[Pw_forum] Monolayer MoS2 band Structure
thomas.brumme at mpsd.mpg.de
Thu Sep 24 10:47:37 CEST 2015
I think that the main problem is your lattice parameter.
You use 5.8364 bohr which is 5.8364*0.529177 = 3.088 Angstrom.
Thus, your MoS2 is under compressive strain. That's why you
(correctly) get an indirect band gap between K and Q.
See also Fig. 3(b) of Phys. Rev. B 85, 033305:
On 09/24/2015 08:20 AM, Cameron Foss wrote:
> I am attempting to obtain the band structure of monolayer MoS2,
> however my results so far do not agree well with what has been
> documented for monolayer (ML) MoS2. I consistently get an indirect
> band gap for ML MoS2 caused by the 'Q-valley' minimum seen in bulk MoS2.
> I have tested the code with interplanar distances of 15 and 30
> angstroms to eliminate any interplanar interactions. There have been
> several papers that report the band structure for ML MoS2 from first
> principles, they have used functionals from LDA, GGA, and an HSE
> hybrid functional. My best success has been with GGA-PW91(see input
> file below). Note in all my simulations I have measured a band gap of
> ~1.9eV which is in agreement with reported values.
> I am uncertain as to what the issue could be? I have tested 3
> different PPs.
> Details on simulations:
> Specifically, my simulations continue to show that the 'Q-valley' is
> slightly lower (16meV~30meV) than the minimum at the K point,
> suggesting an indirect band gap. However ML mos2 has been widely shown
> to have a direct band gap at the K point where this 'Q-valley' along
> the conduction band is suppressed above the K-point minimum.
> I run a scf (pw.x) calculation first, followed by an nscf (pw.x) run,
> and a bands calculation with pw.x (and of course bands.x to retrieve
> the energy values). I specify 16 bands for nbnd, kpoints along
> symmetry paths, and a MP grid of 8x8x1 with a 1 1 1 offset.
> Input file:
> calculation='scf' !nscf, then bands
> !pseudo_dir='directory where pseudopotentials are stored/',
> !outdir='directory where large files are written/'
> ibrav=4, celldm(1)=5.8364, celldm(3)=10,
> nat=3, ntyp=2, ecutwfc =70, ecutrho=300 ! specified nbnd=16
> conv_thr = 1.0d-15 ! reduced to 1.0d--12 for
> nscf, bands
> mixing_beta = 0.5 ! increased to 0.7 for nscf,
> Mo 95.94 Mo.pw91-n-van.UPF
> S 32.065 S.pw91-n-mt.UPF
> ATOMIC_POSITIONS bohr
> S 0.00002 -0.00001 0.000000000
> Mo 2.91822 1.68481 2.929886569
> S 0.00002 -0.00001 5.859870374
> K_POINTS automatic
> 8 8 1 1 1 1
> I ran into some convergence issues with all the bands with this
> conv_thr in the nscf and bands calculations, so i had to reduce it to
> 1.0d-12 for those calculations. I also used a mixing beta of 0.7 for
> both the nscf and bands calculations. I am uncertain as to whether
> changing mixing_beta's between calculations is of importance or not as
> well, but I do not think this is the case.
> Best regards,
> Pw_forum mailing list
> Pw_forum at pwscf.org
Dr. rer. nat. Thomas Brumme
Max Planck Institute for the Structure and Dynamics of Matter
Luruper Chaussee 149
Tel: +49 (0)40 8998 6557
email: Thomas.Brumme at mpsd.mpg.de
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