A quantum-chemical study of some properties and reactions of H2CN−, H2CN+, H2CNH2+, H2CNH, and HCN, using small and intermediate-sized sets of basis functions

1970 ◽  
Vol 48 (12) ◽  
pp. 1820-1833 ◽  
Author(s):  
J. B. Moffat
Keyword(s):  
Small Molecules ◽  
Quantum Chemical Study ◽  
Chemical Study ◽  
Basis Functions ◽  
Basis Sets ◽  
Atomic Orbitals ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field ◽  
Gaussian Orbitals

It is suggested that given two molecules potentially capable of being involved in the same reaction, one as a product and one as a reactant, it seems reasonable that the calculated difference in energy between these molecules may become relatively constant with smaller basis sets than the calculated energies themselves. To examine this suggestion, and at the same time to provide information on small molecules containing bonds related to the nitrile bond, a number of linear combination of atomic orbitals-molecular orbitals-self consistent field (l.c.a.o.-m.o.-s.c.f.) calculations using small or intermediate sizes of basis sets of Gaussian orbitals were performed on H2CNH, H2CN−, H2CNH2+, H2CN+, and HCN. The change of energy in passing from one molecule to another is shown to converge to a reasonably constant value for smaller basis sets than are required for convergence of individual molecular energies.

A simple quality test for self-consistent-field atomic orbitals

1993 ◽  
Vol 71 (2) ◽  
pp. 175-179 ◽  
Author(s):  
N. Desmarais ◽  
G. Dancausse ◽  
S. Fliszár
Keyword(s):  
Basis Functions ◽  
Quality Test ◽  
Linear Combinations ◽  
Atomic Orbitals ◽  
Hartree Fock ◽  
Consistent Field ◽  
Valence Region ◽  
Self Consistent ◽  
Self Consistent Field ◽  
Finite Linear

A quality test is proposed for SCF atomic orbitals, [Formula: see text] approximated as finite linear combinations of suitable basis functions [Formula: see text] The key is in a function, readily derived from the Hartree–Fock equation [Formula: see text] which is identically zero for true Hartree–Fock spin orbitals and not so for approximate orbitals. In this way, our test measures how closely approximate orbital descriptions approach the true Hartree–Fock limit and thus provides a quality ordering of orbital bases with respect to one another and with respect to that limit, in a scale uniquely defined by the latter. Moreover, this analysis also holds for atomic subspaces of our choice, e.g., the valence region. Examples are offered for representative collections of Slater- and Gaussian-type orbital expansions.

Basis set convergence of atomic axial tensors obtained from self‐consistent field calculations using London atomic orbitals

1994 ◽  
Vol 100 (9) ◽  
pp. 6620-6627 ◽  
Author(s):  
Keld L. Bak ◽  
Poul Jo/rgensen ◽  
Trygve Helgaker ◽  
Kenneth Ruud ◽  
Hans Jo/rgen Aa. Jensen
Keyword(s):  
Basis Set ◽  
Set Convergence ◽  
Atomic Orbitals ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field

Multiconfigurational self‐consistent field calculations of nuclear shieldings using London atomic orbitals

1994 ◽  
Vol 100 (11) ◽  
pp. 8178-8185 ◽  
Author(s):  
Kenneth Ruud ◽  
Trygve Helgaker ◽  
Rika Kobayashi ◽  
Poul Jo/rgensen ◽  
Keld L. Bak ◽  
...  
Keyword(s):  
Atomic Orbitals ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field

Universal Gaussian basis functions in relativistic quantum chemistry: atomic Dirac–Fock–Coulomb and Dirac–Fock–Breit calculations

1992 ◽  
Vol 70 (6) ◽  
pp. 1822-1826 ◽  
Author(s):  
G. L. Malli ◽  
A. B. F. Da Silva ◽  
Yasuyuki Ishikawa
Keyword(s):  
Relativistic Quantum ◽  
Basis Set ◽  
Basis Sets ◽  
Interaction Energies ◽  
Gaussian Basis Sets ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field ◽  
Gaussian Basis Set ◽  
Good Agreement

Matrix Dirac–Fock–Coulomb and Dirac–Fock–Breit self-consistent field calculations are performed for a number of neutral atoms. He (Z = 2) through Xe (Z = 54), using the universal Gaussian basis set (18s, 12p, 11d) reported recently by Da Silva etal. The total Dirac–Fock–Coulomb, the Dirac–Fock–Breit, and the Breit interaction energies calculated with this universal Gaussian basis set are in good agreement with the corresponding values obtained by using an extensive well-tempered Gaussian basis set for the He through Ca (Z = 20) atoms. Although this universal Gaussian basis set is inadequate for the calculation of total Dirac–Fock–Coulomb and Dirac–Fock–Breit energies for the Kr, Sr, and Xe atoms, the Breit interaction energies calculated with this basis for these three atoms are in very good agreement with the corresponding Breit interaction energies obtained by using the extensive well-tempered Gaussian basis sets. Work is in progress to generate a more extensive and energetically better universal Gaussian basis set for He through Xe for its use in non-relativistic Hartree–Fock as well as Dirac–Fock self-consistent field calculations on polyatomics involving heavy atoms.

On the dissociation energy of Ti(OH2)+. An MCSCF, CCSD(T), and DFT study

1996 ◽  
Vol 74 (10) ◽  
pp. 1824-1829 ◽  
Author(s):  
A. Irigoras ◽  
J.M. Ugalde ◽  
X. Lopez ◽  
C. Sarasola
Keyword(s):  
Dissociation Energy ◽  
Density Functional ◽  
Basis Sets ◽  
Coupled Cluster ◽  
Functional Theory ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field ◽  
Self Consistent Field Theory ◽  
Effective Core Potentials

The dissociation energy of the Ti(OH2)+ ion–molecule complex was calculated by the multiconfigurational self-consistent field theory, coupled cluster theory, and two density functional theory based methods, using both all-electron basis sets and effective core potentials. The calculations show that approximate density functional theory gives results in better agreement with experiment than either the multiconfigurational self-consistent field theory or the coupled cluster theory, with both all-electron basis sets and effective core potentials. Nevertheless, the optimized geometries and harmonic vibration frequencies are very similar, irrespective of the level of theory used. The interconfigurational energy ordering of the two valence electronic configurations dn−1s and dn−2s2 of the 4F electronic state of the titanium cation were also calculated and are discussed. Key words: ab initio, dissociation energy, ion–molecule complex, effective core potentials, transition metals.

scholarly journals Multi-reference Approach to the Computation of Double-Core-Hole Spectra

2021 ◽  
Author(s):  
Bruno Nunes Cabral Tenorio ◽  
Piero Decleva ◽  
Sonia Coriani
Keyword(s):  
Small Molecules ◽  
Ground State ◽  
Binding Energies ◽  
Wave Functions ◽  
Correlation Effects ◽  
Core Hole ◽  
Active Space ◽  
Consistent Field ◽  
Self Consistent ◽  
Self Consistent Field

Double-Core Hole (DCH) states of small molecules are assessed with the restricted<br>active space self-consistent field (RASSCF) and multi-state restricted active space perturbation<br>theory of second order (MS-RASPT2) approximations. To ensure an unbiased<br>description of the relaxation and correlation effects on the DCH states, the neutral<br>ground state and DCH wave functions are optimized separately, whereas the spectral<br>intensities are computed with a biorthonormalized set of molecular orbitals within the<br>state-interaction (SI) approximation. Accurate shake-up satellites binding energies and<br>intensities of double-core-ionized states (K<sup>-2</sup>) are obtained for H<sub>2</sub>O, N<sub>2</sub>, CO and C<sub>2</sub>H<sub>2n</sub><br>(n=1–3). The results are analyzed in details and show excellent agreement with recent<br>experimental data.

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