[CP2K-user] [CP2K:19518] Re: Problem with the calculation of the CUBE file and Wannier Centres using the ROKS method?

[Ilya Fedorov]

I solved the problem and it was accepted into the code.

   1. As I understand it, for ROKS the UKS base is used, and different 
   spins of the same orbital have the same density. This allows to rely on the 
   UKS codes, while you can use MO_CUBES only for spin-1. (regtest: 
   QS/regtest-lsroks/O2_mo_cubes.inp)
   
   2. I added such an implementation in the code. Only two method supports:
      - NONE: No rotation, just print the orbital centers.
      - JACOBI: Only doubly occupied orbitals rotate; for singly occupied 
      orbitals, no rotation occurs (like the NONE method). (regtest: 
      QS/regtest-lsroks/O2_loc_wan_jac.inp)
   
It is possible to use only NONE and JACOBI. Other methods can be added in 
the future, but ROKS calculates quite slowly, and speeding up the Wannier 
calculation does not make a big contribution here.

Commits: https://github.com/cp2k/cp2k/pull/3108
четверг, 24 августа 2023 г. в 15:19:45 UTC+3, Ilya Fedorov: 

> Dear colleagues, 
>
>  Could you please help me to understand the CP2K implementation of ROKS 
> and the Wannier Centers.
>
> I am facing the following two problems. I can't find an answer in the 
> documentation. And, unfortunately, I don't really understand in the code.
>
> 1) The ROKS implementation in CP2K uses a spin-restricted calculation with 
> multiple density matrices. As I understand it, this leads to some problems 
> with printing CUBE files (for example, for each orbital it prints two cube 
> files for spin_1 and spin_2). Which one is correct? Maybe the sum of them 
> gives a correct density? 
>
> (in log it print “Unclear how we define MOs in the restricted case ... 
> skipping”)
>
>  
>
> 2) I’m trying to use Wannier Centres with ROKS, but it doesn’t work in 
> CP2K. As I understand this is also a multiple density matrix problem. I 
> need Wannier Centres only (Many-body Position operator, no Jacobi 
> rotation). Right now I use Wannier + ROKS in CPMD, and in CPMD the rotation 
> is just switched off for the last two orbitals (diag(1,1)). 
>
> Best regards
>
> Ilya
>

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