Many quantum chemical methods used for large complexes are based on a limited treatment of electrons due to the computational demand dictated by the number of electrons that must be explicitly considered, especially when considering the chemical environment. Such treatments can fail to correlate accurately with electronic spectra. Ab initio electronic structure theory using the spin-orbit configuration interaction method is applied in a study of spectral transitions in PtCl4 2- including counter-ion environmental effects. In this method, electronic wave functions are eigenfunctions of the total angular momentum operator belonging to one of the symmetry types of the molecular double group. PtCl4 2- is investigated as a charged gas phase complex, a point-charge-neutralized complex, and a pseudopotential-neutralized complex. Results indicate that the use of a whole-atom relativistic effective core potential for the potassium cation provides a more accurate representation of the environment than a point charge and accurately represents electronic states without increasing the complexity of the calculation and, therefore, its computational demand.

Four methods of computational quantum chemistry are used in a study of hyperconjugation in protonated aromatic molecules. Benzene, benzenium, toluene, and four isomeric forms of toluenium are examined using the self-consistent field level of theory followed by configuration interaction and coupled cluster calculations, as well as density functional theory. Results for proton affinities, geometric parameters, atomic populations, dipole moments, and polarizabilities are reported. The calculated results are in good agreement with previous computational studies and with experimental data. The presence of hyperconjugation is evident from the shortened carbon–carbon bond lengths in the aromatic ring and concomitant changes in dipole moments and polarizabilities. The proton affinities of benzene and toluene compare well with experimental values. The examination of all of the toluenium isomers reveals that the position of the methyl group has a minor impact on the strength of hyperconjugation, although the most stable isomer is found to be the para form. Mulliken population analyses indicate that the addition of a proton contributes to aromatic hyperconjugation and increases the strength of π-bonds at the expense of σ-bonds.

A code MolecGeom, based on algorithms for stepwise distortions of bond lengths, bond angles and dihedral angles of polyatomic molecules, is presented. Potential energy surfaces (PESs) are curated in terms of the energy for each molecular geometry. PESs based on the Born–Oppenheimer approximation, by which the atomic nuclei within a molecule are assumed stationary with respect to the motion of its electrons, are calculated. Applications requiring PESs involve the effects of nuclear motion on molecular properties. These include determining equilibrium geometries corresponding to stationary and saddle point energies, calculating reaction rates and predicting vibrational spectra. This multi-objective study focuses on the development of a new method for the calculation of PESs and the analysis of the molecular geometry components in terms of incremental changes that provide comprehensive sampling while preserving the precision of PES points. MolecGeom is applied to generate geometric data to calculate PESs for theoretical calculations of vibrational-rotational spectra of water and formaldehyde. An ab initio PES comprising 525 and 2160 intramolecular nuclear configurations results in vibrational frequencies in agreement with experiment, having errors less than 0.08% and 0.8%, respectively. Vinyl alcohol, with a total of 14 internal coordinates, generates a PES of 1458 unique geometries. Ascorbic acid, with 54 internal coordinates, generates a 1,899,776 point PES.

Relativistic calculations of the structural and spectral properties of the PbO molecule can provide fundamental information about the importance of a proper treatment of angular momentum coupling among electrons in order to achieve accurate computational results for spectral properties. Specifically, the nature of these couplings in PbO is expected to be intermediate between the LS- and jj-coupling limits because of its light/heavy element composition. This article reports potential energy curves, transition energies, electric dipole transition moments, permanent dipole moments and spectroscopic constants of PbO calculated using a multireference single plus double excitations spin-orbit configuration interaction approach in the context of relativistic effective core potentials and their concomitant spin-orbit coupling operators. The calculated results are in general agreement with both available experimental results as well as earlier calculations. New values for properties of excited states are also reported. It is noteworthy that certain properties show larger deviations from previous calculations. These deviations are attributed to direct and indirect relativistic effects resulting from diatomic electron-electron angular momentum coupling effects, which are included consistently in the calculations reported herein.

N-Heterocyclic sulfones and sulfides are key functional motifs in medicinal and agricultural chemistry and important building blocks in organic synthesis. Currently available methods produce N-heterocyclic sulfones in low yields and under harsh conditions. Here, we describe a rapid sulfone synthesis under ambient conditions that is initiated by persulfate with water as a cosolvent. The reaction has a broad scope and is readily expanded to the chemodivergent synthesis of symmetrical N-heterocyclic sulfones and sulfides. The products can be isolated by simple filtration. Our combined experimental and computational study suggests that the remarkable persulfate-initiated acceleration of the sulfone formation in the biphasic system that enables the otherwise sluggish reaction under ambient conditions is due to the combination of the previously unknown rapid acidification of the persulfate-sulfinate system, the self-catalysis of the reaction of sulfinic acid with halo-N-heterocycles, and the substantial acceleration of the reaction in the aqueous phase.

A self-consistent-field (SCF) program for the calculation of atomic energies and wave functions defined in jj-coupling using two-component atomic spinors and relativistic effective core potentials (RECPs) is described. The code is based on the linear combination of atomic orbitals SCF algorithm for atomic states defined in LS-coupling developed by Roothaan and Bagus. Hamiltonian matrix elements with respect to one- and two-electron operators, including RECPs, are calculated for two-component atomic spinor basis functions of either Gaussian-type orbitals (GTOs) or Slater-type orbitals (STOs). Electronic states are defined as eigenfunctions of the total angular momentum squared operator and tables of the required vector coupling coefficients that define such pure states are provided. In addition, one or more GTO expansions of large- and small-core RECPs and their corresponding GTO basis sets are supplied for all elements Z=3 through Z=118. Optimized two-component basis sets of STOs or GTOs can be calculated for use in molecular structure codes based on RECPs and relativistic electronic structure theory. Atomic asymptotic state energies at the SCF level of theory for analysis of molecular dissociation limits can be studied. Program summary Program title: jjatom Program Files doi: http://dx.doi.org/10.17632/zs4twp8r67.1 Licensing provisions: GPLv3 Programming language: Fortran 90 Nature of problem: Relativistic atomic energies and wave functions; optimization of two component spinor basis sets. Solution method: Atomic spinors defined in jj-coupling and expansions in two-component spinor basis functions of Gaussian- or Slater-type functions. Self-consistent field optimization of the total energy. Used for optimization of two-component atomic spinor basis sets and calculations of valence spectra of heavy elements. (C) 2018 Elsevier B.V. All rights reserved.

We present relativistic Dirac–Fock calculations of atomic properties for atomic numbers Z=121–138, extending a previous tabulation of Desclaux. The calculations assume a single LS ground state configuration and include a correction for finite nuclear size, with an approximation for the mean nuclear mass A(Z) based on the liquid-drop model.

An implementation of a massively parallel spin – orbit confi guration interaction ( PSOCI ) method is described. This is an extension of a conventional CI method that explicitly includes one-electron spin – orbit operators and certain scalar relativistic effects extracted from relativistic effective core potentials. The performance of the PSOCI code is analyzed on several large-scale computing platforms.

Ab initio single plus double excitations configuration interaction calculations in the context of relativistic effective core potentials are reported for C-8, C-10, Pt@C-8 and Pt@C-10 clusters in their neutral and ionic forms. The predicted geometries of cyclic C-8(2-) and C-10(2-) correctly justify double coincidence mass spectra results as compared to linear C-8(2-) and C-10(2-). The effects of Pt encapsulation in these clusters are discussed in terms of binding energies and equilibrium geometries. The Pt@C-8 and Pt@C-10 clusters have binding energies of 1662 kJ/mol and 2200 kJ/mol, respectively. Binding energies for Pt encapsulation are only favorable for the doubly charged carbon clusters, indicating that stable Pt encapsulation only occurs for the C-8(2-) and C-10(2-) clusters. (C) 2013 Elsevier B.V. All rights reserved.

A procedure for calculating electric dipole transition moments and permanent dipole moments from spin–orbit configuration interaction (SOCI) wave functions has been developed in the context of the COLUMBUS ab initio electronic structure programs. The SOCI procedure requires relativistic effective core potentials and their corresponding spin–orbit coupling operators to define the molecular Hamiltonian, electric dipole transition moment and permanent dipole moment matrices. The procedure can be used for any molecular system for which the COLUMBUS SOCI circuits are applicable. Example applications are reported for transition moments and dipole moments for a series of electronic states of LiBe and LiSr defined in diatomic relativistic ωω-coupling.

A procedure for structuring generally contracted valence–core/valence basis sets of Gaussian-type functions for use with relativistic effective core potentials (gcv-c/v-RECP basis sets) is presented. Large valence basis sets are enhanced using a compact basis set derived for outer core electrons in the presence of small-core RECPs. When core electrons are represented by RECPs, and appropriate levels of theory, these basis sets are shown to provide accurate representations of atomic and molecular valence and outer-core electrons. Core/valence polarization and correlation effects can be calculated using these basis sets through standard methods for treating electron correlation. Calculations of energies and spectra for Ru, Os, Ir, In and Cs are reported. Spectroscopic constants for RuO2+, OsO2+, Cs2 and InH are calculated and compared with experiment.

Three low-lying states of RuO2+ are analyzed using large-scale configuration interaction (CI) calculations based on multireference wavefunctions. Relativistic effects are included using relativistic effective core potentials and a spin-orbit (SO) CI approach. The ground state is predicted to be a triply bonded system of 0(+) ((1)Sigma(+)) symmetry having a dissociation energy of 83.8 kcal/mol, an equilibrium bond length of 1.55 angstrom and a vibrational frequency of 1227 cm(-1). Two close-lying states (3 U) and (3 D) states have dissociation energies, bond lengths and frequencies of 82.2 and 68.5 kcal/mol, 1.83 and 1.90 angstrom, and 974 and 974 cm(-1), respectively. The states differ in energy at their respective minima by 551 and 4777 cm(-1). (C) 2011 Elsevier B.V. All rights reserved.

It is now possible to calculate many properties including the energetics (total bond dissociation energies or heats of formation) of molecules containing light elements to high accuracy by using correlation-consistent basis sets, coupled cluster theory and including additive corrections for core-valence and relativistic effects and careful treatment of the zero point energy. We propose to develop software for ab initio electronic structure calculations based on molecular orbital theory and density functional theory with the proper treatment of relativistic effects to study complexes of heavy elements in order to assist in understanding and predicting the chemistry of the actinides, lanthanides, and heavy transition metals, molecules critical to DOE missions including environmental management. The proposed work will focus on the development of these electronic structure methods and their implementation in software on advanced massively parallel processor (MPP) computer architectures capable of multi-tens of teraflops to petaflops. The core of the software will be developed within the NWChem and Columbus software suites. We propose to make the software broadly available so that other scientists can use these tools to address the complex environmental problems facing the Department of Energy's nuclear production sites as well as other waste sites in the Nation. Our implementation of relativistic quantum chemical methods for massively parallel computers will enable us to simulate the behavior of heavy-element compounds at the same type of level currently available for light-element compounds. In addition, this work will enable us to provide better methods for benchmarks of the additive energetic schemes currently available for light atom compounds. The theoretical and computational methodology so developed will be an invaluable supplement to current, very expensive experimental studies of the actinides, lanthanides, and radioactive heavy transition metal elements, allowing limited experimental data to be extrapolated to many other regimes of interest. The program objectives will be attained through a multi-site collaboration from PNNL, Ohio State University, University of Memphis and Eloret that includes leading researchers in the areas of high-performance computational chemistry and relativistic theoretical chemistry. The new tools can be used to study, for example, the interaction of actinides with organic complexing agents present in tank wastes and with natural aqueous systems (carbonates) in order to better understand their fate and transport in the environment, as well as interactions with new materials such as phosphates and amides for the design of innovative in situ remediation technologies and separation materials. In addition, the proposed work will allow scientists to tackle the complexity of excited states in heavy element compounds especially those comprised of actinide, lanthanide, and heavy transition metal atoms.