Dear Fedor, thank you for your message. I have found a (fairly OK) solution to applying higher fields that seems to work OK with graphene and is actually described in example 10 of PW but I think the sample does not apply the technique. I quote:
"To perform a calculations with an electric field, an estimate of the optimized wavefunctions is needed to build the electric field operator (See: I. Souza, J.Iniguez and D. Vanderbilt, PRB 69, 085106, 2004). Therefore when lelfield ==.true. a copy of the wavefunctions is read from disk (i.e. startingwfc should be 'file')." therefore one first runs the scf input file with everything present but the efield turned off (efield_cart(1,2,3)=0.0). After converging this one copies edits the efield (efield_cart(3)=0.02) and adds "startingwfc='file'); this has allowed me to use much higher fields than a "cold start" (startingwfc='random') and the behavior seems consistent with literature! It seems that in the zero-field case all efield related inputs have to be present, otherwise I ran into some I/O error ( Error in routine gk_sort (1): array gk out-of-bounds) Hope this helps people encountering convergence problems in the future! With best regards, Chris On Fri, Jan 5, 2018 at 12:40 AM, Fedor Goumans <[email protected]> wrote: > > Dear Christoph, > > While I don’t have an answer to your specific QE question, the application of an electric field to a 2D material in a plane wave code may be problematic to begin with. > We had someone try out band gap closure in the ‘MoWSeS’ materials under electric fields (which would amount to sawtooth potentials in PW codes if I understood correctly). > In that case PW codes would just give wrong behavior, while localized AO codes with prober 2D pbc (and a homogenous electric field) would allow for polarization across the surface. > See e.g.: https://www.scm.com/highlights/closing-band-gap-2d-semiconductors/ > > Hope this helps, > Best wishes, > Fedor > > On Jan 1, 2018, at 13:13, Christoph Wolf <[email protected]> wrote: > > Dear all, > > a happy new year! > > I have recently played with 2-D materials (yes, graphene) and electric fields. I encountered several situations where convergence is really hard to achieve and I was wondering which of the following parameters is usually considered to be helping with convergence > > &control > .... > lelfield=.true. > gdir=3 > nberrycyc=6 > nppstr=1 > / > > &ELECTRONS > .... > mixing_beta=0.4 > mixing_mode='TF' > efield_cart(3)=0.00275 > / > > > the system is separated in z-direction by ~20A of vacuum. the cutoffs for (NC) PPs were converged in the field-free case. > > What is a suggested "systematic" approach to get convergence in fields of this magnitude? > > Your help is greatly appreciated! > > With best wishes for the new year, > > Chris > -- > Postdoctoral Researcher > Center for Quantum Nanoscience, Institute for Basic Science > Ewha Womans University, Seoul, South Korea > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum > > > Dr. T. P. M. (Fedor) Goumans > Business Developer > Software for Chemistry & Materials > Vrije Universiteit, FEW, Theoretical Chemistry > De Boelelaan 1083 > 1081 HV Amsterdam, The Netherlands > T +31 20 598 7625 > https://www.scm.com > https://twitter.com/SCM_Amsterdam > https://www.linkedin.com/company/software-for-chemistry-&-materials > > > -- Postdoctoral Researcher Center for Quantum Nanoscience, Institute for Basic Science Ewha Womans University, Seoul, South Korea
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