Sum of Interaction Between Fragments Ab Initio SIBFA

SIBFA [2, 13] is a polarizable molecular mechanics procedure, formulated as a sum of five energy contributions, each of which is destinated to reproduce its counterpart from reference EDA ab initio computations. The intermolecular interaction energy is formulated as  

Which denotes respectively the short-range penetration corrected electrostatic multipolar (EMTP ) energy, short-range repulsion (Erep ), polarization (Epoi), charge-transfer (Ed), and dispersion (EdiSp) contributions. In presence of an open-shell cation, a ligand field correction is introduced (Elf)- 

We have previously [2] emphasized the features that an MM methodology should have in view of a meaningful reproduction of QC, namely separability, anisotropy, non-additivity and transferability. 

In SIBFA, electrostatics is computed upon using distributed multipoles (monopoles, dipoles, quadupole) located on atoms and bond midpoints as  

EmTP = Emono-mono + Em0no-dip + Em0no-quad + Edjp-djp + E(jip-qUaij + EqUaij-qUa(j 

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Accurate energy-decomposition schemes Other force fields build on both atomic multipoles and polarizability to provide an accurate decomposition of intermolecular energies. The sum of interaction between fragments ab initio (sibfa) [83, 84] decomposes the... 

Abstract This chapter discusses molecular mechanics (MM)-based approaches to investigate organometallic complexes. In particular, ligand field MM (LFMM), Sum of Interactions Between Fragments Ab Initio (SIBFA), and VALBOND with its extension to VALBOND-TRANS are presented in some detail. Two particular applications of VALBOND-TRANS to an Ir(III) and a Pt(II) complex are presented. Possible future extensions, including the study of chemical reactions and polarization effects, are briefly discussed at the end. 

SCC-DFTB self-consistent charge-density functional tight binding SCRFPCM self-consistent reaction field polarizable continuum model SIBFA sum of interactions between fragments ab initio computed... 

The modifled SIBFA (sum of interactions between fragments ab initio computed) molecular mechanics method has been employed for the study of the conformation at 1 atm and 15kbar of chiral crotonate (131) (Scheme 19) and of the complexes formed with the diphenylmethylamine and the three solvent molecules present in the experiment. The results obtained suggest that the diastereoselectivity of this Michael addition (18% de at 1 atm and 98% de at ISkbar), induced by high pressure and by the presence of methanol, originates from an important stabilization of the pro-R reactive complex in which the crotonate has a stacked-fransoid conformation. This study has demonstrated that it is possible to account theoretically for the influence of pressure on molecular conformation and/or complex sttucture, using a molecular mechanics method that is able to take into account the variation of volumes of the different entities present in the system studied. ... 

SIBFA Sum of interactions between fragments Ab initio computed... 

The SIBFA (sum of interactions between fragments ab initio computed) force field for small molecules and flexible proteins, developed by Gresh, Piquemal et al. is one of the most sophisticated polarizable force fields because it incorporates polarization, electrostatic penetration, " and charge transfer effects. ... 

On the basis of a sound analysis of intermolecular interactions, performed by means of a quantum perturbational approach, Claverie derived a force field that could suitably represent intermolecular interactions. The electrostatic interactions are described by means of a distributed multipole analysis, and induction effects are taken into account. The force field sum of interactions between fragments completed ab initio (SIBFA) originated from this study and was subsequently applied successfully to many biophysical problems. 

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