[Pw_forum] transition state using NEB

[Giuseppe Mattioli]

Dear Ravi
You are using a *very* small cell. Try to calculate the H concentration. It will probably be a huge, unphysical value. Moreover, the localized H 
(probably a covalent hydride H- in a metal) is strongly interacting with its periodically replicated images, which are at a very short distance.
Try to use a larger supercell and see how much the results change.
HTH
Giuseppe

On Friday, January 30, 2015 05:13:18 PM Ravi Kiran wrote:
> Hi,
> 
> I am using neb to calculate activation energy of hydrogen in unit cell of
> nickel. I have placed hydrogen in octahedral position and I am moving it to
> another octahedral position as shown below. My question is whether neb can
> calculates transition state which is tetrahedral site?. I have used a
> path_thr of 0.01eV with 7 images. I have calculated the activation energy
> which I am getting is 1.05 eV as shown in output, whereas the experiments
> indicate 0.42.
> 
> *input *
> 
> FIRST_IMAGE
> ATOMIC_POSITIONS crystal
>     Ni 0 0 0
>     Ni 0 0.5 0.5
>     Ni 0.5 0 0.5
>     Ni 0.5 0.5 0
>     H  0.5 0.5 0.5
> LAST_IMAGE
> ATOMIC_POSITIONS crystal
>     Ni 0 0 0
>     Ni 0 0.5 0.5
>     Ni 0.5 0 0.5
>     Ni 0.5 0.5 0
>     H  0.0 0.5 0.0
> END_POSITIONS
> *output*
>  ------------------------------ iteration  56 ------------------------------
> 
>      tcpu =   6675.4    self-consistency for image   1
>      tcpu =   6683.4    self-consistency for image   2
>      tcpu =   6764.1    self-consistency for image   3
>      tcpu =   6846.9    self-consistency for image   4
>      tcpu =   6948.8    self-consistency for image   5
>      tcpu =   7031.7    self-consistency for image   6
>      tcpu =   7113.1    self-consistency for image   7
> 
>      activation energy (->) =   1.024248 eV
>      activation energy (<-) =   1.024248 eV
> 
>      image        energy (eV)        error (eV/A)        frozen
> 
>          1      -4690.3920838            0.000000            F
>          2      -4690.3237895            0.006072            F
>          3      -4689.7348781            0.005158            F
>          4      -4689.3678358            0.006904            F
>          5      -4689.7349752            0.004005            F
>          6      -4690.3237535            0.006484            F
>          7      -4690.3920838            0.000000            F
> 
>      path length          =  5.711 bohr
>      inter-image distance =  0.952 bohr

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   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
   v. Salaria Km 29,300 - C.P. 10                
   I 00015 - Monterotondo Stazione (RM)          
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