[Pw_forum] The cell blowing up in MD simulation

[Paolo Giannozzi]

On Sep 26, 2012, at 19:55 , Tian Lan wrote:

> So It means that I cannot exactly copy the setup of scf calculation  
> to the cp calculation
> because in scf I used a much denser k-mesh but cp calculation only  
> uses the Gamma
> point. Then how could I do the best to eliminate this difference in  
> the MD calculation?
> I just find a blowing supercell in MD that otherwise in equilibrium  
> in scf.

the simplest and fastest test is to compare the results of self- 
consistent calculations
for cp.x (no dynamics, just electronic minimization) and for pw.x for  
the same data
(use card K_POINTS gamma). Compare the energies and the stresses. The  
choice
of nr1b, nr2b, nr3b (if needed) is not completely obvious: you have  
to find a compromise
between speed (incrases for decreasing values), and accuracy, taking  
into account that
accuracy doesn't actually improve if you increase those values beyond  
some limits
(useless long-range oscillations of the augmentation charges is all  
you see)

Paolo
---
Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222