RE2:G98: ONIOM and Amber on TM systems

  Hi Stefan and CCl members!
 Your description seems to be reasonable, but if one assumes so,
 this means that current G98 ONIOM implementation is not suitable
 at all for running oniom(ab-initio:Amaber) or oniom(ab-initio:AM1/PM3)
 calculations for transition metal containing systems.
 Moreover, very unlikely in the nearest future due to known
 difficulties of MM and semiempirical treatment of TM systems.
 Sounds a bit pessimistic. ( I know about UFF, but it does
 not seem to work well, especially for charged molecules)
 >From the other hand, in JPC 1996,100,19357 oniom(b3lyp:HF:MM3)
 calculations for platinum complexes are described. However,
 I am not aware of any MM3 parametrization for platinum.
 is there a way to repeat such calculations in G98?
 regards, Valentin.
 > Hi Valentine,
 >
 > The ONIOM method requires 3 calculations for
 > a molecule: a low level calc of the whole molecule
 > (ll/all), a low level calc of the high level part (ll/part)
 > and a high level calc of the high level part (hl/part).
 > The ONIOM energy is defined as
 > E(ONIOM) = E(ll/all) - E(ll/part) + E(hl/part)
 >
 > Although the low level energy contributions of the
 > high level part seem to cancel out, that is not
 > completely true. In order to have well behaved
 > high level parts, broken bonds are saturated with
 > hydrogen. This causes a difference in the MM
 > energy terms between ll/all and ll/part that reaches
 > at least three atoms inside the high level part
 > (dihedral angle with the saturation H). For that
 > reason (and programming reasons, I assume),
 > you need MM parameters for all atoms in the
 > molecule.
 >
 > In the last few days there was a thread concerning
 > ONIOM energies. One of the mails pointed to an
 > article that explains the ONIOM method in more
 > detail.
 >
 > Stefan
 > __________________________________________________________________
 > Dr. Stefan Fau                    |      fau ^at^ qtp.ufl.edu
 >
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