Warning on forces using DFT_PLUS_U LOWDIN. Implemented or not?

[Gabriele]

Dear Matthias,

Thanks for the quick reply. After restarting the calculations a few times 
with subsequently larger values of U, the SCF and the whole geometry 
optimization converged using MULLIKEN. However, I would like to run MD on 
this system and after about 100 steps the same warning on unphysical 
Mulliken charges and negative U contribution to the energy appears and the 
SCF does not converge anymore. Using U_RAMPING [eV] 0.1 and 
INIT_U_RAMPING_EACH_SCF did not help. It seems that not only DFT+U is 
sensible to changes in the charge densities in the first SCF but also to 
changes from the previous MD step. I wonder if you or somebody else has 
experienced a similar issue and have any hint on that.

Best wishes,
Gabriele.

On Wednesday, February 5, 2014 7:51:56 AM UTC, Matthias Krack wrote:
>
> Dear Gabriele,
>
> it means that forces are not available for the DFT+U method LOWDIN. You 
> have to use the DFT+U method MULLIKEN. You may try to converge the initial 
> SCF run with U=0eV firstly and then try to restart with DFT+U. DFT+U is 
> sensible to weird charge densities which may easily occur during the first 
> SCF iteration steps when starting from scratch.
>
> Matthias
>
> On Tuesday, February 4, 2014 8:58:27 PM UTC+1, Gabriele wrote:
>>
>> Hi all,
>>
>> I am using DFT+U to relax a defective surface system. Specifically, I am 
>> using the LOWDIN method because I could not make SCF converge using the 
>> MULLIKEN based methods. The relaxation completes fine and the resulting 
>> structure agrees with the literature and calculations performed with a PW 
>> code. However, the following warning appears when computing the forces 
>> using LOWDIN:
>>
>>  *** 18:28:47 WARNING in dft_plus_u:lowdin :: Forces are not yet fully ***
>>  *** implemented for DFT+U method LOWDIN                   
>>                   ***
>>
>> What does it mean that the forces are not fully implemented? Is it 
>> possible just that they have not been fully tested?
>>
>> Thanks.
>> Gabriele
>>
>
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