Trond Saue

The Dalton quantum chemistry program system

Dalton is a powerful general‐purpose program system for the study of molecular electronic structure at the Hartree–Fock, Kohn–Sham, multiconfigurational self‐consistent‐field, Møller–Plesset, configuration‐interaction, and coupled‐cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic‐structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge‐origin‐invariant manner. Frequency‐dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one‐, two‐, and three‐photon processes. Environmental effects may be included using various dielectric‐medium and quantum‐mechanics/molecular‐mechanics models. Large molecules may be studied using linear‐scaling and massively parallel algorithms. Dalton is distributed at no cost from http://www.daltonprogram.org for a number of UNIX platforms.

On the origin and contribution of the diamagnetic term in four-component relativistic calculations of magnetic properties

The relativistic Dirac Hamiltonian that describes the motion of electrons in a magnetic field contains only paramagnetic terms (i.e., terms linear in the vector potential A) while the corresponding nonrelativistic Schrodinger Hamiltonian also contains diamagnetic terms (i.e., those from an A2 operator). We demonstrate that all diamagnetic terms relativistically arise from second-order perturbation theory and that they correspond to a “redressing” of the electrons by the magnetic field. If the nonrelativistic limit is taken with a fixed no-pair Hamiltonian (no redressing), the diamagnetic term is missing. The Schrodinger equation is normally obtained by taking the nonrelativistic limit of the Dirac one-electron equation, we show why nonrelativistic use of the A2 operator is also correct in the many-electron case. In nonrelativistic approaches, diamagnetic terms are usually considered in first-order perturbation theory because they can be evaluated as an expectation value over the ground state wave function...

Full four‐component relativistic calculations of NMR shielding and indirect spin–spin coupling tensors in hydrogen halides

Various methods for the inclusion of relativistic effects in the calculation of NMR parameters are discussed. Benchmark values for the NMR shieldings and indirect nuclear spin–spin coupling tensors for the hydrogen halides are calculated using the four‐component relativistic random phase approximation method. Apart from recovering the well‐known trend of increasing hydrogen isotropic shielding going from HF to HI, we also find a large effect on the anisotropy that decreases along this series. Inclusion of spin‐orbit coupling in a nonrelativistic formalism suffices to recover both effects on the hydrogen shieldings but fails to reproduce the much larger effect on the halogen shieldings. This effect can be explained by considering the relativistic mass‐velocity operator that contains correction terms to the nonrelativistic magnetic field operators. We recommend routine inclusion of the one‐electron spin‐orbit correction in calculations of hydrogen shieldings for hydrogens bonded to heavy atoms. For the heavy nucleus shielding one should include an additional mass‐velocity correction. The relativistic effect on the indirect nuclear spin–spin coupling tensor is large and affects mainly the isotropic values; the effect on the anisotropy is small.u2003©1999 John Wiley & Sons, Inc.u2003J Comput Chem 20: 1262–1273, 1999

Principles of direct 4-component relativistic SCF: application to caesium auride

A theory of 4-component direct SCF calculations is presented using a quaternion formulation of the Dirac–Fock equations. Screening of integral batches is supplemented with screening on individual integrals and with separate screening of Coulomb and exchange contributions to the Fock matrix. The direct SCF method is applied to study bonding in caesium auride. The caesium–gold bond is found to be highly ionic, with gold present as the anion. A relativistic bond contraction of 41 pm is observed.

The molecular mean-field approach for correlated relativistic calculations

A new approach for relativistic correlated electron structure calculations is proposed by which a transformation to a two-spinor basis is carried out after solving the four-component relativistic Hartree-Fock equations. The method is shown to be more accurate than approaches that apply an a priori transformation to a two-spinor basis. We also demonstrate how the two-component relativistic calculations with properly transformed two-electron interaction can be simulated at the four-component level by projection techniques, thus allowing an assessment of errors introduced by more approximate schemes.

THE ELECTRONIC-STRUCTURE OF THE PTH MOLECULE - FULLY RELATIVISTIC CONFIGURATION-INTERACTION CALCULATIONS OF THE GROUND AND EXCITED-STATES

Fully relativistic all‐electron self‐consistent field calculations based on the Dirac–Coulomb Hamiltonian have been performed on the three lowest lying states of the PtH molecule. The resulting four‐component Dirac–Hartree–Fock (DHF) molecular spinors are subsequently used in relativistic configuration interaction (CI) calculations on the five lower states of PtH. Spectroscopic properties are obtained by fitting the potential curve to a Morse function and show good agreement with experimental data. The effect of relativistic corrections to the Coulomb electron–electron interaction is investigated at the DHF level and is found to be insignificant for the molecular spectroscopic properties investigated by us. The CI wave functions are found to have only one dominant configuration, indicating a lack of static correlation. Dynamic correlation in the d shell is, however, important for the spectroscopic properties of PtH. The results conform with a bonding scheme in which the three lower and two upper states of...

Progress toward the first observation of parity violation in chiral molecules by high-resolution laser spectroscopy†

Parity violation (PV) effects in chiral molecules have so far never been experimentally observed. To take up this challenge, a consortium of physicists, chemists, theoreticians, and spectroscopists has been established and aims at measuring PV energy differences between two enantiomers by using high-resolution laser spectroscopy. In this article, we present our common strategy to reach this goal, the progress accomplished in the diverse areas, and point out directions for future PV observations. The work of André Collet on bromochlorofluoromethane (1) enantiomers, their synthesis, and their chiral recognition by cryptophanes made feasible the first generation of experiments presented in this article.

Theoretical studies of the actinides: method calibration for the UO22+ and PuO22+ ions

Abstract As part of method assessment for the theoretical study of actinide systems, we have performed 1-component relativistic pseudopotential calculations for the uranyl and plutonyl ions. The calculated spectroscopic constants compare well with fully relativistic 4-component results at both the Hartree–Fock and correlated levels of theory. We deduce that second-order spin–orbit effects in these systems are minor and show that the 1-component method chosen (B3LYP in particular) gives reliable results at low computational cost. The ground state of the plutonyl ion has been determined as 3 H g .

Relativistic four‐component multiconfigurational self‐consistent‐field theory for molecules: Formalism

A formalism for relativistic four‐component multiconfigurational self‐consistent‐field calculations on molecules is presented. The formalism parallels a direct second‐order restricted‐step algorithm developed for nonrelativistic molecular calculations. The presentation here focuses on the differences required by the use of the Dirac Hamiltonian with the incorporation of time‐reversal symmetry and point group symmetry for D2h and subgroups, providing the expressions in this framework which correspond to the nonrelativistic expressions. It is found that an efficient algorithm requires only twice the memory used by the largest nonrelativistic calculation in the equivalent basis, due to the complex arithmetic. The feasibility of the calculations is then determined more by the disk space for storage of integrals and N‐particle expansion vectors.

Molecular relativistic calculations of the electric field gradients at the nuclei in the hydrogen halides

Electric field gradients at the position of the nuclei in the hydrogen halides are calculated using four-component relativistic methods. Benchmark values at the Dirac–Hartree–Fock level of theory are obtained by using large uncontracted basis sets. Electron correlation corrections are obtained by means of finite field MP2, CCSD, and CCSD(T) calculations in smaller basis sets. The importance of spin–orbit coupling and the so-called picture change effect are discussed.