[Wien] 4f and LDA+U

[Stefaan Cottenier]

> I performed spin-polarized calculations on NdTiO3 compound and as 
> excepted the fermi level  lies at the 4f states (due to the strong 
> localisation).

(Probably a word is missing in your last sentence, which gives it the 
opposite meaning? ==> de-localization) The reason why LDA puts the 4f 
states at the fermi level is that it cannot sufficiently localize these 
states. They are hence (incorrectly) described as itinerant states.

> Thereafter, I performed spin-polarized LDA+U (Ueff=6.5 
> ev) calculations 

This value of U might be somewhat at the lower side for lanthanides. Try 
8.5 eV (see http://link.aps.org/doi/10.1103/PhysRevB.74.014409 and 
http://link.aps.org/doi/10.1103/PhysRevB.77.155101 , and references 
therein).

> which split the 4f (up) states : the occupied states 
> down by 3 ev below the Ef and empty states rises by about 5 ev above the 
> Ef. I got two different values of Ef(up) and Ef(dn).
> 
> By applying Ueff=6.5 ev I expected a little split that will let the 4f 
> occupied states at the top of the valence band (around the Ef).    
> Can someone give me a comment about this ? Are also normal to have two 
> different values of Ef (up and dn)?

Such two different values of Ef I've never seen. Are you sure you aren't 
by mistake making an applied field calculation (which is another input 
number in the same case.inorb file you use for LDA+U).

What should happen for Nd is that all dn-states (which are unoccupied) 
move up and find themselves all above Ef, while the up-states split in 
an occupied part several eV below Ef and an unoccupied part several eV 
above Ef.

Stefaan