MP2 vs exact reaction energies



Dear CCL-readers,
 consider a chemical reaction A + B --> AB.
 Using MP2 with a good basis set, can any general
 statements be made about the calculated reaction
 energy E(AB)-E(A)-E(B) as compared with the
 exact reaction energy?
 For example: The reaction of 4 AlH with 4 H2AlOH
 resulting in (Al2H4O)4 is calculated to be exothermic
 by 329, 339, and 374 kcal/mol at the Hartree-Fock,
 BP86, and MP2 level, respectively. What, if anything,
 can then be said about the exact energy of this reaction?
 sincerely,
 ------------------------------------
 Jon Andreas Støvneng
 Statoil Research Centre, N-7005 Trondheim, Norway
 jast.,at,.statoil.com
 Tel: +47 73584824   Fax: +47 73584345
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