Hi, if you are dealing with semiconductor or semi-metal system, then valance band will not touch to the Fermi energy level as difference between valance band and conductance band will determine the bandgap of the studied material. So its solely depend on the material you are investigating.

Thank you Sujoy for replying.

My material is semiconductor having band gap almost 3.0 eV. My question was that in DFT simulation people report bandstructure in which valance band maxima touches zero axis label and then gap comes up to value of band gap and then conduction band starts.

My VB maxima is coming in -ve direction but I am getting right band gap (difference between VB maxima and CB minima). So I want to know how does shift VB maxima to zero label. People do manually by adding some value in yaxis value or any other way.

Hi.

Firstly I would like to ask is your '0 - line' the Fermi energy on your plot? If yes, than probably you sholud look in other BZ directions but:

Fermi level should touch the maximum in valence band, so I suppose that you simply did not lower the 0 line mark on energy axis. If that is the case just check your Fermi  energy level and set this value to 0 on the plot. Then you will see that bang gap is in fact 3.0 eV

Konrad 

 Dear Konrad Gruszka thanks for reply .

I have not accounted any fermi enrgy in my plot. My point was that I calculated bandstructure from VASP code after that I plotted it. I am getting bandstructure as I attached above so I wanted to ask how to shift maxima of VB to zero axis level. Since I have seen in literature people report bandstructure VB maxima to zero level and write fermi energy shifted to zero axis level after that they count bandgap starting from zero up to minima of CB. So I want to ask how to do so ?

The energy scale is of course completely arbitrary, and you can put your zero wherever you like (the celebrated freedom of gauge, a shift just means that you are adding a constant to the electrostatic potential). What to do depends on what you want to illustrate.

But let's start with what you have in your plot. I guess that you have first done a self-consistent calculation, gotten the Fermi level out of that and then calculated the band structure based on the self-consistent density. Right? This is perfectly fine, were I a referee, I would have no objection to this choice of zero of energy.

However, we should note that whether this Fermi level really deserves the name "Fermi level" is not clear. That would depend on your choice of Brillouin zone integration method: if you have used Fermi-Dirac smearing, then the output Fermi level really is the Fermi level of an intrinsic semiconductor, in the traditional language of semiconductor physics. If you have used Gaussian smearing, the tetrahedron method or something else, then it has no physical meaning. Beware of the term "Fermi energy" here, I would suggest to have a look at what Wikipedia has to say about the terms "Fermi energy" and "Fermi level".

But what to put is arbitrary. Some like to put the Fermi level at zero kelvin (i.e. the middle of the gap). Personally, I like the choice to set the valence band maximum to zero energy. The reason is just that it makes it easy to read off the band gap from the plot.

As for how you should technically do it, I don't think there is any way to fix this so that it comes out according to a specific recipe in any DFT code that I am aware of. You have to just add a constant to all y-values in your plot.

Thank You Dr. Torbjörn Björkman for your kind help !

I am getting right bandgap value comparative with other literature of same system. But my confusion was that regarding VB maxima in negative side. So now I have got all things I will do it manually to zero axis level.

A simple way to shift the VBM to 0 eV is to open the vasprun.xml file in p4vasp, save the bandstructure data as a .dat file and open that data in excel. Then find the actual energy value for the VBM, and shift every eigenvalue by the VBM energy. This will manually shift your entire bandstructure up so that the VBM is sitting at 0 eV.

Hello,

Comprehensively INtegrated Environment for Advanced MAterials Simulations (CINEMAS) is a cross-platform(Windows/Linux/macOS) freeware GUI-based application.

CINEMAS in its current version supports the VASP code.

One can manually setup and execute bandstructure calculations within CINEMAS, and plot bandstructure without any reformatting, all through easy GUI.

Bandstructure can also be automatically be calculated just by browsing a structure file, and rest of the input files are prepared by CINEMAS automatically, all through an easy GUI.

Youtube tutorial on calculating bandstructure automatically: https://youtu.be/s8LatjV8Zhs

CINEMAS documentation: https://cinemas-doc.ikst.res.in/

Thanks