Search

Abstract.: Transport cross sections and collision integrals are tabulated for a wide range of energies and temperatures for the interactions B–B and Al–Al. For aluminum, a semiclassical approximation was used to determine the scattering phase shifts from which the transport cross sections were calculated. For boron, the smaller reduced mass and the deep potential wells required the phase shifts at lower energies to be determined from a numerical solution of the time-independent Schroedinger equation; the semiclassical approximation was used at higher energies where the two methods agree. The variations of the collision integrals for viscosity and diffusion are presented graphically as a function of temperature. The results are applied to estimate the transport properties of gallium.

Summary Energy-optimized Gaussian basis sets of triple-zeta quality for the atoms Rb-Xe have been derived. Two series of basis sets are developed; (24s 16p 10d) and (26s 16p 10d) sets which we expand to 13d and 19p functions as the 4d and 5p shells become occupied. For the atoms lighter than Cd, the (24s 16p 10d) sets with triple-zeta valence distributions are higher in energy than the corresponding double-zeta distribution. To ensure a triple-zeta distribution and a global energy minimum the (26s 16p 10d) sets were derived. Total atomic energies from the largest basis sets are between 198 and 284µEH above the numerical Hartree-Fock energies.

Summary Potential energy curves for the weakly bound6Σ+,6Π, and4Σ+ states of NO are presented at various levels of correlation treatment. The binding energies for the van der Waals minima vary from about 30 cm−1 for the6Σ+ state to about 20 cm−1 for the4Σ+ and6Π states. We investigate the importance of constraining the wave function to dissociate to a spherically symmetric O atom where the oxygen 2p orbitals are equivalent. For high levels of correlation treatment, we find that these restrictions have little effect on the potential, while greatly increasing the length of the CI expansion.

The molecular structure of the positive ions of the diatomic and triatomic systems containing the metals Cu, Ag, and Au are determined from ab initio calculations. The bond lengths of the positive diatomic ions are similar to those of the corresponding anions, because they all have a bond order of one half. The ionization potentials (IPs) of the homonuclear trimers are considerably smaller than those for either the atoms or diatomics, since the highest occupied molecular orbital is only weakly bonding. The neutral and positively charged trimers have comparable structures resulting in similar vertical and adiabatic IPs. The trends in the dimer and trimer IPs and atomization energies are explained by the fact that the IP of Au is larger than either Ag or Cu.

NHF and NMCSCF results for Cu2 are compared with calculations employing basis set expansions. We find that nearly all previous SCF calculations using Gaussian basis sets have underestimated the bond length by about the same amount (0.03 Å) as that attributed to the unlinked cluster and relativistic corrections. The error is shown to be due to deficiencies in the 3d primitive set which yield sizable basis set superposition errors.

Summary The invariance of the configuration interaction (CI) energy with respect to orbital rotation is considered. The inclusion of all spin couplings versus only those from the first-order interacting space is considered. A definition for the analog of a second-order CI calculation when inactive electrons are present is proposed.

Summary The relative importance of the valencep functions for describing the bonding in the valence isoelectronic Na2, K2, and Cu2 molecules and their positive and negative ions is investigated. In absolute magnitude the contribution of thep functions to the dissociation energy follows the trend Cu>Na>K while by percentage of the dissociation energy the importance of thep functions follows the polarizabilities, i.e. K>Na>Cu. The bonding in K2, K2+, and K2- is analyzed to explain the observed trends.

All-electron, non-relativistic ab initio self-consistent field (SCF) quantum mechanical methods were applied to the unique enneahydridorhenate dianion (ReH2-9, D3h). Three basis sets were constructed and used for rhenium: the (20s14p11d7f/17s11p8d2f) basis is loosely designated DZ; the (23s17p14d9f/18s14p10d3f) is similarly designated TZ; and TZ plus polarization plus diffuse is designated TZP +. The largest basis set, TZP +, has 24s20p15d10f primitive Gaussian functions contracted to 19s17p11d4f. Four basis sets were used for H: the (5s/3s) is designated TZ; (5s2p/3s2p) is designated TZ2P; (6s2p/4s2p) is designated QZ2P; and QZ2P plus one diffuse s function is designated QZ2P +.The well-known experimental D3h structure was investigated, with the three independent internal coordinates optimized using analytic gradient techniques. The larger basis sets were handled using the direct SCF approach. The largest basis set for which the geometry was optimized was TZP + for Re and QZ2P + for H (with 252 basis functions, where pure 5d and 7f sets of functions were used), and should approach closely the non-relativistic Hartree-Fock limit. Harmonic vibrational frequencies were obtained for two basis sets, the larger of which is TZ for Re and QZ2P for H (for a total of 221 basis functions). The molecular geometry seems to have approached the Hartree-Fock limit, and the six symmetry-equivalent prism Re-H bonds are predicted to be longer than the three cap Re-H bonds by 0·06 Å. The predicted equilibrium geometry and harmonic vibrational frequencies generally agree with available experimental data. The reason for the apparent agreement may be the accidental cancellation of relativistic effects and electron correlation effects.

The heats of formation of SiCl n and SiCl n , for n = 1-4, have been determined using the G2(B3LYP/MP2/CC) approach. The results for the neutral systems are in very good agreement with previous work. High level calibration calculations allow us to refine the G2(B3LYP/MP2/CC) values. While the computed and experimental IPs of SiCl 4 agree, the calculations show that the adiabatic IP is about 7 kcal/mol smaller than the accepted value. The temperature dependence of the heat of formation, heat capacity, and entropy are computed for 300 to 4000 K and fit to a polynomial.

The transport cross sections and collision integrals for HH2interactions have been calculated from the results of accurate ab initio structure calculations using sudden scattering approximations. The low-temperature diffusion and viscosity coefficients agree well with the results of a close-coupling scattering calculation. The values calculated from the potential energies deduced from scattering measurements are in agreement with the theoretical results. The viscosity coefficients for HH and H2H2have also been calculated; the H2H2results are very close to the measured data for temperatures in the range 200–400 K.