[CP2K-user] [CP2K:19983] Inquiry on ROKS Calculation Schemes within CP2K

[Lukas Razinkovas]

Dear CP2K Community,


As a newcomer to CP2K (my experience is with VASP, GPAW, and Quantum 
Espresso), I have been exploring CP2K's capabilities, particularly for 
modeling low-spin bi- and tri-radical states of crystal defects through 
ROKS (Restricted Open-Shell) calculations for potential energy surface 
analysis. I am pleasantly surprised by this code's performance and 
capabilities. 


However, I am slightly confused with ROKS calculations within CP2K, 
especially regarding the implementation and application of its varying 
schemes, namely:



   - High-Spin ROKS (default ROKS_SCHEME value)
   - GENERAL (an alternative ROKS_SCHEME value)
   - Low-Spin ROKS
   
   
I would greatly appreciate any directed literature or resources that 
elaborate on these schemes' implementation and practical use.


Additionally, I have a few specific inquiries that I hope could be 
clarified:



   1. Is the High-Spin ROKS scheme tailored for single-determinant maximal 
   spin states, where all unpaired electrons align in one spin direction? Can 
   it also model mixed (spin-contaminated) single-determinant states for the 
   von Barth/approximate spin projection method?
   2. For modeling the doublet state in a triradical scenario, I am 
   considering the following configuration:
   &LOW_SPIN_ROKS 
     # DOBLET: E(D) = E(Q) - 3/2*E(Q) + 3/2*E(M) 
     ENERGY_SCALING -1.5 1.5 
     SPIN_CONFIGURATION 1 1 1 # Psi(Q) |a a a> 
     SPIN_CONFIGURATION 1 1 2 # Psi(M) |a a b> 
   &END LOW_SPIN_ROKS 
   Is this the correct approach?
   3. I encountered difficulties running LOW_SPIN_ROKS with the R2SCAN 
   functional (however, it worked with PBE). Are there compatibility issues 
   with meta-GGA functionals?
   4. Can the energy outcomes from maximal-spin and low-spin calculations 
   be compared to deduce exchange splitting (excitation) energy?
   
   
I look forward to any recommendations or advice you could provide.



Best wishes,

Lukas 

-- 
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 on the web visit https://groups.google.com/d/msgid/cp2k/025e1887-09f0-4460-a1ae-24662777baf9n%40googlegroups.com.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20240302/596cc01f/attachment.htm>