[Pw_forum] About the part of molteplicities in resp_mat.f90 script of U-calculation

huangxu1706 at sina.com huangxu1706 at sina.com
Thu Apr 10 00:04:06 CEST 2014

Dear all,
I'm confused about the part of "molteplicities" in the resp_mat.f90 script which is used to calculate U value of metal oxides. This part is after the construction of the first matrix = chi0m1 - chim1, and is important for the U-extrapolation from primitive cell to supercell. But I'm not sure the basic idea of this part, because it is beyond the theoretical introduction of the linear response (M. Cococcioni and S. de Gironcoli, Phys. Rev. B 71, 035105 (2005)). 
For this part, I checked the output Umat.n.n.n.out files and found that the variables in the loops, i00, d0, mol, kp, kp0 and spinp, must have something to do with the "number of shells, shell #n: pc, sc, spinp dist chi_pc and chi_sc" in the output. But what is the physical meaning of those variables? How are they correlated with the chi0 and chi in primitive cell, and those in super cell? Why is the "molteplicities" necessary?
I'm working on a project about adapting the U-calculation which was designed for 3-D bulk system ny QE to 2-D surface system. I've made a lot of changes in the resp_mat.f90 script. I got reasonable U values in the first matrix = 
chi0m1 - chim1, but when it reached the molteplicities part, the calculated U values are strange. I believe that this part is also for 3-D system that some variables or loops also need to be modified for 2-D system. I can't treat it as a "black box" and trust its output. So I have to know how this part works.

Thank you,Xu Huang
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