[Pw_forum] Acoustic sum rule in 2D surfaces

[Charlie Ruffman]

Hi all,


My group has recently begun using QE to simulate the Raman spectra of 2D bulk MoS2 surfaces. The surface is periodic in the x and y direction.


We typically calculate at least one imaginary mode of vibration (at ~ 34 cm-1), and were wondering if it was valid to apply a "crystal" acoustic sum rule, which removes the imaginary frequency. Also, does anyone have insight into whether we should be applying a different type of acoustic sum rule than crystal (eg. one-dim or zero-dim)?


Thanks for your time,


Charlie Ruffman


University of Otago,

New Zealand


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