--- Ameya Joshi <ajoshi at mines.edu> wrote: Hi Ameya,
> I'm a recent convert to Espresso. Yes, it is about time that this crusade has started to bring in some fresh converts :-) Now, if only people could get converted away from using Microsoft formats such as *.xls ... >... >... >... > 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. It seems that you could always compute the energy of CO on the nickel surface, as well as a few Angstroms away from the surface. Then you get the energy difference from an identical setup, just different geometries. See if you still get the 15 kcal/mol difference. Now, if you computing the energy of Ni-CO with respect to (Ni+C+O), that one can easily find this 15 kcal error coming from the improperly handled reference substances. Anyway, BDEs are often rather challenging to compute correctly (one has to deal with reference atomic states and such), so try to avoid doing that if possible, and stick to the smallest possible changes. And, if you really want to learn about minimizing errors for chemical reactions, check out the definition of "isodesmic" : http://en.wikipedia.org/wiki/Isodesmic_reaction Kostya __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
