Relativistic four-component MRCISD+Q calculations of the six lowest valence states of molecular [Formula: see text] anion including breit interactions.

CONTEXT AND RESULTS: This study aimed to obtain potential energy curves within a multireference 4-component relativistic method and to present spectroscopic constants (R[Formula: see text],[Formula: see text],[Formula: see text]x[Formula: see text],[Formula: see text]y[Formula: see text], D[Formula: see text], D[Formula: see text], B[Formula: see text],[Formula: see text],[Formula: see text],[Formula: see text] ), accurate extended Rydberg analytical form, and rovibrational levels for the 6 low-lying states of the I[Formula: see text] anion. For these states, some spectroscopic constants, rovibrational levels, and an accurate analytical form are presented for the first time in literature, and they are of interest for femtosecond and dynamics experiments of I[Formula: see text] as well as for electron attachment of I[Formula: see text]. This study suggests that the inclusion of relativistic and correlation effects treated at the MRCISD+Q level is needed to obtain reliable results, specially for D[Formula: see text]. COMPUTATIONAL AND THEORETICAL TECHNIQUES: The potential energy curves of the ground and the excited states of the molecular iodine anion (I[Formula: see text]) were investigated at multireference configuration interaction (MRCISD) with Davidson size-extensivity correction (denoted as +Q) within a fully relativistic four-component relativistic framework including Breit interaction.

Electronic and dynamical properties of non-covalent diatomic aggregates formed by He with neutral and ionic Li and Be.

CONTEXT AND RESULTS: This work aims to study the influence of the absence and presence of permanent charges on the electronic and dynamical properties of the non-covalent bound diatomic systems involving He and Li, Be as neutral and ionic partners. The charge displacement results suggest that in the formation of HeLi[Formula: see text], HeBe[Formula: see text], and HeBe[Formula: see text], the neutral He atom undergoes, in the electric field of the ion, a pronounced electronic polarization, and the natural bond order theoretical approach indicates that in the formation of the molecular orbital He acts as a weak electron donor. The energy decomposition analysis provides the dispersion and induction components as the attractive leading terms controlling the stability of all systems, confirming that the formed bond substantially maintains a non-covalent nature which is also supported by the Quantum Theory of Atoms in Molecules (QTAIM) analysis. Finally, it was found that the HeLi and HeBe neutral systems are unstable under any condition, HeLi[Formula: see text] and HeBe[Formula: see text] ionic systems are stable below 317K and 138K, respectively, while the HeBe[Formula: see text] system becomes unstable only after 3045K. COMPUTATIONAL AND THEORETICAL TECHNIQUES: The potential energy curves and interactions in all systems were studied theoretically based on coupled-cluster singles and doubles method with perturbative inclusion of triples CCSD(T) method with an aug-cc-pV5Z basis set. More precisely, it was determined the potential energy curves describing the stability of the HeLi, HeLi[Formula: see text], HeBe, HeBe[Formula: see text], and HeBe[Formula: see text] systems, the charge displacement within the formed adducts, the decomposition of their total interaction energy, the topological analysis of their bonds, their rovibrational energies, their spectroscopic constants and lifetimes.

A Detailed Study of Electronic and Dynamic Properties of Noble Gas-Oxygen Molecule Adducts.

In this work, the binding features of adducts formed by a noble gas (Ng = He, Ne, Ar, Kr, Xe, and Rn) atom and the oxygen molecule (O2) in its ground Σg-3, in the past target of several experimental studies, have been characterized under different theoretical points of view to clarify fundamental aspects of the intermolecular bond. For the most stable configuration of all Ng-O2 systems, binding energy has been calculated at the theory's CCSD(T)/aug-cc-pVTZ level and compared with the experimental findings. Rovibrational energies, spectroscopic constants, and lifetime as a function of temperature were also evaluated by adopting properly formulated potential energy curves. The nature of the interaction involved was deeply investigated using charge displacement analysis, symmetry-adapted perturbation theory (SAPT), and natural bond orbital (NBO) methods. In all adducts, it was found that the charge transfer plays a minor role, although O2 is an open shell species exhibiting a positive electron affinity. Obtained results also indicate that the dispersion attraction contribution is the main responsible for the complex stability.

Fully relativistic study of polyatomic closed shell E121X3 (X = F, Cl, Br) molecules: effects of Gaunt interaction, relativistic effects and advantages of an exact-two component (X2C) hamiltonian.

In this study, all electron relativistic calculations with 4-component Dirac-Coulomb-Breit (DCB), 4-component Dirac-Coulomb (DC), Dyall's spin-free Dirac-Coulomb (SFDC), exact two-component (X2C) and Levy-Leblond non-relativistic hamiltonians calculations were performed in polyatomic closed shell E121X3 (X = F, Cl, Br) within density functional theory (DFT) with hybrid functional B3LYP, where E121 is the superheavy element (SHE) with Z = 121. The aims of this study were to investigate relativistic effects in polyatomic E121X3 (X = F, Cl, Br) and verify the importance of Gaunt effects. The results demonstrate that although the effect of Gaunt interaction is small on change equilibrium bond lengths and bonding, it is important to obtain reliable vibrational frequencies. Moreover, it is possible to use the X2C spin-free hamiltonian to lower computational costs in a fully relativistic investigation of polyatomics including the SHE of the 8th period. Finally, a comparison between electron localization function (ELF) analysis and Mulliken population analysis suggests bonding similarity between LaBr3 and E121Br3. Graphical Abstract Relativistic 4-Component calculations suggest bond similarity between LaBr3 and E121Br3.

Relativistic four-component MRCISD+Q calculations of the six lowest valence states of molecular F[Formula: see text] anion including Breit interactions.

In this study, the potential energy curves of the ground and the excited states of molecular fluorine anion (F[Formula: see text]) were investigated at multireference configuration interaction (MRCISD) with Davidson size-extensivity correction (denoted as +Q) within fully relativistic four-component relativistic framework including Breit interaction. Spectroscopic constants (Re, ωe, ωexe, ωeye, De,D0,Be, αe, ße, γe ), accurate extended Rydberg analytical form and rovibrational levels for ground state X:[Formula: see text] are presented, as well as spectroscopic constants for non dissociative excited states. For most states these spectroscopic constants are presented for the first time in literature and they are of interest for experimental studies, specially regarding electron attachment of F2. Results suggest that inclusion of relativistic effects at 4-component level and correlation effects treated at MRCISD+Q level are needed to obtain reliable results, which we report for X:[Formula: see text] ground state's Re, ωe and De the values of 1.999 Å, 391 cm- 1 and 1.22 eV, respectively.

Relativistic four-component potential energy curves for the lowest 23 covalent states of molecular astatine (At2).

The potential energy curves (PECs) of all covalent states of Molecular Astatine (At2) have been investigated in this work within a four-component relativistic framework using the MOLFDIR program package. The ground state was determined using multireference configuration interaction with all single and double excitations including Davidson size-extensivity correction (MRCISD+Q) whereas the 22 excited states were treated by complete open shell configuration interaction (COSCI). Spectroscopic constants (Re,ωe,ωexe,ωeye, De,Be,αe,ße,Te) are presented for all states as well as vertical excitations obtained at COSCI, MRCISD and MRCISD+Q levels. In addition, it is also presented accurate extended Rydberg analytical form for the ground state X: (1)0g+.

Theoretical Investigation on H2O2-Ng (He, Ne, Ar, Kr, Xe, and Rn) Complexes Suitable for Stereodynamics: Interactions and Thermal Chiral Rate Consequences.

Although molecular collisions of noble gases (Ng) can be theoretically used to distinguish between the enantiomers of hydrogen peroxide - H2O2 (HP), little is known about the effects of HP-Ng interactions on the chiral rate. In this work, the chiral rate as a function of temperature (CRT) between enantiomeric conformations of HP and Ng (Ng=He, Ne, Ar, Kr, Xe, and Rn) are presented at MP2(full)/aug-cc-pVTZ level of theory through a fully basis set superposition error (BSSE) corrected potential energy surface. The results show that: (a) the CRT is highly affected even at a small decrease in the height of trans-barrier; (b) its smallest values occur with Ne for all temperatures between 100 and 4,000 K; (c) that the decrease of CRT shows an inverse correlation with respect to the average valence electron energy of the Ng and (d) Ne and He may be the noble gases more suitable for study the oriented collision dynamics of HP. In addition to binding energies, the electron density ρ and its Laplacian ∇2 ρ topological analyses were also performed within the atoms in molecules (AIM) theory in order to determine the nature of the HP-Ng interactions. The results of this work provide a more complete foundation on experiments to study HP's chirality using Ng in crossed molecular beams without a light source.