[QE-users] pw.x, Green function method, finite size

[KRISHNENDU MUKHERJEE]

Dear Lorenzo Paulatto, 

Thank you for your reply. I am replying with a separate thread. Of course surface effects can put a question mark for the approach. The following article, “A Reduction in Particle Size Generally Causes Body-Centered-Cubic Metals to Expand but Face-Centered-Cubic Metals to Contract” concludes that the metal to metal bond length decreases from center to the surface as well as the co-ordination number. 

But if the nano-grain size is bigger say in the range of 50 nm then may be the effect of surface will be decreased (in the above mentioned article the cluster size is less than 2 nm). Nevertheless, I am willing to take up the study in the near future. This approach would have the additional benefit that if the nano-grain experiences a negative hydrostatic pressure due to significant volume of grain-boundary present that can be added to the unit-cell. 

Best regards, 
Krishnendu 

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[QE-users] Phonon Dispersion of graphene 
PAULATTO Lorenzo lorenzo.paulatto at cnrs.fr 
Sun Dec 25 16:22:02 CET 2022 
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Maybe one could do something, i.e. Wannier functions are not too dissimilar from force constants. But would the effect of the surface properly taken into account? These are not simple questions, a proper study takes years, and starts with reading the available literature (which I have not done) 
Hth 

________________________________ 
From: users <users-bounces at lists.quantum-espresso.org> on behalf of KRISHNENDU MUKHERJEE <krishnendu at nmlindia.org> 
Sent: Sunday, December 25, 2022 3:49:35 PM 
To: users 
Subject: [QE-users] Phonon Dispersion of graphene 


Dear Lorenzo Paulatto, 

Can the finite size as a perturbation with Green function methods be added to pw.x calculations too ? For example can the Self-consistent field energy calculated for unit cell be modified with the Green function methods to that of a finite sized crystal ? 

Regards, 
Krishnendu 

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[QE-users] Phonon Dispersion of graphene 
PAULATTO Lorenzo lorenzo.paulatto at cnrs.fr 
Sat Dec 24 11:30:59 CET 2022 
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Dear Jahid, you have to decide precisely what you want, than you may be able to simulate it in different ways. A width of 10nm is probably too large for a direct DFT calculation of phonons, in this case you can use the phonons for the unit cell and add the finite size as a perturbation with Green function methods. I know a paper where this is done, but there are probably others, and other methods. https://hal.archives-ouvertes.fr/hal-03011389 


Hth 


LP 
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From: users <users-bounces at lists.quantum-espresso.org> on behalf of Md. Jahid Hasan Sagor <md.sagor at maine.edu> 
Sent: Saturday, December 24, 2022 10:17:28 AM 
To: Quantum ESPRESSO users Forum 
Subject: [QE-users] Phonon Dispersion of graphene 

Hi, 

Please help if you can. I am trying to find out the dispersion relation of graphene. I know that to find out the relation I have to use pw.x, ph.x, q2r.x and matdyn.x. But the problem is, after applying all the packages, I might get a phonon dispersion relation of graphene which is infinitely long in x and y direction. However, in my model I am using a finite width of graphene around 10nm (24 unit cell in the vertical direction). Which command in QE can do this for me so that I can model a graphene which is infinitely long in x direction and 10 nm in y direction? 

Best Regards 
Md Jahid Hasan 
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