Atomic natural orbitals energy calculations

Calculations of ionization energies and electron affinities were performed with a modified development version of Gaussian 99 [48], Pople and Effective Core Potential (ECP) basis sets are provided in this software [49], Dunning and Atomic Natural Orbital (ANO) basis sets were obtained from the EMSL Gaussian Basis Set Library [50],... 

Atomic charge, orbital energy, and population are important pieces of information for determining electronic configuration, net charge association, and the nature of the bond. Mulliken population analysis is a widely used method in most ab initio molecular orbital calculations. However, reports about Mulliken population analysis that fail to yield reliable characterization of molecular systems have appeared. A more accurate method for population analysis, NBO, was... 

ABSTRACT. Recent advances in electronic structure theory and the availability of high speed vector processors have substantially increased the accuracy of ab initio potential energy surfaces. The recently developed atomic natural orbital approach for basis set contraction has reduced both the basis set incompleteness and superposition errors in molecular calculations. Furthermore, full Cl calculations can often be used to calibrate a CASSCF/MRCI approach that quantitatively accounts for the valence correlation energy. These computational advances also provide a vehicle for systematically improving the calculations and for estimating the residual error in the calculations. Cdculations on selected diatomic and triatomic systems will be used to illustrate the accuracy that currently can be achieved for molecular systems. In particular, the F-I-H2 - HF+H potential energy hypersurface is used to illustrate the impact of these computational advances on the calculation of potential energy surfaces. 

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