Extended Rydberg function

Murrell and Sorbie have proposed an extended Rydberg function as... 

An analytical expression for the potential function ( extended-Rydberg function [11]) was based upon available data for re, We, cOeX . and De [12]. 

The monoatomic terms are constant and can be taken as zero in their ground states. For diatomic terms extended Rydberg (ER) can be used. The three-body term is expressed as a polynomial multiplied by a product of switching functions... 

Ab Initio Calculations. All calculations on the electronic structures of CH3S are performed using the GAMESS program [122]. The calculations are based on the MCSCF and the FOCI methods. The standard 6-31G(d, p) basis set is used. To properly describe the excited states of CH3S, we have extended the basis set to include the Rydberg functions with = 0.023, = 0.020 and = 0.015 for the sulfur atom and = 0. = 0.040 for... 

MCSCF and the FOCI methods. The standard 6-31G(d,p) basis set [111] is used for all other calculations. To properly describe the excited states of thiophene, we have extended the basis set to include the Rydberg functions... 

For diatomic molecules, it is often sufficiently accurate to describe the interaction by using a Morse potential. This has also been explicitly assumed in some of the previous sections. However, near the dissociation limit additional accuracy can be obtained by using a functional form containing additional parameters. Such a function is the extended Rydberg (ER) function, given by... 

The above considerations do not hold when studying excited states with Rydberg character These transitions require more extended basis sets [6-31- -G(d,p) is the minimal basis set possible], the inclusion of diffuse functions is mandatory, and their energies converge more slowly with the size of the basis set. 

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