Multiplicity usage

ashish dabral ashishd... at gmail.com
Fri Feb 19 17:28:01 CET 2016


Hello,

I am new to CP2K and would be glad if someone could comment on the the 
following scenario. 

I am having trouble dealing with the MULTIPLICITY keyword. I am working 
with systems that have vacancies and different atoms added on top of that
and I perform unit_cell_ionic relaxations to compute energies.

e.g. an MoS2 suerpcell (say 8x8x1) with one Mo defect. 

1) How can I specify the multiplicity of such a system with a defect. For a 
monolayer MoS2 without defect, I just use MUL=1 and it works (using 2S+1).
    I can randomly try some multiplicity but that doesn't sound right or 
maybe I need more explanations. Sometimes the system won't converge for a 
random MUL.
2) How can I specify the multiplicity of a system with a defect plus an 
additional atom. Say, a Mo defect plus an oxygen atom somewhere in the cell.

My idea of Multiplicity keyword was that if I set it to a particular value, 
the sytem will be forced to converge in a configuration with that kind of 
multiplicity.
if that is true, how can we ensure that we have the right multiplicity? And 
if I specify a multiplicity, am I not presuming against the relaxation? 
because 
I want a relaxed structure with a defect and an extra atom and I tell it to 
go to a particular state which may not be right. Is there some sort of 
prediction involved 
here as to what I want finally?

My apologies, if the question sounds absurd. I am just trying to make sense 
of the keyword especially for systems with default magnetic states.

Any additional information or link is welcome.


Thanks
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