[QE-users] phonon calculations on polar slabs - imaginary modes

Thomas Brumme thomas.brumme at uni-leipzig.de
Fri Apr 6 16:08:45 CEST 2018

Dear Chris,

I think that the dipole correction is not working in ph.x, but
you could try the new Coulomb cutoff technique implemented
in both pw.x and ph.x by Sohier and coworkers, see
assume_isolated = '2D'



On 06.04.2018 15:57, Christoph Wolf wrote:
> Dear all,
> I am curious if someone could shed some light onto the following:
> I am currently calculating phonons of MgO using QE 6.2.1 and NC PPs 
> from the ONCV library (requirement of post-processing with YAMBO). 
> Bulk properties (lattice and vibrational) are very nicely reproduced.
> When moving to slabs (1,2,3 layers with ca 20 A vacuum, dipfield 
> correction applied) phonons become considerably "ugly" (very high 
> energy imaginary modes). I was wondering if there is a "trick" to get 
> better phonons in slabs with polar surfaces either during ph.x (I 
> tried tighter convergence down to 10e-16, higher k grids in pw.x, 
> higher q grids in ph.x without much success) or post-processing (not 
> sure if the usual ASR are applicable in slabs)?
> Since calculations on the slabs are rather time consuming any 
> suggestion is very welcome!
> A nice weekend to everyone from San Sebastian,
> Chris
> -- 
> Postdoctoral Researcher
> Center for Quantum Nanoscience, Institute for Basic Science
> Ewha Womans University, Seoul, South Korea
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Dr. rer. nat. Thomas Brumme
Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
Leipzig University
Phillipp-Rosenthal-Strasse 31
04103 Leipzig

Tel:  +49 (0)341 97 36456

email: thomas.brumme at uni-leipzig.de

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