[Pw_forum] Is the Graphite surface flat ?
Giuseppe Mattioli
giuseppe.mattioli at mlib.ism.cnr.it
Tue Jul 6 12:22:00 CEST 2010
Dear Masoud
> this pseudopotential reproduces the experimental cell
> parameter of the bulk correctly and exactly. the predicted cell parameter
> in z-direction (c) by the other pseudopotentials is not so exact and
> sometimes, a difference about 1 angstrom compared to experimental value
> appears.
I do not know if you catch the point... You are using a pseudopotential which
contains a core hole into the C 1s shell. it CAN NOT be used to simulate in a
proper way the graphite bulk! You will collect (actually, have collected...)
weird results! You have luckily obtained a better interlayer distance because
DFT generally fails when dealing with graphite, where the layers are not
connected by covalent bonds. So, if you use a proper C pseudopotential, you
achieve poor results for the c parameter in a vc-relax calculation.
> london=.true. closes the atoms in the different layers to each other in the
> relax calculation and did not solve the problem.
Have you tryed to perform a vc-relax calculation of the graphite bulk by using
a standard pseudopotential (us or nc, as you like) and by switching on the
london=.true. keyword and, after that, to perform a relax calculation with
the same pseudo and at the cell a and b parameters you found in the previous
vc-run in order to optimize your tri-layer graphite slab?
hth
Giuseppe
On Tuesday 06 July 2010 13:09:28 Masoud Nahali wrote:
> Dear pwscf users
>
> answer to the comments:
> (many thanks for your kind attention and help but I could not solve the
> problem)
>
> to G. Scluuzero: I have used the experimental C-C distance but then I have
> vc-relaxed the bulk cell and found the new positions. After vc-relax I have
> used these coordinates to "relax" the atoms in the cell with vacuum. Also
> the innermost layer is not graphite-like and is rippled.
>
> to D. C. Andera: this pseudopotential reproduces the experimental cell
> parameter of the bulk correctly and exactly. the predicted cell parameter
> in z-direction (c) by the other pseudopotentials is not so exact and
> sometimes, a difference about 1 angstrom compared to experimental value
> appears.
>
> to G. Mattioli:
> london=.true. closes the atoms in the different layers to each other in the
> relax calculation and did not solve the problem.
>
> Now I am trying to relax a 5-layer sample and see the result. but it has
> not completed yet. really I do not know the surface of graphite is "ripple"
> in the nature (experimentally) or not? I appreciate your help.
>
> > On 07/05/2010 08:19 PM, Masoud Nahali wrote:
> > > Dear Quantum Espresso users
> > >
> > > I optimized the graphite bulk and the layers were completely flat. But
> > > when I try to "relax" the graphite surface (slab 2*2 with 3 monolayer)
> > > with 10 angstrom vacuum all the layers become extremely ripple!!! I
> > > can not find the problem. May it related to the number of layers?
> > > anyhow the number of layers is like the bulk. Your help would be a
> > > great gift.
>
> G. Scluuzero:
> > > __
> >
> > Are you using the experimental or the theoretical value for the in-plane
> > (graphene) C-C distance? I guess that the PBE value is larger than the
> > experimental one, so that if you start from the experimental C-C
> > distance in the graphene layer and let everything relax, then the atoms
> > would like to go towards the theoretical equilibrium distance and this
> > may cause the rippled structure.
> > Secondly, I don't know if you can pretend that the innermost layer is
> > graphite bulk-like, having only three layers in total.
>
> Dal Corso Andrea :
> > Check the pseudopotential. This is a PP with a core hole for special
> > purposes not for standard simulations.
>
> Giuseppe Mattioli :
> > Dear Masoud
> > apart from the pseudo problem issued by Andrea, you could try the keyword
> > london=.true.
> > It adds a Van der Waals contribution to total energy and it is likely to
> > improve the interlayer interactions in your system.
> > Hope this helps
> > Giuseppe
>
> input file:
>
> &CONTROL
>
> calculation = "relax",
> pseudo_dir =
> "/home/koa/soft/qe4.2/espresso-4.2/pseudo",
> outdir =
> "/home/koa/tmp",
> etot_conv_thr= 1.0D-4,
> forc_conv_thr= 1.0D-3,
>
> nstep=150,
> /
> &SYSTEM
> ibrav = 4,
> a =
> 4.9318,
> b = 4.9318,
> c = 16.7029,
>
> cosab = -0.5,
> cosac = 1.0,
> cosbc = 1.0,
>
> nat = 24,
> ntyp = 1,
> ecutwfc = 40.D0,
>
> ecutrho = 400.D0,
> occupations = 'smearing'
> smearing ='mp',
>
> degauss = 0.01,
> nspin = 2,
> starting_magnetization(1)= 1.0,
>
> /
> &ELECTRONS
> conv_thr = 1.D-6,
> mixing_beta = 0.7D0,
>
> diagonalization = "david",
> /
> &IONS
> ion_dynamics="bfgs"
> /
> ATOMIC_SPECIES
> C
> 12.0107 C.star1s-pbe-rrkjus.UPF
> ATOMIC_POSITIONS {angstrom}
> C
> 0.000000 0.000000 0.000000
> C 2.465900 0.000000
> 0.000000
> C -1.232950 2.135532 0.000000
> C 1.232950
> 2.135532 0.000000
> C 0.000000 1.423688 0.000000
> C
> -1.232950 3.559220 0.000000
> C 2.465900 1.423688
> 0.000000
> C 1.232950 3.559220 0.000000
> C 0.000000
> 0.000000 3.351450
> C 2.465900 0.000000 3.351450
> C
> -1.232950 2.135532 3.351450
> C 1.232950 2.135532
> 3.351450
> C 1.232950 0.711844 3.351450
> C 0.000000
> 2.847376 3.351450
> C 3.698850 0.711844 3.351450
> C
> 2.465900 2.847376 3.351450
> C 0.000000 0.000000
> 6.702900
> C 2.465900 0.000000 6.702900
> C -1.232950
> 2.135532 6.702900
> C 1.232950 2.135532 6.702900
> C
> 0.000000 1.423688 6.702900
> C -1.232950 3.559220
> 6.702900
> C 2.465900 1.423688 6.702900
> C 1.232950
> 3.559220 6.702900
> K_POINTS {automatic}
> 4 4 1 1 1 1
>
>
> out
> put (optimized positions):
>
> C 0.000000000
> -0.000000000 -0.686394528
> C 2.465900000 -0.003714144
> -0.758610095
> C -1.229733457 2.137389072 -0.758610095
> C
> 1.229733457 2.137389072 -0.758610095
> C 0.000000000
> 1.427474855 -0.213813075
> C -1.229670488 3.557326573
> -0.213813075
> C 2.465900000 1.423688000 -0.285079086
> C
> 1.229670488 3.557326573 -0.213813075
> C -0.000000000
> 0.000000000 3.630366631
> C 2.465900000 -0.014904710
> 3.544792504
> C -1.220042143 2.142984355 3.544792504
> C
> 1.220042143 2.142984355 3.544792504
> C 1.220249305
> 0.704511250 3.106073641
> C 0.000000000 2.847376000
> 3.022325711
> C 3.711550695 0.704511250 3.106073641
> C
> 2.465900000 2.862041499 3.106073641
> C 0.000000000
> 0.000000000 7.468882932
> C 2.465900000 0.008344370
> 7.466151214
> C -1.240176436 2.131359815 7.466151214
> C
> 1.240176436 2.131359815 7.466151214
> C 0.000000000
> 1.414904155 6.963129179
> C -1.240557033 3.563611923
> 6.963129179
> C 2.465900000 1.423688000 6.961528237
> C
> 1.240557033 3.563611923 6.963129179
>
>
>
> Many Thanks
> Masoud Nahali
> Sharif
> University of Technology
>
>
> _________________________________________________________________
> Hotmail: Free, trusted and rich email service.
> https://signup.live.com/signup.aspx?id=60969
--
********************************************************
- Article premier - Les hommes naissent et demeurent
libres et ègaux en droits. Les distinctions sociales
ne peuvent être fondèes que sur l'utilitè commune
- Article 2 - Le but de toute association politique
est la conservation des droits naturels et
imprescriptibles de l'homme. Ces droits sont la libertè,
la propriètè, la sùretè et la rèsistance à l'oppression.
********************************************************
Giuseppe Mattioli
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
v. Salaria Km 29,300 - C.P. 10
I 00016 - Monterotondo Stazione (RM)
Tel + 39 06 90672836 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>
More information about the users
mailing list