[Pw_forum] Hubbard U of Zn in ZnO

[Yu Xue]

Hello,all,

I am trying to use LDA+U to do some calculations on ZnO.
First,I need to decide Hubbard U of Zn in the scheme of Dr.Cococcioni,see 
PRB 71,035105(2005)-----(*)
Everything looks good,just the result is unreasonable:

d(alpha)/d(n)=-440.3838054 eV
d(alpha_0)/d(n_0)= -2.2765143 eV
U=(-d(alpha)/d(n))-(-d(alpha_0)/d(n_0))=2.2765143-440.3838054=-438.1072911 
eV

In Shujun Hu's paper,PRB 73, 245205(2006),he mentioned that "The method 
mentioned above is invalid to gain the Hubbard Uzn since diagonal elements 
indicating the Zn sites in Eq(19) of (*) are close to zero due to fully 
occupying of Zn 3d states. " So he uses Uzn as a fitting parameter.I don't 
quite understand that,and wonder,then we can't use  
constrained-density-functional and linear response scheme to calculate 
Hubbard U of Zn?Do we have some tricks to gain Uzn using this scheme?

I appreciate any suggestions from you
Thanks a lot

Sally

_________________________________________________________________
Puzzles, trivia teasers, word scrambles and more. Play for your chance to 
win! http://club.live.com/home.aspx?icid=CLUB_hotmailtextlink