Dear Daniel,
I aim to try to induce some sp3 bonds between the layers, forcing them by
hydrogenating (or by other chemical groups) a couple of carbon atoms (the
non-constrained atoms) and strain. In fact, I'm trying to obtain the 2D
diamond structure and then trying to use the same methodology in other
structures (doped ones, for example).
I understood your comments and now believe I can perform these calculations
with your advice, I am immensely grateful.
Em sáb., 8 de abr. de 2023 às 17:00, Daniel Bennett
escreveu:
> Hi Ramon,
>
> I'm not sure if this is such a good idea, at least in your example. If I
> understand correctly, you freeze the first graphene layer (in the z=0 plane
> say), then the second graphene layer is at some z which is larger than the
> optimal one which minimizes the van der Waals energy. Then you move the
> second layer in the negative z direction, closer to the first, until it
> reaches the minimum distance. But in relaxations, the coordinates
> oscillating about the minimum until they converge below a given tolerance.
> As soon as the second layer passes to the other side of that minimum, the
> energy will explode, because it can only move closer to the first layer.
> The same thing will happen if you constrain the atoms to move in the other
> direction and begin with the second layer too close to the first: the
> second layer will move to the other side of the cell in the z-direction,
> and you will have the same problem on the other side of the first graphene
> layer. It might work if you get lucky and the system happens to get very
> close to the minimum without going beyond it, but I think this would be
> very unlikely to happen
>
> Are you trying to do this for graphene, or something more complicated?
> Because with bilayer graphene if you freeze the first layer, the xy
> components of the second, and force the z components of the second to be
> equal, only one parameter needs to be optimized, and siesta can do this
> very efficiently with its native geometry constraints.
>
> Daniel Bennett
>
>
> --
> *From:* siesta-l-requ...@uam.es on behalf of
> Ramon Sampaio Ferreira
> *Sent:* 07 April 2023 11:13
> *To:* siesta-l@uam.es
> *Subject:* [SIESTA-L] Constraints in positive or negative z-direction
>
>
> Hi there,
>
> I know that SIESTA allows some restrictions on atomic displacements.
> However, I didn’t find in the manual a way to allow atomic displacement
> only in the negative or positive z-direction during the relaxation process
> for specific atoms. For example: During the relaxation process of a
> graphene bilayer, I would like to freeze the atoms on one sheet (I know how
> to do that) and allow specific atoms on the other sheet to move only in the
> negative z-direction.
>
> Is it possible to enforce this kind of restriction? My idea is that it is
> possible to do this by modifying the construct.f routine, am I right in
> thinking this way? There are other ways to do that?
>
> Thank you so much for your help.
>
> --
>
> *Ramon Sampaio Ferreira*
> Doutorando em Física
> Programa de Pós-Graduação em Física - Universidade Federal do Ceará
> Campus do Pici - Bloco 928
>
> --
> SIESTA is supported by the Spanish Research Agency (AEI) and by the
> European H2020 MaX Centre of Excellence
> (https://urldefense.com/v3/__http://www.max-centre.eu/__;!!D9dNQwwGXtA!TJ4BQ9j0GGUqe7PUKu5fA9-bjaslnczB01iSHZu0ZZ2NU-wdu2oEm-ALq0XLt4YQ4g9diYHMJcuA-diKjg$
> )
>
--
*Ramon Sampaio Ferreira*
Doutorando em Física
Programa de Pós-Graduação em Física - Universidade Federal do Ceará
Campus do Pici - Bloco 928
--
SIESTA is supported by the Spanish Research Agency (AEI) and by the European
H2020 MaX Centre of Excellence (http://www.max-centre.eu/)
