Messages

961

General Questions and Answers / Re: Band structure of Bulk MoS2 (10 Layers)

« on: August 27, 2017, 21:25 »

The difference is actually explained in my reply, bulk MoS2 vs 10 monolayer MoS2 thin film. It would then be more efficient if you explain what you call  "bulk MoS2 (10 layers)" in your original post, and give more details of what kind of calculations you are doing or want to do. 

962

General Questions and Answers / Re: Band structure of Bulk MoS2 (10 Layers)

« on: August 27, 2017, 13:22 »

The description of what you are doing is not really clear in your post. Are you studying bulk MoS2 or 10 monolayer MoS2 thin film? Also the method (DFT functional, basis set etc) adopted for this calculation is not mentioned. Could you enclose a python script related to your ATK calculation of MoS2 for which you got the band gap of 0.81 eV?

What do you exactly mean by saying "I want the band gap of 1.1eV   (using DFT - LDA+PW)"? Do you want to modify the plane-wave basis set based DFT-LDA approach to get this energy gap of 1.1 eV?

What makes you believe that the band gap of the material system of your study is supposed to have this band gap?

963

General Questions and Answers / Re: interlayer distance

« on: August 27, 2017, 12:28 »

You have to build the two molecule structure in the Builder, and then do total energy calculations, using one of ATK calculators. This will allow you to do geometry optimization to get an equilibrium separation distance between the molecules or between two molecular layers; in your post, it is not clear if you mean two isolated molecules or molecular layers.  Please search and read our online tutorials at http://docs.quantumwise.com/. As an example, you may have a look at this one, https://docs.quantumwise.com/tutorials/geometry_optimization/geometry_optimization.html?highlight=geometry%20optimization.

964

General Questions and Answers / Re: PDOS

« on: August 27, 2017, 12:18 »

You may read about it in our online documentation https://docs.quantumwise.com/, e.g., https://docs.quantumwise.com/manuals/Types/ProjectedDensityOfStates/ProjectedDensityOfStates.html. In general, for any issue like this you may do searching the online documentation, using keywords, e.g., PDOS or projected density of states in this particular case. Searching docs is always a good starting point when one wants to find out about VNL-ATK features, analysis tools, case studies, building structure and many other things related to the VNL-ATK. 

965

General Questions and Answers / Re: Electrostatic difference potential vs coordinate of c direction

« on: August 27, 2017, 12:11 »

That is correct. The EDP plot of a device does not show the potential in the electrode regions, only in the central region. If you have chosen the central region is large enough (as it should be), the potential in the left (right) electrode extension, which is part of the central region, is to be virtually the same as the potential in the left (right) electrode region. In other words, the central region must be longer than the screening length.

966

General Questions and Answers / Re: Phonon dispersion with supercell

« on: August 25, 2017, 09:20 »

If you have no imperfections in the structure, you can then build this structure (whatever it is) with a minimal unit cell and calculate the dynamical matrix for this cell, using some repetitions along the three lattice vectors of your minimal unit cell.

More repetitions you set for this calculation - more accurately the phonon band structure will be computed. Even so, you adopt repetitions, i.e., de-facto doing supercell calculations, the phonon bands will be computed and visualized for the minimal unit cell, i.e., the bands are given in the Brillouin zone of the minimal unit cell adopted, not the supercell.

If the minimal unit cell of the graphene-Cu system is not a primitive cell of a graphene sheet, then you have a natural folding of the phonon bands of the Cu-graphene hybrid system and that cannot be avoided.  It might be that you could do an (approximate) unfolding using the spectral function to get an effective band structure, as done for electronic bands in Phys. Rev. B 85, 085201 – Published 2 February 2012, but I am not aware of any code doing it for phonon band structures.       

967

General Questions and Answers / Re: Optimization of any bulk crystal

« on: August 24, 2017, 09:34 »

But i need to fit the Murnaghan EOS with different volumes.

You may then do a set of ion relaxation calculations for your crystal structure with different unit cell volumes, keeping the optimized c/a fixed; you certainly have to first calculate this ratio, as suggested by Ulrik. It means that you only need do ion relaxation for a given unit cell volume. In this case, you have to keep "Constrain Lattice Vectors" ticked in geometry optimization settings.

968

General Questions and Answers / Re: Phonon dispersion with supercell

« on: August 22, 2017, 09:05 »

If you want to calculate the phonon dispersion and DOS for pristine graphene only, there is no need to use a graphene supercell structure as an initial structure for phonon calculations. To increase accuracy of the phonon band structure calculations, one only needs increasing the number of repetitions for calculating the dynamical matrix (DM). This has an advantage over the direct supercell approach, as the method implemented in the ATK for DM calculation takes into account symmetries of the system of study, i.e., graphene's lattice symmetry in your case. 

If your graphene structure has defects, adatoms or ripples, you then certainly have to start from a graphene supercell structure that includes this kind of structural imperfections.

969

General Questions and Answers / Re: Local Bandstruct.

« on: August 21, 2017, 16:11 »

I have not fully understood what exactly you want to do. You may check in the manual information on local band structure calculations at https://docs.quantumwise.com/manuals/Types/LocalBandstructure/LocalBandstructure.html, to see if it gives you what you are looking for. 

970

General Questions and Answers / Re: Temperature effect on magnetic tunnel junction

« on: August 21, 2017, 16:04 »

It really depends on what you mean by "temperature variation on Magnetic Tunnel Junction"?

971

General Questions and Answers / Re: optimize bond length

« on: August 21, 2017, 16:02 »

It really depends on the actual interface between the two materials, as well as on the computational method used for electronic structure calculation and related geometry optimization. So, you have to build the actual junction structure of your interest and do structural optimization using an appropriate electronic structure method for the junction.

972

General Questions and Answers / Re: Hubbard U

« on: August 21, 2017, 15:52 »

Have you tried consulting Google Scholar or Web of Science? It is more likely that you find this kind of information in published peer-reviewed papers, as there are many people working on these materials.

973

General Questions and Answers / Re: About VASP file

« on: August 20, 2017, 11:48 »

You need a license from VASP developers, as well as a VNL license  that includes the VASP plugin. 

974

General Questions and Answers / Re: how to analyse lammps trajectory file in ATK

« on: August 18, 2017, 14:05 »

In the Builder, you can set lattice parameters for the slab structure, using the Builder plugin, Bulk Tools -> Lattice parameters.

975

General Questions and Answers / Re: cdse nanotube bond length

« on: August 17, 2017, 09:32 »

You may get the Cd-Se bond length from bulk CdSe structure that is available in the VNL database, go to Add->From Database-> Search for CdSe-> Add the structure to the Stash in the Builder -> Measure the bond length. Using the initial guess for the bond,  you can further do geometry optimization for CdSe tube in the VNL-ATK to get the actual equilibrium separation distance between Cd and Se atoms.