Available 116 Gaussian wavefunctions

Several commercial quantum chemical programs like Gaussian (by Gaussian, Inc., www.gaussian.com) and Spartan (by Wavefunction, Inc., www.wavefun.com) are available for the solution of the electronic Schrodinger equation. 

When calculating the wavefunction it is important to make a choice of basis set J. t that is suitable for the available computing power and the accuracy desired. A straightforward early approach to basis set construction was to fit an accurate Slater-type atomic orbital (STO) with n gaussians,called STO- G. The quality of STO- G wavefunctions increases as n increases. It was determined that = 3 was a good starting point, and the STO-3G basis set has been widely used, particularly where computing resources were limited or for lai er molecules. 

Sidebar 11.1, variational multistate methods generally involve finding a desired root of the characteristic secular polynomial equation for the multistate Hamiltonian matrix H associated with the chosen theoretical level (method and basis set). In this simplified introduction, we focus on some current multistate options of the Gaussian 09 (G09) program system, describing the keyword syntax for specifying the chosen root and available options (if any) for NBO/NRT analysis of the resulting wavefunction. 

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