[Pw_forum] Comments on Graphene on BN relaxation

mohamed sabri majdoub majdoub at gmail.com
Tue Jan 26 20:24:55 CET 2010


Dear Linh,

I am trying to understand what you just explain.
If I keep the bottom and middle layer fixed (BN layers) and I only translate
the third layer on the top of them (graphene) by an amount corresponding to
the interlayer increase d. For example delta d =0.1 Ang.
Originally, the interlayer distance is for example d=3.3 Ang  is increased
to 3.4 Ang by moving top layer up by 0.1 Ang and increasing the supercell
size in the z direction by 0.1 Ang. I mean adding 0.1 Ang more vacuum on the
top layer to keep a vacuum distances on the top graphene and bottom BN layer
of 8 Ang for each side.
Is it the right way?

Thank you very much for your help.

On Tue, Jan 26, 2010 at 1:00 PM, Ngoc Linh Nguyen <nnlinh at sissa.it> wrote:

> mohamed sabri majdoub wrote:
> > Dear Linh,
> >
> > Thank you for your response.
> > So, do you suggest that I should increase the supercell size (by the
> > same amount of d increase) each time I increase the value of d?
> You should do that if d values change by moving 1st and 3rd layer and
> keep middle layer.
> Somehow, let try to keep away the interactions of the layers between
> neighbor supercells.
> > Thanks,
> >
> > On Tue, Jan 26, 2010 at 11:02 AM, Ngoc Linh Nguyen <nnlinh at sissa.it
> > <mailto:nnlinh at sissa.it>> wrote:
> >
> >      > When I plot the graph, it looks like ecutwfc =60 is optimal. Is it
> >     right? Is it the right way to do > it? Is the final energy (obtained
> >     from last relaxation step) the right quantity?
> >     I think what you did for checking E vs. ecutwfc is right. However,
> >     with
> >     the big model it could be quite expensive. You can do like that: you
> >     choose an ecutwfc value firstly, for example ecutwfc = 40 Ry, and
> >     relax
> >     your model with that value, then increase the value ecutwcf and
> >     run scf
> >     only, you can obtain a relation E vs. ecutwfc in similar.
> >
> >      > For Final energy (obtained from last relaxation step) vs d
> >     interlayer
> >     distance at cutoff ecutwfc = 50.0:
> >      > .... ecutwfc = 60.0
> >     I am confusing about increasing of d values in your models.
> >         If you keep the sizes of supercell unchanged, when increasing the
> >     value of d, the 3rd layer of the above supercell and 1st layer of the
> >     below supercell should be approached too close together, i.e. ,
> >     let try
> >     visualizing by Xcryden at different values of d. And it can reduce an
> >     increase of energy of your models as d is lager.
> >
> >     Good luck,
> >     Linh
> >     mohamed sabri majdoub wrote:
> >     > Dear all,
> >     >
> >     > I run calculations of 1 layer of graphene on bilyaer boron nitride.
> >     > I am trying to study the Energy vs cutoff and Energy vs interlayer
> >     > distance d between the graphene layer and top of BN layer.
> >     > I got the following results after several runs. Is it the right
> >     way to
> >     > do it?
> >     > Here is the input file I am using:
> >     >
> >
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> >     >  &control
> >     >              title = 'GphBN'
> >     >        calculation = 'relax'
> >     >             outdir = '/pwscf/pwscftemp'
> >     >             prefix = 'GphBN'
> >     >         pseudo_dir = '/pseudopot-C-B-N'
> >     >           tprnfor  = .t.
> >     >       restart_mode = 'from_scratch'
> >     >         wf_collect = .true.
> >     >            disk_io = 'low'
> >     >  /
> >     >  &system
> >     >              ibrav = 0,
> >     >          celldm(1) = 1.8897261
> >     >                nat = 72,
> >     >               ntyp = 3,
> >     >            ecutwfc = 60.0
> >     >        occupations = 'smearing'
> >     >           smearing = 'gaussian'
> >     >            degauss = 0.003675
> >     >
> >     >  /
> >     >  &electrons
> >     >     mixing_mode = 'local-TF'
> >     >     mixing_beta = 0.05
> >     >     diagonalization = 'david'
> >     >     conv_thr = 1.D-5
> >     >  /
> >     >  &ions
> >     >   trust_radius_ini = 0.10
> >     >
> >     >  /
> >     >  &cell
> >     >
> >     > ATOMIC_SPECIES
> >     >  B    10.81100   B.pz-vbc.UPF
> >     >  C    12.01070   C.pz-vbc.UPF
> >     >  N    14.00674   N.pz-vbc.UPF
> >     > ATOMIC_POSITIONS angstrom
> >     >  B         0.710000        8.607000       11.306000
> >     >  B         0.710000       11.066000       11.306000
> >     >  B         2.840000        7.377000       11.306000
> >     >  B         0.710000        6.148000       11.306000
> >     >  B         6.390000        6.148000        8.000000
> >     >  B         6.390000        8.607000        8.000000
> >     >  B         6.390000       11.066000        8.000000
> >     >  B         2.840000        9.836000       11.306000
> >     >  B         7.100000        7.377000       11.306000
> >     >  B         7.100000        9.836000       11.306000
> >     >  B         7.100000       12.295000       11.306000
> >     >  B         4.970000       11.066000       11.306000
> >     >  B         2.840000       12.295000       11.306000
> >     >  B         4.970000        6.148000       11.306000
> >     >  B         4.970000        8.607000       11.306000
> >     >  B         4.260000        7.377000        8.000000
> >     >  B         2.130000       11.066000        8.000000
> >     >  B         2.130000        8.607000        8.000000
> >     >  B         2.130000        6.148000        8.000000
> >     >  B         4.260000        9.836000        8.000000
> >     >  B         0.000000        7.377000        8.000000
> >     >  B         0.000000        9.836000        8.000000
> >     >  B         4.260000       12.295000        8.000000
> >     >  B         0.000000       12.295000        8.000000
> >     >  C         2.130000        6.148000       14.106000
> >     >  C         2.130000        8.607000       14.106000
> >     >  C         2.130000       11.066000       14.106000
> >     >  C         0.000000       12.295000       14.106000
> >     >  C         0.000000        9.836000       14.106000
> >     >  C         0.000000        7.377000       14.106000
> >     >  C         0.710000       11.066000       14.106000
> >     >  C         0.710000        8.607000       14.106000
> >     >  C         0.710000        6.148000       14.106000
> >     >  C         6.390000        8.607000       14.106000
> >     >  C         6.390000        6.148000       14.106000
> >     >  C         4.970000       11.066000       14.106000
> >     >  C         6.390000       11.066000       14.106000
> >     >  C         7.100000       12.295000       14.106000
> >     >  C         7.100000        9.836000       14.106000
> >     >  C         7.100000        7.377000       14.106000
> >     >  C         4.970000        8.607000       14.106000
> >     >  C         2.840000       12.295000       14.106000
> >     >  C         2.840000        9.836000       14.106000
> >     >  C         2.840000        7.377000       14.106000
> >     >  C         4.260000        7.377000       14.106000
> >     >  C         4.970000        6.148000       14.106000
> >     >  C         4.260000       12.295000       14.106000
> >     >  C         4.260000        9.836000       14.106000
> >     >  N         0.000000       12.295000       11.306000
> >     >  N         0.000000        9.836000       11.306000
> >     >  N         0.000000        7.377000       11.306000
> >     >  N         2.840000        7.377000        8.000000
> >     >  N         2.840000        9.836000        8.000000
> >     >  N         2.840000       12.295000        8.000000
> >     >  N         4.970000       11.066000        8.000000
> >     >  N         4.970000        8.607000        8.000000
> >     >  N         4.970000        6.148000        8.000000
> >     >  N         7.100000       12.295000        8.000000
> >     >  N         7.100000        9.836000        8.000000
> >     >  N         7.100000        7.377000        8.000000
> >     >  N         0.710000        6.148000        8.000000
> >     >  N         0.710000        8.607000        8.000000
> >     >  N         0.710000       11.066000        8.000000
> >     >  N         6.390000       11.066000       11.306000
> >     >  N         6.390000        8.607000       11.306000
> >     >  N         6.390000        6.148000       11.306000
> >     >  N         2.130000       11.066000       11.306000
> >     >  N         2.130000        8.607000       11.306000
> >     >  N         2.130000        6.148000       11.306000
> >     >  N         4.260000       12.295000       11.306000
> >     >  N         4.260000        9.836000       11.306000
> >     >  N         4.260000        7.377000       11.306000
> >     > K_POINTS automatic
> >     > 10 10 1 1 1 0
> >     > CELL_PARAMETERS
> >     > 8.51980 0.00000 0.00000
> >     > 0.00000 7.37600 0.00000
> >     > 0.00000 0.00000 22.6120
> >     >
> >
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> >     > The results are :
> >     >
> >     > 1- Final energy (obtained from last relaxation step) vs cutoff
> >     (ecutwfc)
> >     >
> >     > cut20: Final energy   =    -857.6291985882 Ry
> >     > cut30: Final energy   =    -876.5012327526 Ry
> >     > cut40: Final energy   =    -885.4765196610 Ry
> >     > cut50: Final energy   =    -890.0493283821 Ry
> >     > cut60: Final energy   =    -892.0114549785 Ry
> >     > cut70: Final energy   =    -892.8706506804 Ry
> >     > cut80: Final energy   =    -893.2520149989 Ry
> >     >
> >     > When I plot the graph, it looks like ecutwfc =60 is optimal. Is it
> >     > right? Is it the right way to do it? Is the final energy (obtained
> >     > from last relaxation step) the right quantity?
> >     >
> >     >
> >
> ------------------------------------------------------------------------------------------------------------------------------------------------------------
> >     > 2- For Final energy (obtained from last relaxation step) vs d
> >     > interlayer distance at cutoff ecutwfc = 60.0:
> >     >
> >     > d=2.5= Final energy   =    -892.0122348924 Ry
> >     > d=3.0= Final energy   =    -892.0119194861 Ry
> >     > d=3.1= Final energy   =    -892.0089055437 Ry
> >     > d=3.2= Final energy   =    -892.0104083862 Ry
> >     > d=3.3= Final energy   =    -892.0115677649 Ry
> >     > d=3.4= Final energy   =    -892.0113018510 Ry
> >     > d=3.5= Final energy   =    -892.0121118001 Ry
> >     > d=3.6= Final energy   =    -892.0113544429 Ry
> >     > d=3.7= Final energy   =    -892.0096184164 Ry
> >     > d=3.9= Final energy   =    -892.0041914533 Ry
> >     >
> >     > There are fluctuations in the data? Is it normal?
> >     >
> >
> -----------------------------------------------------------------------------------------------------------------------------------------------------
> >     >
> >     > 3-  For Final energy (obtained from last relaxation step) vs d
> >     > interlayer distance at cutoff ecutwfc = 50.0:
> >     >
> >     > d=2.5= Final energy   =    -890.0504214490 Ry
> >     > d=2.8= Final energy   =    -890.0503533642 Ry
> >     > d=2.9= Final energy   =    -890.0503471460 Ry
> >     > d=3.0= Final energy   =    -890.0486572147 Ry
> >     > d=3.1= Final energy   =    -890.0491375298 Ry
> >     > d=3.2= Final energy   =    -890.0480863744 Ry
> >     > d=3.3= Final energy   =    -890.0492074574 Ry
> >     > d=3.4= Final energy   =    -890.0501303488 Ry
> >     > d=3.6= Final energy   =    -890.0488317041 Ry
> >     > d=3.5= Final energy   =    -890.0492797825 Ry
> >     > d=3.7= Final energy   =    -890.0470527582 Ry
> >     > d=3.8= Final energy   =    -890.0443250729 Ry
> >     > d=3.9= Final energy   =    -890.0412177248 Ry
> >     >
> >     > Same thing for these data.
> >     > Is there any thing wrong?
> >     > Your suggestions are welcomed.
> >     >
> >     > Thank you in advance for your help!
> >     >
> >     > Regards,
> >     >
> >     > ME
> >     > University of Houston
> >     >
> >     >
> >     >
> >     >
> >     >
> >
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