# [Pw_forum] how to determine the value of U in a lda+U calculation

Matteo Cococcioni matteo at umn.edu
Mon Apr 5 23:52:51 CEST 2010

```Only atoms for which you want to compute U should be listed.
same thing in the file of positions.

Matteo

duchl06 wrote:
> Dear Matteo
> thanks for your quick reply, so another question as i mentioned in the
> former email.
> if we have different atoms with different number, how we set the value
> of the keyword below
> >> ntyp = 1 # number of types of atoms
> >> na(1) = 2 # number of atoms per type
> or is it only relate to the atom with a nonzero U value.
> best regards!
> du
>
> ÔÚ2010-04-05 21:48:59£¬"Matteo Cococcioni" <matteo at umn.edu> Ð´µÀ£º
> >
> >Dear Du,
> >
> >the input you found below is to extract the U values from a series of
> >scf calculations.
> >You can give a look (besides the reference cited below) to the tutorials
> >you find in this webpage:
> >http://www.quantum-espresso.org/wiki/index.php/QESB09.
> >Unfrtunately the value of U is generally not portable and changes
> >depending on the invironment of the atom in the
> >specific crystal you are considering. the one you cite is a good
> >example: Fe in bulk Fe and in FeO.
> >So in principles we need to recompute it each time.
> >
> >hope this helps.
> >
> >Matteo
> >
> >
> >duchl06 wrote:
> >> dear pw users
> >> i want to do a calculation of V chain absorb on a plane with DFT+U,
> >> but i donot know how to determine the value of U.
> >> i found a PPT on the pwscf's media site, they said the value of U
> >> could be decised by a linear response approach.
> >> but i really donot understand that like the input file resp_mat.in
> >>
> >> &input_mat
> >> ntyp = 1 # number of types of atoms
> >> na(1) = 2 # number of atoms per type
> >> if we have different type atoms with different number, how we set these?
> >>
> >> nalfa = 5 # number of perturbations (alpha)
> >> filepos = 'pos_sc1' # file containing the atomic positions and the
> >> vectors of the unit cell
> >> back = 'neutral' # to add a neutralizing ¡°background¡±. see PRB 71
> >> 35105 (2005)
> >> what does this mean
> >> filednda = 'file_sc1' # file containing the names of the files dn*dat
> >> n1 = 4
> >> n2 = 4 # number of unit cells in each direction to construct the
> >> supercell for
> >> n3 = 4 # extrapolation (in this case a 4x4x4 supercell of the SC one)
> >> &end
> >>
> >> and they get the U is about 2.4ev for the iron, and they use 4.3ev for
> >> the FeO calculation,
> >> we always need a linear response approach to get the U for every system
> >> or just a U for a certain pseudopotential (i mean if we get a U for V
> >> bulk, then if i could use this value for another system with V atom,
> >> like V2O3 etc.)
> >> any suggestions or comment would be OK.
> >> thanks
> >>
> >> Du
> >> xiaguanying university
> >>
> >>
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>
>
>
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--
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Matteo Cococcioni
Department of Chemical Engineering and Materials Science,
University of Minnesota
421 Washington Av. SE
Minneapolis, MN 55455
Tel. +1 612 624 9056    Fax +1 612 626 7246
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