reaction energies and box sizes

[Geoffrey Wood]

Hello everyone.

I'm a little bit confused as what to do with the energy convergence as a 
function of box size when computing reaction energies.

For example using the BLYP functional and the TZVP-MOLOPT-GTH basis set and 
a cut off of 1200 Ry (an example of the input deck that I used is attached) 
I computed the energy for the Cl atom (neutral) as a function of the box 
size. This converges at about 12 Angstroms but there are oscillations and 
the minimum actually  at 7 Angstroms, well before convergence (see attached 
spreadsheet.

My question for the community is if you are computing a  reaction energy, 
say:

A  + B =  AB

do you 

a) use consistent Box sizes for all species?
b) use the minimum energy found as a function of box size for all three 
species?
c) the converged energy as a function of box size (even though this may not 
be the minimum) for all three species?

Thanks, Geoff.






-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20141117/eb4c620c/attachment.htm>
-------------- next part --------------
5	-14.88061504
6	-14.88072017
7	-14.88075945
8	-14.88074955
9	-14.88074759
10	-14.88074601
11	-14.88075068
12	-14.88074402
13	-14.880745
14	-14.8807442
15	-14.88074437
-------------- next part --------------
A non-text attachment was scrubbed...
Name: cl_7.inp
Type: chemical/x-gamess-input
Size: 1438 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20141117/eb4c620c/attachment.inp>