[Pw_forum] total force ascend in the course of VC-relax

[Lorenzo Paulatto]

In data 15 ottobre 2009 alle ore 15:38:39, Q.J.Wang <wangqj1 at 126.com> ha  
scritto:

> Dear all
>     I did geometry optimization with vc-relax in a supercell. When I  
> increase the concentration of doped atoms ,the value of total force  
> ascend instead of declining.Before I did not increase the concentration  
> of doped atoms ,It converges well .Anyone who encounter the same problem  
> as me ?

I sounds normal to me, when you perturb the system you will have to redo  
the relaxation... why do you find it puzzling?


>     The second problem is when I increase the relative distance of the  
> two doped atoms in the supercell and did geometry optimization with  
> vc-relax,and the error turn up as like : from c_bands : error #         1
>                         too many bands are not converged
> So I am puzzled why before I increase relative position of two doped  
> atoms the vc-relax converged and the latter turns up error in the same  
> parameter .

It happens with peculiar configurations, the easiest way to get rid of it  
is normally to increase the number of bands.

cheers



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Lorenzo Paulatto
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