Gaussian atomic-orbitals

BasisE ib This is a library file whichcontains gaussian atomic orbital basis sets for Hydrogen - Neon. The basis sets available to choose from are ... 

Raffenetti, R.C. General contraction of Gaussian atomic orbitals core, valence, polarization, and diffuse basis sets Molecular integral evaluation, J. Chem. Phys. 1973, 58,4452. 

The nife field method, e.g., a variational approach in which the interaction with a weak homogeneous electric field is included in the Hamiltonian. The components of the polarizability are computed as the second derivatives of the energy with respect to the corresponding field components (the derivatives are calculated at the zero field). In practical calculations within the LCAO MO approximation, we often use the Sadlej relation that connects the shift of a Gaussian atomic orbital with its exponent and the electric field intensity. 

In some variational calculations for a molecule without electric field the positions of the atomic orbitals have been optimized. In the finite field variational method a small shift of a certain Gaussian atomic orbital off a nucleus... 

It was decided to improve these calculations by using better electronic wavefunctions 0. Single configuration molecular orbital wavefunctions were still used. However, the molecular orbitals were expressed in terms of a so-called extended basis set of gaussian atomic orbitals (for details see reference (3)). The Hartree-Fock-self-consistent-field (HFSCF) procedure was carried out with the digital computer program POLYATOM, The quality of the wavefunctions is not quite what would be called Hartree-Fock limit wavefunctions. Calculations were carried out at several intemuclear distances and C was calculated with the inclusion of the factor A correctly calculated. The calculations were extended to include the ground states of several ions and also of HCl. 

Fig. 12.7. A molecule in a homogeneous electric field (a). In Fig. (b) rj is a parameter describing the shift of the Gaussian atomic orbitals along the electric field , with rj = 0 showing the centring...

Fig. 12.8. A molecule in a homogeneous electric field (a). In (b), r is a parameter describing the shift of the Gaussian atomic orbitals along the electric field, with rj = 0 showing the centering on the nuclei. The total energy E S,x) is a function of the electric field intensity S and the basis set shift parameter t]. Optimization of r gives a result close to the Sadlej value rj =. Larger absolute rj values first lead to an increase of E, but then end up in a decrease toward a catastrophe limx -ooE , x) = —oo.

R. C. Raffenetti, /. Chem. Phys., 58,4452 (1973). General Contraction of Gaussian Atomic Orbitals Core, Valence, Polarization and Dif se Basis Sets Molecular Integral Evaluation. 

R. C. Raffenetti, Int. J. Quantum. Chem. Symp., 9, 289 (1975). Even-Tempered Gaussian Atomic Orbitals First-Row Atoms. 

The second DFT LCAO linear-scaling method by Scuseria and Kudin (SK method) [379] uses Gaussian atomic orbitals and a fast multipole method, which achieves not only linear-scaling with system size, but also very high accuracy in aU infinite summations [397]. This approach allows both all-electron and pseudopotential calculations and can be applied also with hybrid HF-DFT exchange-correlation functionals. 

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