# Rydberg functions

Rather than using the molecular orbitals directly, NBO uses the natural orbitals. Natural orbitals are the eigenfunctions of the first-order reduced density matrix. These are then localized and orthogonalized. The localization procedure allows orbitals to be defined as those centered on atoms and those encompassing pairs of atoms. These can be integrated to obtain charges on the atoms. Analysis of the basis function weights and nodal properties allows these transformed orbitals to be classified as bonding, antibonding, core, and Rydberg orbitals. Further decomposition into three-body orbitals will yield a characterization of three center bonds. There is also a procedure that searches for the 7t bonding patterns typical of a resonant system. This is not a rigorous assignment as there may be some electron occupancy of antibonding orbitals, which a simple Lewis model would predict to be unoccupied. [c.101]

The analytic PES function is usually a summation of two- and three-body terms. Spline functions have also been used. Three-body terms are often polynomials. Some of the two-body terms used are Morse functions, Rydberg [c.176]

Diffuse functions are those functions with small Gaussian exponents, thus describing the wave function far from the nucleus. It is common to add additional diffuse functions to a basis. The most frequent reason for doing this is to describe orbitals with a large spatial extent, such as the HOMO of an anion or Rydberg orbitals. Adding diffuse functions can also result in a greater tendency to develop basis set superposition error (BSSE), as described later in this chapter. [c.231]

See pages that mention the term

**Rydberg functions**:

**[c.96] [c.82]**

Computational chemistry (2001) -- [ c.82 ]