Natural Atomic Orbital-Point Charge

Molecular dipole moments are often used as descriptors in QPSR models. They are calculated reliably by most quantum mechanical techniques, not least because they are part of the parameterization data for semi-empirical MO techniques. Higher multipole moments are especially easily available from semi-empirical calculations using the natural atomic orbital-point charge (NAO-PC) technique [40], but can also be calculated rehably using ab-initio or DFT methods. They have been used for some QSPR models. 

BFGS = Broyden-Fletcher-Goldfarb-Shanno optimizer NLLSQ = nonlinear least squares optimization PECi = pair excitation Cl NAO-PC = natural atomic orbital-point charge model. 

Great attention has been paid to the fast, accurate calculation of molecular electrostatic properties within VAMP. The natural atomic orbital-point charge (NAO-PC) model for representing the molecular electron density as a... 

An important difference between the BO and non-BO internal Hamiltonians is that the former describes only the motion of electrons in the stationary field of nuclei positioned in fixed points in space (represented by point charges) while the latter describes the coupled motion of both nuclei and electrons. In the conventional molecular BO calculations, one typically uses atom-centered basis functions (in most calculations one-electron atomic orbitals) to expand the electronic wave function. The fermionic nature of the electrons dictates that such a function has to be antisymmetric with respect to the permutation of the labels of the electrons. In some high-precision BO calculations the wave function is expanded in terms of basis functions that explicitly depend on the interelectronic distances (so-called explicitly correlated functions). Such... 

The three-dimensional nature of the electrostatic potential makes it difficult to simultaneously visualize its spatial distribution and its magnitude. However, we can deal with the electrostatic potential on the van der Waals surface of a molecule, which is of major importance for the molecular contact between a ligand and a receptor. The electrostatic potential can be calculated by a point charges derived from partial atomic charges, the latter of which can be calculated by iterative partial equalization of orbital electronegativity (PEOE), a well-established empirical method for the rapid calculation of charge distributions [104]. 

So far we have presented cDFT as a means to impose a charge or a spin density on a group of atoms. However, we have not specified how such charges are calculated in practice. It is well known that atomic charges cannot be strictly defined in quantum mechanics and, as a corollary, that multiple population analysis (PA) approaches can be developed to reach this goal. A central point PAs have to address is to define a criterion for assigning each fraction of the electronic density of every point in space to the individual atoms. Some PAs realize this partition with criteria relying on the KS molecular orbital coefficients. The MuUiken [227], Lowdin [228], and the more sophisticated Natural Bond Orbital [229,230] approaches are examples of... 

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