[Pw_forum] questions about lda+u calculation

[Максим Иванов]

Dear PW-users,
I have question about calculating the response matrice in lda+u calculation. At the tutorial with examples at page http://media.quantum-espresso.org/santa_barbara_2009_07/index.php is used input file to calculate the matrice. In this input file you need file containing the atomic positions and the vectors of the unit cell plus number of unit cells in each direction to construct the supercell. As I understand response matrice is resiprocal matrix of matrix containing dn/dalfa derivatives. So, why does author include atomic positions in his program? 
In the case when there are more than two Fe atoms in FeO unit cell (let's say 8) is it correct to make perturbation only for one Fe atom? Or should I make perturbation for 8 Fe atoms and calculate 8x8 matrix?
Thanks in advance,
Maxim Ivanov







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