[Pw_forum] Question on stress in a system with constraints

[Nicola Marzari]

Stefano de Gironcoli wrote:

> 
> Dear Nicola and Kostya,
> I did not think deeply about the question, so I may be wrong, but I agree
> with Kostya.
> 
> Stress is a first order derivative and as such only GS properties should
> be needed.
> 

Yes - apologies I forgot to correct this. For some reason I was
thinking at elastic constants, thus at second derivatives of the
energy. Bottom line - all my previous emails would be correct if you
were looking at an elastic constant. For stress, what Stefano and
Kostya said was right.

				nicola

---------------------------------------------------------------------
Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758  fax 617.2586534  marzari at mit.edu  http://nnn.mit.edu