SCF Xα SW calculations of chemical shifts of X-ray and electron emission lines and relaxation properties of SiX4 molecules

SCF Xα SW calculations of the 1s and 2p binding energies, KLL Auger energies and Kα transition energies for the molecules SiH₄, SiCl₄ and SiF₄ 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.     

The MT-MSXα(R) method: Applications to Li2, F2, and N2 molecules

The multiple scattering Xα(R) method with the scaling parameter α expressed as a function of the internuclear distance is applied to the Li₂, N₂, and F₂ molecules. Compared with the results obtained by the Xα method, the calculated Xα(R) equilibrium distances are smaller, the total energies are lower, and the dissociation energies are larger.     

Calculations of XPS spectra for oxyanions and related compounds by the discrete variational-Xα method

Calculations of molecular-orbital energies and x-ray photoelectron spectra have been carried out for the third-row oxyanions, transition-metal oxyanions, SiO₂ and TiO₂, by the discrete variational-Xα cluster method. The calculated orbital energies are consistent with those determined from the XPS experiments. Theoretical XPS line shapes with Gaussian are generally in good agreement with the observed spectra. However, underestimation has been found for the photopeak intensities in the low-binding-energy region of TiO₂. The discrepancy is partially attributed to the use of inaccurate photoionization cross-section for the Ti3d orbital.     

Ionization energies and electronic structure of N3P3Cl6 as determined by UV photoelectron spectroscopy and the Xα scattered wave method

Ionization energies have been measured for N₃P₃Cl₆ by He I photoelectron spectroscopy and they are compared with values calculated with the overlapping-spheres version of the Xα scattered wave method; the average discrepancy is less than 0.4 eV. The wavefunctions and associated charge distributions are used for assessing models of ring π bonding, and comparisons are made with previous calculations for N₃P₃F₆ and N₄P₄F₈. The calculated charge distributions are related to trends in measured core electron binding energies, and have important implications for the interpretation of Faraday effect measurements on cyclic phosphazenes.     

SCF-SW-Xα Calculations on molybdenum—halogen cluster compounds

The electronic structures of the cluster cations Mo₆ X⁴⁺₈ (X = F, Cl, Br, I) have been calculated using the SCF—SW—Xα method. The eigenvalue spectra obtained are discussed and compared with results of other quantum-chemical studies of such systems. The results of population analysis are used to discuss the charge distribution in the clusters studied. A qualitative discussion of the Mo-Mo and Mo-X bond strengths is also presented. Finally, calculated bond energies are compared with adsorption energies.     

Ionisation energies of CH2F2 calculated by the SCF Xα technique

Ionisation energies have been calculated for CH₂F₂ using the SCF Xα technique. Agreement with experiment is excellent, and the results are compared with those conventional Hartree-Fock calculations.     

Energetic stability and electronic properties of exohedral derivatives of C20: C20Xn (X = H,F, Cl; n = 1–4)

Exohedral derivatives of the smallest fullerene, C₂₀, with the general formula of C₂₀X_n (X = H, F, Cl; n = 1–4) have been systematically investigated to evaluate the energetic stability of these molecular structures and determine their respective electronic properties. Analysis of the theoretical results indicate that the addition of exohedral atoms increase the stability of the caged‐structure to varying degrees according to the predicted HOMO‐LUMO gaps, ionization energies, and electron affinities. Further support for increasing stability is deduced from the calculated reaction and binding energies of the exohedral atoms. © 2012 Wiley Periodicals, Inc.     

X‐ray photoelectron and carbon Kα emission measurements and calculations of O‐, CO‐, N‐, and S‐containing substances

X‐ray fluorescence measurements for O‐containing [polyethylene oxide, polyvinyl alcohol, polyvinyl methyl ether], CO‐containing [polyvinyl methyl ketone, polyethylene terephthalate], N‐containing [poly‐4‐vinylpyridine (P4VP), polyaniline oligomer (PAO)], and S‐containing [polyphenylene sulfide] substances are presented. Carbon Kα X‐ray emission spectra (XES) and X‐ray photoelectron spectra (XPS) are compared with our DFT calculations performed with the Amsterdam density functional (ADF) program. The combined analysis of valence XPS and carbon Kα XES allows us to determine the individual contributions from pσ‐ and pπ‐bonding molecular orbitals of the polymers. The ΔSCF calculations yield the accurate C1s core‐electron binding energies (CEBEs) for all carbon sites of the organic compound. We calculate all CEBEs of the model molecules using the ΔE _KS approach. Our simulated C1s photoelectron and C Kα emission spectra are in good agreement with our measurements. We also obtain WD (work function and the other energies) values for the polymers and PAO from the difference between calculated (gas‐phase) and measured (solid) CEBE values. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 162–172, 2007     

Density functional calculations on CO attached to PtnRu(10−n) (n = 6–10) clusters

B3LYP and SCF‐Xα calculations have been performed on Pt_nRu_(10−n)CO (n = 6–10) clusters. The work aims to simulate the adsorption of CO on the (111) surface of platinum metal and to examine the electronic effects that arise when some Pt atoms are replaced with Ru. Adsorption energies and Pt C and C O stretching frequencies have been calculated for each cluster. Ru does affect the electronic structure of the clusters, the calculated adsorption energies, and frequencies, the Pt C frequency more than the C O. The donation‐backbonding mechanism that accompanies the shift in CO stretching frequency that occurs when CO adsorbs on platinum does not explain the differences in frequency shift observed in CO on various Pt/Ru surfaces. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 589–598, 2000     

New Insights into Factors Influencing B?N Bonding in X:BH3−nFn and X:BH3−nCln for X=N2, HCN,LiCN, H2CNH,NF3, NH3 and n=0–3: The Importance of Deformation

Understanding the bonding in complexes X:BH_3?nF_n and X:BH_3?nCl_n, for X=N₂, HCN, LiCN, H₂CNH, NF₃, NH₃ with n=0–3, is a challenging task. The trends in calculated binding energies cannot be explained in terms of any of the usual indexes, including π donation from the halogen lone pairs to the p(π) empty orbital on B, deformation energies, charge capacities, or LUMO energies, which are normally invoked to explain the higher Lewis acidity of BCl₃ relative to BF₃. The results of the high‐level G3B3 ab initio calculations reported in this study suggest that the interaction energies of these complexes are determined by a combination of at least three factors. These include the decrease in the electron‐accepting ability of B as a result of π donation by the halogen atom, the increase in the electron‐acceptor capacity of B due to deformation of the acid, and the large increase in the deformation energy of the acid with increasing halogen substitution. The dominant effects are those derived from the electronic effects of acid deformation. Deformation not only has direct energetic consequences, which are reflected in the large differences between dissociation (D₀) and interaction (E_int) energies, but also leads to an enhancement of the intrinsic acidities of BH_3?nF_n and BH_3?nCl_n moieties by lowering the LUMO energies to very different extents, consistent with the frontier orbital model of chemical reactivity. Although this lowering depends on both the number and the nature of the halogen substituents, binding energies do not systematically increase or decrease as the number of halogen atoms increases.     

Xα scattered wave calculations of the ionisation energies of N3P3F6 and N4P4F8

Ionisation energies have been calculated for N₃P₃F₆ and N₄P₄F₈ with the overlapping sphere version of the Xα scattered wave method and with the inclusion of a vacacy sphere for the interior of each PN ring. Experimental energies are calculated to within 1 eV on average for both sets of calculations, but the spacings of the levels are reproduced better with the vacancy sphere model.     

Dependence of collision‐induced dissociation energy on molecular degrees of freedom as a means to assess relative binding affinity in multivalent complexes

In collision‐induced dissociation mass spectrometry experiments, the collision energy required for dissociation linearly depends on the degrees of freedom in the precursor ion. The magnitude of the slope of this relationship previously has been shown to qualitatively correlate to the relative binding strength of a noncovalently bound, monovalent complex. The goal of the work presented here is to determine if a similar methodology can be applied for assessing relative binding strengths in multivalent species. We have tested the method on complexes formed from 18‐crown‐6 and a variety of protonated, primary alkylamines, [C_nH_2n+1NH₃]⁺ (n = 9, 12, 14, 16 and 18) and alkyldiamines, [H₃NC_nH_2nNH₃]²⁺ (n = 3, 5, 6, 9 and 12), and compared our results with dissociation energies calculated using density functional theory at the B3LYP/6‐31G* level. We found that the method correctly assessed the stronger crown ether/headgroup interaction in the two divalent species (1:1 and 2:1 complexes formed from the diaminoalkanes) compared with the weaker interaction in the monovalent species (1:1 complexes formed from mono‐aminoalkanes). However, the experimental method could not distinguish between the binding strengths of the two divalent complexes, perhaps because their calculated dissociation energies were quite similar. Our preliminary results suggest that this method could potentially be used for a quick and simple analysis of binding strengths in multivalent species if the binding strengths of the species are significantly different from one another. Copyright © 2011 John Wiley & Sons, Ltd.     

Relativistic electronic structures of the Ag2 and Au2 molecules

The relativistic electronic structures of the Ag₂ and Au₂ molecules have been calculated using the recently developed self-consistent-field Xα Dirac-scattered-wave programs. Calculations have been carried out for transition energies and ionization potentials for selected molecular orbitals. The results indicate a large degree of s-d hybridization in the ground state of the Au₂ molecule. The calculations are in good agreement with other theoretical work and with existing experimental results.     

Structures and bonding patterns of nanoannular carbon clusters (C4–C20) through AIM analyses

Structures, binding energies, harmonic frequencies, dipole moments, HOMO–LUMO energy gaps and particularly atoms in molecules (AIM) analyses of some nanoannular carbon clusters (C₄–C₂₀) are investigated at B3LYP/6-31+G(d) level of theory. No correlation is found by plotting the calculated binding energies as a functional number of carbon atoms of carbon clusters. The calculated binding energies sharply increase from C₄ to C₁₀ while slowly from C₁₀ to C₂₀. The binding energies of C_4n+2 clusters including C₆, C₁₀, C₁₄, and C₁₈ have a clear increase when compared with others indicating their aromatic characters which is confirmed by results of HOMO–LUMO energy gaps and geometrical parameters. AIM analyses show that most of our carbon clusters are topologically normal (non-conflict) with stable structures. Nevertheless, the topological networks of small antiaromatic rings, C₄ and C₈, at their equilibrium geometries may change via molecular vibrations. The existence of straight bond paths in 3D molecular graphs of carbon clusters with n > 10 implies that ring strains are decreased as the ring sizes grow. Except for C₄ and C₈, the ellipticity values for the remaining carbon clusters are small indicating that the C–C bond is conserved in these clusters. Dipole moments of even-numbered structures are negligible, whereas odd-numbered ones have μ values of 0.09−0.73 D.     

The remarkably invariant interaction energies of lithium first-row compounds with water and with ammonia

Solvation energies of lithium first-row compounds LiX (X ? H, Li, BeH, BH₂, CH₃, NH₂, OH, F) and of the lithium cation with the model solvents, water and ammonia, have been calculated ab inito (MP2/6-31 + G^*//6-31G^* with zero-point vibrational energy corrections at 3-21G//3-21G). The solvation energies are found to be remarkably constant: ?18.0 ± 1.2 and ?21.5 ± 1.3 kcal/mol for the hydrates and ammonia solvates, respectively. This independence on the nature of X is due largely to the ionic character of the LiX compounds (dipole moments 4.7–6.6 debye). The unexpectedly high solvation energies of the lithium molecule (?14.3 and ?17.8 kcal/mol, respectively) are due to the polarizability of Li₂. At the same level, the lithium cation has interaction energies with H₂O and NH₃ of ?34.1 and ?39.7 kcal/mol, respectively. For the hydrates of LiOH and LiF cyclic structures with hydrogen bonds and somewhat increased solvation energies also are described.     

Ground state electronic structures of some metal atom cluster compounds

The ground state electronic structures of several metal atom cluster compounds, Re₃Cl₉, Re₃Cl^3?₁₂ and Mo₆Cl^2?₁₄, have been calculated by the SCF Xα SW method. The results are consistent with the earlier d-orbital overlap patterns and with the reported spectroscopic properties.     

Discrete variational Xα calculations for Sc2 and Ti2

The electronic structures of the Se₂ and Ti₂ molecules have been calculated by the DV Xα method. For these molecules ¹∑_g⁺ ground states are obtained which correspond to triple and quadruple bonding in Se₂ and Ti₂ respectively. Both the calculated ionization potentials and optical transition energies are in good agreement with experimental data. Equilibrium bond lengths of 2.21 and 1.96 À have been obtained for Se₂ and Ti₂ respectively.     

Density functional theory calculation of 2p spectra of SiH4, PH3, H2S,HCl, and Ar

The method developed recently for prediction of 1s electron spectra is now extended to the 2p spectra of SiH₄, PH₃, H₂S, HCl, and Ar. The method for X‐ray absorption spectra involves the use of ΔE for the excitation and ionization energies, and application of time‐dependent density functional theory using the exchange‐correlation potential known as statistical average of orbital potentials for the intensities. Additional assumptions and approximations are also made. The best exchange‐correlation functional E_xc for the earlier calculation of ΔE in 1s spectra of C to Ne (namely Perdew–Wang 1986 exchange, combined with Perdew–Wang 1991 correlation) is no longer used in this work on 2p spectra of Si to Ar. Instead, recently tested E_xc good for 2p core‐electron binding energies (known as OPTX) for exchange and LYP for correlation, plus scalar zeroth‐order regular approximation is adopted here for the ΔE calculations. Our calculated X‐ray absorption spectra are generally in good agreement with experiment. Although the predictions for the higher excitations suffer from basis set difficulties, our procedure should be helpful in the interpretation of absorption spectra of 2p electrons of Si to Ar. In addition, we report calculated results for other kinds of electron spectra for SiH₄, PH₃, H₂S, HCl, and Ar, including valence electron ionizations and excitations as well as X‐ray emission. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008