A fully ab initio potential curve of near-spectroscopic quality for OH− ion: importance of connected quadruple excitations and scalar relativistic effects (original) (raw)
Related papers
2001
A benchmark study has been carried out on the ground-state potential curve of the hydroxyl anion, OH − , including detailed calibration of both the 1particle and n-particle basis sets. The CCSD(T) basis set limit overestimates ω e by about 10 cm −1 , which is only remedied by inclusion of connected quadruple excitations in the coupled cluster expansion-or, equivalently, the inclusion of the 2π orbitals in the active space of a multireference calculation. Upon inclusion of scalar relativistic effects (-3 cm −1 on ω e), a potential curve of spectroscopic quality (sub-cm −1 accuracy) is obtained. Our best computed EA(OH), 1.828 eV, agrees to three decimal places with the best available experimental value. Our best computed dissociation energies, D 0 (OH −)=4.7796 eV and D 0 (OH)=4.4124 eV, suggest that the experimental D 0 (OH)=4.392 eV may possibly be about 0.02 eV too low.
Journal of Molecular Spectroscopy, 1988
We have measured 43 transitions in the pure rotational and fundamental vibrational spectra of "OH+. These data, together with all ground state transitions and combination differences of OD+ and 160H' available from the literature, have been fit to an explicitly internuclear distance dependent rovibrational Hamiltonian to yield several descriptions of the OH+ potential function. Significant adiabatic and rotationally and vibrationally nonadiabatic corrections are required to fit all 407 isotopomeric transitions simultaneously. Similar fits are also performed on the closed shell species ArH+, yielding an approximate vibrational correction to the recently determined experimental permanent dipole moment of that ion. 0 1988 Academic press, Inc.
The treatment of atomic anions with Kohn− Sham density functional theory (DFT) has long been controversial because the highest occupied molecular orbital (HOMO) energy, E HOMO , is often calculated to be positive with most approximate density functionals. We assess the accuracy of orbital energies and electron affinities for all three rows of elements in the periodic table (H−Ar) using a variety of theoretical approaches and customized basis sets. Among all of the theoretical methods studied here, we find that a nonempirically tuned range-separated approach (constructed to satisfy DFT-Koopmans' theorem for the anionic electron system) provides the best accuracy for a variety of basis sets, even for small basis sets where most functionals typically fail. Previous approaches to solve this conundrum of positive E HOMO values have utilized non-self-consistent methods; however, electronic properties, such as electronic couplings/gradients (which require a self-consistent potential and energy), become ill-defined with these approaches. In contrast, the nonempirically tuned range-separated procedure used here yields well-defined electronic couplings/gradients and correct E HOMO values because both the potential and resulting electronic energy are computed self-consistently. Orbital energies and electron affinities are further analyzed in the context of the electronic energy as a function of electronic number (including fractional numbers of electrons) to provide a stringent assessment of self-interaction errors for these complex anion systems.
Journal of Computational Chemistry, 2015
Using four-component (4c) relativistic spinors, we present a computationally economical relativistic ab initio method for molecular systems employing our recently proposed secondorder state-specific multireference perturbation theory (SSMRPT) incorporating the improved virtual orbital-complete active space configuration interaction (IVO-CASCI) reference wavefunction. The resulting method, 4c-IVO-SSMRPT [calculate one state at a time] is tested in pilot calculations on the homonuclear dimers including Li 2 , Na 2 , K 2 , Rb 2 , F 2 , Cl 2 , and Br 2 through the computations of the ground state potential energy curves (PECs). As SSMRPT curbs intruder effects, 4c-IVO-SSMRPT is numerically stable. To our knowledge, the SSMRPT in the 4c relativistic framework has not been explored in the past. Selective spectroscopic constants that are closely related to the correct shape and accuracy of the energy surfaces have been extracted from the computed PECs. For the halogen molecules, a relativistic destabilization of the bond has been found. Relativistic and electron correlation effects need to be incorporated to get reliable estimates. Our results are in good accordance with reference theoretical and experimental data which manifests the computational accuracy and efficiency of the new 4c-IVO-SSMRPT method. The method opens for an improved description of MR systems containing heavy elements. The inexpensiveness of IVO-CASCI makes 4c-IVO-SSMRPT method promising for studies on large systems of heavy elements. V
Journal of the American Chemical Society, 1989
Two recently developed coupled-cluster (CC) schemes, quasi-restricted Hartree-Fock CC (QRHF-CC) and multireference CC (MR-CC), which are expected to be capable of calculating molecular ionization potentials (IPS) to a high accuracy, have been compared with each other, with conventional single-reference CC schemes (CCSD and CCSDT-I), with other theoretical techniques, and with experiment by calculating the vertical valence IPS of the important isovalent transients methyleneamine, CH2NH, and methylenephosphine, CH2PH. In addition, we report results for P2 to assess the quality of the P basis set. Several different basis sets are considered. The QRHF-CC and MR-CC schemes give very similar results, which are in excellent agreement with the CCSDT-1 approach, when the latter is applicable. At the highest level, agreement with experiment is excellent, with mean errors of less than 0.2 eV. The influence of triple-excitation effects in the MR-CC and QRHF-CC methods on IPS is considered. 17, 805. (b) Saute, M.; Paldus, J.; Cizek, J. In?. J . Quantum Chem. 1979, 15, 463. (IO) Rittby, M.; Bartlett, R. J. J. Phys. Chem. 1988, 92, 3033. (11) Bartlett, R. J.; Purvis, G. D.; Fitzgerald, G. B.; Harrison, R. J.; Lee, Y. S.; Laidig, W. D.; Cole, S. J.; Magers, D. H.; Salter, E. A,; Trucks, G. W.; Sosa, C.; Rittby, M.; Pal, S . ; Watts, J. D.
The interaction of OH(X²Π) with H₂: ab initio potential energy surfaces and bound states
The Journal of chemical physics, 2014
For the interaction of OH(X(2)Π) with H2, under the assumption of fixed OH and H2 bond distances, we have determined two new sets of four-dimensional ab initio potential energy surfaces (PES's). The first set of PES's was computed with the multi-reference configuration interaction method [MRCISD+Q(Davidson)], and the second set with an explicitly correlated coupled cluster method [RCCSD(T)-F12a] sampling the subset of geometries possessing a plane of symmetry. Both sets of PES's are fit to an analytical form suitable for bound state and scattering calculations. The CCSD(T) dissociation energies (D0) of the OH-para-H2 and the OH-ortho-H2 complexes are computed to be 36.1 and 53.7 cm(-1). The latter value is in excellent agreement with the experimental value of 54 cm(-1).
Ionisation potentials and electron affinity of oganesson with relativistic coupled cluster method
2021
We present high accuracy relativistic coupled cluster calculations of the first and second ionisation potentials and the electron affinity of the heaviest element in the Periodic Table, Og. The results were extrapolated to the basis set limit and augmented with the higher order excitations (up to perturbative quadruples), the Breit contribution, and the QED self energy and vacuum polarisation corrections. We have performed an extensive investigation of the effect of the various computational parameters on the calculated properties, which allowed us to assign realistic uncertainties on our predictions. Similar study on the lighter homologue of Og, Rn, yields excellent agreement with experiment for the first ionisation potential and a reliable prediction for the second ionisation potential.
Core ionization potentials from self-interaction corrected Kohn-Sham orbital energies
The Journal of Chemical Physics, 2007
We propose a simple self-interaction correction to Kohn-Sham orbital energies in order to apply ground state Kohn-Sham density functional theory to accurate predictions of core electron binding energies and chemical shifts. The proposition is explored through a series of calculations of organic compounds of different sizes and types. Comparison is made versus experiment and the "⌬Kohn-Sham" method employing separate state optimizations of the ground and core hole states, with the use of the B3LYP functional and different basis sets. A parameter ␣ is introduced for a best fitting of computed and experimental ionization potentials. It is found that internal parametrizations in terms of basis set expansions can be well controlled. With a unique ␣ = 0.72 and basis set larger than 6-31G, the core ionization energies ͑IPs͒ of the self-interaction corrected Kohn-Sham calculations fit quite well to the experimental values. Hence, self-interaction corrected Kohn-Sham calculations seem to provide a promising tool for core IPs that combines accuracy and efficiency.