### [SIESTA-L] K-grid cutoff problem

```Dear all,

I am a new user of Siesta. I am working on graphene and Zigzag Carbon
nanotubes. I have encountered a serious problem with defining k-grid
cutoff in my jobs. Here is a part of my input:

kgrid cutoff 15.003 Ang

But I have this in my output file:

siesta: k-grid: Number of k-points = 1
siesta: k-grid: Cutoff (effective) = 2.460 Ang
siesta: k-grid: Supercell and displacements
siesta: k-grid:0   1   0  0.000
siesta: k-grid:1   0   0  0.000
siesta: k-grid:0   0   1  0.000
Naive supercell factors: 441

Which gives 2.46 Ang cutoff an just gamma point!!! I tried the
kgrid_Monkhorst_Pack with 31X31X1 grid for graphene, but from the
outputs I can say that the effective k-grid cutoff is totally
independent of the mesh grid I've defined in my input and it just
changes by changing the length of the vector in Z direction (which is
perpendicular to the graphene plane) in my unit cell.

Could anybody guide me why I get these weird outputs?!

Elham Beheshti,
Department of Electrical Engineering,
University of British Columbia

```

### Re: [SIESTA-L] K-grid cutoff problem

```
Hi,

You must type  kgrid_cutoff  not  kgrid cutoff , just as it
is written in the manual.
Good luck.

R.

On Fri, 24 Jul 2009, Elham Beheshti wrote:

Dear all,

I am a new user of Siesta. I am working on graphene and Zigzag Carbon
nanotubes. I have encountered a serious problem with defining k-grid
cutoff in my jobs. Here is a part of my input:

kgrid cutoff 15.003 Ang

But I have this in my output file:

siesta: k-grid: Number of k-points = 1
siesta: k-grid: Cutoff (effective) = 2.460 Ang
siesta: k-grid: Supercell and displacements
siesta: k-grid:0   1   0  0.000
siesta: k-grid:1   0   0  0.000
siesta: k-grid:0   0   1  0.000
Naive supercell factors: 441

Which gives 2.46 Ang cutoff an just gamma point!!! I tried the
kgrid_Monkhorst_Pack with 31X31X1 grid for graphene, but from the
outputs I can say that the effective k-grid cutoff is totally
independent of the mesh grid I've defined in my input and it just
changes by changing the length of the vector in Z direction (which is
perpendicular to the graphene plane) in my unit cell.

Could anybody guide me why I get these weird outputs?!

Elham Beheshti,
Department of Electrical Engineering,
University of British Columbia

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```