[CP2K-user] [CP2K:19542] Re: Problem with the calculation of the CUBE file and Wannier Centres using the ROKS method?

[Ilya Fedorov]

Dear Matthias,

I am sorry for the delay in answering your question.

Indeed, sometimes I observed poor convergence of OT with ROKS, but 
sometimes the convergence is much better than diagonalization in СPMD. But 
at the moment I do not have a systematic understanding of the roots of this 
problem.

I made various comparisons between CPMD and CP2K in terms of calculations 
with ROKS: comparing forces, trajectories, orbitals and Wannier centers, in 
general I got a fairly close agreement.

In the near future I plan to collect these results into one report and post 
it here.

Best

Ilya

четверг, 16 ноября 2023 г. в 15:31:03 UTC+3, Krack Matthias: 

> Hi Ilya
>
>  
>
> Thanks for contributing and fixing the print issue.
>
>  
>
> Indeed, ROKS produces only one set of orbitals, since there is also only 
> one Hamiltonian, i.e. Kohn-Sham matrix, but different orbital occupations 
> are applied for spin-up (alpha) and spin-down (beta) electrons which 
> results in an alpha and beta electronic density matrix.
>
>  
>
> The LOW-SPIN ROKS implementation in CP2K based on OT plus ROTATION is 
> experimental as indicated by a warning printed in the output. That 
> implementation has not been maintained since a long time. Therefore, I am 
> wondering, if the implementation works properly, e.g. for the new test case 
> O2_mo_cubes.inp. I tried tighter thresholds and a larger cutoff and box 
> size, but the SCF did not converge. What’s your experience and how do the 
> results compare to ROKS in CPMD?
>
>  
>
> Best
>
>  
>
> Matthias
>
>  
>
> *From: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Ilya 
> Fedorov <ilyafe... at gmail.com>
> *Date: *Thursday, 16 November 2023 at 10:59
> *To: *cp2k <cp... at googlegroups.com>
> *Subject: *[CP2K:19518] Re: Problem with the calculation of the CUBE file 
> and Wannier Centres using the ROKS method?
>
> 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:
>
> o    NONE: No rotation, just print the orbital centers.
>
> o    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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