Full Valence Configuration Interaction Research Articles

Electronic Structure, Spectroscopy, Cold Ion–Atom Elastic Collision Properties, and Photoassociation Formation Prediction of the (MgCs)+ Molecular Ion

In this paper, we extensively study the electronic structure, interactions, and dynamics of the (MgCs)+ molecular ion. The exchanges between the alkaline atom and the low-energy cationic alkaline earths, which are important in the field of cold and ultracold quantum chemistry, are studied. We use an ab initio approach based on the formalism of non-empirical pseudo-potential for Mg2+ and Cs+ cores, large Gaussian basis sets, and full-valence configuration interaction. In this context, the (MgCs)+ cation is treated as an effective two-electron system. Adiabatic potential energy curves and their spectroscopic constants for the ground and the first 20 excited states of 1,3Σ+ symmetries are determined. Furthermore, we identify the avoided crossings between the electronic states of 1,3Σ+ symmetries. These crossings are related to the charge transfer process between the two ionic limits, Mg/Cs+ and Mg+/Cs. Therefore, vibrational-level spacings and the transition and permanent dipole moments are presented and analyzed. Using the produced potential energy data, the ground-state scattering wave functions and elastic cross-sections are calculated for a wide range of energies. In addition, we predict the formation of a translationally and rotationally cold molecular ion (MgCs)+ in the ground-state electronic potential energy through a stimulated Raman-type process aided by ion–atom cold collision. In the low-energy limit (<1 mK), elastic scattering cross-sections exhibit Wigner law threshold behavior, while in the high-energy limit, the cross-sections act as a function of energy E go as E−1/3. A qualitative discussion about the possibilities of forming cold (MgCs)+ molecular ions by photoassociative spectroscopy is presented.

Theoretical study of MgNa+ ionic system: potential energy curve, vibrational levels, dipole moments, radiative lifetimes and laser-cooling analysis

An extensive ab-initio quantum chemistry study and a discussion of the possible laser cooling and formation of the heteronuclear ionic MgNa+ molecule is presented in this paper. Our work is based on the use of non–empirical pseudo-potentials for the Mg2+ and Na+ cores, large Gaussian basis sets, parametrized l–dependent polarization potentials, and full valence configuration interaction calculations. We present here adiabatic potential energy curves of the ground and 44 low-lying excited electronic states of 1,3Σ+, 1,3Π, 1,3Δ symmetries, and their spectroscopic parameters (Re, De, Te, ωe, ωexe, and Be). Furthermore, numerous ionic – neutral avoided crossings, specially between higher adjacent electronic states of 1,3Σ+, 1,3Π symmetries, are identified and interpreted. The energy separations between these avoided crossings are also calculated. The electric dipole moment curves have been computed for a wide range of inter-nuclear distances. The vibrational energies are obtained by solving the nuclear Schrodinger equation, using the calculated potential energy curves. Thereafter, spontaneous and black-body radiation induced transition rates are calculated to obtain the ground and excited states vibrational level lifetimes. It has been observed that the lifetimes of the ground state vibrational levels are of the order of a second, while those of the excited states, mainly the 21Σ+ state, have the order of a nanosecond.

Spectroscopic proprieties of the ground and the higher excited states of the KCs

Potential energy curves, spectroscopic parameters, electric dipole moments (PEDM and TEDM) and vibrational levels’ spacing for 141Σ+, 133Σ+, 81,3Π, and 31,3Δ electronic states, including the ionic limit K−Cs+, are highly computed and presented in adiabatic representation. These properties are determined by the use of an ab initio method involving non-empirical pseudo-potentials, the core polarization potentials, the l-dependent cut-off functions, and the full valence configuration interaction. An important shape where an ionic state behaving as (−1/R), has been clearly pointed out in the 1Σ+ symmetry. This irregularity has been made due to the ionic charge transfer state (K−Cs+), which induces a series of avoided crossings at intermediate and long internuclear ranges. It is interesting to note that the ionic character linked to the ionic charge transfer K−Cs+ state has been clearly illustrated in the PEDM. The current calculations on the KCs molecule are complementary to the published theoretical works, including recently observed electronic states that had not been calculated previously. For the low-lying electric states, spectroscopic constants, PEDM, as well as TEDM are in good agreement with the available experimental data. The relevant data of the KCs molecule are meaningful and useful in several prospective experiments such as photo-association experiments or the manipulation of ultra-cold molecules.

Spectroscopic, structural and lifetime calculations of the ground and low-lying excited states of the BeNa+, BeK+, and BeRb+ molecular ions

Based on the ab-initio approach and using the non-empirical pseudo-potential formalism for Be2+, Na+, K+ and Rb+ cores, large Gaussian basis sets and full valence configuration interaction (FCI), alkali-metal atom and the Beryllium ionic pairs are treated as effective two-electron systems. The potential energy curves and their spectroscopic constants for the low-lying excited states of different1,3Σ+, 1,3Πand 1,3Δ symmetries of these molecular ions have been performed. In addition to the vibrational properties, permanent and transition dipole moments functions have been also calculated and analyzed. The lifetimes of the vibrational states of the ground state are calculated taking into account the decay rates of the vibrational states in terms of spontaneous emission, and stimulated emission induced by black body radiation. The radiative lifetimes of the vibrational levels of the first A1Σ+ and second C1Σ+excited states are calculated using both ‘Franck-Condon’ and ‘Sum rule’ approximations. In all studied alkali-metal Beryllium molecular ions the ground states X1∑+ have much longer lifetimes than any excited states with an order of second, while an order of nanosecond is found for the first and second excited states, A1Σ+ and C1Σ+.

Electronic structure and photoassociation scheme of ultracold (MgK+) molecular ions

The adiabatic potential energy curves, permanent and transition dipole moments (TDMs) of the highly-excited states of the MgK+ molecular ion have been computed as a function of the inter-nuclear distance R. The results are obtained by an ab initio approach involving a non-empirical pseudo-potential for the Mg and K cores, correlation treatment for core valence through an effective core polarisation potential, and full valence configuration interaction. The molecule is thus treated as a two electron system. Ab initio electronic TDM functions are calculated for all dipole-allowed transitions among the 42 states of MgK+. Many of these moment functions exhibit interesting behaviour due to charge transfer or ion-atom pair correlations. The positions of a number of satellite bands are predicted from the potential energy difference curves. We verified our results by performing complete active space self-consistent field calculations followed by a multireference configuration interaction and including Davidson correction. We observe a rather good agreement for most of them especially for the ground and lower excited states. We investigate ion-atom cold collisions at quantum regime. Furthermore, we explore ion-atom elastic collisions at low temperatures, predicting the formation of translationally and rotationally cold molecular ion MgK+ in the ground state electronic potential by stimulated Raman type process. Our results are important in the perspective of upcoming experiments aiming at merging cold alkali atom and alkaline-earth ion in a hybrid trap for the creation of cold molecular ions by photoassociation.

Adiabatic and Diabatic Investigation of Numerous Electronic States for the Alkali Dimer FrNa.

The current paper reports a global investigation of all excited states below the ionic limit Fr+Na- of FrNa molecule following diabatic and adiabatic representations. The adiabatic and diabatic potential energy curves (PECs) for Σ+, Π, and Δ symmetries have been calculated for a dense grid of internuclear distances. The transition and permanent dipole moments (TDM and PDM) have been reported for both representations. Regarding the pseudopotential approach and full valence configuration interaction (FCI), the ab initio computation has been performed. Furthermore, the diabatization method was achieved by the use of the variational effective Hamiltonian theory (VEH). This latter served to assess the nonadiabatic coupling between the treated adiabatic states and to eliminate it employing a suitable unitary transformation matrix. The detailed computation of the PECs and PDM and TDM curves of the ground and excited states play a key role to coordinate experimental efforts in order to create cold and ultracold molecules in their ground stable rovibrational levels.

An adiabatic spectroscopic investigation of the CsRb system in ground and numerous excited states

Via ab-initio approximations, we investigate the electronic and structural features of the CsRb molecule. Adiabatic potential energy curves of 261,3Σ+, 181,3Π and 61,3Δ electronic states with their derived spectroscopic constants as well as vibrational levels spacing have been carried out and well explained. Our approach is founded on an Effective Core Potential (ECP) describing the valence electrons of the system. Using a large Gaussian basis set, the full valence Configuration Interaction can be applied easily on the two-effective valence electrons of the CsRb system. Furthermore, a detailed analysis of the electric dipolar properties has been made through the investigation of both permanent and transition dipole moments (PDM and TDM). It is significant that the ionic character connected with electron transfer that is linked to Cs+ Rb− state has been clearly illustrated in the adiabatic permanent dipole moment.

Theoretical study of the SrLi+ molecular ion: structural, electronic and dipolar properties

ABSTRACTThe structural and electronic properties of (SrLi)+ molecular ion have been determined by the use of ab initio approaches. Potential energy curves (PECs) with their spectroscopic constants (Re, De, ωe, Te, Be and ωeχe) have been calculated. Also, the vibrational properties and the electric dipole moments, either permanent (PDM) or transition (TDM) ones, have been investigated and analysed. Large Gaussian basis sets, the full valence configuration interaction (FCI) and the formalism of non-empirical pseudo-potential including the two approaches, effective core potential (ECP) and core polarisation potential (CPP), are analysed. Therefore, (SrLi)+ is considered as a two effective electrons system. Numerous excited states of symmetries 1,3Σ+, 1,3Π and 1,3Δ dissociating below the ionic limit Sr2+Li− have been investigated. This study shows interesting behaviours around the avoided crossing related to charge transfer involving important processes in physics and astrophysics such as dynamics, pre-dissociation and inelastic transitions.

Ab initio calculation of the electronic structure of the strontium hydride ion (SrH+)

The potentials, spectroscopic properties and electric dipole moments of SrH+ are computed for 63 molecular states dissociating up to Sr2+ + H− using an ab initio approach. The ab initio formalism is based on large basis sets, nonempirical atomic pseudopotential for strontium core, correlation treatment for core valence through the effective core polarization potentials and for valence through full valence configuration interaction. Our theoretical molecular constants match published values very well and a large amount of new results is produced. Unusual potential shapes are found in 1Σ+ states often caused by avoided crossing series between them and imprinted by the ionic state Sr2+H−. The high potential energy curves suggest, it is possible to form H− or at least to neutralize H+ in collisions with strontium. © 2014 Wiley Periodicals, Inc.

Ab initio spectroscopic study for the NaRb molecule in ground and excited states

A wide adiabatic study is performed for NaRb molecule, involving 151Σ+ electronic states including the ionic state Na−Rb+, as well as 143Σ+, 1–91,3Π, and 1–51,3Δ states. This investigation is performed using an ab initio approach which involves the effective core potential, the core polarization potential with l‐dependent cut‐off functions. The NaRb system has been treated as a two‐electron system and the full valence configuration interaction is easily achieved. The spectroscopic constants Re, De, Te, ωe, ωexe, Be, and D0 for all these states are derived. We have also computed the vibrational levels as well their spacing for different values of J. In addition, permanent and transition dipole moments are determined and analyzed. The Dunham coefficients have been used to perform experimental spacing to compare directly with our results. The present calculations on NaRb extend previous theoretical works to numerous electronic excited states in the various symmetries. © 2014 Wiley Periodicals, Inc.

Ab Initio Investigation of Electronic Properties of the Magnesium Hydride Molecular Ion

In this work, adiabatic potential energy curves, spectroscopic constants, dipole moments, and vibrational levels for numerous electronic states of magnesium hydride molecular ion (MgH(+)) are computed. These properties are determined by the use of an ab initio method involving a nonempirical pseudopotential for the magnesium core (Mg), the core polarization potential (CPP), the l-dependent cutoff functions and the full valence configuration interaction (FCI). The molecular ion is thus treated as a two-electron system. Our calculations on the MgH(+) molecular ion extend previous theoretical works to numerous electronic excited states in the various symmetries. A good agreement with the available theoretical and experimental works is obtained for the spectroscopic constants, the adiabatic potential energy curves, and the dipole moments for the lowest states of MgH(+).

Ab Initio Diabatic energies and dipole moments of the electronic states of RbLi molecule

For all states dissociating below the ionic limit Li(-) Rb(+) , we perform a diabatic study for (1) Σ(+) electronic states dissociating into Rb (5s, 5p, 4d, 6s, 6p, 5d, 7s, 4f) + Li (2s, 2p, 3s). Furthermore, we present the diabatic results for the 1-11 (3) σ, 1-8 (1,3) Π, and 1-4 (1,3) Δ states. The present calculations on the RbLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. The calculations rely on ab-initio pseudopotential, core polarization potential operators for the core-valence correlation and full valence configuration interaction approaches, combined to an efficient diabatization procedure. For the low-lying states, diabatic potentials and permanent dipole moments are analyzed, revealing the strong imprint of the ionic state in the (1) Σ(+) adiabatic states. The transition dipole moment is used to evaluate the radiative lifetimes of the vibrational levels trapped in the 2 (1) Σ(+) excited states for the first time. In addition to the bound-bound contribution, the bound-free term has been evaluated using the Franck-Condon approximation and also exactly added to the total radiative lifetime.

Adiabatic ab Initio Study of the BaH+ Ion Including High Energy Excited States

An adiabatic study of 1-34 (1,3)Σ(+) electronic states of barium hydride ion (BaH(+)) is presented for all states dissociating below the ionic limit Ba(2+)H(-). The 1-20 (1,3)Π and 1-12 (1,3)Δ states have been also investigated. In our approach, the valence electrons of the Ba(2+) ion described by an effective core potential (ECP) and core polarization potential (CPP) with l-dependent cutoff functions have been used. The ionic molecule BaH(+) has been treated as a two-electron system, and the full valence configuration interaction (CI) is easily achieved. The spectroscopic constants Re, De, Te, ωe, ωexe, and Be are derived. In addition, vibrational level spacing and permanent and transition dipole moments are determined and analyzed. Unusual potential shapes are found and also accidental quasidegeneracy in the vibrational spacing progression for various excited states. The (1)Σ(+) states exhibit ionic charge transfer avoided crossings series which could lead to neutralization or even H(-) formation in collisions of H(+) with Ba.

Transition dipole moments between the low-lying Ωg,u(+/−) states of the Rb2 and Cs2 molecules

For the Rb(2) and Cs(2) molecules, the adiabatic potential-energy curves and the transition dipole moments of the 43 Ω((+∕-)) (g,u) low-lying states dissociating adiabatically to the limits up to ns+(n-1)d (n = 5,6 for Rb(2) and Cs(2), respectively), have been computed as a function of the internuclear distance R for a large and dense grid. Each molecule was treated as a two-electron system. We used an ab initio approach involving a relativistic non-empirical pseudo-potential for Rb and Cs cores, core-valence polarization potentials, and full valence configuration interaction calculations for the two valence electrons. Spin-orbit effects were taken into account through semi-empirical spin-orbit pseudopotentials. Equilibrium distances, transition energies, rotational constants, and harmonic frequencies as well as depths of wells and heights of barriers are reported for all the molecular states investigated in Hund's cases (a) and (c). Extensive tables of energy values and transition dipole moments are given in an auxiliary (EPAPS) files as a database for future studies on Rb(2) and Cs(2).

Ab Initio Adiabatic and Diabatic Energies and Dipole Moments of the CaH+ Molecular Ion

The diabatic and adiabatic potential-energy curves and permanent and transition dipole moments of the highly excited states of the CaH(+) molecular ion have been computed as a function of the internuclear distance R for a large and dense grid varying from 2.5 to 240 au. The adiabatic results are determined by an ab initio approach involving a nonempirical pseudopotential for the Ca core, operatorial core-valence correlation, and full valence configuration interaction. The molecule is thus treated as a two-electron system. The diabatic potential energy curves have been calculated using an effective metric combined to the effective Hamiltonian theory. The diabatic potential-energy curves and their permanent dipole moments for the (1)∑(+) symmetry are examined and corroborate the high imprint of the ionic state in the adiabatic representation. Taking the benefit of the diabatization approach, correction of hydrogen electron affinity was taken into account leading to improved results for the adiabatic potentials but also the permanent and transition electric dipole moments.

Ab initio study of spectroscopic properties of the calcium hydride molecular ion

In the present work, all adiabatic potential energy curves, spectroscopic constants and dipole moments of CaH+ molecular ion dissociating below the ionic limit Ca2+H− are presented. These curves are determined by an ab initio approach involving a non-empirical pseudo-potential for the Ca core, core-valence correlation accounted in operator form with two types of core polarization potentials (CPP) and full valence Configuration Interaction. The molecule is thus treated as a two-electron system. The potential energy curves and the spectroscopic constants are presented. In addition, the permanent and transition dipole moments are calculated for most of the states and reveal the underlying ionic states. A rather good agreement with the available theoretical works in the literature is obtained for the spectroscopic constants of the lowest states of the CaH+ molecule.

Electronic Structure Analysis of the Ground-State Potential Energy Curve of Be2†

The recently measured ground-state potential energy curve of the diatomic beryllium molecule is reproduced to within an accuracy of 20 cm(-1) by a full valence configuration interaction calculation based on augmented correlation-consistent double-, triple-, and quadruple-zeta basis sets, followed by a two-tier extrapolation to the complete basis set limit and complemented by a configuration interaction estimate of the core and core-valence correlations. The origin of binding in Be(2) as well as the unusual shape of its potential energy curve is elucidated by an in-depth analysis of the contributions of the various components of this wave function to the bonding process. Beyond the bonding region, the 6/8 London dispersion interaction is recovered.

Ab initio potential curves for the [formula omitted] and [formula omitted] states of [formula omitted]: Existence of a double minimum

We report ab initio calculations of the X 2 Σ u + and B 2 Σ g + states of the Be 2 + dimer. Full valence configuration interaction calculations were performed using the aug-cc-pVnZ basis sets and the results were extrapolated to the CBS limit. Core–core and core–valence effects are included at the CCSDT/MTsmall level of theory. Two local minima, separated by a large barrier, are found in the expected repulsive B 2 Σ g + state. Spectroscopic constants have been calculated and good agreement is found with the recent measurements of Merritt et al. Bound vibrational levels, transition moments and lifetimes have also been calculated.

Theoretical Study of 1Σ+ States of Alkali Hydride XH Molecule (X = Na, K and Rb) in Adiabatic and Nonadiabatic Representations

In this work, we present an adiabatic and nonadiabatic study for all the (1)Sigma(+) states dissociating below the ionic limits [i.e., Na (3s, 3p, 4s, 3d, 4p, 5s, 4d, 4f), K (4s, 4p, 5s, 3d, 5p, 4d, 6s, 4f) and Rb (5s, 5p, 4d, 6s, 6p, 5d, 7s, 4f) + H (1s)]. The ab initio calculations rely on pseudopotential, operatorial core valence correlation and full valence CI (configuration-interaction) approaches, combined to an efficient diabatization procedure. For the low-lying states, our vibrational level spacings and spectroscopic constants are in good agreement with the available experimental data. Nonadiabatic potentials and dipole moments are analyzed, revealing the strong imprint of the ionic state in the (1)Sigma(+) adiabatic states, while improving the results. This paper can be used as theoretical support for experimental work.

Accurate ab initio potential energy curve of F2. I. Nonrelativistic full valence configuration interaction energies using the correlation energy extrapolation by intrinsic scaling method

The recently introduced method of correlation energy extrapolation by intrinsic scaling (CEEIS) is used to calculate the nonrelativistic electron correlations in the valence shell of the F(2) molecule at 13 internuclear distances along the ground state potential energy curve from 1.14 A to 8 A, the equilibrium distance being 1.412 A. Using Dunning's correlation-consistent double-, triple-, and quadruple-zeta basis sets, the full configuration interaction energies are determined, with an accuracy of about 0.3 mhartree, by successively generating up to octuple excitations with respect to multiconfigurational reference functions that strongly change along the reaction path. The energies of the reference functions and those of the correlation energies with respect to these reference functions are then extrapolated to their complete basis set limits. The applicability of the CEEIS method to strongly multiconfigurational reference functions is documented in detail.