Hey guys,
Can you explain the meaning of "on-site energy" in the following context?
The edge carbon atoms of our GNRs (armchair graphene nanoribbons) are passivated by hydrogen atoms so that the σ bonds between hydrogen and carbon and the on-site energies of the carbons at the edges would be different from those in the middle of the GNRs.
Thanks in advance,
Luis
Are you familiar with the tight-binding model? In this model a minimal basis set of localized orbitals is used to expand the electronic states. In the case of graphene a simple single orbital per site basis, corresponding to the cabon 2p_z orbitals, and a nearest neighbor hopping provides a quite good description for the bands closer to the Fermi energy. The model has just two parameters: the hopping element, which is of the order of 3eV and the site-energies, which in the case of pristine infinite graphene is the same for all carbon atoms, and fixes the band filling. The site energy has the loose meaning of the energy level for orbitals in the isolated atoms, but within the TB model is just a parameter. It is reasonable to assume that it can take a different value at the edges than in the bulk material.
On site energy means atom energy on yourself and is constant for any atom.
Thank you Nader for you answer; but still not so clear. Anyone else?
Are you familiar with the tight-binding model? In this model a minimal basis set of localized orbitals is used to expand the electronic states. In the case of graphene a simple single orbital per site basis, corresponding to the cabon 2p_z orbitals, and a nearest neighbor hopping provides a quite good description for the bands closer to the Fermi energy. The model has just two parameters: the hopping element, which is of the order of 3eV and the site-energies, which in the case of pristine infinite graphene is the same for all carbon atoms, and fixes the band filling. The site energy has the loose meaning of the energy level for orbitals in the isolated atoms, but within the TB model is just a parameter. It is reasonable to assume that it can take a different value at the edges than in the bulk material.
Wow that was neat Alfredo. And nope; I do not know much about the TB model. I am currently studying GNRs and simulation methods. I work with DFT though. Do you have any bibliography that can guide me? For example, I have seen that the parameters for TB simulations are taken from experiments or from DFT simulations. Do you have literature on this regards you can share (like a tutorial)? Thank you in advance
It seems to me that is the adsorptin vocabular. There are: on-site (or atop? or A-) adsorption when the adatom is connected only with one surface atom lust below it;: the bridge case (B-adsorption) when adatom is connected with two neearest-neigbor (n.n) surface atoms, and the central (C-ads) when adatom is in the cener of surface cell and interacts with all corresponding n.n.
Regards,
S.D.
The term "on-site energy" (or "on-site matrix element") is used mainly in the Tight Binding Approximation. It is the matrix element , where |n> is the n atomic-like orbital of the base, which is used to express the wave function as a linear combination of atomic (or atomic-like) orbitals. For more details on Tight Binding see the Harrison's book "Electronic Structure and the Properties of Solids".
What you are talking sounds a lot like what is on this elaborated here: http://inspirehep.net/record/860544?ln=en...
Sergeys explanation is close to what you are looking for, I think, Zacharias explanation of the term is more or lass correct, and literature's good for basics.
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