Many-body exchange-repulsion in polarizable molecular mechanics. I. orbital-based approximations and applications to hydrated metal cation complexes
✍ Scribed by Robin Chaudret; Nohad Gresh; Olivier Parisel; Jean-Philip Piquemal
- Publisher
- John Wiley and Sons
- Year
- 2011
- Tongue
- English
- Weight
- 183 KB
- Volume
- 32
- Category
- Article
- ISSN
- 0192-8651
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✦ Synopsis
We have quantified the extent of the nonadditivity of the short-range exchange-repulsion energy, E exch-rep , in several polycoordinated complexes of alkali, alkaline-earth, transition, and metal cations. This was done by performing ab initio energy decomposition analyses of interaction energies in these complexes. The magnitude of E exch-rep(n-body, n > 2) was found to be strongly cation-dependent, ranging from close to zero for some alkali metal complexes to about 6 kcal/mol for the hexahydrated Zn 2þ complex. In all cases, the cation-water molecules, E exch-rep(three-body) , has been found to be the dominant contribution to many-body exchange-repulsion effects, higher order terms being negligible. As the physical basis of this effect is discussed, a three-center exponential term was introduced in the SIBFA (Sum of Interactions Between Fragments Ab initio computed) polarizable molecular mechanics procedure to model such effects. The three-body correction is added to the two-center (two-body) overlap-like formulation of the short-range repulsion contribution, E rep , which is grounded on simplified integrals obtained from localized molecular orbital theory. The present term is computed on using mostly precomputed two-body terms and, therefore, does not increase significantly the computational cost of the method. It was shown to match closely E three-body in a series of test cases bearing on the complexes of Ca 2þ , Zn 2þ , and Hg 2þ . For example, its introduction enabled to restore the correct tetrahedral versus square planar preference found from quantum chemistry calculations on the tetrahydrate of Hg 2þ and [Hg(H 2 O) 4 ] 2þ . V