Relativistic electronic structure theory

The theoretical and technical foundations are presented for the efficient relativistic electronic structure theories to treat heavy-atomic molecular systems. This review contains two surveys of four-component and two-component quasi-relativistic approaches. First, we review our highly efficient computational scheme for four-component relativistic ab initio molecular orbital (MO) methods over generally contracted spherical harmonic Gaussian-type spinors (GTSs). Illustrative calculations, which are performed with a new four-component relativistic ab initio molecular orbital program package REL4D, clearly show the efficiency of our computational scheme by the Dirac-Hartree-Fock (DHF) and Dirac-Hartree-Fock (DKS) methods. Next, in the two-component quasi-relativistic framework, two relativistic Hamiltonians, RESC and higher order Douglas-Kroll (DK) Hamiltonians, are introduced, and several illustrative calculations are shown. Numerical results for several systems show that good accuracy can be obtained with our third-order DK (DK3) Hamiltonian.     

Relativistic effects on the electronic structure of allyl mercury

Conclusions Relativistic effects can destabilize the -complexes of allyl mercury compounds and weaken the effects of , conjugation, which leads to a decrease in the first ionization potentials; their effect on the distribution of electron density in the allyl mercury molecule (manifested, in particular, by a decrease in the positive charge on the mercury atom) is almost independent of the conformation of the molecule.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1570–1573, July, 1989.     

Theoretical electronic structure of the molecule ScBr

The potential energy curves have been investigated for the 23 lowest electronic states in the ^2s+1Λ^± representation of the molecule ScBr via CASSCF and MRCI (single and double excitations with Davidson correction) calculations. Seventeen electronic states have been studied theoretically for the first time. The harmonic frequency ω_e, the internuclear distance r_e, and the electronic energy with respect to the ground state T_e have been calculated. By using the canonical functions approach, the eigenvalues E_v, the rotational constant B_v, and the abscissas of the turning points (R_min, R_max) have been calculated for electronic states up to the vibrational level v = 32. The comparison of these values to the theoretical and experimental results available in the literature shows a good agreement. © 2007 Wiley Periodicalsm Inc. Int J Quantum Chem, 2008     

Theoretical electronic structure of the molecule ScI

Theoretical investigation of the 18 lowest electronic states of the molecule ScI in the representation ^2S+1Λ^(±) has been performed via CASSCF and MRCI (single and double excitation with Davidson correction) calculations. To the best of our knowledge these calculated electronic states are the first ones from ab initio methods. Thirteen electronic states between 4,500 cm^?1 and 21,000 cm^?1 have been studied for the first time and have not yet been observed experimentally. The harmonic frequency ω_e, the internuclear distance R_e, the electronic transition energy with respect to the ground state T_e, and the rotational constant B_e have been calculated for the considered electronic states. By using the canonical functions approach the eigenvalues E_υ and the rotational constants B_υ have also been calculated for the six lowest‐lying electronic states. The comparison of these results with the theoretical and the experimental data available in the literature shows a good agreement. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Spatial and electronic structure of the BEDT-TTF molecule

The spatial structure of the molecule of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) has been determined by the semiempirical SCF-MO-LCAO method in the all-valence-electron MNDO approximation with the use of the formalism of the restricted Hartree-Fock method, and its principal energy and charge characteristics have been calculated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, pp. 352–355, May–June, 1986.We thank I. I. Ukrainskii for taking an interest in the work and V. A. Zaits for providing the program and helping in the performance of the calculations.     

A separated-electron pair study of the electronic structure of the Li2O molecule

A separated pair calculation of the electronic structure of the Li₂O molecule is described. Rather extensive calculations were made of the potential surface for symmetric configurations of Li₂O using a double zeta Slater orbital basis. A linear configuration with LiO bond length of 1.71 Å is found to be most stable. The electron distribution and correlation effects are discussed.     

Broken symmetry in the electronic structure of the ferrocene molecule

Attempts to calculate the metal–ring distance in the ferrocene molecule using a well-tried minimal basis reveal serious deficiencies in the minimal-basis SCF model of the electronic structure of organometallics. It is found that the lowest state of the molecule in this approximation is a triplet and that there is a whole manifold of “states” in the ground-state region that have broken spatial symmetry and high-spin multiplicity.     

The electronic spectrum of the UO2 molecule

The electronic spectrum of the UO(2) molecule has been determined using multiconfigurational wave functions together with the inclusion spin-orbit coupling. The molecule has been found to have a (5fphi)(7s), (3)Phi(2u), ground state. The lowest state of gerade symmetry,( 3)H(4g), corresponding to the electronic configuration (5f)(2) was found 3330 cm(-1) above the ground state. The computed energy levels and oscillator strengths were used for the assignment of the experimental spectrum in the energy range 17,000-19,000 and 27,000-32,000 cm(-1).     

Theoretical electronic structure of the lowest-lying states of the YI molecule

CAS-SCF/MRCI calculations have been performed for 15 molecular states in the representation ^2S+1Λ^(+/−) (neglecting spin–orbit effects) for the molecule YI. The corresponding 33 molecular states in the representation Ω^(+/−) (including spin–orbit effects) have been calculated using a semi-empirical spin–orbit pseudopotential built up for yttrium. Calculated potential energy curves and spectroscopic constants are reported, to the best of our knowledge they are the first ones from ab initio methods for this molecule. Present results are compared to experimental accurate data available for the ground X¹Σ⁺ and 3 excited states (1)¹Π, (2)¹Σ⁺ and (2)¹Π.     

Ultrasoft X-ray emission and the electronic structure of the acetaldehyde molecule

The electronic structure of the acetaldehyde molecule was studied by the ultrasoft X-ray emission method with the use of quantum-chemical calculations. The OK _?? and CK _?? spectra of the compound in the gas phase were obtained. Quantum-chemical calculations were performed at the RHF/6-311++G** level. The calculation results were used to construct theoretical X-ray spectra. The experimental spectra are interpreted.     

Relativistic electronic structure of cadmium(II) multidecker phthalocyanine compounds

Cadmium phthalocyanines (Pc) give rise to multilayered compounds, which may have potential application in material science. The Cd(II) single macrocycle (1) (C_4v), double decker [CdPc₂] (2) (D₄), triple decker [Cd₂Pc₃] (3) (D_4h) and quadruple decker [Cd₃Pc₄] (4) (D_4d), are already characterized experimentally. The electronic structures of the multidecker compounds were compared against the single macrocycle (1) which is used as benchmark. Relativistic electronic structure were carried out via DFT calculations using the two components ZORA Hamiltonian including both scalar and spin–orbit effects. Double point groups were used to take into account the inclusion of the spin–orbit coupling, and their group correlation is shown. The calculations show that the quadruple decker is the most reactive and behaves like a one-dimensional molecular metal.