[CP2K-user] [CP2K:13797] SMEAR vs. LSD+RELAX_MULTIPLICITY/MULTIPLICITY

[Marcella Iannuzzi]

Dear Ivan, 

in addition to what Matthias already wrote, by default the multiplicity is 
not fixed with SMEAR + LSD. 

Working with fractional orbital occupations requires the use of 
diagonalisation schemes, which are in general  more demanding in terms of 
computational costs if compared with the orbital transformation (OT) 
method. 

Kind regards
Marcella


On Tuesday, August 18, 2020 at 4:42:07 PM UTC+2 Matthias Krack wrote:

> Dear Ivan
>
>  
>
> a)       SMEAR allows for fractional orbital occupations whereas LSD with 
> RELAX_MULTIPLICITY is meant for systems with integer occupations, e.g. to 
> allow for the spin flip needed to switch automatically from a singlet to a 
> possibly lower lying triplet state. Thus, these schemes are not equivalent.
>
> b)      The expectation value of S**2 is only defined for calculations 
> with integer orbital occupations Therefore this properties is not 
> calculated/printed when SMEAR is active.
>
>  
>
> HTH
>
>  
>
> Matthias
>
>  
>
> *From:* c... at googlegroups.com <c... at googlegroups.com> *On Behalf Of *Ivan 
> Gladich
> *Sent:* Dienstag, 18. August 2020 15:56
> *To:* cp2k <c... at googlegroups.com>
> *Subject:* [CP2K:13797] SMEAR vs. LSD+RELAX_MULTIPLICITY/MULTIPLICITY
>
>  
>
> Dear CP2K users,
>
>  
>
> I would like some clarifications about SMEAR vs. LSD +RELAX_MULTIPLICTY in 
> cp2k. I am trying to simulate a metallic nanoparticle (few tens of atoms) 
> in water
>
>  
>
> I have two (maybe simple) questions:
>
>  
>
> a) From this post 
>
> https://groups.google.com/forum/#!topic/cp2k/GEKLwRQat_M
>
>  
>
> my understanding is that the SMEAR option populates the alpha and beta 
> channel according to a Fermi-Dirac 
>
>  
>
> In LSD + MULTIPLICITY (or LSD + RELAX MULTIPLICITY)
>
>
> https://groups.google.com/forum/#!searchin/cp2k/smearing$20spin%7Csort:date/cp2k/ugkJLz4PSSI/C-ProBR6BwAJ
>
>  
>
> my understating is that after energy levels are calculated, electrons are 
> placed according to Aufbau principle, from the lowest to the highest in an 
> unrestricted scheme. If MULTIPLICITY is set, the multiplicity is fixed, 
> with RELAX_MULTIPLICITY no
>
>  
>
> Please correct me if my understanding is mistaken.
>
>  
>
> Question: are the two approaches (SMEAR vs. LSD +RELAX_MULTIPLICTY) 
> equivalent? One approach is more appropriate than the other for particular 
> systems? Is the computational cost the same?
>
>  
>
> b) If I use LSD +MULTIPLICTY in the output I get the
>
>  
>
> “Integrated absolute spin density” and  “Ideal and single determinant S**2”
>
>  
>
> That are equations (2.271) and (2.272) in “Modern Quantum Chemistry: 
> Introduction to Advanced Electronic Structure Theory,Attila Bangha Szabo, 
> Neil S. Ostlund “
>
>  
>
> https://groups.google.com/forum/#!topic/cp2k/flEEaseAd7c
>
>  
>
>  
>
> If I see the output of my calculation with SMEAR I do not see such or any 
> other information about the spin state of my system. 
>
>  
>
> Question: Is this expected? How I can easily get information about the 
> spin state of my system when using SMEAR?
>
>  
>
> Thank you very much for any possible help
>
>  
>
> Best regards
>
> Ivan
>
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