[Pw_forum] Strain Tensor

[Stefano Baroni]

Hi! Welcome to this forum. As you will learn staying with us, we all much appreciate our forum-pals to sign their posts, and also provide their affiliation. Please, do the same in the future.

This being said, your question has nothing to do with Quantum ESPRESSO. You have first to understand what the strain tensor is supposed to represent: it is nothing but the linear relation describing a scale transformation of the tipe r'=(1+e)r, where r' are the scaled variables of a pont in real space, r the unscaled ones, "1" the 3x3 identity matrix, and "e" the 3x3 infinitesimal (symmetric) strain tensor. The above matrix relation trivially holds for the primitive vectors of a lattice, but not for the internally coordinates of individual atoms, if the lattice is not primitive (i.e. if it has a basis). In the latter case, internal coordinates have to be optimized upon application of the strain.

Hope this helps
Stefano Baroni
 
On May 30, 2010, at 10:49 AM, savaş ağduk wrote:

> 
>               Hi ,
> 
>          I 'm new in Quantum Espresso and I don't know how to apply strain tensor to
>    primitive vectors. In fact, I have read some articles to learn how to calculate elastic
>    modulus but they don't help for quantum espresso way. Any help is much appreciated !
>     
>                      Thanks .
>                              
>                                         ;     
>                                                   
> 
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
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