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

[duchl06]

could you tell me what does the first three rows mean 

i saw they are all
10.d0 0.d0 0.d0
0.d0 10.d0 0.d0
0.d0 0.d0 10.d0
in your example.

and the others must be in internal crystal coordinates?
Thanks!
Du


在2010-04-06 05:52:51，"Matteo Cococcioni" <matteo at umn.edu> 写道：
>
>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
>>
>> 在2010-04-05 21:48:59，"Matteo Cococcioni" <matteo at umn.edu> 写道：
>> >
>> >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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>
>-- 
>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>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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