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SUMMARY:Long-range screening and interatomic forces: from 3D to 2D - Mique
 l Royo\, Institut de Ciència de Materials de Barcelona
DTSTART:20220124T143000Z
DTEND:20220124T150000Z
UID:TALK167264@talks.cam.ac.uk
CONTACT:Dr M. Simoncelli
DESCRIPTION:The foundation of modern theory of lattice dynamics rests on t
 he separation between short-range and long-range interatomic force constan
 ts\, where the latter are associated with macroscopic electric fields acti
 ng in a neighborhood of the Brillouin zone center. In three-dimensional (3
 D) insulators\, the famous dipole-dipole formula was established long ago 
 by Cochran and Cowley\; the subsequent work of Pick\, Cohen and Martin pro
 vided a formal derivation in the framework of first-principles theory.\nRe
 cently\, we have incorporated higher-order interactions involving\, e.g.\,
  dynamical quadrupoles\,[1] and demonstrated their role in the accurate in
 terpolation of phonon band structures.[2] In this talk\, I shall retrace a
 n analogous journey in the context of two-dimensional (2D) crystals\, by p
 resenting a rigorous derivation of the long-range screening and interatomi
 c forces in 2D.[3] This enables a systematic generalization of the existin
 g formulas [4] to an arbitrary multipolar order. In particular\, I will di
 scuss how to incorporate out-of-plane dipoles and dynamical quadrupoles in
  the long-range part of the dynamical matrix\, and how to achieve an optim
 al representation of the dielectric function. Numerical tests on monolayer
  BN\, SnS2 and BaTiO3 membranes demonstrate a drastic improvement in the d
 escription of the long-range electrostatic interactions\, with comparable 
 benefits to the quality of the interpolated phonon band structure.[3]\n\n[
 1] M. Royo and M. Stengel\, Physical Review X 9\, 021050 (2019).\n\n[2] M.
  Royo\, K. Hahn and M. Stengel\, Physical Review Letters 125\, 217602 (202
 0).\n\n[3] M. Royo and M. Stengel\, Physical Review X 11\, 041027 (2021).\
 n\n[4] T. Sohier et al.\, Nano Letters 6\, 3758 (2017).
LOCATION:Venue to be confirmed
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