Finding band gap of a polymer.

[shyam]

Dear sir,
I m very new to vasp.
I have to calculate band gap of a one dimensional polymer with help of vasp.
Please tell me the procedure.i have read vasp manual. But dont get any method to do it.
And also if i calculate band gap for 2d and 3d polymers,what will be the changes in input files

[admin]

Vasp performs always 3D calculation. Structures with decreased dimensions, like 2D use a vacuum layer. 1D structure is a chain of atoms surrounded by vacuum. Sampling of the k-space is performed only along directions in which the structure is not truncated (e.g. x x 1 for the layer with the surface vertical to the z-vector).

[shyam]

Dear sir,
It will be very kind of you to explain it in detail.
I have to extend my polymer in x-direction and to find its band gap.
Then firstly i have made a box significantly large in y and z direction and slightly large in x direction to put my polymer.
Can you please help further to find band gap.

[shyam]

dear sir,
May be you are finding difficulty in getting my problem.
I know the procedure of finding DOS and band structure of a solid in vasp.
But for a polymer I am somewhat confused.
I have to calculate band gap of polymer.
Please explain the needful.

[admin]

You need to sample only one direction of the k-space corresponding to the direction in which your polymer extends. The calculated line of k-points represents the complete band structure and can be used for the evaluation of band gaps.

[shyam]

Dear sir,
Thank you very much for the guidance.
I have made my k-point as-
10
Line mode
Cart
0 0 0
1 0 0

I have also plotted the graph from the eigenval file.

Is the band gap only can be calculated from graph or it can be printed in the output file as we find tha in gaussian pbc job.