Core-valence Correlation Research Articles

Accurate spectroscopic properties of 10 Λ-S states and 25 Ω states of BS+ cation including the electronic transition properties

The potential energy curves of 10 Λ–S states of BS+ yielded from the first four dissociation limits are calculated by the internally contracted multireference configuration interaction approach with the Davidson correction. The core-valence correlation and scalar relativistic corrections are included. Basis on the calculated potential energy curves, the spectroscopic parameters are evaluated. All the PECs are extrapolated to the complete basis set limit. The spin-orbit coupling are taken into account by the state interaction method with the Breit-Pauli Hamiltonian. Finally, the transition dipole moments, Franck-Condon Factors and radiative lifetimes of transitions from the 23Π0-, 23Π0+, 23Σ0- and 23Σ1- states to ground state 13Π2 are predicted for future experiment.

Calculations of 21 Λ-S and 42 Ω states of BC molecule: Potential energy curves, spectroscopic parameters and spin-orbit coupling effect

The potential energy curves (PECs) were calculated for the 42 Ω states generated from the 21 Λ-S states (X4Σ−, A4Π, B4Σ−, a2Π, b2Σ−, c2Δ, d2Σ+, e2Π, 32Π, 42Π, 52Π, 22Σ−, 32Σ−, 22Σ+, 32Σ+, 22Δ, 32Δ, 14Σ+, 24Π, 14Δ and 12Φ), which originated from the lowest two dissociation channels, B(2Pu)+C(3Pg) and B(2Pu)+C(1Dg), of the BC molecule. The PECs were calculated for internuclear separations from 0.08 to 1.10nm using the CASSCF method, which was followed by the icMRCI approach with the aug-cc-pV6Z basis set. Of these 21 Λ-S states, the e2Π, 22Δ, 22Σ−, 42Π, 12Φ and 32Δ possess the double wells. The A4Π, a2Π, c2Δ, 24Π, 42Π, 52Π, 14Δ and 12Φ states are inverted with the spin-orbit coupling (SOC) effect taken into account. The first well of e2Π state and the second well of 42Π and 22Δ states do not have any vibrational states whether with or without the SOC effect included. All the Λ-S and Ω states involved in this paper are bound states. Scalar relativistic correction was included by the third-order Douglas–Kroll Hamiltonian approximation at the level of an aug-cc-pV5Z basis set. Core-valence correlation correction was included at the level of an aug-cc-pCV5Z basis set. The SOC effect was accounted for by the state interaction method with the Breit–Pauli Hamiltonian and the all-electron cc-pCV5Z basis set. The PECs of all the states were extrapolated to the complete basis set limit. The spectroscopic parameters were obtained. The vibrational properties of several Λ-S and Ω states with the relatively shallow wells were evaluated. The SOC effect on the spectroscopic parameters is not obvious for almost all the states. The spectroscopic properties reported in this paper can be expected to be reliably predicted ones.

Quality Structures, Vibrational Frequencies, and Thermochemistry of the Products of Reaction of BrHg(•) with NO2, HO2, ClO, BrO, and IO.

Quantum chemical calculations have been carried out to investigate the structures, vibrational frequencies, and thermochemistry of the products of BrHg(•) reactions with atmospherically abundant radicals Y(•) (Y = NO2, HO2, ClO, BrO, or IO). The coupled cluster method with single and double excitations (CCSD), combined with relativistic effective core potentials, is used to determine the equilibrium geometries and harmonic vibrational frequencies of BrHgY species. The BrHg-Y bond energies are refined using CCSD with a noniterative estimate of the triple excitations (CCSD(T)) combined with core-valence correlation consistent basis sets. We also assess the performances of various DFT methods for calculating molecular structures and vibrational frequencies of BrHgY species. We attempted to estimate spin-orbit coupling effects on bond energies computed by comparing results from standard and two-component spin-orbit density functional theory (DFT) but obtained unphysical results. The results of the present work will provide guidance for future studies of the halogen-initiated chemistry of mercury.

Accurate calculations on 20 Λ–S states of the BP radical: potential energy curves, spectroscopic parameters, and electronic transition properties

The potential energy curves of 20 Λ–S states of BP yeilded from the first two dissociation limits B(2Pu) + P(4Su) and B(2Pu) + P(2Du) have been calculated by the internally contracted multireference configuration interaction approach with the Davidson correction. Especially the core–valence correlation and scalar relativistic corrections are included in the present work. Potential energy curves are also extrapolated to the complete basis set limit. According to the potential energy curves, the spectroscopic parameters are determined and compared with those available in the literature. The convergent behavior of the present calculations is discussed with respect to the basis set and level of theory. Of the 20 states, the 23∑– and 33∑– states have the avoided crossings, which are very weakly bound ones, the 21∑–, and the 13Δ and 23Δ states possess a double well. Subsequently, the transition dipole moments, Franck–Condon factors, and radiative times of the transitions 31Π–b1Π, 23Δ–X3Π, 23∑––A3∑–, 33∑––A3∑–, and 15∑––15Π are calculated.

Extended calculations of level and transition properties in the nitrogen isoelectronic sequence: Cr XVIII, Fe XX, Ni XXII, and Zn XXIV

Extensive multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations and relativistic configuration interaction (RCI) calculations are performed for 272 states of the 2s 2 2p 3 ,2 s2p 4 ,2 p 5 ,2 s 2 2p 2 3l ,2 s2p 3 3l, and 2p 4 3l (l = 0, 1, 2) configurations in the nitrogen-like ions Cr XVIII, Fe XX, Ni XXII, and Zn XXIV. Valence, core-valence, and core-core electron correlation effects are accounted for through large configuration state function expansions. Calculated energy levels are compared with data from other calculations and with experimental data from the NIST database. Lande gJ-factors; hyperfine structures; isotope shifts; and radiative electric dipole (E1), electric quadrupole (E2), and magnetic dipole (M1) transition rates are given for all ions. The accuracy of the calculated energy levels �

Ab initio study of Ba+Arn (n = 1–4) clusters: spectroscopic constants and vibrational energy levels

ABSTRACTThis study is interested in the illustration of ab initio potential energy curves for Ba+Arn (n = 1–4) clusters. The electronic structures of these molecules are calculated using [Ba2+] and [Ar] non-empirical core pseudo-potentials complemented by the core polarisation operators for both atoms, which allow the consideration of core valence correlation effects. The structure and stabilities of Ba+Arn (n = 1–4) clusters are investigated. These molecules are treated as one-electron active system. Spectroscopic constants and vibrational energy levels have been derived from their potentials. The analysis of the geometric forms, basing on the potential energy curves and the spectroscopic constants, clearly shows the importance of rare gas induced dipole. We also show that the dipolar interactions can influence the coupling between atoms.

Transition probabilities of the low-lying levels of Kr XXIV

Energy levels, radiative rates, and wavelengths are calculated for all levels of 3s23p, 3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d and 3s3d2 configurations of Al-like krypton ion (Kr XXIV). Multiconfigurational Dirac–Hartree–Fock (MCDHF) method is adopted for calculating energy levels and radiative rates. Transition probabilities are reported for E1 and M2 transitions from the ground level. The valence–valence and core–valence correlation effects are accounted for in a systematic way. Breit interactions and quantum electrodynamics effects are estimated in subsequent relativistic configuration interaction calculations. Comparisons are made with the available data in the literature and good agreement has been found which confirms the reliability of our results.

CI Calculations of the Ground State Ionization Potential and Electron Affinity of Aluminum

(Received May 2, 2015; in nal form May 12, 2015) Nonrelativistic con guration interaction study for Al, Al and Al− are presented, included calculations of ionization potential and electron a nity of the P o ground state of Al. CI calculations up to double, triple and quadrupole excitations for Al, Al and Al−, respectively, where neon xed core is considered. Appropriate Slater type basis functions were developed suitable to recover both of core-valence and core core correlation e ect. The relativistic e ect on both ionization potential and electron a nity are taken into account at the relativistic Hartree Fock level. The calculated electron a nity is 432.811 meV which is in excellent agreement with experimental value of Sheer et al. 432.83(5) meV, whereas the calculated ionization potential is 5985.764 meV, the latter is in perfect agreement with experimental value of 5985.768 meV. DOI: 10.12693/APhysPolA.128.268

An ab initio investigation on the ground electronic state of chlorine monoxide and its singly charged cation and anion

The MRCI method has been utilized to calculate the equilibrium structure of the ground electronic state for the ClO radical and its singly charged cation and anion, ClO+ and ClO−. The augmented correlation-consistent basis sets up through sextuple-zeta quality are used to derive equilibrium structural parameters, potential energy curves and spectroscopic constants of the systems. Two extrapolating schemes enable us to remove the basis set truncation error and to estimate the complete basis set limit. Corrections of core-valence correlation and relativistic effect are included in our calculations. By solving the radial Schrödinger equation of nuclear motion, the vibrational energy levels as well as rotational and centrifugal distortion constants of the ground electronic states for the three species are obtained. Ionization potentials and the electron affinities are also obtained on the RCCSD(T)/AV6Z level. The knowledge extracted from this work are anticipated to extend our understanding on molecular characteristics of the ClOn (n=−1, 0, +1) systems and can serve as guidelines for further experimental or theoretical researches.

Configuration interaction calculations on the spectroscopic and transition properties of magnesium chloride**Project supported by the National Natural Science Foundation of China (Grand Nos. 11564019, 11147158, 11264020, and 11574114) and Jiangxi Provincial Education Department Project, China (Grand No. GJJ170654).

The potential energy curves (PECs) of 14 Λ–S states for magnesium chloride (MgCl) have been calculated by using multi-reference configuration interaction method with Davidson correction (MRCI + Q). The core-valence correlation (CV), scalar relativistic effect, and spin–orbit coupling (SOC) effect are considered in the electronic structure computations. The spectroscopic constants of X2Σ+ and A2Π states have been obtained, which are in good agreement with the existing theoretical and experimental results. Furthermore, other higher electronic states are also characterized. The permanent dipole moments (PDMs) of Λ–S states and the spinorbit (SO) matrix elements between Λ–S states are also computed. The results indicate that the abrupt changes of PDMs and the SO matrix elements are attributed to the avoided crossing between the states with the same symmetry. The SOC effect is taken into account with Breit–Pauli operator, which makes the 14 Λ–S states split into 30 Ω states, and leads to a double-well potential of the Ω = (3)1/2 state. The energy splitting for the A2Π is calculated to be 53.61 cm−1 and in good agreement with the experimental result 54.47 cm−1. The transition dipole moments (TDMs), Franck–Condon factors (FCFs), and the corresponding radiative lifetimes of the selected transitions from excited Ω states to the ground state X2Σ + 1/2 have been reported. The computed radiative lifetimes τν′ of low-lying excites Ω states are all on the order of 10 ns. Finally, the feasibility of laser cooling of MgCl molecule has been analyzed.

Thermochemistry of HO2 + HO2 → H2O4: Does HO2 Dimerization Affect Laboratory Studies?

Self-reaction is an important sink for the hydroperoxy radical (HO2) in the atmosphere. It has been suggested (Denis, P. A.; Ornellas, F. R. J. Phys. Chem. A, 2009, 113 (2), 499-506) that the minor product hydrogen tetroxide (HO4H) may act as a reservoir of HO2. Here, we compute the thermochemistry of HO2 self-reactions to determine if either HO4H or the cyclic hydrogen-bound dimer (HO2)2 can act as reservoirs. We computed electronic energies using coupled-cluster calculations in the complete basis set limit, CCSD(T)/CBS[45]//CCSD(T)/cc-pVTZ. Our model chemistry includes corrections for vibrational anharmonicity in the zero-point energy and vibrational partition functions, core-valence correlation, scalar relativistic effects, diagonal Born-Oppenheimer, spin-orbit splitting, and higher-order corrections. We compute the Gibbs energy of dimerization to be (-20.1 ± 1.6) kJ/mol at 298.15 K (2σ uncertainty), and (-32.3 ± 1.5) kJ/mol at 220 K. For atmospherically relevant [HO2] = 10(8) molecules per cm(3), our thermochemistry indicates that dimerization will be negligible, and thus H2O4 species are atmospherically unimportant. Under conditions used in laboratory experiments ([HO2] > 10(12) molecules per cm(3), 220 K), H2O4 formation may be significant. We compute two absorption spectra that could be used for laboratory detection of HO4H: the OH stretch overtone (near-IR) and electronic (UV) spectra.

Accurate ab initio potential energy surface, thermochemistry, and dynamics of the F(-) + CH3F SN2 and proton-abstraction reactions.

We develop a full-dimensional global analytical potential energy surface (PES) for the F(-) + CH3F reaction by fitting about 50 000 energy points obtained by an explicitly correlated composite method based on the second-order Møller-Plesset perturbation-F12 and coupled-cluster singles, doubles, and perturbative triples-F12a methods and the cc-pVnZ-F12 [n = D, T] basis sets. The PES accurately describes the (a) back-side attack Walden inversion mechanism involving the pre- and post-reaction (b) ion-dipole and (c) hydrogen-bonded complexes, the configuration-retaining (d) front-side attack and (e) double-inversion substitution pathways, as well as (f) the proton-abstraction channel. The benchmark quality relative energies of all the important stationary points are computed using the focal-point analysis (FPA) approach considering electron correlation up to coupled-cluster singles, doubles, triples, and perturbative quadruples method, extrapolation to the complete basis set limit, core-valence correlation, and scalar relativistic effects. The FPA classical(adiabatic) barrier heights of (a), (d), and (e) are -0.45(-0.61), 46.07(45.16), and 29.18(26.07) kcal mol(-1), respectively, the dissociation energies of (b) and (c) are 13.81(13.56) and 13.73(13.52) kcal mol(-1), respectively, and the endothermicity of (f) is 42.54(38.11) kcal mol(-1). Quasiclassical trajectory computations of cross sections, scattering (θ) and initial attack (α) angle distributions, as well as translational and internal energy distributions are performed for the F(-) + CH3F(v = 0) reaction using the new PES. Apart from low collision energies (Ecoll), the SN2 excitation function is nearly constant, the abstraction cross sections rapidly increase with Ecoll from a threshold of ∼40 kcal mol(-1), and retention trajectories via double inversion are found above Ecoll = ∼ 30 kcal mol(-1), and at Ecoll = ∼ 50 kcal mol(-1), the front-side attack cross sections start to increase very rapidly. At low Ecoll, the indirect mechanism dominates (mainly isotropic backward-forward symmetric θ distribution and translationally cold products) and significant long-range orientation effects (isotropic α distribution) and barrier recrossings are found. At higher Ecoll, the SN2 reaction mainly proceeds with direct rebound mechanism (backward scattering and hot product translation).

Accurate ab initio potential for the krypton dimer and transport properties of the low-density krypton gas.

A new highly accurate potential energy curve for the krypton dimer was constructed using coupled-cluster calculations up to the singles, doubles, triples, and perturbative quadruples level, including corrections for core-core and core-valence correlation and for relativistic effects. The ab initio data points were fitted to an analytic potential which was used to compute the most important transport properties of the krypton gas. The viscosity, thermal conductivity, self-diffusion coefficient, and thermal diffusion factor were calculated by the kinetic theory at low density and temperatures from 116 to 5000 K. The comparisons with literature experimental data as well as with values from other pair potentials indicate that our new potential is superior to all previous ones. The transport property values computed in this work are recommended as standard values over the complete temperature range.

CI-MBPT: A package of programs for relativistic atomic calculations based on a method combining configuration interaction and many-body perturbation theory

This package of programs allows us to carry out relativistic calculations for many-electron atoms and ions. One can find energy levels and a number of atomic properties: g-factors, magnetic-dipole and electric-quadrupole hyperfine structure constants, electric- and magnetic-multipole transition amplitudes, and matrix elements of the parity nonconserving interactions. Method of calculation is based on a combination of conventional configuration interaction (CI) method and many-body perturbation theory (MBPT). The former explicitly accounts for the interaction between valence electrons, while the latter includes core–core and core–valence correlations. These two methods are combined to acquire benefits from both approaches and attain better accuracy. Program summaryProgram title: CI-MBPTCatalogue identifier: AEWV_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEWV_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 102640No. of bytes in distributed program, including test data, etc.: 583539Distribution format: tar.gzProgramming language:Fortran 90.Computer: Intel Core i5 CPU, 3.2 GHz.Operating system: Linux (CentOS 5, Ubuntu 12.04 LTS, SUSE 13.2).RAM: 8 GbClassification: 2.1.Nature of problem: Prediction of atomic or ionic energy levels and different observables in the framework of relativistic approach.Solution method: The package of programs determines energy levels and associated many-electron wave functions for states of atoms and ions in the pure CI or CI+MBPT approximations. Using the wave functions, different atomic properties can be obtained, including g-factors, magnetic-dipole and electric-quadrupole hyperfine structure constants, electric- and magnetic-multipole transition amplitudes, P-odd and P,T-odd amplitudes.Restrictions: The package is not designed for calculations of high Rydberg and autoionizing states. It becomes inefficient for the number of valence electrons exceeding four or five. It has not been tested for superheavy elements. The maximal number of Hartree–Fock–Dirac (HFD) orbitals when HFD equations are solved is 32.Unusual features: One-electron orbitals outside the nucleus are defined on radial grid points. Inside the nucleus they are described in a form of the Taylor expansion over r/R, where R is the nuclear radius.Additional comments: All programs have been compiled, linked, and tested with both “ifort” and freely available “gfortran”.Running time: Changes from tens of minutes for atoms with two valence electrons to tens of hours for more complex systems.

Energy levels and oscillator strengths for Mg-like copper

Energy levels and oscillator strengths for electric-dipole (E1), electric-quadrupole (E2), magnetic-dipole (M1), and magnetic-quadrupole (M2) transitions among the lowest 185 levels arising from the n≤5 configurations in Cu XVIII are calculated through second-order many-body perturbation theory (MBPT). To illustrate the improvement of many-body perturbation corrections, we have also carried out the parallel calculations using the standard relativistic configuration-interaction (RCI) approach. Furthermore, to confirm the accuracy of the present MBPT results and show further the importance of valence–valence and core–valence correlation effects, we have performed another independent calculation using the multiconfiguration Dirac–Fock (MCDF) method within the GRASP code in the active space approximation. The accuracies of the present level energies, wavelengths, transition rates and lifetimes are assessed by comparing to available experimental and other theoretical results. The present MBPT and MCDF results are believed to be the most comprehensive and accurate ones to date.

Accurate calculation of the potential energy curve and spectroscopic parameters of X2Σ+ state of 12Mg1H**Project supported by the National Natural Science Foundation of China (Grand Nos. 11147158, 91221301, and 11264020)

High level calculations on the ground state of 12Mg1H molecule have been performed using multi-reference configuration interaction (MRCI) method with the Davidson modification. The core–valence correlation and scalar relativistic corrections are included into the present calculations at the same time. The potential energy curve (PEC) of the ground state, all of the vibrational levels and spectroscopic parameters are fitted. The results show that the levels and spectroscopic parameters are in good agreement with the available experimental data. The analytical potential energy function (APEF) is also deduced from the calculated PEC using the Murrell–Sorbie (M–S) potential function. The present results can provide a helpful reference for the future spectroscopic experiments or dynamical calculations of the molecule.

Comparative Assessment of DFT Performances in Ru- and Rh-Promoted σ-Bond Activations.

In this work, the performances of 19 density functional theory (DFT) methods are calibrated comparatively on Ru- and Rh-promoted σ-bond (C-H, O-H, and H-H) activations. DFT calibration reference is generated from explicitly correlated coupled cluster CCSD(T)-F12 calculations, and the 4s4p core-valence correlation effect of the two 4d platinum group transition metals is also included. Generally, the errors of DFT methods for calculating energetics of Ru-/Rh-mediated reactions appear to correlate more with the magnitude of energetics itself than other factors such as metal identity. For activation energy calculations, the best performing functionals for both Ru and Rh systems are MN12SX < CAM-B3LYP < M06-L < MN12L < M06 < ωB97X < B3LYP < LC-ωPBE (in the order of increasing mean unsigned deviations, MUDs, of less than 2 kcal/mol). For reaction energy calculations, best functionals with MUDs less than 2 kcal/mol are PBE0 < CAM-B3LYP ≈ N12SX. The effect of the DFT empirical dispersion correction on the performance of the DFT methods is beneficial for most density functionals tested in this work, reducing their MUDs to different extents. After including empirical dispersion correction, ωB97XD, B3LYP-D3, and CAM-B3LYP-D3 (PBE0-D3, B3LYP-D3, and ωB97XD) are the three best performing DFs for activation energy (reaction energy) calculations, from which B3LYP-D3 and ωB97XD can notably be recommended uniformly for both the reaction energy and reaction barrier calculations. The good performance of B3LYP-D3 in quantitative description of the energetic trends further adds value to B3LYP-D3 and singles this functional out as a reasonable choice in the Ru/Rh-promoted σ-bond activation processes.

Valence and Core-Valence Effects in N-Like Kr, Rb and Sr Ions

(Received December 17, 2013) Energy levels, wavelengths, transition rates and line strengths are reported for the 2s2p 2s2p transition array in Kr(XXX), Rb(XXXI) and Sr(XXXII). Wave functions were determined using the multicon guration Dirac Fock method with account for valence and core-valence correlation e ects. The present results are presented and compared with experimental data and with values from other calculations. The calculated values including corevalence correlation are in good agreement with other available theoretical and experimental values, and therefore can be used for the further astrophysical investigations.

Theoretical study of LiCl− and LiBr− molecular ions

The molecular structures and spectroscopic constants of the ground electronic states of LiCl− and LiBr− are investigated with the coupled-cluster method. To improve the accuracy of our calculations, we have employed the extrapolation schemes as well as corrections of the core–valence correlation and scalar relativistic effect. The equilibrium parameters, potential energy curves, force constants, vibrational energy levels and spectroscopic parameters of both molecular ions are derived, in which those of LiBr− are reported for the first time. The electron affinities and vertical detachment energies of neutral and anionic LiCl and LiBr are also evaluated.

Spectroscopy and heats of formation of CXI (X = Br, Cl, F) iodocarbenes: quantum chemical characterisation of the X̃(1 A′), ã(3 A″) and Ã(1 A″) states

The equilibrium energies of the iodocarbenes CXI (X = Br, Cl, F) in their , and states and their atomisation and dissociation energies in the complete basis limit were determined by extrapolating valence correlated (R/U)CCSD(T) and Davidson corrected multi-reference configuration interaction (MRCI) energies calculated with the aug-cc-pVxZ (x = T,Q,5) basis sets and the ECP28MDF pseudopotential of iodine plus corrections for core and core–valence correlation, scalar relativity, spin–orbit coupling and zero-point energies. Spin–orbit energies were computed in a large basis of configurations chosen so as to accurately describe dissociation to the 3P and 2P states of C and of the halogens X and I, respectively. The computed singlet–triplet splittings are 13.6, 14.4 and 27.3 kcal mol−1 for X = Br, Cl and F, respectively. The enthalpies of formation at 0 K are predicted to be 97.4, 82.6 and 38.1 kcal mol−1 with estimated errors of ±1.0 kcal mol−1. The excitation energies (T00) in CBrI and CClI are calculated to be 41.1 and 41.7 kcal mol−1, respectively. The Renner–Teller intersections in both molecules are predicted to be substantially higher than the dissociation barriers on the surfaces. By contrast, in CFI the state is found to be unbound with respect to dissociation.