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

[Ivan Gladich]

Dear Matthias and Marcella

thank you very much for your reply. 
Now is much more clear.

However, I still have one doubt.

While in LSD we know the spin state of the system (i.e., S**2 and 
integrated spin mentioned above) at any step,
it seems to me that in SMEAR we lost such information: as Matthias said, 
.S**2 and integrated spin cannot be calculated for fractional occupation in 
SMEAR.

Using SMEAR, is it possible to define some average quantities defining the 
spin state of the system?
I do not know, for example,  the average occupation of the alpha and beta 
channels?
Or something else?

Thank you very very much for your replies and help

Best
Ivan 



On Tuesday, August 18, 2020 at 5:54:48 PM UTC+3, Marcella Iannuzzi wrote:
>
> 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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>>
>
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