[Pw_forum] Single point energy calculation within PWSCF.

[Hongsheng Zhao]

On 05/25/2011 01:15 AM, mohnish pandey wrote:
> Dear Hongsheng!
>  The flag is "calculation" = 'scf' for single point energy 
> calculation. But I will suggest you if you want  to test the 
> convergence for structure then you must relax the atomic position as 
> well as cell volume, because the single point energy calculation will 
> not relax the stress and forces. So for bulk structures "calculation = 
> 'vc-relax' is the way to test the convergence with respect to energy, 
> because that will release the stress and forces in the system. I hope 
> it helps. Feel free to ask any doubt further.

1- What do you mean by saying "for bulk structures", do you mean 3D, 
other than 2D/1D/0D case?  If so, what should I use for the non-bulk 
structures, in this case, if I want to determine the convergence for 
structure, the single point calculation is enough?

2- If I can run a series of single-point energy calculations w.r.t 
different cut-off energies, k-point samplings, fine grids, cell size, 
and etc. Then look for when the energies, forces and stresses are all 
converged adequately.  In this way, I'll achieve the same aim as 
'vc-relax' done for me, am I right?  I mean, if the energy, forces and 
stresses are all accurately converged based on a series of single-point 
energy calculations, then the final structure will also be accurate.

Regards.
-- 

Hongsheng Zhao<zhaohscas at yahoo.com.cn>
School of Physics and Electrical Information Science,
Ningxia University, Yinchuan 750021, China