[QE-users] [SUSPICIOUS MESSAGE] Question on Initial and final energies in NEB

[Giuseppe Mattioli]

Dear Martina

> 1) How is the energy for the Initial and final structure estimated  
> when I keep the two configurations frozen?

By performing a single-point scf calculation. This is done in the  
first neb.x step

> 2)Should it be exactly the same as the final relaxed energies that I  
> would get from completely separate calculations with the same  
> simulation conditions and same geometries?
> 3) If they are not expected to be exactly the same which factors  
> does the difference I may see depend on?

The energy should be the same, but keep also in mind that 1) neb.x  
energies are printed in eV, pw.x energies in Ry; 2) conv_thr may be  
different in the two calculations. It can be lowered down to two order  
of magnitude below the input value near convergence of bfgs in "relax"  
calculations, and it is strictly corresponding to the input value in  
the first neb.x iteration; 3) You may be trapped in a different spin  
state, you should check the PW.out file of the corresponding image to  
be sure.

HTH
Giuseppe

"Stella, Martina" <martina.stella at kcl.ac.uk> ha scritto:

> Hi,
>
> I am new to NEBs calculations and I am getting familiar with the  
> method. I have a couple of questions, maybe trivial, but for which I  
> don't have an answer yet. Hopefully someone can help.
>
> 1) How is the energy for the Initial and final structure estimated  
> when I keep the two configurations frozen?
> 2)Should it be exactly the same as the final relaxed energies that I  
> would get from completely separate calculations with the same  
> simulation conditions and same geometries?
> 3) If they are not expected to be exactly the same which factors  
> does the difference I may see depend on?
>
> Thanks.
>
>
>
> M. Stella
>
> Post-Doctoral researcher
>
> Physics Department, King's College London
>
> Strand,London WC2R 2LS UK



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>