[Pw_forum] Irreps and vibrational modes

[Paolo Giannozzi]

On Mon, 2012-05-14 at 03:07 +0100, Elie M wrote:

> (1) Are all the modes vibrational?

there are always three translational modes

> (2) Are any modes missing from the calculation

there shouldn't be anything missing

> (3) i did the calculation and got two of the modes negative

if they go to zero when you apply the acoustic sum rule, with all
other modes unchanged or litle affected, it is not a problem

P.

-- 
Paolo Giannozzi, IOM-Democritos and University of Udine, Italy