.com.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20250317/97cc8643/attachment.htm>