Core-valence Corrections Research Articles

All-electron basis sets for H to Xe specific for ZORA calculations: Applications in atoms and molecules

Abstract A segmented basis set of quadruple zeta valence quality plus polarization functions (QZP) for H through Xe was developed to be used in conjunction with the ZORA Hamiltonian. This set was augmented with diffuse functions to describe electrons farther away from the nuclei adequately. Using the ZORA-CCSD(T)/QZP-ZORA theoretical model, atomic ionization energies and bond lengths, harmonic vibrational frequencies, and atomization energies of some molecules were calculated. The addition of core-valence corrections has been shown to improve the agreement between theoretical and experimental results for molecular properties. For atomization energies, a similar observation emerges when considering spin-orbit couplings. With the augmented QZP-ZORA set, static mean dipole polarizabilities of a set of atoms were calculated and compared with previously published recommended and experimental values. Performance evaluations of the ZORA and Douglas–Kroll–Hess Hamiltonians were made for each property studied.

Ab initio investigation on predissociation of the A2Σ+ state of the SeH radical induced by spin-orbit coupling

High-level ab initio calculations are performed to investigate potential energy curves (PECs) of seven low-lying Λ-S states associated with the two lowest dissociation limits of the SeH radical by utilizing the internally contracted multireference configuration interaction (icMRCI) method in combination with the aug-cc-pwCV5Z Gaussian basis set. The scalar relativistic effect (SR), the electronic core-valence (CV) correction, and Davidson (+Q) modification are included in our calculations. The fourteen Ω states generated from the seven Λ-S states are yielded when the spin-orbit coupling (SOC) effect is taken into account by using the Breit-Pauli operator. On the ground of the obtained PECs, the spectroscopic constants of the bound Λ-S and Ω states are evaluated, which reproduce pretty well the available experimental and theoretical values. By virtue of SOC matrix elements between the bound A2Σ+ state and repulsive 4Σ–(I), 2Σ–(I), or 4∏(I) states crossing with the A2Σ+ state PEC, the spin-orbit perturbations in the A2Σ+ rovibrational manifold in the crossing region and the A-state predissociation mechanism are analyzed. It is clearly exhibited that the avoided crossing phenomena between electronic states possessing the same Ω quantum number provide obvious spectroscopic effects in the transition dipole moments (TMDs) and Franck-Condon factors (FCFs) of the A2Σ+-X2Π transition. The radiative lifetimes of the A2Σ+ vibrational sublevels are determined. In addition, we finalized our study of the SeH molecule by optimizing its equilibrium ground state geometry in terms of a restricted coupled cluster approach including singles and doubles with perturbative triples account (RCCSD(T) method) plus CV, SR, and SOC corrections with extrapolating to complete basis set (CBS) limit.

A larger basis set describes atomization energy core-valence correction better than a higher-order coupled-cluster method.

The accuracy of coupled-cluster methods for the computation of core-valence correction to atomization energy was assessed. Truncation levels up to CCSDTQP were considered together with (aug-)cc-pwCVnZ (n = D, T, Q, 5) basis sets and three different extrapolation techniques (canonical and flexible Helgaker formula and Riemann zeta function extrapolation). With the exception of CCSD, a more accurate correction can be obtained from a larger basis set using a lower-level coupled-cluster method, and not vice versa. For the CCSD(T) level, it also implies faster computations with modern codes. We also discussed the importance of moving to higher-order or all-electron methods for geometry optimizations. The present study provides the general knowledge needed for the most accurate state-of-the-art computations.

Canonical Unified Statistical Rate Constants Using a High-Level Composite Coupled Cluster Energy Scheme for the CH4 + CH Reaction

We report an ab initio study on the kinetics and chemical dynamics of the CH4 + CH reaction using a coupled cluster based composite scheme that includes unrestricted coupled cluster singles and doubles with perturbative connected triples method, UCCSD(T), energies extrapolated to the complete basis set limit, in addition to core-valence, higher-order correlation, and relativistic corrections. With this protocol, the reaction enthalpies for the two main reaction channels, C2H4 + H and CH2 + CH3, are reproduced with an absolute deviation of 0.04 kcal mol–1 relative to experimental data. At the UCCSD(T)/complete basis set (CBS) level of theory, the formation of the C2H5 intermediate is barrierless, in contrast with the low submerged barrier (–1.87 kcal -mol–1 relative to the reactants) found at the UCCSD(T)/augmented correlation-consistent polarized double-zeta (aug-cc-pVDZ) level of theory. With the correlation-consistent polarized triple-zeta (cc-pVTZ) basis set, we describe structural variations for the reaction bottleneck along the reaction path, finding at least three canonical variational transition states for the temperature range from 20 to 800 K. The thermal rates were obtained via the canonical unified statistical theory (CUS), using the canonical variational transition state theory (VTST) for the inner-transition state and long-range transition state theory (LRTST) for the outer-transition state. Our calculations agree with literature measurements and show inverse Arrhenius behavior, as observed experimentally. At 298 K, the computed rate constant is 2.65 × 10–10 cm3 molecule–1 s−1 and reported experimental measurements range from 2.5 × 10−12 to 3.0 × 10–10 cm3 molecule–1 s−1. Our theoretical study represents an improvement on previous computational investigations and highlights that even relatively simple gas-phase reactions can require high levels of theory to be modeled accurately.

Electronic structure of hafnium monocarbide (HfC) and its ion (HfC+)

The electronic structures of the diatomic hafnium mono-carbide (HfC) and its cation (HfC+) have been investigated by multireference methods and at the MRCI level the ground state of HfC is X1Σ+ with the 3Σ+ is 292 cm−1 higher. With spin-orbit and core-valence corrections, the energy separation increases to 578 cm−1. The 2Σ+ is the ground state of the cation. We report the spectroscopic constants, dipole moments, and dissociation energies of the 19 states of HfC and 4 states of HfC+. The origin of the states and the nature of chemical bonding are discussed.

Energy Levels and Radiative Rates in Ga XVII

Сomplete and consistent atomic data, including energy levels, wavelengths, lifetimes, and E1, E2, M1, and M2 transition rates, are reported for the low-lying 41 levels of Ga XVII, belonging to the n = 3 states (1s22s22p6)3s23p3, 3s3p4, and 3s23p23d. High-accuracy calculations act as benchmarks for accurate treatments of relativity, electronic correlation, and quantum electrodynamic (QED) effects in multi-valence-electron systems. The calculated energy levels are in excellent agreement with the experimental results and the experimentally compiled energy values of the National Institute for Standards and Technology wherever available. The calculated values, including core–valence correction, are found to be in good agreement with other theoretical and experimental values.

Energy levels and radiative rates in P-like Krypton

Excitation energies, lifetimes, hyperfine structures and Landé gJ-factors belonging to the n = 3 states (1s22s22p6)3s23p3, 3s3p4, and 3s23p23d configurations of phosphorus-like Kr XXII have been performed with the multiconfiguration Dirac-Hartree-Fcok (MCDHF) method, as well as wavelengths, line strengths, oscillator strengths, transitions rates for electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1), magnetic quadrupole (E2) transitions among these levels. High-accuracy calculations have been calculated as benchmarks in the request for accurate treatments of relativity, electron correlation and quantum electrodynamic (QED) effects in multi-valence-electron systems. Comparisons are made between the present two data sets, as well as with the experimental results and the experimentally compiled energy values of the National Institute for Standards and Technology wherever available. The calculated values including core-valence correction are found to be in a good agreement with other theoretical and experimental values. The present results are accurate enough for identification of emission lines involving the n = 3 levels, and are also useful for modeling and diagnosing plasmas.

Systematic calculations of energy levels and transitions rates in Mo XXVIII

Abstract Complete and consistent atomic data, including excitation energies, lifetimes, wavelengths, hyperfine structures, Landé g J -factors and E1, E2, M1, and M2 line strengths, oscillator strengths, transitions rates are reported for the low-lying 41 levels of Mo XXVIII, belonging to the n = 3 states (1s 22s 22p 6)3s 23p 3, 3s3p 4, and 3s 23p 23d. High-accuracy calculations have been performed as benchmarks in the request for accurate treatments of relativity, electron correlation, and quantum electrodynamic (QED) effects in multi-valence-electron systems. Comparisons are made between the present two data sets, as well as with the experimental results and the experimentally compiled energy values of the National Institute for Standards and Technology wherever available. The calculated values including core-valence correction are found to be in a good agreement with other theoretical and experimental values. The present results are accurate enough for identification and deblending of emission lines involving the n = 3 levels, and are also useful for modeling and diagnosing plasmas.

Transition properties between low-lying electronic states of SiO+

In this work, we investigate the potential energy curves (PECs), transition dipole moments (TDMs) and spin-orbit couplings for low-lying electronic states of SiO+ based on ab initio calculations. The PECs of seventeen low-lying electronic states are calculated by the internally contracted multireference configuration interaction (icMRCI) method with the Davidson correction, as well as the basis set extrapolation, core-valence (CV) correction and scalar relativistic correction. The Schrödinger equation of nuclear movement is solved over the PEC to obtain the rotational and vibrational energy levels, which are used to fit the spectroscopic parameters. The Einstein coefficients, Franck-Condon factors and oscillator strengths for dipole-allowed transitions are calculated with the PECs and TDMs. The radiative lifetimes of some excited states are also obtained. Our calculated radiative lifetime of 67.8 ns for B2Σ+(υ′ = 0) is in excellent agreement with the recent experimental measurement of 66 ± 2 ns. The spin-orbit coupling integrals related to the X2Σ+, A2Π, B2Σ+, 14Σ+, 14Π and 14Σ− states are calculated using the Breit-Pauli Hamiltonian. In addition, the effects of spin-orbit couplings on the potential energies of the Λ-S electronic states are discussed.

Theoretical study on low-lying electronic states of CP radical: Energy levels, Einstein coefficients, Franck-Condon factors and radiative lifetimes

The state-of-the-art ab initio-based valence internally contracted multireference configuration-interaction (icMRCI) method, including the Davidson correction, core-valence correction and scalar relativistic correction and the basis-set extrapolation, is used to calculate the potential energy curves (PECs) of the X2Σ+, B2Σ+, A2Π, 12Σ−, 12Δ, 22Δ, 22Σ−, 14Σ+, 24Σ+, 14Π, 14Δ, 14Σ−, 24Δ, 24Σ− 16Σ+ and 26Σ+ electronic states for CP radical. We also calculate the transition dipole moments (TDMs), Einstein coefficients and Franck-Condon factors for nineteen dipole allowed transitions between these sixteen states. The PECs are used to fit spectroscopic parameters, which are in excellent agreement with previous experimental and theoretical ones. The computed Franck-Condon factors also agree quite well with accurate semi-empirical results for the A2Π-X2Σ+ and B2Σ+-X2Σ+ systems. Such good agreement implies that the results are accurate enough to assist identification of the spectra from astrophysical sources. Large amounts of energy levels and transition data of high accuracy are provided in this work for CP radical of astrophysical interest, where experimental data are still scarce.

Energy levels, transition dipole moment, transition probabilities and radiative lifetimes for low-lying electronic states of PN

The valence internally contracted multireference configuration-interaction (icMRCI) method is used to compute potential energy curves (PECs) of the X1Σ+, A1Π, C1Σ−, D1Δ, 21Π, a3Σ+, b3Π, d3Δ, e3Σ−, 23Δ, 23Σ−, 15Σ+ and 15Π states for PN, together with the Davidson, core-valence (CV) and scalar relativistic corrections, as well as the basis-set extrapolation. Transition dipole moments (TDMs) of fifteen dipole-allowed transitions between the thirteen states are calculated by the icMRCI approach with the aug-cc-pV6Z basis set. The vibrational band origins, Einstein coefficients and Franck-Condon factors of all spontaneous emissions for the fifteen band systems are determined, seeking to theoretically predict the strong emissions at least of the order of 103 s−1 for Einstein coefficients. Comparing with experimental measurements, our calculations can well reproduce the band origins and Franck-Condon factors of the A1Π-X1Σ+ system. Similar accuracy is assumed for the other band systems. Many emissions for the A1Π-X1Σ+, 21Π-A1Π, 21Π-X1Σ+, 21Π-C1Σ−, 21Π-D1Δ, b3Π-a3Σ+, e3Σ−-b3Π, 23Δ-13Δ, 23Σ−-13Σ−, 23Σ−-b3Π and 15Π-15Σ+ systems are found to be strong according to our calculated Einstein coefficients, whereas the emissions are weak for the 23Δ-b3Π system. Radiative lifetimes for the first 15 vibrational levels are evaluated to be about tens of nanoseconds for the 21Π state, about several hundred nanoseconds for the A1Π state, about several to tens of microseconds for the b3Π, 23Δ, 23Σ− and 15Π states and about several to several hundred microseconds for the e3Σ− state. The results can be used as guidelines for line identification and diagnostics of astrophysical plasma.

Radiative transition probabilities between low-lying electronic states of N2

ABSTRACTThis work mainly investigates the transition dipole moments (TDMs) and radiative transition probabilities of dipole-allowed transitions between the , , , , , , , , and states of N2. Many of these transition properties are previously unknown. For completeness, another 14 electronic states that correlate to four lowest dissociation limits are also calculated. The potential energy curves (PECs) are calculated at the valence internally contracted multireference configuration-interaction (icMRCI) level of theory, along with the Davidson correction, the core-valence (CV) correction and the scalar relativistic correction, as well as the basis-set extrapolation. These corrections, especially the CV correction, greatly improve the accuracy of the PECs, as shown by the excellent agreement of the fitted spectroscopic parameters with the available experimental data. In order to verify the accuracy of transition properties, we calculate the Einstein coefficients of the extensively studied band transition systems and compute the radiative lifetimes of states, which are in good agreement with the experimental data. Similar accuracy can be assumed for the previously undetermined band transition systems. The large Einstein coefficients of these band systems can provide guidelines for observing such newly predicted band transitions in the appropriate spectroscopy experiments.

The role of dispersion and anharmonic corrections in conformational analysis of flexible molecules: the allyl group rotamerization of matrix isolated safrole.

Conformational changes of the monomeric safrole (5-(2-propenyl)-1,3-benzodioxole) isolated in low temperature xenon matrices were induced thermally or using narrow-band UV radiation. The rotation of the allyl group taking place in the studied matrices was followed by FTIR spectroscopy. Safrole represents a challenging example of a flexible molecule highlighting the importance of dispersion interactions and anharmonic effects in the structural, spectroscopic and energetic analysis. Structures of the safrole conformers, their energetics and infrared spectra have been calculated using various computational methods ranging from density functional theory (DFT) to coupled cluster (CC). The best theoretical results were obtained by integrating CCSD(T) energies including complete basis set extrapolation and core-valence corrections with B2PLYP-D3 equilibrium structures and hybrid B2PLYP-D3/B3LYP-D3 anharmonic computations for IR spectra and thermodynamics.

Theoretical study of laser cooling of potassium chloride anion

The potential energy curves and transition dipole moments (TDMs) for three Λ-S states (X<sup>2</sup>Σ<sup>+</sup>, A<sup>2</sup>Π, and B<sup>2</sup>Σ<sup>+</sup>) of potassium chloride anion (KCl<sup>–</sup>) are investigated by using multi-reference configuration interaction (MRCI) method. The def2-AQZVPP-JKFI of K atom and AV5Z-DK all-electron basis set of Cl atom are used in all calculations. The Davidson correction, core-valence (CV) correction, and spin-orbit coupling effect (SOC) are also considered. In the complete active self-consistent field (CASSCF) calculations, eight molecular orbitals are selected as active orbitals, which includ K 4s4p and Cl 3s3p shells; K 3p shell is closed orbital, and the remaining shells (K 1s2s3s and Cl 1s2s2p) are frozen orbitals. In the MRCI+<i>Q</i> calculations, K 3p shell is used for the CV correction. There are 15 electrons in the correlation energy calculations. Then, their spectroscopic parameters, Einstein coefficients, Franck-Condon factors, and radiative lifetimes are obtained by solving the radial Schrödinger equation. The spectroscopic properties and transition properties for the Ω states are predicted. Highly diagonally distributed Franck-Condon factor <i>f</i><sub>00</sub> values for the (2)1/2↔(1)1/2 and (1)3/2↔(1)1/2 transition are 0.8816 and 0.8808, respectively. And the short radiative lifetimes for the (2)1/2 and (1)3/2 excited states are also obtained, i.e. <i>τ</i>[(2)1/2] = 45.7 ns and <i>τ</i>[(1)3/2] = 45.5 ns, which can ensure laser cooling of KCl<sup>–</sup> anion rapidly. The results indicate that the (2)1/2↔(1)1/2 and (1)3/2↔(1)1/2 quasicycling transitions are suitable to the building of laser cooling projects. For driving the (2)1/2↔(1)1/2 transition, a main pump laser (λ<sub>00</sub>) and two repumping lasers (λ<sub>10</sub> and λ<sub>21</sub>) are required. Their wavelengths are λ<sub>00</sub> = 1065.77 nm, λ<sub>10</sub> = 1090.13 nm and λ<sub>21</sub> = 1087.76 nm. For driving the (1)3/2↔(1)1/2 transition, the wavelengths are λ<sub>00</sub> = 1064.24 nm, λ<sub>10</sub> = 1088.54 nm, and λ<sub>21</sub> = 1086.17 nm. The cooling wavelengths of KCl<sup>-</sup> anion for two transitions are both deep in the infrared range. Finally, the Doppler temperature and recoil temperature for two transitions are also calculated, respectively. The Doppler temperatures for (2)1/2↔(1)1/2 and (1)3/2(1)1/2 transitions are 83.57 μK and 83.93 μK, and the recoil temperatures for two transitions are 226 nK and 227 nK, respectively. for two transitions are 226 nK and 227 nK, respectively.

Potential energy curves and transition properties for the ground and excited states of BH+ cation

BH+ cation is one of the candidates for laser cooling. The potential energy curves (PECs) for nine electronic states (X2+, A2, B2+, a4, b4+, 32+, 22, 32, 42+) relating to the B+(1Sg)+H(2Sg), B+(3Pu)+H(2Sg), B(2Pu)+H+(1Sg), and B+(1Pu)+H(2Sg) dissociation channels of BH+ cation are obtained using highly accurate multi-reference configuration interaction (MRCI) plus Davidson correction. All-electron basis sets AV5Z-DK for H and ACV5Z-DK for B are used in PEC calculations for the -i-S states of BH+ cation, respectively. In complete active space self-consistent field (CASSCF) calculation, H(1s2s2p3s3p) and B(2s2p) are chosen as active orbitals, B(1s) is the closed shell; in the MRCI calculation, the core-valence (CV) correction is considered, i.e., B(1s) shell is used for CV correlation. Spin-orbit coupling effects are considered with Breit-Pauli operators. Spectroscopic constants are fitted using the Murrell-Sorbie function. Spectroscopic constants for the X2+, A2, and B2+ states are in excellent agreement with the available experimental data; spectroscopic constants for the b4+, 32+, 32, and 42+ states are reported. Two potential wells for the 32 and 42+ states are found. The maximum fitting error of all electronic states is only 3.407 cm-1. In addition, PECs for the A2 and B2+ states are crossed at about 2.7 . Then, the transition dipole moments (TDMs) for the A2 X2+, B2+X2+, 32+X2+, B2+ A2, 32 X2+ and b4+ a4 transitions are also obtained. The strength for the B2+ A2 transition is very weak. Based on the accurate PECs and TDMs, the Franck-Condon factors and spontaneous radiative lifetimes are calculated. A strongly diagonal Franck-Condon factor (f00) for the A2X2+ transition is obtained, which equals 0.9414. Spontaneous radiative lifetime for the A2 and B2+ states is also predicted. i.e., (A2)=239.2 ns and (B2+)=431.2 ns. When SOC effect is considered, the A21/2 and B21/2+ states avoid crossing in the Franck-Condon region (R is about 2.7 ). Calculated f00 for the A21/2 X21/2+ transition is 0.9430; spontaneous radiative lifetime for the A21/2 is 239.0 ns. Our calculated results indicate that the influence for laser cooling BH+ cation via the crossing between B2+ and A2 states can be ignored.

Accurate Theoretical Study of LiS Radical and Its Singly Charged Cation and Anion in their Ground Electronic State

Potential energies of LiS(2Π), LiS−(1Σ+) and LiS+(3Σ−) are calculated by using the multireference configuration interaction method including Davidson correction and the augmented correlation-consistent basis sets aug-cc-PV(X+d)Z (X=T, Q). Such obtained potential energies are subsequently extrapolated to the complete basis set limit. Both the core-valence correction and the relativistic effect are also considered. The analytical potential energy functions are then obtained by fitting such accurate energies utilizing a least-squares fitting procedure. By using such analytical potential energy functions, we obtain the accurate spectroscopic parameters, complete set of vibrational levels and classical turning points. The present results are compared well with the experimental and other theoretical work.

Multiconfiguration Dirac–Fock calculations of excitation energies and wavelengths in highly charged tungsten ions

The fully relativistic multiconfiguration Dirac–Fock (MCDF) method is employed to calculate the excitation energies and wavelengths for nine isoelectronic sequences of tungsten ions. In calculations, electron correlations, quantum electrodynamical (QED) effect, and Breit correction are taken into account. The core–valence and valence–valence corrections are analyzed in a systematic way. The core setting was systematically studied for four cases of one electron occupying the outermost s orbital, one electron occupying the outermost p orbital, three electrons occupying the outermost p orbital, and one electron occupying the outermost d orbital. In our research, at least two calculation models are adopted for every tungsten ion. Through analyzing our results, it is found that the following three calculation models can help to get results closer to measured values: (i) setting the closed shells as core; (ii) taking core–valence corrections into account when there is only one valence electron; (iii) taking valence–valence corrections into account when the number of valence electrons is not less than three. The purpose of this paper is to provide some references on configuration selection and configuration interaction in calculations for a multi-electron system of highly charged tungsten ions.

Benchmark ab Initio Conformational Energies for the Proteinogenic Amino Acids through Explicitly Correlated Methods. Assessment of Density Functional Methods.

The relative energies of the YMPJ conformer database of the 20 proteinogenic amino acids, with N- and C-termination, have been re-evaluated using explicitly correlated coupled cluster methods. Lower-cost ab initio methods such as MP2-F12 and CCSD-F12b actually are outperformed by double-hybrid DFT functionals; in particular, the DSD-PBEP86-NL double hybrid performs well enough to serve as a secondary standard. Among range-separated hybrids, ωB97X-V performs well, while B3LYP-D3BJ does surprisingly well among traditional DFT functionals. Treatment of dispersion is important for the DFT functionals; for the YMPJ set, D3BJ generally works as well as the NL nonlocal dispersion functional. Basis set sensitivity for DFT calculations on these conformers is weak enough that def2-TZVP is generally adequate. For conformer corrections to heats of formation, B3LYP-D3BJ and especially DSD-PBEP86-D3BJ or DSD-PBEP86-NL are adequate for all but the most exacting applications. The revised geometries and energetics for the YMPJ database have been made available as Supporting Information and should be useful in the parametrization and validation of molecular mechanics force fields and other low-cost methods. The very recent dRPA75 method yields good performance, without resorting to an empirical dispersion correction, but is still outperformed by DSD-PBEP86-D3BJ and particularly DSD-PBEP86-NL. Core-valence corrections are comparable in importance to improvements beyond CCSD(T*)/cc-pVDZ-F12 in the valence treatment.

Low-Lying Electronic States of Irn Clusters with n = 2–8 Predicted at the DFT, CASSCF, and CCSD(T) Levels

Low-lying structures of the small iridum clusters Ir(n) (n = 2-8) were optimized using DFT methods. Ir2 and Ir3 were also optimized using the CASSCF method. MRCI-SD (for Ir2) energies and CCSD(T) (for Ir2 and Ir3) energies of the leading configurations from the CASSCF calculations were done to predict the low-lying states. The normalized atomization energies (<AE>) for Ir(n) (n = 2-8) were calculated at the CCSD(T) level up to the complete basis set (CBS) limit in some cases using the B3LYP optimized geometries. The ground state for Ir2 is predicted to be (5)Δg, and the ground state of Ir3 is linear (2)Δg, with the D3h(4)A"1 state ~10 kcal/mol higher in energy at the CASSCF level without core-valence corrections and ~15 kcal/mol higher at the CCSD(T)/CBS level with spin-orbit and core-valence corrections. Inclusion of the spin orbit corrections in the normalized bond dissociation energies <AE> for Ir(n) is critical and will decrease the <AE> by ~15 kcal/mol for n ≥ 4. The <AE> for Ir(n) increases as n increases in general, and the <AE> is far from convergence to the bulk value at n = 8. The average coordination number (CN) and average bond length for the low energy Ir(n)clusters are far from being converged to the bulk values by n = 8.

Theoretical study of the spectroscopically relevant parameters for the detection of HNPq and HPNq (q = 0, +1, −1) in the gas phase

High level ab initio electronic structure calculations at different levels of theory have been performed on HNP and HPN neutrals, anions, and cations. This includes standard coupled cluster CCSD(T) level with augmented correlation-consistent basis sets, internally contacted multi-reference configuration interaction, and the newly developed CCSD(T)-F12 methods in connection with the explicitly correlated basis sets. Core-valence correction and scalar relativistic effects were examined. We present optimized equilibrium geometries, harmonic vibrational frequencies, rotational constants, adiabatic ionization energies, electron affinities, vertical detachment energies, and relative energies. In addition, the three-dimensional potential energy surfaces of HNP(-1,0,+1) and of HPN(-1,0,+1) were generated at the (R)CCSD(T)-F12b∕cc-pVTZ-F12 level. The anharmonic terms and fundamentals were derived using second order perturbation theory. For HNP, our best estimate for the adiabatic ionization energy is 7.31 eV, for the adiabatic electron affinity is 0.47 eV. The higher energy isomer, HPN, is 23.23 kcal∕mol above HNP. HPN possesses a rather large adiabatic electron affinity of 1.62 eV. The intramolecular isomerization pathways were computed. Our calculations show that HNP(-) to HPN(-) reaction is subject to electron detachment.