Frozen-core versus fully-correlated configuration interaction on the ground and lowest excited states of N + and N (original) (raw)
Related papers
Journal of Physics B Atomic Molecular and Optical Physics
A series of multireference configuration interaction (CI) calculations using an extended Gaussian basis set have been performed on the X 'Xf ground state of the PN molecule in order to accurately determine the potential energy surface in the vicinity of the minimum. With the help of this curve a wide assortment of spectroscopic observables have been computed. The overall agreement with experiment is good. Marked correlation energy effects are found for the electric dipolelquadrupole moments and nitrogen nuclear coupling. Pure rotational excitations calculated by means of the numerical solutions of the radial Sch:Bdinger equation are found to be in quite goad agreement with experiment. Average values of the electric dipole moment over the fin1 vibrational levels have been derived and the trend exhibited by the experimental data is well reflected by the theoretical results. Vibraratatianal transitions, pure vibrational and vibrorotational lifetimes have also been deterzined which, to d z e , hzue ED: been de:e:z-ised expc:lzentz!!y.
Journal of Physics B Atomic Molecular and Optical Physics
A series of multireference configuration interaction (CI) calculations using an extended Gaussian basis set have been performed on the X 'Xf ground state of the PN molecule in order to accurately determine the potential energy surface in the vicinity of the minimum. With the help of this curve a wide assortment of spectroscopic observables have been computed. The overall agreement with experiment is good. Marked correlation energy effects are found for the electric dipolelquadrupole moments and nitrogen nuclear coupling. Pure rotational excitations calculated by means of the numerical solutions of the radial Sch:Bdinger equation are found to be in quite goad agreement with experiment. Average values of the electric dipole moment over the fin1 vibrational levels have been derived and the trend exhibited by the experimental data is well reflected by the theoretical results. Vibraratatianal transitions, pure vibrational and vibrorotational lifetimes have also been deterzined which, to d z e , hzue ED: been de:e:z-ised expc:lzentz!!y.
Molecular Physics, 1990
Potential energy and spectroscopic constants for the X'-r.: ground state of a;, were calculated by configuration-interaction (Cl) methods, using large basis sets with polarization and diffuse functions. From these CI wavefunctions, the isotropic (a~~o) and dipolar (Ad 1 .,) components of the hyperfine coupling constant were obtained. The effects of various s, p basis sets, polarization and diffuse functions, as weil as the infl.uence of reference configurations and configuration selection thresholds were investigated. The best values obtained are 35•31 G for a 110 and 29•440 for Adlp• tobe compared with experimental values of 37 ± 1 G and 32 ± 1 G, respectively. It is shown that the contributions to a 1 so of the K and L shells are opposite in sign, differing by about 4 G. Upon vibrational averaging, both a 1 so and Adtp move towards smaller values as v increases. An adiabatic electron affinity of 2•46eV was obtained for 0 1 , and a vertical electron detachment energy of 3•71 eV for Cl;.
Electronic States of SnS and SnS + : A Configuration Interaction Study
The Journal of Physical Chemistry A, 2005
Ab initio based multireference configuration interaction calculations are carried out for SnS and its monopositive ion using effective core potentials. Potential energy curves and spectroscopic constants of the low-lying states of SnS and SnS + are computed. The ground-state dissociation energies of the neutral and ionic species are about 4.71 and 2.86 eV, respectively which compare well with the available thermochemical data. The effect of d-electron correlation on the spectroscopic constants of a few low-lying states has been studied. The spinorbit interaction has also been included to investigate its effect on the spectroscopic properties of both SnS and SnS +. Dipole moment and transition moment curves are also constructed as a function of the bond length. Transition probabilities of some dipole-allowed and spin-forbidden transitions are studied. Radiative lifetimes of a few low-lying states are estimated. The E 1 Σ +-X 1 Σ + transition of SnS is predicted to be the strongest one. The components of the A 2 Σ + 1/2-X 2 2 Π 1/2 transition with parallel and perpendicular polarization are separately analyzed. The vertical ionization energies of the ground-state SnS to the ground and low-lying excited states of the monopositive ion are calculated.
Evaluation and Comparison of the Configuration Interaction Calculations for Complex Atoms
Atoms, 2014
Configuration interaction (CI) methods are the method of choice for the determination of wave functions for complex atomic systems from which a variety of atomic properties may be computed. When applied to highly ionized atoms, where few, if any, energy levels from observed wavelengths are available, the question arises as to how a calculation may be evaluated. Many different codes are available for such calculations. Agreement between the results from different codes in itself is not a check on accuracy, but may be due to a similarity in the computational procedures. This paper reviews basic theory, which, when applied in a systematic manner, can be the basis for the evaluation of accuracy. Results will be illustrated in the study of 4s 2 4p 5 (odd) and 4s 2 4p 4 4d (even) levels in W 39+ and the transitions between them.
Atomic configuration interaction and studies of He, Li, Be, and Ne ground states
Physical Review A, 1997
The atomic configuration interaction (CI) is reconsidered. We compare the algebraic and geometric approaches to the construction of the CI matrix and point out advantages of the latter. One-electron basis sets of quality comparable to numerical multiconfigurational Hartree-Fock are readily obtained. The generation of large CI lists of symmetry eigenfunctions is monitored by a prescription establishing an a priori identification of relevant contributions to the wave function. Systematic and well-defined truncations to multireference CI's are examined. A formula for energy contributions of six-excited unlinked clusters is derived and shown to give reasonable estimates. Ensuing nonrelativistic CI calculations on He, Li, Be, and Ne ground states yield the lowest upper bounds in the literature, capturing 99.978, 99.923, 99.919, and 99.59% of the accepted correlation energies, respectively.
Journal of Chemical Physics, 1994
The hyperfine structures of the isoelectronic molecules CCO. CNN, and NCN in their triplet ground states (X 3 I-) are investigated by means of ab initio methods. The infrared frequencies and geometries are detennined and compared with experiment. Configuration selected multireference configuration interaction calculations in combination with perturbation theory to correct the wave function (MRD-CI/B K) employing extended atomic orbital (AO) basis sets yielded very accurate hyperfine properties. The theoretical values for CCO are in excellent agreement with the experimental values determined by Smith and Weltner [J. Chem. Phys. 62,4592 (1975)]. For CNN,. the first assignment of Smith and Weltner for the two nitrogen atoms has to be changed. A qualitative discussion of the electronic structure discloses no simple relation between the structure of the singly occupied orbitals and the measured hyperfine coupling constants. Vibrational effects were found to be of little importance.
1995
The electronic transition moment functions between the B3IIg state and the AEu, W3Au, B'3~,u-states of N2 are studied using the internally contracted multireference configuration interaction method based upon complete active space SCF reference wavefunctions. The dependence of the moments on both the one and n-particle basis sets has been investigated in detail. The calculated radiative lifetimes for the vibrational levels of the B3IIg state are in excellent agreement with the most recent data published for v' = 5 to 12, measured by laser induced fluorescence, and for v' = 0, measured by electron impact induced fluorescence.
Correlation Energy of Atomic Nitrogen
Physical review, 1972
The Brueckner-Goldstone many-body perturbation theory is applied to stu the electronic structure of the atomic nitrogen in its ground 4$ state. A complete orthonormal set of the V" single-particle states with angular symmetry up to) = 5 is explicitly used to calculate the correlationmnergy diagrams. The contribution from higher l (& 5) is estimated by a hydrogenic approximation of the continuum wave functions. Our final correlation energy is-0.1895 + 0.003 a.u. , as compared with-0.1886+ 0.0094 a.u. from the semiempirical estimate made by Veillard and Clementi. The sum of the exchange-core-polarization and pair-correlationenergy diagrams give a total of-Q. 207 28 a.u. , which is 110% of the semiempirical estimate. This contains a contribution of-0.00610 a.u. (3.2 %} from L &3 states and-0.05825 a.u. (31 %) from the excitations into the valence 2p orbitals, the latter arising from the open-shell nature of the nitrogen atom. The overestimate (10 %) of the correlation energy is remedied by the pair-pair correlation of 0. 01137 a. u. (6%) and the many-electron (three and four) effect of 0.00642 a.u. (3.4 %). A comparison with earlier configuration-interaction results is also made.