CCL: Computing AsMe3

[John McKelvey <jmmckel(!)gmail.com>]

 Sent to CCL by: John McKelvey [jmmckel\a/gmail.com]
 It would be interesting to see what PM6 results would be.
 John McKelvey
 On Mon, Oct 4, 2010 at 7:13 AM, Gerald Knizia
 knizia|,|theochem.uni-stuttgart.de <owner-chemistry*o*ccl.net> wrote:
 >
 > Sent to CCL by: Gerald Knizia [knizia---theochem.uni-stuttgart.de]
 > On Monday 04 October 2010 11:51, osama T Akoubeh dolkeen(_)hotmail.com
 wrote:
 >> I computed the compound AsMe3 " As(CH3)3 " using PM5 and many
 functional
 >> methods to get the enthalpy of formation , entropy at various
 temperature
 >> to study its behavior reaction [..]
 >>
 >> The value from Chemkin data base is 2,9kcal/mol , the difference
 between
 >> both will make the reaction Gibbs favorable at 2.8 and not at 2.9
 kcal/mol
 >>
 >> I computed the compound using PM5 methaod anf got 3.2118 kcal/mol what
 >> functional method you suggest to get 2.8 even I tested B88-PW91 with no
 >> good results
 >
 > This kind of accuracy is far beyond what you could possibly expect from any
 > DFT or semiempirical method. In fact, I doubt that there currently are any
 > computational methods capable of achieving this kind of accuracy for this
 > system, not even for the electronic part alone.
 >   The least you'd need to even get reliably into the 1kJ/mol accuracy
 range
 > is a compound method (like W4 or HEAT) which includes at least a CCSDT(Q)
 > calculation and additionally a F12 or CBS[45] (better CBS[56]) calculation
 of
 > the CCSD(T) basis set limit. My patience would certainly not be sufficient
 to
 > do a CCSDT(Q) calculation on such a system.
 > --
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 >
 >
 --
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