Fragment/bond methods

Meylan, W., Howard, PH. (1991) Bond contribution method for estimating Henry s law constants. Environ. Toxicol. Chem. 10,1283-1293. Meylan, W., Howard, P.H., Boethling, R.S. (1992) Molecular topology/fragment contribution method for predicting soil sorption coefficient. Environ. Sci. Technol. 26(8), 1560-1567. 

The local self-consistent field (LSCF) or fragment SCF method has been developed for treating large systems [105,134-139], in which the bonds at the QM/MM junction ( frontier bonds ) are described by strictly localized bond orbitals. These frozen localized bond orbitals are taken from calculations on small models, and remain unchanged in the QM/MM calculation. The LSCF method has been applied at the semiempirical level [134-137], and some developments for ab initio calculations have been made [139]. Gao et al. have developed a similar Generalized Hybrid Orbital method for semiempirical QM/MM calculations, in which the semiempirical parameters of atoms at the junction are modified to enhance the transferability of the localized bond orbitals [140]. Recent developments for ab initio QM/MM calculations include the method of Phillip and Friesner [141], who use Boys-localized orbitals in ab initio Hartree-Fock QM/MM calculations. These orbitals are again taken from calculations on small model systems, and kept frozen in QM/MM calculations. 

Kairys, V, Jensen, J. H. [2000J. QM/MM Boundaries across Covalent Bonds A Frozen Localized Molecular Orbital-Based Approach for the Effective Fragment Potential Method,/ Phys. Chem. A, 104, 6656-6665. 

Fig. 1 The directional bonding method fragments a target polygon or polyhedron (a) at logical breaking points (b) to define the angularity and directionality of individual precursors (c) which can be combined in specific ratios to generate a supramolecular analogue (d)...

Abstract The perfonnance of the thennodynamic fragment energy method (FEM) in the context of natural orbital functional theory (NOFT) in its PNOF5 implementation is assessed. Two test cases are considered the linear chains C H2 +2 ( = 10) and the hydrogen-bonded (FH) ... 

More recently Wulff and coworkers introduced a method based on the reaction of diynes 4 with bis(carbene) complexes 3 (Eq. 4.2) [6]. In contrast to the classical fragment condensation method, two phenol rings are formed during the key cyclization step. Since bonds to the substituted methylenes are not cleaved in the cyclization step, this method allows the preparation of chiral, optically active methylene-substituted calix[4]arenes, starting from the appropriate enantiopure precursors. 

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