[Pw_forum] Monolayer WSe2 band structure related problems
Thomas Brumme
thomas.brumme at mpsd.mpg.de
Mon Mar 6 13:25:05 CET 2017
Dear Anindya,
please provide an affiliation.
Hard to say why you don't get the correct band structure
but let me give me a few advices:
Before attempting to relax your unit cell you should test
the convergence with respect to several parameters with
the known experimental structure. For example
convergence with respect to sampling of the BZ and
number of plane wave (ecutwfc)...
Why do you set ecutrho if you're using norm conserving
pseudos? Do one needs to set it for optimized norm-
conserving Vanderbilt pseudos? I think the standard
value of 4 times ecutwfc is just fine.
Additionally, you're using norm-conserving pseudos...
I guess that ecutwfc=40 is just too small. This brings me
back to first point: Check convergence!! And why do you
need 200 bands? Are the pseudos all-electron ones?
Regards
Thomas
On 03/06/2017 12:55 PM, Anindya Bose wrote:
> Dear Sir,
> I have used this code but I didn't get the direct band gap structure
> of monolayer WSe2.
> &CONTROL
> calculation='vc-relax',
> outdir='monolayer WSe2',
> prefix='calc',
> pseudo_dir='/home/anindya/Desktop/pseudopotential',
> verbosity='high',
> disk_io='high',
> wf_collect=.true.,
> nstep = 50,
> etot_conv_thr=1d-02,
> forc_conv_thr=1d-02,
> /
>
> &SYSTEM
> ibrav=4,
> celldm(1)=6.2020811408d0, celldm(3)=4.3566118221d0,
> nat=3,
> ntyp=2,
> ecutwfc=40.0d0,
> ecutrho =130.0d0,
> nbnd=200,
> vdw_corr='Grimme-D2',
> force_symmorphic=.true.,
> input_dft='PBE',
> occupations='fixed',
> /
>
> &ELECTRONS
> diagonalization='david',
> conv_thr=1d-08,
> mixing_mode='plain',
> mixing_beta=0.700d0,
> /
>
> &ions
> ion_dynamics ='bfgs',
> /
>
> &cell
> cell_dynamics ='bfgs',
> cell_factor=15,
> /
>
> ATOMIC_SPECIES
> Se 78.960000d0 Se_ONCV_PBE-1.0_r.oncvpsp.upf
> W 183.840000d0 W_ONCV_PBE-1.1_r.oncvpsp.upf
>
> ATOMIC_POSITIONS {alat}
> W 0.5000000000d0 0.2886751346d0 2.1782995738d0
> Se 0.5000000000d0 -0.2886751346d0 1.6692977456d0
> Se 0.5000000000d0 -0.2886751346d0 2.6873014019d0
>
> K_POINTS {automatic}
> 10 10 1 0 0 0
>
> I have enclosed my output band structure with this mail.Can you please
> help me in this regard.How can I get the correct band diagram of
> monolayer WSe2(direct bandgap). I have used all the codes for spin
> calculation and I got the spin orbit coupling but didn't find perfect
> band diagram.I will be waiting for your response.
>
> On Wed, Mar 1, 2017 at 9:04 PM, Giovanni Cantele
> <giovanni.cantele at spin.cnr.it <mailto:giovanni.cantele at spin.cnr.it>>
> wrote:
>
> I never use ism, maybe you can read relevant papers in the
> literature. However, if your purpose is just to simulate an
> isolated monolayer, just add to the lattice vector orthogonal to
> the monolayer
> plane (a3, in your case) vacuum space, so if the current length
> is, just to make an example, 5 A, try to use 15 A. This is the so
> called supercell approach, discussed several times in the forum.
>
> Giovanni
>
>> On 1 Mar 2017, at 16:17, Anindya Bose <anindya at iiita.ac.in
>> <mailto:anindya at iiita.ac.in>> wrote:
>>
>> Actually I have used esm_bc to add vacuum in the structure.How
>> can I add vacuum in this monolayer WSE2 structure using quantum
>> espresso.Which code should be used.
>>
>> On Wednesday, March 1, 2017, Giovanni Cantele
>> <giovanni.cantele at spin.cnr.it
>> <mailto:giovanni.cantele at spin.cnr.it>> wrote:
>>
>> It is not clear how and to what extend your band structure
>> differs from shat you expect.
>> However, one issue I can see is that if you want to study
>> MONOLAYER WSe2, you should be aware of the fact that the
>> vacuum space, separating the periodic replicas
>> along your z direction should be large enough to prevent them
>> from interacting (otherwise, you are considering a periodic
>> crystal also along
>> that direction). Currently, as far as I can see such vacuum
>> is < 5A, definitely too small to simulate a monolayer.
>> Additionally, you also include vdw_corr, usually introduced
>> to better describe inter-layer interaction, whereas you are
>> claiming that you want to study a system composed by a single
>> layer.
>> Also, I think that you don’t need to use the variable esm_bc
>> just to calculate the properties of a monolayer.
>>
>> Giovanni
>>
>>
>>
>>
>> > On 1 Mar 2017, at 14:01, Anindya Bose <anindya at iiita.ac.in>
>> wrote:
>> >
>> > Dear Sir,
>> >
>> > &CONTROL
>> > calculation='nscf',
>> > outdir='monolayer WSe2',
>> > prefix='calc',
>> > pseudo_dir='/home/anindya/Desktop/pseudopotentials',
>> > verbosity='low',
>> > disk_io='high',
>> > wf_collect=.true.,
>> > etot_conv_thr=1d-02,
>> > forc_conv_thr=1d-02,
>> > /
>> >
>> > &SYSTEM
>> > noncolin=.true.,
>> > lspinorb=.true.,
>> > ibrav=0,
>> > celldm(1)=6.2020811408d0, celldm(3)=4.3566118221d0,
>> > nat=3,
>> > ntyp=2,
>> > ecutwfc=40.0d0,
>> > nbnd=200,
>> > vdw_corr='Grimme-D2',
>> > starting_magnetization=0.05,
>> > force_symmorphic=.true.,
>> > input_dft='PBE',
>> > esm_bc='bc1',
>> > no_t_rev=.false.,
>> > /
>> >
>> > &ELECTRONS
>> > diagonalization='david',
>> > conv_thr=1d-08,
>> > mixing_mode='plain',
>> > mixing_beta=0.700d0,
>> > /
>> >
>> > &ions
>> > ion_dynamics ='bfgs',
>> > /
>> >
>> > &cell
>> > cell_dynamics ='bfgs',
>> > cell_factor=15,
>> > /
>> >
>> > ATOMIC_SPECIES
>> > Se 78.960000d0 Se_ONCV_PBE-1.0_nr.oncvpsp.upf
>> > W 183.840000d0 W_ONCV_PBE-1.1_nr.oncvpsp.upf
>> >
>> > CELL_PARAMETERS (alat= 6.20208114)
>> > 1.008112278 0.000000000 0.000000000
>> > -0.504056139 0.873050842 0.000000000
>> > 0.000000000 0.000000000 2.445357065
>> >
>> > ATOMIC_POSITIONS {alat}
>> > W 0.504056139 0.291016947 1.222674975
>> > Se 0.504056139 -0.291016947 0.699051439
>> > Se 0.504056139 -0.291016947 1.746298512
>> >
>> >
>> > K_POINTS {crystal_b}
>> > 4
>> > # Gamma-K-M-Gamma
>> > 0 0 0 20 !G
>> > 0.33 0.33 0 20 !K
>> > 0.5 0 0 20 !M
>> > 0 0 0 20 !G
>> >
>> > I am not getting the WSe2 monolayer band structure, can you
>> please help me in this regard.
>> > _______________________________________________
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>>
>> --
>>
>> Giovanni Cantele, PhD
>> CNR-SPIN
>> c/o Dipartimento di Fisica
>> Universita' di Napoli "Federico II"
>> Complesso Universitario M. S. Angelo - Ed. 6
>> Via Cintia, I-80126, Napoli, Italy
>> e-mail: giovanni.cantele at spin.cnr.it
>> Phone: +39 081 676910
>> Skype contact: giocan74
>>
>> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
>> <http://www.researcherid.com/rid/A-1951-2009>
>> Web page: http://people.na.infn.it/~cantele
>> <http://people.na.infn.it/%7Ecantele>
>>
>>
>>
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>
> --
>
> Giovanni Cantele, PhD
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at spin.cnr.it
> <mailto:giovanni.cantele at spin.cnr.it>
> Phone: +39 081 676910
> Skype contact: giocan74
>
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> <http://www.researcherid.com/rid/A-1951-2009>
> Web page: http://people.na.infn.it/~cantele
> <http://people.na.infn.it/%7Ecantele>
>
>
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--
Dr. rer. nat. Thomas Brumme
Max Planck Institute for the Structure and Dynamics of Matter
Luruper Chaussee 149
22761 Hamburg
Tel: +49 (0)40 8998 6557
email: Thomas.Brumme at mpsd.mpg.de
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