Dear venkataramana,
I would guess that the problem is that you have extracted the
"dispersion energy" - please be aware that this can only be "defined" in
the case of DFT-D2, not with vdW-density fucntionals, as there also the
density is changed etc - for the whole system (that includes also the
dispersion between the atoms of the substrate and intra-molecular
contributions of methane) whereas Henkelman et alia only consider the
difference in the binding, or adsorption, energy. Please calculate the
adsorption energies and see if then the value makes more sense.
Greetings from Zurich,
apsi
-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
Ari Paavo Seitsonen / ari.p.seitso...@iki.fi / http://www.iki.fi/~apsi/
Ecole Normale Supérieure (ENS), Département de Chimie, Paris
Mobile (F) : +33 789 37 24 25 (CH) : +41 79 71 90 935
On Sat, 10 Oct 2015, Venkataramana Imandi wrote:
Dear QE users,
The geometry of methane molecule on the top of Iridium slab is relaxed.
In that relaxed geometry, methane molecule is sitting 4.32 angstroms on the top
of Iridium atom, which is exactly same as Henkelman results (prl,
86,664-667,2001).
The total energy of relaxed geometry is -5861698.6 kJ/mol. (val1)
I took that relaxed geometry coordinates and then I applied dispersion
interactions of that configuration only. (input file is attached, Dispersion
interactions with
non-local functional)
The total energy with dispersion interactions is -5893444.5 kJ/mol. (val2)
The difference of val2 and val1 is -31745.9 kJ/mol.
Moreover, I used grimme-d2 dispersion interactions (commenting out
input_dft='vdw-df') , then total energy is -5876733.8 kJ/mol. (val3)
The difference of val3 and val1 is -15035.2 kJ/mol.
I want to reproduce the results of Henkelman. In these results the total energy
difference between with dispersion and without dispersion is roughly 10 kJ/mol.
I am unable to find out where the mistake is. are input parameters correct in
the input file (input file is attached).
Thanks in advance for any suggestions and help.
...
venkataramana
PhD student
IIT Bombay
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