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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>To All:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>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).<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>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.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I hope I’ve made the issue/question clear and haven’t said anything egregriously stupid.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks in advance,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Paul Grant<o:p></o:p></p><p class=MsoNormal>IBM Research Staff Member Emeritus<o:p></o:p></p><p class=MsoNormal>Visiting Scholar, Stanford<o:p></o:p></p></div></body></html>