[Wien] Pressure and elastic constants

[Víctor Luaña Cabal]

On Tue, Apr 14, 2015 at 12:52:29PM +0530, Shakeel Khandy wrote:
> thanks sir for your suggession.I got c12 a negative quantity as given
> below.How can i calculate elastic constants at 0 pressure .what changes i
> have to make.

Shakeel,

1) Pressure and elastic constants ... You have started a question where
   there still is some debate about what is correct.

2) Some people would say that you must study the curvature of the
   internal energy (the total electronic energy of your solid) with
   respect to the strain deformations.

3) Some perople (myself) would say that it is better to examine the
   Gibbs energy and use whatever exact or aproximate treatment of
   the pressure and temperature of your system.

4) From the E(V) data you have a family of codes to determine the
   Bulk modulus and other elastic terms under a range of pressure and
   temperature.

Read the paper on the gibbs code (freeware) to know how to introduce
pressure and temperature under the QHA (quasi-harmonic, aka Debye,
approximation):

MA Blanco et al, Comput Phys Commun 158 (2004) 2004

The next two papers explain some improvements in the programming and
theory:

A. Otero-de-la-Roza and V.Luaña, Comput Phys Commun 182 (2011) 1708.
A. Otero-de-la-Roza and V.Luaña, Comput Phys Commun 182 (2011) 2232.

If you want to examine further applications on converting the internal
energy data en elastic constants I can provide you more articles in the
subject. You may be interested in

T. Ouahrani et al, Physica B: Condensed Matter 405 (2010) 3658

Best regards,
            Dr. Víctor Luaña
--
     .  .    "Research is to see what everybody else has seen, and to
    / `' \   think what nobody else has thought"                             
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  /`. \/ .'\ 
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 |  |'`'`|  | actitud"
  \/`'`'`'\/          -- Jorge Wasenberg, 2015
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! Dr.Víctor Luaña, in silico chemist & prof. ! Mediocre is worse than
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