QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: markmick on March 18, 2016, 09:13

Title: kpoints and hexagons
Post by: markmick on March 18, 2016, 09:13

I'm straining a transition metal dichalcognide (MoS2 for example), and my band diagrams are as expected.  However, I want to measure the change in geometry of the BZ unit cell, as shown in the attached image.  How do I measure geometrical distances with VASP?

The x,y,z positions for G, M and K are angular values, and don't tell you anything about the actual dimension. When the hexagon is strained, the geometry is changed.

How can I show there has been a physical dimension change in the hexagon from unstrained to strained?  The more I try this, the more confused I get.  Hope this makes sense.

Thanks
Mark

Title: Re: kpoints and hexagons
Post by: zh on March 19, 2016, 08:24

"The x,y,z positions for G, M and K are angular values"
What is the meaning of regular values here?

Once the lattice vectors are given, the reciprocal lattice vectors can be easily computed. From the fractional coordinates of special and high symmetry k points, you can know the Cartesian coordinates of these points. Then you can know how these points in the BZ of strained lattice  change with respect to them in the BZ of unstrained lattice.

I guess you are using the fractional coordinates of the high symmetry k points to measure the change. This may make you confused.

Title: Re: kpoints and hexagons
Post by: Anders Blom on March 20, 2016, 19:11

Also note very carefully that the actual band extrema may not be at the high symmetry point any more in the strained lattices. Plus, that you break degeneracy so K' and K are no longer equivalent. But generally speaking, the analysis of the Brilluoin zone shape is independent of the code you use, it's a purely geometrical problem.