[Pw_forum] ph.x and Nesting Fermi Surfaces

[W2AGZ]

To All:

 

I'm running some exercises on electron-phonon interactions in narrow band
metal monolayers (actually tetragonal unit cells with "large" c/a
parameters...and think doped transition metal oxides).  In this quasi-2D
system, several of the Fermi surfaces approach planarity (actually, "Fermi
lines"), suggesting  strong electron-phonon interaction should be driven by
the "nesting" wave vector (think CDW and/or Peierls-Froehlich).

 

However, I'm having difficulty seeing how to structure the input to ph.x to
select this wavevector alone (or indeed if this is even possible with ph.x).
Imagine a square-planar BZ with dimensions (0.5, 0.5) in 2pi/a units, with a
"Fermi line" perpendicular to, and kf distance along the (1,1) direction
from the BZ origin.  Now, as far as I can see from the ph.x documentation,
nq1, etc., is only for defining the Monkhorst-Pack grid for the desired
phonon grid-mesh (and are integers anyway).  In principle, one could set the
"line of input" xq's to the desired kf (fractional values are presumably
allowed), but which would have its origin at BZ center, whereas one would
like to "drive" or "excite" the phonons at -kf, +kf together.

 

I hope I've made the issue/question clear and haven't said anything
egregriously stupid.

 

Thanks in advance,

 

Paul Grant

IBM Research Staff Member Emeritus

Visiting Scholar, Stanford

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