[Pw_forum] Doubts in U (Hubbard parameter) calculation

[Ifeanyi John ONUORAH]

I suggest you take your time to read this if you have not yet, I am also
learning like you. I might try to experiment with you system to see what I
get with same pseudopotentials as you used.

http://urania.sissa.it/xmlui/handle/1963/2507

and then look at this tutorial

http://www.iiserpune.ac.in/~smr2626/hands_on/week1/july4/

2016-10-16 11:54 GMT+02:00 Phanikumar Pentyala <phani12.chem at gmail.com>:

> Hello QE users
>
> I want to find U value for CeO2 which is having 81 atoms. I already
> calculated this value by using linear response (http://hjklol.mit.edu/
> content/calculating-hubbard-u). I got the U value initially in negative
> numbers in this case *diago_thr_init* value was default, so that I
> changed *diago_thr_init* to 10^-11 then I got U value as 0.00881. From
> literature I found this value should be around 4.5 - 7eV  (Phy. Rev. B 75,
> 035109, 2007͒). I have some doubts regarding this calculation
>
> Is that correct, occupations means I took value in the name of *"N of
> occupied +U levels" *(i.e sum of Tr[ns(na)] values on all 27 Ce atoms)?
>
> What is the unit for value I got (0.00881)? (Ry or eV or any other )
>
> Is U parameter value depend on number of atoms in unit cell?
>
> Is there any other mistake I done in my input file ? (input file attached)
>
> *Conditions I applied in my calculations:*
> Surface calculation with vacuum 15A
> First three layers relaxed (two oxygen and one ceria layers) remaining are
> frozen
>
>
> Thanks in advance and I will be greatly appreciated for your help
>
> (input file and results of my calculation attached)
>
>
> Phanikumar
> Research Scholar
> Indian Institute of Technology Kharagpur
> India
>
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