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Relativistic coupled-cluster calculations of the ionization potential, dissociation energy, and excited electronic states under 35,000 cm$^{-1}$ are presented for the actinium monofluoride (AcF) molecule. The ionization potential is calculated to be IP$_e=48,866$ cm$^{-1}$, and the ground state is confirmed to be a closed-shell singlet and thus strongly sensitive to the $\mathcal{T}$,$\mathcal{P}$-violating nuclear Schiff moment of the Ac nucleus. Radiative properties and transition dipole moments from the ground state are identified for several excited states, achieving an uncertainty of $\sim$450 cm$^{-1}$ for the excitation energies. For higher-lying states that are not directly accessible from the ground state, possible two-step excitation pathways are proposed. The calculated branching ratios and Franck-Condon factors are used to investigate the suitability of AcF for direct laser cooling. The lifetime of the metastable $(1)^3\Delta_1$ state, which can be used in experimental searches of the electric dipole moment of the electron, is estimated to be of order 1 ms.

Generalized relativistic pseudopotentials (GRPP) of atomic cores implying the use of different potentials for atomic electronic shells with different principal quantum numbers give rise to accurate and reliable relativistic electronic structure models of atoms, molecules, clusters, and solids. These models readily incorporate the effects of Breit electron–electron interactions and one-loop quantum electrodynamics effects. Here, we report the computational procedure for evaluating one-electron integrals of GRPP over contracted Gaussian functions. This procedure was implemented in a library of routines named LIBGRPP, which can be integrated into existing quantum chemistry software, thus enabling the application of various methods to solve the many-electron problem with GRPPs. Pilot applications to electronic transitions in the ThO and UO2 molecules using the new library and intermediate-Hamiltonian Fock space relativistic coupled cluster method are presented. Deviations of excitation energies obtained within the GRPP approach from their all-electron Dirac–Coulomb–Gaunt counterparts do not exceed 50 cm−1 for the 31 lowest-energy states of ThO and 110 cm−1 for the 79 states of UO2. The results clearly demonstrate that rather economical tiny-core GRPP models can exceed in accuracy relativistic all-electron models defined by Dirac–Coulomb and Dirac–Coulomb–Gaunt Hamiltonians.

We report the value of the electric quadrupole moment of $^{209}\mathrm{Bi}$ extracted from the atomic data. For this, we performed electronic structure calculations for the ground $^{4}S_{3/2}^{o}$ and excited $^{2}P_{3/2}^{o}$ states of atomic Bi using the Dirac-Coulomb-Breit Hamiltonian and the Fock space coupled-cluster method with single, double, and full triple amplitudes for the three-particle Fock space sector. The value of the quadrupole moment of $^{209}\mathrm{Bi}, Q{(}^{209}\mathrm{Bi})=\ensuremath{-}418(6)$ mb, derived from the resulting electric field gradient values and available atomic hyperfine splittings is in excellent agreement with molecular data. Due to the availability of the hyperfine constants for unstable isotopes of Bi, current atomic calculation allows also to correct their quadrupole moments.

Modern molecular spectroscopy of diatomic molecules is the precision study of the structure and dynamics of electronically excited states of isolated molecules in the gas phase. At the same time, the energy, radiation, magnetic, and electrical characteristics of excited molecules, which are of interest for different physicochemical applications, must be determined and predicted at the experimental (spectral) level of accuracy in a broad range of electron vibrational and rotational excitations. This problem cannot be solved within spectroscopy’s traditional adiabatic approximation, since a large number of intramolecular interactions (so-called perturbations) inevitably distorts not only the regular energy structure of different levels but he nodal structure of the corresponding wave functions as well. The most accurate solution to both direct and inverse spectroscopic problems with respect to perturbed molecular states is based on constructing a reduced system of the coupled radial Schrodinger equations encountered in the quantum-mechanical modeling of the nonadiabatic interaction of electronic states. The nonadiabatic approach can be employed successfully only through the joint use of precision spectroscopic data and highly precise calculations of electronic structure.

The determination of the matrix elements of single-electron operators for the transitions between electronic states (primarily, the dipole moments of electron transitions) is one of the critical problems in simulating the atomic and molecular spectra. In this study, the efficiency of a simple version of the finite-field method for calculating these values within the Fock-space coupled-cluster theory has been investigated.

Chemical shifts of the Kα1 and Kα2 lines (the 2p3/2 → 1s1/2 and 2p1/2 → 1s1/2 transitions, respectively) of the X-ray emission spectrum of the Yb atom in fluorides have been calculated by ab initio modeling the electronic structure. The valence transition Yb(II) → Yb(III) has been analyzed by examples of YbF2, YbF3, and Yb2F4 molecules and YbF2+ cation. The relativistic pseudopotential and basis sets corresponding to it have been constructed for the ytterbium atom. They were used in calculations by the two-component noncollinear version of the density functional theory (DFT) with the PBE0 exchange-correlation functional. Results for the three-coordinated Yb(II) in the FYbF2YbF dimer demonstrated a very weak dependence of the chemical shift on the coordination number of the Yb atom and on the molecular association of ytterbium difluoride. Chemical shifts of the X-ray emission spectrum for the ytterbium compound are related mainly to the change in the occupation of the 4 f shell.

Chemical shifts of the Kα1 and Kβ1 lines of X-ray-emission spectra of niobium in oxides (Nb2O5)n, n = 1–4, relative to metal Nb have been calculated. Stoichiometric clusters (Nb2O5)n the electronic structure of which was calculated using accurate relativistic pseudopotentials and two-component version of the density functional theory are considered as prototypes for modeling different crystal forms of niobium(V) oxide. The chemical shifts were calculated using the method based on using the property of approximate proportionality of valence spinors in the core region of the heavy atom [11]. Corrections to values of chemical shifts have been determined with allowance for deviations from the abovementioned proportionality. Rapid convergence of results with respect to the size of the niobium oxide cluster has been demonstrated.

The Ti:Saphire laser operated within 13800 - 11800 cm − 1 range was used to excite the c 3 Σ + state of KCs molecule directly from the ground X 1 Σ + state. The laser-induced fluorescence (LIF) spectra of the c 3 Σ + → a 3 Σ + transition were recorded with Fourier-transform spectrometer within 8000 to 10000 cm − 1 range. Overall 673 rovibronic term values belonging to both e / f -components of the c 3 Σ + ( Ω = 1 ± ) state of 39 KCs, covering vibrational levels from v = 0 to about 45, and rotational levels J ∈ [ 11 , 149 ] were determined with the accuracy of about 0.01 cm − 1 ; among them 7 values for 41 KCs. The experimental term values with v ∈ [ 0 , 22 ] were involved in a direct point-wise potential reconstruction for the c 3 Σ + ( Ω = 1 ± ) state, which takes into account the Ω -doubling effect caused by the spin-rotational interaction with the nearby c 3 Σ + ( Ω = 0 − ) state. The analysis and interpretation were facilitated by the fully-relativistic coupled cluster calculation of the potential energy curves for the B 1 Π , c 3 Σ + , and b 3 Π states, as well as of spin-forbidden c − X and spin-allowed c − a transition dipole moments; radiative lifetimes and vibronic branching ratios were calculated. A comparison of relative intensity distributions measured in vibrational c → a LIF progressions with their theoretical counterparts unambiguously confirms the vibrational assignment suggested in [J. Szczepkowski, et al., JQSRT, 204, 133–137 (2018)].

We report first-principle based studies of the adsorption interaction of astatine species on a gold surface. These studies are aimed primarily at the support and interpretation of gas chromatographic experiments with superheavy elements, tennessine (Ts, Z = 117 ), a heavier homologue of At, and possibly its pseudo-homologue nihonium (Nh, Z = 113 ). We use gold clusters with up to 69 atoms to simulate the adsorption sites and estimate the desorption energies of At & AtOH from a stable gold (1 1 1) surface. To describe the electronic structure of At - Au n and AtOH - Au n complexes, we combine accurate shape-consistent relativistic pseudopotentials and non-collinear two-component relativistic density functional theory. The predicted desorption energies of At and AtOH on gold are 130 ± 10 kJ/mol and 90 ± 10 kJ/mol, respectively. These results confirm the validity of the estimates derived from chromatographic data ( 147 ± 15 kJ/mol for At, and 100 - 10 + 20 kJ/mol for AtOH).

The spin-orbit (SO) interactions in low-lying electronic states of the LiM (M = Na, K, Rb, Cs) molecular series are studied through ab initio calculations of potential energy curves and SO coupling matrix elements as functions of the interatomic distance, R. Two different approaches are employed: (a) the Fock-space relativistic coupled-cluster calculations (FS-RCC) which directly yield full relativistic energies, Urel(R); the SO coupling functions, ξso(R), are extracted a posteriori through projecting scalar-relativistic wave functions onto the subspaces spanned by their full-relativistic counterparts; (b) the evaluation of the scalar-relativistic electronic energies, Usr(R), and relevant ξso(R) functions using the configuration interaction method with core-valence correlation accounted for using core polarization potentials (CI-CPP). The SO-free potentials and SO coupling functions obtained within the framework of both approaches are in good agreement with each other and their prior theoretical and empirical counterparts.

Radium compounds have attracted recently considerable attention due to both development of experimental techniques for high-precision laser spectroscopy of molecules with short-lived nuclei and amenability of certain radium compounds for direct cooling with lasers. Currently, radium monofluoride (RaF) is one of the most studied molecules among the radium compounds, both theoretically and recently also experimentally. Complementary studies of further diatomic radium derivatives are highly desired to assess the influence of chemical substitution on diverse molecular parameters, especially on those connected with laser cooling, such as vibronic transition probabilities, and those related to violations of fundamental symmetries. In this article high-precision \emph{ab initio} studies of electronic and vibronic levels of diatomic radium monochloride (RaCl) are presented. Recently developed approaches for treating electronic correlation with Fock-space coupled cluster methods are applied for this purpose. Theoretical results are compared to an early experimental investigation by Lagerqvist and used to partially reassign the experimentally observed transitions and molecular electronic levels of RaCl. Effective constants of $\mathcal{P}$-odd hyperfine interaction $W_{\rm{a}}$ and $\mathcal{P,T}$-odd scalar-pseudoscalar nucleus-electron interaction $W_{\rm{s}}$ in the ground electronic state of RaCl are estimated within the framework of a quasirelativistic Zeroth-Order Regular Approximation approach and compared to parameters in RaF and RaOH., Comment: 18 pages, 2 figures, 5 tables

Modern challenges arising in the fields of theoretical and experimental physics require new powerful tools for high-precision electronic structure modelling; one of the most perspective tools is the relativistic Fock space coupled cluster method (FS-RCC). Here we present a new extensible implementation of the FS-RCC method designed for modern parallel computers. The underlying theoretical model, algorithms and data structures are discussed. The performance and scaling features of the implementation are analyzed. The software developed allows to achieve a completely new level of accuracy for prediction of properties of atoms and molecules containing heavy and superheavy nuclei.

The 4503 rovibronic term values belonging to the mutually perturbed $A^1\Sigma^+_u$ and $b^3\Pi_u$ states of Cs$_2$ were extracted from laser induced fluorescence (LIF) $A\sim b\rightarrow X^1\Sigma^+_g$ Fourier transform spectra with the 0.01 cm$^{-1}$ uncertainty. The experimental term values of the $A^1\Sigma^+_u\sim b^3\Pi_u$ complex covering the rotational levels $J\in [4,395]$ in the excitation energy range $[9655,13630]$ cm$^{-1}$ were involved into coupled-channel (CC) deperturbation analysis. The deperturbation model takes explicitly into account spin-orbit coupling of the $A^1\Sigma^+_u(A0^+_u)$ and $b^3\Pi^+_{0_u}(b0^+_u)$ states as well as spin-rotational interaction between the $\Omega=0$, $1$ and $2$ components of the $b^3\Pi^+_{\Omega_u}$ state. The \emph{ab initio} relativistic calculations on the low-lying electronic states of Cs$_2$ were accomplished in the framework of Fock space relativistic coupled cluster (FSRCC) approach to provide the interatomic potentials of the interacting $A0^+_u$ and $b0^+_u$ states as well as the relevant $A\sim b$ spin-orbit coupling function. To validate the present CC deperturbation analysis solely obtained by energy-based data, the $A\sim b \to X(v^{\prime\prime}_X)$ LIF intensity distributions were measured and compared with their theoretical counterparts obtained by means of the non-adiabatic vibrational wave functions of the $A\sim b$ complex and the FSRCC $A\sim b \to X$ transition dipole moments calculated by the finite-field method.

The spin-forbidden a 3 Π − X 1 Σ + , a ′ 3 Σ + − X 1 Σ + and spin-allowed A 1 Π − X 1 Σ + electronic transitions dipole moments of carbon monoxide have been ab initio studied in the framework of multi-reference Fock space coupled cluster method combined with the finite-field approach and the generalized relativistic pseudo-potential model for the effective introducing the relativity in all-electron correlation treatment. Radiative lifetimes, τ i ( v ′ , J ′ ) , of the upper i ∈ [ a 3 Π , A 1 Π ] states were evaluated as a function of vibrational, v ′ , and rotational, J ′ , quantum numbers. The τ a -values derived for the triplet a 3 Π 1 ( 0 , 1 ) and a 3 Π 2 ( 0 , 2 ) states at the highest level of computation were found to be 2.59 and 142 ms, which are near perfect agreement with their best experimental counterparts (J. J. Gilijamse, et al., J. Chem. Phys., 127, 221102 (2007)). The intercombination a − X , a ′ − X transition probabilities were numerically proved to be proportional to α 2 , where α = e 2 / ℏ c is the fine structure constant.

We observed the A 1 Σ + ∼ b 3 Π → a 3 Σ + / X 1 Σ + laser-induced fluorescence (LIF) of the RbCs molecule excited from the ground X 1 Σ + state by the Ti:Sapphire laser. The LIF spectra from the common perturbed levels of the singlet-triplet A ∼ b complex was recorded by the Fourier-transform (FT) spectrometer with the instrumental resolution of 0.03 cm − 1 . The relative intensity distribution in the rotationally resolved A ∼ b → a 3 Σ + ( v a ) / X 1 Σ + ( v X ) progressions was measured, and their branching ratio was found to be about of 1 ÷ 5 × 10 − 4 in the bound region of the a 3 Σ + and X 1 Σ + states. The experiment was complemented with the scalar- and full-relativistic calculations of the A / b − X / a transition dipole moments (TDMs) as functions of internuclear distance. The relative systematic error in the resulting ab initio TDM functions evaluated for the strong A − X transition was estimated as few percent in the energy region, where the experimental LIF intensities are relevant. The relative spectral sensitivity of the FT registration system, operated with the InGaAs diode detector and CaF beam-splitter, was calibrated in the range [6 500, 12 000] cm − 1 by a comparison of experimental intensities in the long A ∼ b → X(vX) LIF progressions of the K2 and KCs molecules with their theoretical counterparts evaluated using the ab initio A − X TDMs. Both experimental and theoretical transition probabilities can be employed to improve the stimulated Raman adiabatic passage process, a → A ∼ b → X, which is exploited for a laser assembling of ultracold RbCs molecules.

The four-component relativistic Fock space coupled cluster method is used to describe the magnetic hyperfine interaction in low-lying electronic states of the KCs molecule. Both diagonal and off-diagonal matrix elements as functions of the internuclear separation $R$ are calculated within the finite-field scheme. The resulting matrix elements exhibit very weak dependence on $R$ for the separations exceeding 8 \AA , whereas in the vicinity of the ground-state equilibrium the deviation of molecular HFS matrix elements from the atomic values reaches 15\%. The dependence of the computed HFS couplings on the level of core correlation treatment is discussed., Comment: 3 figures

The Fock space relativistic coupled cluster method (FS-RCC) is one of the most promising tools of electronic structure modeling for atomic and molecular systems containing heavy nuclei. Until recently, capabilities of the FS-RCC method were severely restricted by the fact that only single and double excitations in the exponential parametrization of the wave operator were considered. We report the design and the first computer implementation of FS-RCC schemes with full and simplified non-perturbative account for triple excitations in the cluster operator. Numerical stability of the new computational scheme and thus its applicability to a wide variety of molecular electronic states is ensured using the dynamic shift technique combined with the extrapolation to zero-shift limit. Pilot applications to atomic (Tl, Pb) and molecular (TlH) systems reported in the paper indicate that the breakthrough in accuracy and predictive power of the electronic structure calculations for heavy-element compounds can be achieved. Moreover, the described approach can provide a firm basis for high-precision modeling of heavy molecular systems with several open shells, including actinide compounds.

We present a study of electronic structure and chemical properties of monohydroxide molecules of element 113 (E113), Tl, and At employing accurate relativistic pseudpotentials. Electron correlations are treated at the coupled cluster (CCSD(T)) level, and spin-dependent relativistic effects included using two-component relativistic density functional theory. Our estimates for hydroxyl group elimination at 0 K for E113OH, TlOH, and AtOH are, respectively, 1.95, 3.31, and 1.80 eV. We discuss striking differences in the chemical properties of E113 and Tl and certain similarities in the behavior of E113(I) and At(I).

Actinide compounds are very intriguing objects for the quantum chemistry because, on the one hand, these compounds are of great scientific and technological interest and, on the other hand, quantitative first principle based modeling of their electronic structure is extremely difficult because of strong relativistic effects and complicated electron correlation pattern. The efficiency of high-level all-electron relativistic methods in applications to complex actinide systems of practical interest is questionable and more economical but sufficiently accurate approaches to the studies of such systems are preferable. Recently, generalized relativistic effective core potentials (GRECPs) have been generated for actinides to perform accurate calculations of electronic structure and properties of their compounds with moderate computational cost. The accuracy of different GRECP versions is analyzed in atomic calculations and their applications to molecular and cluster calculations are reviewed. The results are compared with available experimental data and other theoretical studies. © 2015 Wiley Periodicals, Inc.

Ground-state equilibrium geometries, energetics, and vibrational frequencies of AnO3 molecules, An = Pu through Cf, and their isomers are calculated using an accurate small-core pseudopotential model and the two-component relativistic density functional theory. The qualitative features of chemical bonding in these molecules are discussed in terms of oxidation states and bond orders. The actinide oxidation state (VI) is reached only in the plutonium trioxide molecule, whereas heavier actinide atoms in T-shaped trioxide molecules should be considered as pentavalent. At least at low temperatures, PuO3 and, to a lesser degree, AmO3 and BkO3 molecules should be stable both with respect to the isomerization into oxoperoxides or oxosuperoxides and the decay into dioxides and molecular oxygen. These trioxides can form dimers with significant (above 250 kJ mol(-1)) dissociation energies; the oxidation states of actinide atoms in the lowest-energy configurations of these dimers coincide with those in the corresponding monomers. The ability to reach high oxidation states in oxygen compounds gradually decreases from Pu onwards, with the only exception being the unexpectedly stable Bk(v)O3.

The review covers main methods of the first-principle based electronic structure simulation used for the prediction of the properties of superheavy element atoms and compounds. The areas of applicability of these methods and the principal and practical limitations of their accuracy are analyzed. The regularities in the changes of the chemical properties on going from superheavy elements to their closest homologs are discussed.

Molecular properties of the thallium monocyanide (Tl&middot, CN) system in its ground electronic state are studied using high-precision ab initio relativistic two-component pseudopotential replacing 60 inner-core electrons of Tl. A relativistic coupled-cluster method with single, double and perturbative triple amplitudes is employed to account for electronic correlations. Extrapolation of results to the complete basis set limit is used for all studied properties. The global potential energy minimum of Tl&middot, CN corresponds to the linear cyanide (TlCN) isomer, while the non-rigid isocyanide-like (TlNC) structure lies by approximately 11 kJ/mol higher in energy. The procedure of restoration of the wavefunction in the &ldquo, core&rdquo, region of Tl atom was applied to calculate the interaction of the Tl nuclear Schiff moment with electrons. The parameter X of the interaction of the Tl nuclear Schiff moment with electrons in the linear TlCN molecule equals 7150 a.u. The prospects of using the TlCN molecule for the experimental detection of the nuclear Schiff moment are discussed.

Equilibrium structures and energetics of various isomers of molecules with stoichiometry An·4O (An = Pu, Am, and Cm) are studied through electronic structure calculations at the relativistic density functional theory level in the frame of an accurate small-core pseudopotential model. In all cases, the global minima of the An·4O potential energy surfaces correspond to dioxo-superoxido-like species, [AnO2](O2). The stability of the “true” oxides AnO4 decreases from Pu to Cm, whereas the isomers with two O2 groups become relatively more stable. Correlation between the formal oxidation states and the Bader net charges of actinide atoms is discussed. Structural parameters, vibrational frequencies and charge and spin magnetization density distributions are analyzed in order to characterize the different isomers in chemical terms. Decrease of the An oxidation states along the An series is evident.

The electronic structure and energetics were calculated for molecules of binary compounds of element 120 and its homologs with common elements strongly differing in chemical properties. The calculations were performed within the framework of the relativistic density functional theory using the model of precision two-component atomic core pseudopotentials. The results obtained show that all the examined compounds of element 120 should differ from the corresponding compounds of the known heavy metals of the second group (Sr-Ra) in lower strengths and larger lengths of chemical bonds. Therefore, one can suppose that element 120 will be, on the whole, more inert chemically than its nearest homologs.

Structures and energetics of the molecular anions UF 6 − , UF5/−, UF4/−, UO3/t-, and UO2/t- were calculated using the density functional theory within the framework of the precision two-component relativistic pseudopotential model. Differences in the structures of the ions and the corresponding neutral molecules were analyzed, and the adiabatic electron affinities of these molecules were estimated.

The potential curve, dissociation energy, equilibrium internuclear distance, and spectroscopic constants for the ground state of the Ca2 molecule are calculated with the help of the generalized relativistic effective core potential method, which allows one to exclude the inner core electrons from the calculations and to take the relativistic effects into account effectively. Extensive generalized correlation basis sets were constructed and used. The scalar relativistic coupled cluster method with corrections for high-order cluster amplitudes is used for the correlation treatment. The results are analyzed and compared with the experimental data and corresponding all-electron results. © 2013 Wiley Periodicals, Inc.

Pilot applications of Pade-resummed fourth-order many-body perturbation theory to the description of chemical bonds with strong contributions from the interactions of filled d-shells (Au–Au, Au–Hg, and Hg–Hg) are reported. The employed Pade approximants, especially the constrained [0/1, 1] quadratic one, ensure radical improvements of accuracy with respect to the partial summation. The non-separability problem is discussed and bypassed through the direct resummation of perturbative expansions for differential correlation energies.

The conditions are analyzed under which the dissociative attachment of electrons determines the properties of a nonequilibrium glow discharge plasma containing metal halides. The possibility of applying a simplified approach for the estimation of dissociative attachment and vibrational excitation cross sections of metal halides by combining quantum and semiclassical methods is discussed. By way of example, processes in a nonequilibrium Ar-SnI2 plasma are analyzed in detail.

Relativistic pseudopotential approach to the electronic structure simulation of superheavy elements (SHE) compounds is presented. Advanced formulations of this approach leaving both valence and outer-core electronic shells for explicit treatment give rise to simple and efficient computational techniques ensuring highly accurate description of most chemical properties of SHE. At present, the errors due to the use of approximate methods for solving the correlation problem for a subsystem of valence electrons are much larger than those stemming from the pseudopotential approximation itself. Recent applications to the studies of the chemistry of elements 112 (eka-Hg) and 114 (eka-Pb) are reviewed; properties of these elements and their lighter homologues, Hg and Pb, are compared.

The ground electronic state of the eka-mercury dimer (E1122) was studied within the model of generalized relativistic effective core potentials. A combined procedure based on describing correlation effects by the scalar relativistic coupled-cluster method and on taking into account spin-dependent interactions by means of density-functional theory was used in the calculations. A high accuracy of this approach was confirmed by the results of similar calculations for the mercury dimer. It was found that the bond length is nearly 0.4 A shorter in E1122 than in Hg2 and that the dissociation energy of the former is approximately twice as high as that of the latter dimer.

An analysis of theoretical studies on the electronic structures and chemical properties of superheavy elements has been performed. It is noted that the specific features of calculations of molecular systems including superheavy element atoms are determined by the exceptional role of relativistic effects that should be taken into account at all stages of electronic structure modelling. The main approximations for relativistic Hamiltonians and general approaches to the solution of the many-electron problem for both superheavy element atoms and their compounds have been considered and compared. The results of modelling the chemical properties of superheavy elements by ab initio methods and density functional theory have been analysed.

Present-day computational techniques provide a possibility of evaluating properties of macrosystems using ab initio quantum chemistry and theories of elementary processes. Physical and chemical phenomena on very different timescales have to be taken into account (excitation, emission, chemical reactions, diffusion) at different levels of refining. This refining covers a very wide region of parameters starting from the structure of species up to the macro chemical mechanism of their conversion. This multilevel approach is described in detail in the paper and includes interaction and data transfer between different levels of phenomena description. In the framework of the approach, unknown properties of molecules, ions and atoms (structure, potential energy curves, transition dipole moments) are calculated based on quantum-chemical methods. The calculation results are used to evaluate rate characteristics of physical and chemical processes. The developed kinetic state-to-state scheme is then used to calculate the macro properties of the system under investigation. As an example of the multilevel approach, the emission properties of the Ar–GaI3 positive column discharge plasma were calculated using the Chemical Work Bench computational environment. The calculations yield the electron energy balance and emission efficiency as functions of plasma parameters.

Electron impact excitation cross sections of dipole-allowed transitions in diatomic molecules have been evaluated using the similarity function method allowing one to express cross sections through the oscillator strength of the transition and some universal function of the reduced incident electron energy. The necessary characteristics of the molecular terms involved and transition dipoles were determined by ab initio electronic structure calculations using the multireference configuration interaction technique or relativistic multipartitioning many-body perturbation theory. The results of specific calculations performed for CO and NO in a reasonable agreement with the available experimental data and the results of comprehensive quantum-mechanical calculations.

Radiative lifetimes for 2≤v′≤44 rovibronic C1Σ+ state levels of NaRb and quenching collision cross-sections with Rb atoms have been directly measured in a thermal cell by detecting time resolved laser induced fluorescence after pulsed excitation. Many body multipartitioning theory was applied to calculate C1Σ+-X1Σ+ and C1Σ+-A1Σ+ transition dipole moments. The relevant ab initio matrix elements were converted to the C1Σ+ state radiative lifetimes. The strong spin-orbit A1Σ+∼ b3Π coupling effect on the total C → A transition probabilities and lifetimes of the C1Σ+ state is discussed. The measured radiative lifetimes show a decrease from 61 to 34 ns as the v′ values increase, the results being in good agreement with calculations. The averaged collisional quenching cross-section value σ=(3±1)×10-14 cm2 was determined for NaRb (C1Σ+) + Rb collisions from the Stern-Volmer plots.

Interactions of Cn (element 112) atom with small Au clusters are studied using accurate ab initio scalar relativistic coupled cluster method for correlation treatment and two-component relativistic density functional theory (RDFT) to take account of spin-dependent relativistic effects. The results demonstrate the failure of RDFT with simple generalized-gradient and hybrid functionals in describing Cn–Au bonds in complex systems. © 2013 Wiley Periodicals, Inc.

The multipartitioning form of the second-order many-body perturbation theory for state-selective effective Hamiltonians is adapted to stabilization calculations of temporary molecular anionic states. We restrict our attention to the simplest case of a system composed of a closed-shell-like molecule and an electron. Pilot applications to the description of the 2Πg state of the nitrogen molecular anion and the 2Π state of CO− are reported.

The new concept of atoms in compounds (AiC) is used to derive effective atomic configurations of plutonium and transplutonium elements in higher oxide molecules from the results of DFT calculations.

Quasirelativistic multipartitioning many-body perturbation theory is applied to ab initio calculations on electronic transitions in the gold dimer. Potential energy functions and spectroscopic constants for low-lying excited states and transition dipole moment functions for main radiative decay channels of experimentally observed states are reported.

We present a simple method of ab initio calculations on the systems composed of a closed-shell-like molecule (atom) and a weakly bound electron via constructing a state-specific effective Hamiltonian in a model space generated by placing the extra electron on virtual self-consistent field orbitals of the neutral species in all the possible ways. Correlation contributions are incorporated into the effective Hamiltonian by the second-order multipartitioning many-body perturbation theory. The method prevents the appearance of intruder states without destroying the exact size consistency of results and ensures a proper description of the dynamic correlation effects on the spatial localization of the extra electron and continuous behavior of computed characteristics under variations of molecular geometry. A detailed study of perturbative solutions for a model problem with parameter-dependent Hamiltonian and test calculations of Ca, Sr, and Ba atomic anions are reported. The method is also applied to the description of the hypothetical symmetrical isomer of water dimer anion with the extra electron trapped between the water molecules. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

The paper presents the study of the fully mixed A 1Σ+–b 3Π complex of the NaRb molecule based on high-resolution sub-Doppler spectroscopy and intensity measurements, ab initio relativistic calculations of energies, transition moments and spin–orbit interactions, as well as an inverted channel-coupling approach (ICCA) deperturbation analysis. A two-laser V-type pump–probe excitation scheme was employed to obtain A←X transition frequencies to 16 A-state vibrational levels from v=6 to v=21 with J from 8 to 23. Additionally, relative intensities in laser-induced A→X fluorescence spectra have been recorded, including progressions with all observable transitions to the ground state vibronic levels, the latter yielding unambiguous v assignment of the A-state levels observed. All experimental rovibronic term values and all measured intensity distributions were embedded in a direct simultaneous weighted nonlinear fitting in the framework of an elaborated ICCA allowing us to obtain deperturbed relativistic diabatic...

A quasirelativistic perturbative method of ab initio calculations on ground and excited molecular electronic states and transition properties within the relativistic effective core potential approximation is presented and discussed. The method is based on the construction of a state-selective many-electron effective Hamiltonian in the model space spanned by an appropriate set of Slater determinants by means of the second-order many-body multireference perturbation theory. The neglect of effective spin–orbit interactions outside of the model space allows the exploitation of relatively high nonrelativistic symmetry during the evaluation of perturbative corrections and therefore dramatic reduction of the cost of computations without any contraction of the model-space functions. One-electron transition properties are evaluated via the perturbative construction of spin-free transition density matrices. Illustrative calculations on the X0+ − A1, B0+, and (ii)1 transitions in the ICl molecule are reported. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Recently a number of diatomic and polyatomics molecules has been identified as a prospective systems for Doppler/Sisyphus cooling. Doppler/Sisyphus cooling allows to decrease the kinetic energy of molecules down to microkelvin temperatures with high efficiency and then capture them to molecular traps, including magneto-optical trap. Trapped molecules can be used for creation of molecular fountains and/or performing controlled chemical reactions, high-precision spectra measurements and a multitude of other applications. Polyatomic molecules with heavy nuclei present considerable interest for the search for "new physics" outside of Standard Model and other applications including cold chemistry, photochemistry, quantum informatics etc. Herein we would like to attract attention to radium monohydroxide molecule (RaOH) which is on the one hand an amenable object for laser cooling and on the other hand provides extensive possibilities for searching for P-odd and P,T-odd effects. At the moment RaOH is the heaviest polyatomic molecule proposed for direct cooling with lasers., Comment: 14 pages, 2 figures, 2 tables, figures are changed for better representation of the results, supplementary materials added