[QE-users] DFPT of thin metal layer: convergence has not been achieved

Oleksandr Motornyi oleksandr.motornyi at polytechnique.edu
Wed Nov 7 12:37:54 CET 2018

Dear Chris,

Regarding your problem with 11 layers of Cu(111):

1. Is there a specific reason you chose a film with 11 layers and not 9, 
10 or 12? fcc metals has 3 types of lattice planes in (111) direction - 
you might consider to use a slab that contains a number of layers that 
is multiple of 3.

2. Does your slab have the inversion symmetry? I have noticed that in 
some cases convergence were slow or I could not even reach it (for PW or 
TDDFT calculations, so I assume it might happen for phonons too) if 
there was no inversion symmetry for the slab.

Speaking of the slowly decaying surface state - if the state you are 
interesting in is a Shockley state around -0.5 eV at Gamma point it will 
most probably be split in energy by about 0.1 eV as the slab is not 
thick enough to decouple the two surface states of opposite surfaces of 
the slab. Is it what you want?

Best regards,

Oleksandr Motornyi

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