James F. Harrison

On the orbital description of the 4s3dn+1 states of the transition metal atoms

Multiconfiguration Hartree–Fock calculations are presented for the 3F state of Ti and the 2S state of Cu. (AIP)

Some One‐Electron Properties of H2O and NH3

Several one‐electron properties have been evaluated for H2O and NH3 using ab initio SCF functions. The functions are obtained from the Hartree—Fock—Roothman equations using a minimal Gaussian‐lobe basis. The diamagnetic‐susceptibility tensor, quadrupole‐moment tensor, diamagnetic nuclear shielding tensor at O, N, and H, and the nuclear quadrupole coupling constants for 17O, 14N, and D have been evaluated. These properties have been compared, when possible, with experiment. The total magnetic susceptibility tensor for NH3 and H2O and the diagonal elements (in the principal inertia system) of the absolute nuclear shielding tensor at H and N in NH3 have been estimated by combining the ab initio diamagnetic results with the experimental paramagnetic contributions available from measurements of the rotational magnetic moment and the spin—rotation interaction, respectively.

On the Gaussian‐Lobe Representation of Atomic Orbitals

The reliability of angularly dependent properties calculated from wavefunctions constructed over a nonnuclear‐centered Gaussian basis has been explored by examining the spherical harmonic expansion of the Gaussian‐lobe function representation of a pz function. It is found that the component of pz in the Y10 subspace is similar to a double‐zeta function while the component in the Y30 subspace is several orders of magnitude less than the Y10 component.Expectation values for several angularly dependent operators are evaluated over the Gaussian‐lobe function representation of a pz orbital and compared with the expectation value calculated over the corresponding double‐zeta function. The small angular asymmetry in the Gaussian‐lobe function representation of the atomic pz orbitals is reflected in the similarity between the two expectation values.

An SCF–MS–Xα study of a series of d1 transition metal oxohalo complexes

A detailed study of the electronic structures of a series of d1 transition metal oxohalo complexes (MOXn)m−, where M = V, Nb, Cr, Mo, and W and X = F, Cl, and Br (n = 4 or 5), has been carried out by the SCF–MS–Xα method. The results provide values of the d–d transition energies, and also give some understanding of the similarities and differences in bonding characteristics of the penta‐ and hexacoordinated complexes, and of the observed trends in the g and metal hyperfine interaction tensors in these series. The utility of the SCF–MS–Xα method in predicting trends in bonding and in ESR parameters in transition metal complexes is discussed and the results compared with those from ab inito methods.

An Ab Initio Study of the Zero Field Splitting Parameters of 3B1 Methylene

The spin–dipole contribution to the zero field splitting parameters of methylene in the 3B1 state has been studied as a function of geometry. At the computed equilibrium geometry of RCH = 1.05 A and θ = 132.5° we find D = 0.71 cm−1 while E = 0.05 cm−1 (experimental= 0.69 and 0.003 cm−1, respectively). The dependence of E / D on bond angle, bond length, and percent s character in the lone‐pair density is examined. Our results suggest that the spin–orbit contribution to D and E in methylene is negligible.

The gas phase chemistry of bare and ligated transition metal ions: Correlations of reactivity with electronic structure—I. M+ and MCO+

Abstract In the gas phase, univalent cations such as Cr+, CrCO+, Cr(CO)2+, etc. have been generated, and their chemistry with neutral molecules characterized, using a number of mass spectrometric techniques. Presented here are results of ab initio calculations on two transition metal ion—monocarbonyl molecules, ScCO+ and CrCO+. These calculations suggest that the bonding in such systems is predominantly electrostatic in nature; this information is used to evaluate existing data on the gas phase chemistry of a variety of bare and ligated first-row transition metal ions.

Dipole and quadrupole moment functions of the hydrogen halides HF, HCl, HBr, and HI: A Hirshfeld interpretation

The dipole and quadrupole moment functions of the hydrogen halides are calculated using a large polarized basis and correlated wavefunctions and compared to experiment and previous calculations. These functions are analyzed in terms of local moments constructed using the Hirshfeld method. The dipole moment is the sum of the functions q(H)R+mu(H) and mu(X) with q(H) being the charge on the hydrogen atom, R the internuclear separation, mu(H) and mu(X) the atomic dipoles on the hydrogen and halogen atoms. We find that q(H)R+mu(H) is always positive and has a maximum at bond lengths larger than the equilibrium. In HF, mu(F) is slightly positive at the maximum in q(H)R+mu(H) and has little effect on the resultant maximum in the dipole moment function (DMF). mu(Cl), mu(Br), and mu(I), on the other hand, are increasingly more negative at the maximum of q(H)R+mu(H) and have a profound effect on the width of the maximum of the resulting DMF, successively broadening it and completely eliminating it at HI. The quadrupole moment function (QMF) (with the halogen as origin) is given by Theta(HX)=Theta(HX) (proto)+deltaTheta(X)+deltaTheta(H)+2mu(H)R+q(H)R(2), where Theta(HX) (proto) is the quadrupole moment of the separated atoms (the halogen in this instance) and deltaTheta(X)+deltaTheta(H) the change in the in situ quadrupole moments of the halogen and hydrogen atoms. The maximum in the QMF and its slope at equilibrium are determined essentially by 2mu(H)R+q(H)R(2), which is known once the DMF is known. deltaTheta(X)+deltaTheta(H) is always negative while Theta(HX) (proto) is positive, so one can approximate the molecular quadrupole moment to within 10% as Theta(HX)>Theta(HX) (proto)+2mu(H)R+q(H)R(2).

The electronic structure of the low lying sextet and quartet states of CrF and CrCl

The electronic structure of CrF and CrCl in X 6Σ+, 6Π, 6Δ, A6Σ+, 4Σ+, 4Π, and 4Δ states that correlate with the low lying 6S, 6D, and 4D states of Cr+ have been studied, using large atomic natural orbital (ANO) basis sets and a variety of ab initio methods, including multi-reference configuration interaction (MRCI) and coupled cluster with perturbative triples (RCCSD(T)). We include scalar relativistic effects perturbatively and also explore the consequence of correlating the 3s and 3p electrons on the transition metal. We report T e, R e,ωe, as well as dipole moments, bond energies, and charge distributions and compare with the available experimental data as well as previous theoretical results.

Electronic and geometric structure of the diatomics ScN, ScP and ScAs

Abstract The ground and low-lying excited states of ScN, ScP and ScAs have been studied at the MCSCF and MCSCF + 1 + 2 level. They all have a triply bonded 1Σ+ ground state and several low-lying boubly bonded states of 3Σ+, 1Π and 3Π symmetry. The calculated bond energies (relative to the ground state atoms) and bond lengths of the 1Σ+ states are ScN (2.72 eV, 1.768 A) ScP (1.54 eV, 2.277 A) and ScAs (1.36 eV, 2.389 A). Our calculated bond length for ScN is in reasonable agreement with the experimental result (1.695 A) of Ram and Bernath. The 3Σ+ state which has two π bonds and no σ bond is 0.33 eV above the 1Σ+ in ScN and 0.80 and 0.87 eV in ScP and ScAs.

Geminal Product Wavefunctions: A General Formalism

We consider the construction of a wavefunction composed of Nβ singlet coupled geminals and Nα − Nβ α spin orbitals where Nα + Nβ is the total number of electrons. An orthonormal basis {χ} is introduced and each geminal and orbital is expanded in this basis. The wavefunction is expressed as a linear combination of determinants over the {χ} basis and the energy expression is obtained. It is suggested that the geminal and orbital expansion coefficients be obtained using a numerical minimization technique. As an example we construct an APG function for LiH and BH (using only σ orbitals) and compare the energies obtained with this model to the corresponding MO–SCF, APSG, and CI results over the same (σ) basis. We find that the APG function recovers 99.9% and 98.0% of the energy difference between the CI and MO–SCF, while our APSG function recovers 96.6% and 80% for these two molecules. Since most pair function models of electronic structure may be viewed as special cases of the parent APG model, this approach ...