When to use LSD option?

[Niharendu Choudhury]

Hi CP2K experts,

I have a system in which a metal ion and water molecules are there.

My metal ion has different oxidation states and accordingly different number of unpaired electron/s (which gives me different multiplicity). So I have CHARGE and MULTIPLICITY KEYWORDS to specify these two in the input file. Then, should I use LSD, if MULTIPLICITY is not equal to one?

Can anybody clarify it.

Regards

Nihar

[Martin Konôpka]

Dear Nihar,

I am not a CP2K expert but I guess you definitely should use either the LSD keyword or one of its synonyms (e.g. SPIN_POLARIZED or UKS or some further) in the calculations you mentioned. In cases when the number of electrons with spin up differs from the number with spin down, such an option is necessary in my knowledge. Even if some part of the calculations be for systems in a (globally) singlet state, I would apply spin polarisation for consistency between the systems under treatment.

Best

Martin.

st 26. 7. 2023 o 10:02 Niharendu Choudhury <nihar...@gmail.com> napísal(a):

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[Niharendu Choudhury]

I am still confused. CHARGE and MULTIPLICITY KEYWORDS are not enough to describe the unpaired electrons in the systems?

Do I need to use SPIN_POLARIZED or UKS in addition to the above keywords? What is the meaning of LSD then?

@Prof. Hutter or any other developers please clarify.

Cheers

Niharendu Choudhury

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Dr. Niharendu Choudhury

Scientific Officer

Theoretical Chemistry Section

Chemistry Group

Bhabha Atomic Research Centre

Mumbai- 400 085, India.

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[Matt Watkins]

Hello,

the LSD (or UKS etc) allows the spin up and spin down orbitals to relax independently due to the different exchange interactions. There are other methods (ROKS for instance, though less often used) that allow open shell calculations without this extra freedom. 

So you need to specify the charge, the multiplicity and the method (LSD).  

This doesn't apply to metallic systems where you have smearing of electrons.

Matt

[Moon Yue]

Dear Mr. Watkins

Thank you for your comments.

So do you mean that smearing of electrons can't be used when UKS is set ?

Yue