>
> 2)
>
> I learned from Eur. Phys. J. B 40, 371-377(2004) that: Hamiltonian matrix
> elements are partly computed on a real space grid, whose fineness Δx is
> controlled by a grid cutoff, Ec=(p/Δx)2/2.
>
> Does it mean that the charge density is represented on a regular real space
> grid ofΔx? If not, where can I find the regular real space grid that
> represents the charge density?
>
> And what are the units ofΔx and Ec in that formula?
>
>
>
> I will be grateful if anyone can help. Thanks in advance.
>
>
>
> Best wishes!
>
>
>
> Leila
>
Hello Leila,
Yes, the density is represented on a regular real space grid ofΔx, but the
equation Ec=(p/Δx)2/2 is valid only when you have orthogonal unit cell. It
is in atomic units (Δx - Bohr, Ec - Rydbergs).
The stiffness of this grid is controlled by MeshCutoff parameter. If you
look at your Siesta output you''l find something like:
outcell: Cell vector modules (Ang) : 27.174106 27.174107 25.000000
outcell: Cell angles (23,13,12) (deg): 90.0000 90.0000 60.0000
outcell: Cell volume (Ang**3) : 15987.5228
InitMesh: MESH = 216 x 216 x 216 = 10077696
InitMesh: Mesh cutoff (required, used) = 200.000 206.314 Ry
Here 216 is the number of grid points along each spanning vector of
the unit cell.
If you want to have access to charge density values in real space
grid, then yo'll need to find the file
m_iorho.F in siesta/Src, change line 37 from
character(len=*), parameter :: fform = "unformatted"
to
character(len=*), parameter :: fform = "formatted"
and then recompile Siesta. Then add SaveRho .true. in your
fdf file and you 'll get readable *.RHO file.
Kind regards
Ruslan Zhachuk
