error in bond dissociation energy of gas phase molecule

Jun chen... at gmail.com
Wed Apr 6 12:43:35 CEST 2011


Hello everyone,

We did some testing calculations on bond dissociation energies of HO-
OH in vacuum using BLYP and B3LYP. We found a large difference from
reported results using the same functionals in literature; our numbers
are about 0.5 eV too small for both functionals. We also cross-checked
the numbers using gaussian program, indeed cp2k gives smaller bond
dissociation energy. It is not likely to be BSSE, as we use quite
large basis set TZV2P and also checked QZV2P. It is obvious that we
got either the total energy of H2O2 too high or the OH energy too low.
We checked the energy of H2O --> OH + H, which is very close to what
we found in literature. So, the problem appears to be the too high
energy of H2O2.
Also, we checked CH3-CH3, and found the same: CH3-CH3 bond
dissociation energy is 0.3 eV too small for both functionals compared
to literature numbers, while the energy of CH4-->CH3+H agrees well.
The bond dissociation energies (total energies without ZPE) are
summarised below, and inputs for H2O2-->2OH (H2O2.inp and OH.inp) are
uploaded.
                                BLYP             B3LYP
H2O2-->2OH       2.04 eV (2.67)      1.80 eV  (2.27)
H2O-->OH+H        5.10 eV              5.16 eV (5.2)
C2H6-->2CH3     3.64 eV (3.92)       3.69 eV (3.97)
CH4-->CH3+H    4.69 eV (4.77)       4.75 eV (4.67)
Numbers in parentheses are from literature. The geometry is optimised
one taken from literature, which is almost the same as optimised by
cp2k.
Can anyone comment on this? Many thanks in advance.

Cheers,
Jun


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