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<DIV>Hi all,</DIV>
<DIV> </DIV>
<DIV>I'm a recent convert to Espresso. I've computed the bond dissociation
energy (BDE) of the CO molecule ( CO --> C + O ) using several available
pseudos for C and O, but do not find good agreement with the experimental
value of 256 kcal/mol. Attached, please find a summary of
the calculations using the various pseudos. </DIV>
<DIV> </DIV>
<DIV>Most calculations overpredict the BDE by almost 15
kcal/mol, while the one using the BLYP pseudo underpredicts it by 11.6 kcal/mol.
The BDE obtained using the pseudos included in example03 and that using the PZ
(LDA) pseudo give the worst result (almost 40 kcal/mol too high). For
reference, I have also included the value obtained by using CASTEP and the PW91
functional, which yields a value within 5 kcal/mol of the experimental value.
</DIV>
<DIV> </DIV>
<DIV>I'd like to clarify that I am using the triplet states for both O and
C in these calculations. I realize that there might be some errors in
my input files, so include a typical input file towards the end of
this mail. (the only change in the other files is the name of the
pseudo) </DIV>
<DIV> </DIV>
<DIV>Finally, I'd like to share my ultimate motive behind these calculations -
I'm looking to calculate the binding energies of small molecules on nickel
surfaces. I find that in case of CO, the binding energy is lower by about 15
kcal/mol - the same difference as the BDE - as compared to CASTEP. So my guess
is that the absolute energy of CO molecule is not being calculated correctly
with my current settings.</DIV>
<DIV> </DIV>
<DIV>Any thoughts will be appreciated. Also, I should add that I have browsed
the archive carefully and found no reference to this or similar problems there,
but apologize if I've missed any relevant information (in which case please give
a pointer to that discussion thread). </DIV>
<DIV> </DIV>
<DIV>*********</DIV>
<DIV>Input file</DIV>
<DIV>*********</DIV>
<DIV> </DIV>
<DIV><FONT size=2>
<P>&CONTROL</P>
<P>calculation = "relax",</P>
<P>prefix = "CO",</P>
<P>pseudo_dir = "c:/Ameya/Espresso/espresso-3.1.1/pseudo",</P>
<P>outdir = "c:/Ameya/Espresso/espresso-3.1.1/tmp",</P>
<P>/</P>
<P>&SYSTEM</P>
<P>ibrav = 1,</P>
<P>celldm(1) = 20.D0, </P>
<P>nat = 2, </P>
<P>ntyp = 2,</P>
<P>ecutwfc = 29.105D0,</P>
<P>ecutrho = 144.D0,</P>
<P>/</P>
<P>&ELECTRONS</P>
<P>conv_thr = 1.D-7,</P>
<P>mixing_beta = 0.7D0,</P>
<P>/</P>
<P>&IONS</P>
<P>pot_extrapolation = "second_order",</P>
<P>wfc_extrapolation = "second_order",</P>
<P>/</P>
<P>ATOMIC_SPECIES</P>
<P>O 16.00 O.pbe-van_bm.UPF</P>
<P>C 12.01 C.pbe-van_bm.UPF</P>
<P>ATOMIC_POSITIONS {angstrom}</P>
<P>C 0.000 0.0 0.000</P>
<P>O 0.000 0.0 1.100 </P>
<P>K_POINTS {Gamma}</P></FONT></DIV>
<DIV>
<DIV>*********</DIV>
<DIV>End of Input file</DIV>
<DIV>*********</DIV>
<DIV> </DIV>
<DIV> </DIV></DIV>
<DIV>Ameya Joshi,
Postdoc<BR>----------------------------------------<BR>Chemical Engineering
Department<BR>Colorado School of Mines <BR>Ph.
(303)-273-3192<BR>----------------------------------------</DIV></BODY></HTML>