Gaussian electrostatic model densities

As the SIBFA approach relies on the use of distributed multipoles and on approximation derived form localized MOs, it is possible to generalize the philosophy to a direct use of electron density. That way, the Gaussian electrostatic model (GEM) [2, 14-16] relies on ab initio-derived fragment electron densities to compute the components of the total interaction energy. It offers the possibility of a continuous electrostatic model going from distributed multipoles to densities and allows a direct inclusion of short-range quantum effects such as overlap and penetration effects in the molecular mechanics energies. 

Status of the Gaussian Electrostatic Model, a Density-Based Polarizable Force Field... 

In present work ab initio quantum-chemical calculations were performed by Gaussian 03 using density-functional theory for tetraphenylporphyrin. 6-3 lG(d, p) basis was used for all atoms, core electrons of which were simulated with LanL2 pseudopotential with corresponding 2-exponent basis for valence electrons. Theoretical valence band spectra of the molecules were obtained from calculated molecular orbitals. Chemical shift has been modeled as a change of electrostatic potential of atoms and three well-resolved nitrogen states and nine states were obtained situated very closely to each other, so they caimot be resolved ejqterimentally. 

Most commonly used is certainly the molecular electrostatic potential. It can be derived from any kind of charge distribution. Usually, the MEP is first calculated on a grid and subsequently transformed to the sphere or Gaussian representation. Quite important is the electron density distribution, which closely models the steric occupancy by a molecule. Other approaches utilize artificial fields for physicochemical properties commonly associated with binding, like a field for the hydrophobicity [193] or H-bonding potential [133,194]. 

Tel. 714-955-2120, fax 714-955-2118, e-mail support wavefun.com Model building, molecular mechanics, and ab initio (Hartree-Fock, Moller-Plesset, direct HF) and semiempirical (MNDO, AMI, PM3) molecular orbital calculations. Graphical front-end and postprocessor of the output. Electron density and electrostatic plots. Interface to Gaussian 92. Cray, Convex, DEC, HP, IBM, and Silicon Graphics versions. 

The description of the mDC method in the present work is supplemented with mathematical details that we Have used to introduce multipolar densities efficiently into the model. In particular, we describe the mathematics needed to construct atomic multipole expansions from atomic orbitals (AOs) and interact the expansions with point-multipole and Gaussian-multipole functions. With that goal, we present the key elements required to use the spherical tensor gradient operator (STGO) and the real-valued solid harmonics perform multipole translations for use in the Fast Multipole Method (FMM) electrostatically interact point-multipole expansions interact Gaussian-multipoles in a manner suitable for real-space Particle Mesh Ewald (PME) corrections and we list the relevant real-valued spherical harmonic Gaunt coefficients for the expansion of AO product densities into atom-centered multipoles. 

The term weak adsorption implies that the entropic free energy of a chain is comparable to its electrostatic attraction energy to the interface. The chain is assumed to be Gaussian and its conformations are only weakly perturbed by interactions with the surface. This is the most severe approximation of the current model. We also assume that the polyelectrolyte-density profile is built up near the adsorbing surface without disturbing the electrostatic potential and ionic distribution near the interface prescribed by the Poisson-Boltzmann theory. A more general... 

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