[Pw_forum] Convergence with and without U parameter

[Lorenzo Paulatto]

On 16/09/17 06:53, Phanikumar Pentyala wrote:
> Hi QE community,
>
> I am working on improving properties of doped metal oxides. Currently 
> doing relaxation calculations for CeO2. I am facing a problem when 
> relaxation calculation with HUBBARD parameter for 'Ce' (took from 
> literature *U=5eV*), calculation stopped *without any ERROR or CRASH 
> message*.

Dear Phanikumar,
there is always some error message, either from pw.x, from mpi or from 
the operating system. Maybe you did not see, if you are running in a 
computing cluster, ask the administrator for help on how to find out 
what's going on.

A few more comments about your input:
1. you have disabled symmetry, is there any specific reason to do so? 
You system seems to be a unit cel with all the atoms moved around a bit, 
does the unit cell work?
2. you are not using spin polarization, I'm not sure it makes sense to 
do lda+U in this case
3. your cutoff of 40Ry is likely 3 or 4 times too small for FHI 
norm-conserving pseudopotential of Oxygen and Cerium
4. the values of U from literature are to be taken with care, because 
they are system dependent and pseudo-potential dependent.

kind regards


> But when I am trying without HUBBARD parameter of 'Ce', calculation 
> achieving convergence. Another interesting thing I observed from 
> previous posts, When I tried with *U=1eV* (low values of HUBBARD), 
> calculation achieving convergence. Can you please say what will be the 
> reason for this behaviour? and Is there anywhere I am using wrong 
> parameters in the input file? (Here I am attaching my input file for 
> the reference)
>
>
> Thanks in advance
>
>
>
> Regards
>
> Phanikumar
> Research Scholar
> IIT Kharagpur, Kharagpur
> West Bengal, India.
>
>
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-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 442 79822 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/423 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05

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