error in computing dissociation energy

katarína stančiaková stanc... at gmail.com
Tue Jan 17 14:08:00 CET 2017


Dear CP2K users,
I did some basic testing on bond dissociation energies on a small set of 
molecules using PBE functional.
I compared my results with literature (
http://dx.doi.org/10.1007/s00214-007-0401-8 ) and with results obtained 
using ADF. 

However CP2K results are quite different from my reference and ADF. I tried 
to play with settings (e.g. turn off the periodicity), but this did not 
lead to any improvement.
Afterwards I decided to do some basic testing, using test files. Especially 
I tested following input files:

/tests/QS/regtest-hybrid-4/CH3-PBE0_TC.inp
/tests/QS/regtest-hybrid-4/CH3-PBE0_TC_LRC.inp
/tests/QS/regtest-hybrid-4/CH4-PBE0_TC.inp
/tests/QS/regtest-hybrid-4/CH4-PBE0_TC_LRC.inp

However, for CH4 case I obtained quite a difference between the numbers 
given in txt TEST_FILES, where I assume numbers which I should obtain are 
stores. I tested two versions of CP2K (4.0 and 2.6), and numbers are still 
the same. Now I am struggling what might be wrong. Please, do you have any 
suggestions?

Below you can find example of input files and my data

(for all cases we assume homolytic dissociation)

CH3-CH3 -> CH3 + CH3        92.59 (96.79) kcal/mol 
CH3-OCH3 -> CH3 + OCH3       81.48 (87.24) kcal/mol
CH3-isopropyl -> CH3 + isopropyl         86.01 (89.65) kcal/mol
OCH3-isopropyl -> OCH3 + isopropyl                   77.69 (84.08) kcal/mol

Numbers in parentheses are from literature.

The results from testing files:
CH3-PBE0_TC.inp         -7.98384  (-7.94392) a.u.
CH3-PBE0_TC_LRC.inp    -7.34353  (-7.34351) a.u.
cCH4-PBE0_TC.inp        -7.35850  (-7.35848) a.u.
CH4-PBE0_TC_LRC.inp    -8.00130  (-7.96099) a.u.
Numbers in parentheses are from corresponding TXT file TEST_FILES 
(/tests/QS/regtest-hybrid-4/)


Thank you for any help
Best,
Katarina

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