Basis sets for atoms

Gaussian Basis Functions for use in Molecular Calculations III Contraction of (10s, 6p) Atomic Basis Sets for the First-Row Atoms T. FI. Dunning, Jr... 

CIExpan expresses the fact that if an atomic basis set for a specified atom is used in the construction of a Hamiltonian matrix and the eigenvectors of that matrix axe found, then the atomic basis and the eigenvectors can be used to construct a Cl expansion for the specified atom. 

Dunning TH Jr. Gaussian basis functions for use in molecular calculations. I. Contraction of (9s5p) atomic basis sets for the first-row atoms. J Chem Phys 1970 53 2823-33. 

In ONETEP, Wannier functions are constrained in a localisation sphere centred on atoms, i.e. = 0 outside the localisation sphere, providing an atomic basis set. The radius of the localisation sphere is set by considering the electronic structure of the system or it can be increased until convergence of the physical properties is achieved. The nonorthogonal Wannier functions are optimised during the electronic structure calculation, hence they represent the best possible atomic basis functions of a particular system. In our studies of the atomic properties, we used these Wannier functions as the atomic basis set for calculating atomic properties with our definition for these properties given in Eq. 6.8. 

T. H. Dunning,. Chem. Phys., 55, 716 (1971). Gaussian Basis Functions for Use in Molecular Calculations. 111. Contraaion of (10s,6p) Atomic Basis Sets for First Row Atoms. 

Results are reported of ab initio Hartree-Fock CO calculations using a minimal atomic basis set for the single stranded periodic B-DNA models of cytosine (C), thymine (T), adenine (A) and guanine (G) stacks and two polynucleotides with adenylic acid (ASP) and th)miidine (TSP) as repeating unit, respectively. Further the energy band structures of two poly(base pairs), poly(adenine-thymine), (A-T),and poly(guanine-cytosine), (G-C), representing a simple model of B-DNA double helix are discussed. 

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