[Pw_forum] The stability of monolayer compound

[Lorenzo Paulatto]

In data 29 aprile 2009 alle ore 03:31:44, 程迎春 <yccheng.nju at gmail.com>  
ha scritto:
> 1, Is it possible to get the mono layered compounds( AlN, BC2N, GaN,
> ZnO,......)?

Dear 程迎春, this mailing list is not intended for scientific discussion,  
but for technical assistance regarding Quantum-espresso; often some  
scientific notions are involved in the discussions, but only accidentally.  
Furthermore, there is little chance you will get a good answer to such a  
specific question frm this mailing list, although it may happen that some  
of ther readers have specific knowledge on your topic.
Personally, I have no idea if it's possible.


> 2, From the theoretical interests, how to study the stability of mono
> layered compounds by first-principles calculation?

This is a more pertinent question!
You can do a calculation for the material in the bulk configuration first,  
in order to obtain the equilibrium cell parameters and atomic positions.  
Then you can carve out a single layer in the same way you do for graphene,  
extending the cell along the direction perpendicular to the plane (usually  
z) until the periodic images don't interact anymore (the total energy  
converges).
At this point there are several stability tests you can do:
1. how high is the energy of an isolated plane compared to a plane in the  
bulk, i.e how much does the inter-layer bonds contribute to total energy?
2. does the plane structure reform spontaneously if you perturb breaking  
symmetry?
3. phonons can be somehow linked to structural stability, I don't know the  
details, but you can find lot of literature on this argument
4. ... whatever you can think of, use graphene as a reference of something  
that's stable

good luck!
best regards

-- 
Lorenzo Paulatto
SISSA  &  DEMOCRITOS (Trieste)
phone: +39 040 3787 511
skype: paulatz
www:   http://people.sissa.it/~paulatto/

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