One thing i want to ask.... Siesta gives fermi energy in -ve value . What can i
do to set it at Zero. Can i do it or it is default?
Thank You.
Marcos Verissimo Alves <[EMAIL PROTECTED]> wrote:
The variable cell option is useful when you want to determine the lattice
constants in an automatic fashion, but sometimes you don't want to relax
the cell. For example, you could want to determine changes in the band gap
or how the chemical bonds change under uniaxial stress. Then you would
keep lattice vectors fixed and let the atomic positions relax. If you want
the DOS for the equilibrium geometry, you must at least relax the atomic
coordinates at the equilibrium value of the lattice constant, doesn't
matter how you obtained the lattice constant. If you do a variable-cell
calculation, in the end you obtain both - the relaxed geometry at the
equilibrium lattice constant.
For some structures, a variable cell calculation is not necessarily worth
the effort. For example, take a simple metal or a zincblende structure.
For those structures, which can be described by one atom in the unit cell
(two in the case of the ZB), you can simply perform a series of six ir
seven fixed cell calculations around the equilibrium lattice constant -
they will do only one entire SCF cycle because of symmetry, and a
Murnaghan fit will give you the bulk modulus, perhaps in less steps than a
variable-cell would need to find the minimum energy structure. So, how you
obtain the lattice constants is not important, what matters for the DOS is
that the atomic positions be relaxed at the desired lattice constant.
Cheers,
Marcos
Vous avez écrit / You have written / Lei ha scritto / Você escreveu... Ñ»ª
>> Marcos,
>
>
> In the letter you have said that both bands and DOS should be
> calculated from the relaxed structure. Did you mean that the
> MD.VariableCelloption be True? Or others?
>
> Thank you .
>
>
>
>
>
> --
> Best Wishes!
> F.H.Yang
>
--
Dr. Marcos Verissimo Alves
Post-Doctoral Fellow
Unité de Physico-Chimie et de Physique des Matériaux (PCPM)
Université Catholique de Louvain
1 Place Croix du Sud, B-1348
Louvain-la-Neuve
Belgique
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