Re: CCL:charges



 rull-0at0-nmr.chem.ruu.nl (Ton Rullmann) writes:
 > If one decides to use ab initio theory wouldn't it make sense to start from
 the
 > perturbation theoretical approach to intermolecular interactions,
 describing
 > interactions in terms of true unimolecular properties such as multipoles
 and
 > polarizabilities? And if one chooses to stick with pair-additive two-body
 > potentials - for solid practical reasons such as limits of computer time,
 if
 > not (wo)man power needed to redesign a force field - would it be feasible
 > to discriminate between "true charge distributions" derived for
 isolated
 > molecules, and the "charge corrections" needed to get a good fit
 to inter-
 > molecular energies in cases of interest? Does anyone care to venture
 opinions
 > on the issue of using perturbation theory vs. fitting, and on the use of
 > ab initio data?
 > (The case for perturbation theory was argued in: Rullmann & van
 Duijnen,
 > Reports in Molecular Theory 1, 1 (1990). This was a rewrite of a chapter of
 > my PhD thesis. After that I have worked on other things, but I'm very
 > interested to hear opinions on the current state of affairs).
 I vote for perturbation theory! 8-)
 Like Ton, I also did my Ph.D. studying intermolecular forces by
 perturbation theory (and have also since moved on to other things).
 We found that atom based multipoles gave remarkably good results
 compared to more rigorous perturbation theory [Hurst, Fowler, Stone &
 Buckingham, Int. J. Quantum Chem. 29:1223-1239 (1986)].
 Cheers,
 Graham
 ------------
 Graham Hurst (hurst-0at0-hyper.com)
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