[Pw_forum] lattice instability and local minimum energy postion

[Paolo Giannozzi]

Axel Kohlmeyer wrote:

> ... not to mention that several of the pseudopotentials from the 
> vanderbilt library have problems with getting phonons right. not
> sure whether this originates from the definition of the potentials
> or the individual parameters chosen. 
> 
> i've seen this in several vanderbilt pseudopotential that i created:
> they worked fine for all problems that i was using them (MD, geometry
> optimization), but when others used them for calculating phonons, they 
> turned out to be disastrous.

this is also a possibility. I have encountered cases in which
a phonon calculation with ultrasoft pseudopotentials required
a ridicolously large cutoff cutoff for the charge density.
Never understood why.

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