[Pw_forum] Occupation matrix in LDA+U

[elbuesta at icqmail.com]

Dear all,

We have a fews questions/doubts concerning the ns occupation matrix for LDA+U calculations (starting_ns_eigenvalue(m,ispin,I)). Following the idea presented in example 25 of quantum espresso, we are trying to fix the initial occupation of the "d" orbital of Ni in a monolayer of NiO in an anti-ferromagnetic state. The questions we have are:

1) Are each of the diagonal elements of the occupation matrix associated with the d orbitals? Something like, 
(1,1) -> dz2, (2,2) -> dzx, (3,3) -> dzy, (4,4) -> d(x2-y2) and  (5,5) -> dxy   ?
2) If there is this correspondence, is it possible to specify an initial occupation of each of the orbitals after the initial guess is evaluated in the first iteration? For example, in the attached input, how could we specify that only the dz2, dxz and dyz orbitals are initially completely occupied with 2 electrons? In other words, how can we change the "spin down occupation matrix" of the Ni atom from 
0.6 0.0 0.0 0.0 0.0            1.0 0.0 0.0 0.0 0.0
0.0 0.6 0.0 0.0 0.0            0.0 1.0 0.0 0.0 0.0
0.0 0.0 0.6 0.0 0.0     ->    0.0 0.0 1.0 0.0 0.0
0.0 0.0 0.0 0.6 0.0            0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.6            0.0 0.0 0.0 0.0 0.0
??

Thanks very much for your time,
With best regards,

Luca Sementa, Fábio Negreiros
Postdoc students,
IPCF - CNR - Pisa, Italy
 

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