[QE-users] Binding energy for Graphene-metal interface

[Giuseppe Mattioli]

Dear unknown user (please remember to always sign your posts with name  
and affiliation)

Your input is a good starting point for a newbie. think through the  
following hints/suggestions:

1) calculation = 'vc-relax'

You want to relax the lattice parameters of a (possibly) strained  
structure. This may lead to strange structures, different from  
expected. I suppose that no process can alter the subsiding Cu  
lattice, so that I suggest you to stick to Cu lattice parameters, or  
to optimize Cu bulk parameters and then use the results in a simple  
'relax' calculation

2) ecutwfc = 30, ecutrho = 240

Have you performed convergence tests (or used suggested values, they  
should be printed within the files)?
Quoting wallexact--- via users <users at lists.quantum-espresso.org>:

3) Cu.pz-dn-kjpaw_psl.0.2.UPF

you are using Perdew-Zunger (i.e., LDA) exchange-correlation this will  
lead to overbind the graphene sheet to Cu, but in a wrong "covalent"  
fashion rather than by means of dispersion forces. You should rather  
use a GGA functional, either adding a dispersion correction (like D3)  
or a dispersion correlation functional (maybe one belonging to the  
large family of vdwdf)

4) smearing='mv'

'mv' is correct for metals, but less stable than 'gaussian'. I suggest  
to optimize your system with the latter and then restart the converged  
system with the former.

HTH
Giuseppe

> Hello All,
> I started using QE this month and I'm interested in calculating the  
> binding energy of graphene/cu(111) interface using just 1x1 unit  
> cell of both.
> I used vesta to create the cu(111) slab and also join the graphene  
> with the cu(111) slab. I have an input file but I'm not certain if I  
> got all the inputs correctly. Also, do I execute a 'vc-relax' or  
> 'relax' calculation?
> Your advice would be highly appreciated.
> Thanks,



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>