Nonrelativistic Effective Core Potential Research Articles

Scalar Relativistic Study of the Structure of Rhodium Acetate

Rhodium acetate, related rhodium carboxylates, and rhodium amide complexes are powerful catalysts for carbene chemistry. They readily promote the decomposition of diazo compounds and transfer the resulting carbene to a variety of substrates. There have been several quantum chemistry studies of these compounds, particularly of the acetate. These have all used non-relativistic methods, and all have shown optimized Rh-Rh bond lengths significantly longer than the experimental value. In this study we have surveyed several scalar relativistic DFT methods using Gaussian, Slater, and numerical basis functions (in DGAUSS, ADF, and DMOL3). Several combinations of exchange-correlation functionals with relativistic and non-relativistic effective core potentials (ECP) were investigated, as were non-relativistic and all electron scalar relativistic methods. The combination of the PW91 exchange and PW91 correlation functional with the Christiansen-Ermler ECP gave the best results: 2.3918 Å compared to the experimental value of 2.3855±0.0005 Å.

A Relativistic Density Functional Study on the Uranium Hexafluoride and Plutonium Hexafluoride Monomer and Dimer Species

A study on the UF6 monomer and dimer was carried out within the density functional method. The U-F distance in the UF6 monomer was optimized at different levels of theory, pointwise, assuming octahedral geometry, (1) by using an all-electron basis for both U and F in a nonrelativistic calculation; (2) by using a relativistic effective core potential (RECP) on U and nonrelativistic effective core potential (ECP) on the fluorines; and (3) by using RECP on the U atom and an all-electron basis on the F atoms. Atomization energies of 23.11, 33.92, and 35.66 eV were obtained at the three levels, respectively. Relativistic effects lead to about a 50% increase in the atomization energy. For the UF6 dimer, the potential energy curve, as a function of the intermolecular U-U distance, was computed at level 2, and the rotational barrier between the two monomers was determined. Similar calculations were performed on the corresponding PuF6 species. Comparisons are made with experiment and other theoretical studies, where available.

Dipole polarizabilities of the Group IIb atoms obtained from compact variational trial functions

In order to optimize basis sets for future molecular calculations, the energies and dipole polarizabilities of 1S, 3P, and 1P states of Zn, Cd, and Hg have been determined from Hartree–Fock (HF) and multiconfiguration calculations. These utilize either empirically fitted pseudopotentials or ab initio effective core potentials (ECP). Our calculated polarizabilities for ground state atoms agree within 10% with recommended values so long as either the empirical pseudopotentials or the ECP based on relativistic HF calculations are used. Our calculations agree with the measured anisotropy of the polarizability of 3P1 Hg, but disagree with measured values of the 3P2 state anisotropy. Our calculated 3P2 anisotropy is consistent with both the measured and calculated 3P1 Hg anisotropy; the measured 3P2 values are not. We find calculations based on nonrelativistic ECP to give incorrect polarizabilities.

A b i n i t i o studies of the electronic structrue of UF6, UF6+, and UF−6 using relativistic effective core potentials

A b initio calculations are performed on the electronic states of UF6, UF6+, and UF−6 using a relativistic effective core potential (ECP) for uranium and a nonrelativistic ECP for fluorine. In most of the calculations 56 valence electrons are treated explicitly using a contracted [3s3p2d2f/2s2p] Gaussian basis. Various ECP’s were explored, but all yield an overall charge density of U+2.4 (F−0.4)6. The bonding in the ground state of UF6 is discussed. SCF and CI calculations on UF6+ are compared with the experimental photoelectron spectrum and with previous scattered-wave calculations. The role of spin–orbit coupling in the states of UF6+ and UF6− is discussed. The calculated electron affinity of UF6 (7.1 eV) is considerably larger than the current experimental estimates, but the relative energies of the states of UF6− are in excellent agreement (0.1–0.2 eV) with experiment.

A b i n i t i o effective core potentials including relativistic effects. III. Ground state Au2 calculations

SCF calculations have been carried out for the ground 1Σ+g(0+g) state of Au2 using a variety of ab initio effective core potentials (EP). The effective core potentials studied both include a two-component relativistic EP (REP) that includes spin–orbit effects and also averaged relativistic EP (AREP) and a nonrelativistic EP (NREP). All-electron nonrelativistic calculations were also performed. The values of spectroscopic constants obtained from these calculations indicate that relativistic effects account for a decrease in Re of over 0.3 Å and an increase in the bond energy of the order of 1 eV. Various intercomparisons indicate the general validity of effective potential methods, properly applied, but also show certain limitations. In particular, the NREP results agree well with the all-electron, nonrelativistic calculations. Also, various relativistic effective-potential methods agree for SCF calculations provided both the basis sets and the EP are carried to sufficiently high order in angular quantum number. The bond distance calculated relativistically agrees very well with experiment.