SW Calculations Research Articles

Investigation of core-excited quantum yield spectra of high-symmetric boron compounds

The quantum yield spectra of several boron compounds with tetrahedral and trigonal surroundings have been measured in the region of the BK edge using synchrotron radiation. The core-excited states of the fluorine compounds are discussed on the basis of Xα- SW calculations of BF 3, CF 4 and BF − 4-systems. From the correlation between local symmetry and fine structure of the spectra information is derived on the structure of boron—oxygen compounds.

Charge distributions and chemical effects: Part XV. SCF—Xα—SW studies of alkanes

SCF—xα—SW calculations have been performed for the electronic structure of methane, ethane, propane, isobutane and neopentane. The touching and overlapping sphere models with different degrees of overlap were used. The charge distributions were partitioned into atomic charges by means of a modified overlapping sphere model. These charges which indicate a C +H − polarity reflect closely the customary inductive effects and are unique in that they represent the only set of theoretically determined charges which can be related directly to experiment.

Evaluation of Shaly Clastic Reservoir Rocks

Log-derived spectral gamma ray data have been correlated to core-derived Qv data (i.e., cation exchange capacity per total pore volume) in a Texas coast Tertiary sand, east Texas Jurassic sands, and an Alaskan elastic formation. Such correlations can be used to provide a continuous in-situ water saturation estimate in shaly sands based on the Waxman-Smits equation. Introduction Exceptionally few hydrocarbon-bearing clastic reservoir rocks are essentially free of clay minerals. The significant effect of the latter on important reservoir properties such as porosity, water saturation, and permeability and on most geophysical well log responses is well-established.In clastic reservoirs, various types of clay minerals may occur in dispersed, laminated, or structural form. The types of clay distribution, each with a differing effect on effective porosity, can be inferred from crossplots of well logs, visual study of cores, or detailed SEM investigations. The latter distinguish dispersed-clay occurrences such as discrete particles (patchy kaolinite), pore lining, and pore bridging (illite, chlorite, and smectite), each of which have a pronounced but different effect on reservoir permeability.Clay minerals may be characterized in several ways. Table 1 lists composition, density, hydrogen index, cation exchange capacity C ec, and distribution of potassium, thorium, and uranium based on spectral gamma ray information for some of the more common clay minerals.Furthermore, numerous log-derived clay content (shaliness) indicators are reviewed and discussed (Table 2). These techniques basically assume identical properties for clay present in clastic reservoir rocks and adjacent shales. However, this assumption is often unrealistic.With the advent of the Waxman-Smits model to calculate reliable water saturation in shaly sands, emphasis has been focused on log-derived evaluation of C ec per total pore volume, Qv. The novel application of spectral gamma ray data will be discussed in detail. Water Saturation Calculation Models and Associated Parameters Archie, in his classic empirical equation, relates formation conductivity Ct, formation-water conductivity Cw, and the formation resistivity factor F (a function of porosity phi and cementation exponent m) to the formation-water saturation Sw. Ct =Sw CwF(-1), where F= phi (-m). Archie's equation satisfactorily applies to clean sands. The presence of clay minerals, however, has a detrimental effect on Sw calculations. Since such Sw results are often too pessimistic, several clay/quartz distribution models and Sw calculation concepts have been proposed. JPT P. 1641＾

Experimental and theoretical shakeup studies. III. The 1s shakeup in CH4, NH3, and H2O

The core 1s level x-ray photoelectron spectra of CH4, NH3, and H2O have been recorded to high statistics. Several satellite peaks are resolved in each spectrum. The shakeup peaks are assigned with the aid of Xα–SW calculations. A comparison of the ten electron hydride MO diagrams with the neon atomic energy levels reveal the Rydberg character of the empty excited state orbitals. The shakeup transitions in the respective molecules can also be interpreted from atomic models constructed from the experimental shakeup spectrum of neon. The 2p contribution to the total relaxation energy is calculated from a spectral weight analysis of the shakeup spectra.

Dependence of stability, bond strength and electronic structure of dimetal units upon atomic number, oxidation number and chemical environment

The electronic structures of the Cr2 and Mo2 units in the form of neutral diatomic molecules, charged diatomic molecules and coordinated by ligands have been investigated by SCF–Xα–SW calculations, supplemented by projection of the Xα MOs in atomic orbital basis sets (the PXα procedure). The results are compared with the experimental data on Cr2, Mo2 and the many CrII2Ln and MoII2Ln complexes.

SCF Xα SW calculations of chemical shifts of X-ray and electron emission lines and relaxation properties of SiX 4 molecules

SCF Xα SW calculations of the 1s and 2p binding energies, KLL Auger energies and Kα transition energies for the molecules SiH 4, SiCl 4 and SiF 4 and the corresponding atomic Xα calculations for charged free silicon ions have been carried out. The results provide information about relaxation properties and anomalous chemical Kα shifts in hydrides.

Analysis of the CsNpF6 optical spectrum

A new analysis is given of the CsNpF6 optical spectrum, which removes several features of a previous analysis which were questionable. Possible vibronic structure, SCF–Xα–SW calculations, and analyses of related compounds have been used as a basis for the present investigation. It was found that configuration interaction effects are significant and cannot be neglected. By inclusion of linear CI terms, a fit to 33 assigned levels gave an rms deviation of 140.6 cm−1 in a least-squares refinement. The parameters determined are F2=202.2, F4=14.26, F6=1.517, ζ=2137, A4〈r4〉=1431, A6〈r6〉=112.6, α=195.2, β=−5798, and γ=9582 cm−1.

Metal–metal interactions in 2–Fe ferredoxins; SCF-Xα-SW calculations

SCF–Xα–SW calculations on Fe2S2(SH)42– show that (i) the antiferromagnetism of 2–Fe ferredoxins is due to superexchange rather than direct Fe–Fe overlap; (ii) the weak direct Fe–Fe bonding present is concentrated not in the Fe 3d band, but in a lower lying, mainly Fe–(bridging S) orbital.

A study of the electronic structures of SN, S2N2, S4N4, NO, and N2O2 and their implications for (SN)x

SCF–Xα–SW calculations have been carried out for SN, S2N2, and S4N4 as well as the analogous oxides NO and N2O2. The electronic charge distribution of the sulfides is remarkably uniform leading to highly polar SN bonds (∼S+1/2N−1/2) in contrast to the oxides where the NO bonds involve less charge transfer and in the opposite direction. The inclusion of d functions on sulfur is shown to have only minor effects on the electronic structure of the sulfides. Contour plots of several of the molecular orbitals are presented. The importance of the polar bonds in S2N2 in determining the structure of metallic polymeric sulfur nitride (SN)x is discussed. Predictions are made on the likelihood of forming (SN)x analogs with a different Group V or Group VI element.

A simplified SCF Xα scattered-wave procedure for partitionable systems and an application to a water trimer

A simplified procedure for SCF Xα SW calculations on molecular systems, that can be divided into interacting units, is presented. The calculations are carried out on one part of the system at a time, iterating between interacting parts until self-consistency is attained. By exploiting the local molecular symmetry of each component part, the calculations can be further simplified, and only moderate amounts of computer time are required. The standard SCF Xα SW computer program has been modified to perform these calculations. Results for a water trimer are presented as a simple illustration of the method.