Atoms in molecules method

VViberg and Rablen found that the charges obtained with the atoms in molecules method were relatively invariant to the basis set. The charges from this method were also consistent v it i the experimentally determined C-H bond dipoles in methane (in which the carbon is p isitive) and ethyne (in which the carbon is negative), unlike most of the other methods they examined. 

Langeland and Werstuik <2003CJC525> used ab initio and AIM (atoms-in-molecules) methods to study the structures and reactivity of various phosphate ozonides. Activation energies of the bicyclic complexes (4-ethyl-l-phospha-2,6,7-trioxabicyclo[2.2.2]octane ozonide, l-phospha-2,6,7-trioxabicyclo[2.2.2]octane ozonide, and 1-phos-pha-2,8,9-trioxadamantane ozonide) were found to be significantly higher than the monocyclic structures studied. 

Electron Density Integrals and Atoms-in-Molecules Methods... 

Several important developments in the straightforward VB theory have occurred in the past 10 or 15 years. These include the atoms-in-molecules method of Moffitt as modified by Hurley and others, the pair function model of Hurley, Lennard-Jones, and Pople, and the general group function model of McWeeny. These theories can all be usefully discussed within the framework developed in Section 2, and this is done in Section 4. 

Orthogonalized Moffitt (atoms-in-molecules) method. See ref. 55 and also p. 104. 

It seems that atoms-in-molecules methods may develop in two separate directions. The basis of composite functions (112) is not the most suitable in which to expand the molecular wavefunction as many terms are needed in order to express adequately the distortion of the atoms upon the formation of molecules. Thus the OM calculations above require very large basis sets (18 composite functions for Li 2, 100 for HF, and 204 for LiF2) in order to obtain reliable results. The i.c.c. method, on the other hand, which does allow for some distortion, achieves in several instances as good or even better results with much smaller basis sets. An attempt has been made by Arai110 to develop a method of deformed atoms in molecules , in which the composite functions are multiplied through by a certain spatial function, 2(ri, r%. .., tn), to be determined, which expresses the desired distortion. Thus, in hydride molecules, the 1. wavefunction of H, which is of the form exp(— r), is multiplied by a function 2(r)=exp(—<5r), so that the combined function, exp[—(1 + <5)r], with Sx 0.2, is now an adequate representation of... 

The postulates of VSEPR theory are consistent with the partitioning of electron density according to Bader s atoms-in-molecules method [173], in which the electron pairs return as the valence shell charge concentration. 

Adam, K.R. New density functional and atoms in molecules method of computing relative pK(a) values in solution. J. Phys. Chem. A 2002,106(49), 11963-72. 

Abstract In this chapter we discuss the influence of ir-electron delocalization on the properties of H-bonds. Hence the so-called resonance-assisted hydrogen bonds (RAHBs) are characterized since such systems are mainly classified in the literature as those where TT-electron delocalization plays a very important role. Both the intramolecular and intermolecular RAHBs are described. RAHBs are often indicated as very strong interactions thus, their possible covalent nature is also discussed. Examples of the representative crystal structures as well as the results of the ab initio and DFT calculations are presented. Additionally the RAHB systems, and the other complexes where rr-electron delocalization effects are detectable, are characterized with the use of the QTAIM (Quantum Theory Atoms in Molecules ) method. The decomposition scheme of the interaction energy is applied to expand the knowledge of the nature of the RAHBs. 

H-bonds intermolecular H-bonds Tr-electron delocalization topological parameters critical points QTAM (Quantum Theory Atoms in Molecules method) covalent hydrogen bonds interaction energy decomposition scheme. 

Atoms-in-Molecules Methods Rigorous Pseudo-Potential Theories Closed Shell Interaction Model... 

The valence-bond approach plays a very important role in the qualitative discussion of chemical bonding. It provides the basis for the two most important semi-empirical methods of calculating potential energy surfaces (LEPS and DIM methods, see below), and is also the starting point for the semi-theoretical atoms-in-molecules method. This latter method attempts to use experimental atomic energies to correct for the known atomic errors in a molecular calculation. Despite its success as a qualitative theory the valence-bond method has been used only rarely in quantitative applications. The reason for this lies in the so-called non-orthogonality problem, which refers to the difficulty of calculating the Hamiltonian matrix elements between valence-bond structures. 

The methods designated here as semi-theoretical all have in common the fact that they are based on an ab initio approach and deviate from it only in that they introduce a limited number of corrections or approximations. The atoms-in-molecules method involves building up the molecular... 

The quahtative bonding model for stmcture B is supported by a topographical analysis of the calculated electronic structure which rests on the QTAIM (Quantum Theory of Atoms in Molecules) method. Figure 2.7 shows the Laplacian of... 

The problem of how to account for different levels of accuracy in calculations at different points on the potential energy surface goes back a long way and there have been many partial solutions. The atom-in-molecules method of Moffitt [9], the diatomics-in-molecules method of Ellison [10], and the counteipoise model of Boys [11] are all successful in some respects. Unfortunately none of them are helpful for the most commonly met problem by those who are ti ng to fit potential functions to data, which is how to join up data produced by different methods on different regions of the surface. I believe there is no answer to this except scientific judgement... 

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