Re: CCL:TM force fields
I'd like to take up this thread again. Also, I have a
question at the end:
Isaac B. Bersuker wrote:
The open (or quasi-open) d shell is the main reason of
properties of TM systems (TMS)
with regard to modeling:
(1) 3D delocalization and hence strong mutual influence of the M-L
bonds on each other (e.g.,
cis- and trans-effect),
(2) "back donation" and hence local excitation of the
(chemical activation by
(3) degeneracy and pseudodegeneracy and hence the strong Jahn-Teller
and pseudo JT effects.
All this together makes imposible to get reasonable parametrization
of a force field (with
transferable parameters) that could be used in modeling similar to
that of organic and/or
non-TMS, in general.
I am sorry that these important features of TMS remain unknown to
people engaged in their
I completely agree that these effects can make modelling of
transition metals challenging. However, I disagree strongly with the
word "impossible". We are still far from a force field that
this for all conceivable complexes without parameterization, but wide
transferability is not a requirement for force field modelling.
Personally, I design force fields for specific problems (you can
check my web page for examples, see below). Setting up the force
field requires about the same time as doing e few QM/MM calculations,
then I have access to a tool that allows rapid conformational
searching. In the types of problems I'm working with (asymmetric
catalysis), a good sampling of the conformational space is essential.
The force fields are still 3-4 orders of magnitude faster than QM/MM
calculations in this case, and seemingly almost as accurate. An
attractive combination is to use the force field as a search tool,
followed by refinement of a few selected structures by QM/MM.
For the concerns listed above, we've only done simple things
like introduction of specific cross terms to reproduce trans
induction, but others have done a lot more. I'm aware of work by
Landis, Comba, Deeth, and Carlsson, solving different aspects of
these problems. I would like to see more. If you could send me
references on how to treat the above problems, I'll summarize to the
* Per-Ola Norrby, Associate Professor
* The Royal Danish School of Pharmacy, Dept. of Med. Chem.
* Universitetsparken 2, DK 2100 Copenhagen, Denmark
* Tel. +45-35306506, fax +45-35306040
* Email: peo ( ( at ) ) dfh.dk (preferred), peo ( ( at ) ) compchem.dfh.dk
* WWW: http://compchem.dfh.dk/PeO/