The contraction of Gaussian basis functions for use in molecular calculations is investigated by considering the effects of contraction on the energies and one‐electron properties of the water and nitrogen molecules. The emphasis is on obtaining principles which can be used to predict optimal contraction schemes for other systems without the necessity of such exhaustive calculations. Using these principles, contractions are predicted for the first‐row atoms.

Gaussian Basis Functions for Use in Molecular Calculations. III. Contraction of (10s6p) Atomic Basis Sets for the First‐Row Atoms

A Gaussian basis set consisting of 14s‐type, 9p‐type, and 5d‐type functions has been optimized for the third‐row atoms up to Zn. Energy values are reported for different contractions of this basis set.

Gaussian Basis Set for Molecular Wavefunctions Containing Third‐Row Atoms

A contracted Gaussian basis set capable of describing about 63% of the correlation energy of N2 has been used in a detailed configuration-interaction calculation. Second-order perturbation theory overestimated the correlation energy by 23–50% depending on how H0 was chosen. Pair-pair interaction affects the correlation energy by about 20% while quadruple excitations have an 8% effect.

Configuration interaction calculations on the nitrogen molecule

I. Introduction and Scope 231A. Definitions of Atomic Electron Affinities 233B. Definitions of Molecular Electron Affinities 233II. Experimental Photoelectron Electron Affinities 235A. Historical Background 235B. The Photoeffect 236C. Experimental Methods 237D. Time-of-Flight Negative Ion PhotoelectronSpectroscopy239E. Some Thermochemical Uses of ElectronAffinities241F. Layout of Table 10: ExperimentalPhotoelectron Electron Affinities242III. Theoretical Determination of Electron Affinities 242A. Historical Background 2421. Theoretical Predictions of Atomic ElectronAffinities2422. Theoretical Predictions of MolecularElectron Affinities243B. Present Status of Theoretical Electron AffinityPredictions243C. Basis Sets and Theoretical Electron Affinities 244D. Density Functional Theory (DFT) andElectron Affinities245E. Layout of Tables 8 and 9: Theoretical DFTElectron Affinities247F. Details of Density Functional MethodsEmployed in Tables 8 and 9247IV. Discussion and Observations 248A. Statistical Analysis of DFT Results ThroughComparisons to Experiment and OtherTheoretical Methods248B. Theoretical EAs for Species with UnknownExperimental EAs251C. On the Applicability of DFT to Anions and theFuture of DFT EA Predictions251D. Specific Theoretical Successes 251E. Interesting Problems 2521. C

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Atomic and molecular electron affinities: photoelectron experiments and theoretical computations.

The (14s11p5d) primitives basis set of Dunning for the third-row main group atoms Ga-Kr has been contracted (6s4p1d). The core functions have been relatively highly contracted while those which represent the valence region have been left uncontracted to maintain flexibility. Calculations with the (6s4p1d) contraction are reported for a variety of molecules involving third-row atoms. This basis set is found to satisfactorily reproduce experimental properties such as geometric configurations, dipole moments, and vibrational frequencies for a range of molecules. Comparisons are made with the performance of the uncontracted basis set. Polarization functions for the contracted basis set are reported and performance of the basis set with and without polarization functions is examined. A relaxation of the (6s4p1d) contraction to (9s6p2d) for higher level energy calculations is also presented.

Compact contracted basis sets for third-row atoms: Ga-Kr

The use of a linear combination of Gaussian‐type orbitals (CGTO), instead of an individual Gaussian‐type orbital (GTO), as a unit of basis functions for large‐scale molecular calculations, is discussed. A systematic construction of the CGTO basis functions is attempted and the results for the atoms from Li through Ar are reported.

Gaussian‐Type Functions for Polyatomic Systems. II

An arbitrariness of virtual orbitals in the Hartree-Fock theory is discussed, and it is explicitly demonstrated that the energy spectrum of the virtual orbitals can be manipulated so that the convergence property may be improved in the perturbation theory and the configuration interaction calculation based on the Hartree-Fock equation

Virtual orbitals in hartree--fock theory.

The nature of virtual orbitals in the Hartree–Fock theory is discussed. A practical proposal is made to obtain meaningful virtual orbitals in the molecular calculations at the level of Pariser–Parr–Pople‐type and all‐valence‐electron‐type approximations. It is achieved by adding appropriate operators to the original Hartree–Fock operator.

Virtual Orbitals in Hartree–Fock Theory. II

Simple Basis Set for Molecular Wavefunctions Containing First-and Second-Row Atoms

It is demonstrated that the first-order relativistic correction term to the Schrodinger hamiltonian for the hydrogen-like atom, cannot be used safely even for small values of atomic number, Z, in the variational calculation. A modified form of the operator R is proposed so that one may incorporate it into the variational treatment of molecular systems.

Catalina Arnau

Papers

Gaussian‐Type Functions for Polyatomic Systems. II

Virtual orbitals in hartree--fock theory.

Virtual Orbitals in Hartree–Fock Theory. II

Simple Basis Set for Molecular Wavefunctions Containing First-and Second-Row Atoms

Approximate relativistic correction term