Eduardo Hollauer

A generalized multistructural wave function

A generalized multistructural (GMS) wave function is presented which combines the advantages of the self‐consistent‐field molecular orbital (SCF‐MO) and valence bond (VB) models, preserving the classical chemical structures but optimizing the orbitals in a self‐consistent way. This wave function is particularly suitable to treat situations where the description of the molecular state requires localized wave functions. It also provides a very convenient way of treating the electron correlation problem, avoiding large configuration interaction (CI) expansions. The final wave functions are much more compact and easier to interpret than the ones obtained by the conventional methods, using orthogonal orbitals. Applications of the GMS wave functions to a variety of systems are presented.

Vibrational spectra of bis(dmit) complexes of main group metals: IR, Raman and ab initio calculations

This work reports a theoretical-experimental investigation of the infrared/Raman vibrational spectra of several metal 1,3-dithole-2-thione-4,5-dithiolate (dmit) complexes; [NEt4]2[Zn(dmit)2], [NEt4][Sb(dmit)2] and [NEt4][Bi(dmit)2]. IR/Raman spectra of all the solids and the solution IR spectrum of [NEt4]2[Zn(dmit)2] were recorded from 4000 to 100 cm-1. Two regions were clearly identified: below 380 cm-1, the modes presented significant metal-ligand contributions, and above, the modes indicated major ligand contributions. IR/Raman spectra of NEt4Br have also been recorded. The vibrational bands have been assigned starting from the analysis of related compounds, of previous published spectra and compared to several ECPs (SBK, Stuttgart), basis sets (with and without functions d) and methodologies (RHF, MP2 and DFT). Geometries, frequencies and intensities were calculated and compared to the experimental frequencies seeking secure assignment. Thus, an excellent agreement was obtained for several experimental bands.

A generalized multi-structural wavefunction. The He+2 molecule as an example

Abstract A generalized multi-structural wavefunction is presented which combines the advantages of the SCF-MO and VB models, preserving the classical chemical structures but optimizing the orbitals in a self-consistent way. The He + 2 molecule is used as an illustration of the method. The potential energy surface for the 2 Σ + u state is constructed and the resulting internuclear equilibrium distance and dissociation energy are compared to the results of more elaborated calculations and to the experiments.

An experimental and theoretical study of the electronic spectra of tetraethylammonium [bis(1,3-dithiole-2-thione-4,5-dithiolato)M(III)] and tetraethylammonium [bis(1,3-dithiole-2-one-4,5-dithiolato)M(III)] (M = Sb or Bi)

Metal complexes of dmit and related ligands, such as dmio, have been studied extensively over the last few decades: [dmit](2-) = bis(1,3-dithiole-2-thione-4,5-dithiolato); [dmio](2-) = bis(1,3-dithiole-2-one-4,5-dithiolato). While much effort has been placed on determining structural properties, very few vigorous spectroscopic studies of these metal complexes have been undertaken. The spectroscopic features of the infrared, Raman and UV-vis spectra, previously reported, have largely been used to characterize compounds. In particular, many details of the electronic structure are still to be revealed. We now report a detailed analysis of the UV-vis spectra of the [M(dmit)](-1) and [M(dmio)](-1) anions, where M = Sb(III) or Bi(III). Experimental spectra were deconvoluted and analysed by several theoretical methodologies, including ab initio CI, TD and CISD calculations. The results led to the assignments of several MLCT/LMCT bands, occurring between 390 and 300 nm, and the confirmation of metal orbital contributions to the HOMO-LUMO boundary.

Vibrational study of dialkylphosphonates: di-n-propyl- and di-i-propylphosphonates by semiempirical and ab initio methods

Fourier transform infrared and Fourier transform Raman spectra of n-C(3)H(7) and i-C(3)H(7) dialkylphosphonates have been obtained. Semiempirical AM1 and the ab initio orbital molecular RHF/6-31G* theories have been used to study the molecular geometry, and the harmonic vibrational spectra with the purpose to assist the experimental assignments of these compounds. An extensive discussion on the assignment of the C-C, C-O, P-O and P=O stretching is carried out based on experimental data of compounds which have the propyl and isopropyl groups, as well as comparing the vibrational spectra of propane. Most of the RHF/6-31G* and AM1 results, once applied the appropriate scaling factor, showed an excellent agreement with the experimental wavenumbers. A few calculated frequencies related to CC and CO stretching do not agree well with the experimental trends.

Fourier-transform infrared and Raman spectra, and ab initio calculations for cadmium-n-di-iso-propylphosphorylguanidine-di-chloride (CdDPGCl2) complex

Cadmium-n-di-isopropylphosphorylguanidine-di-chloride (CdDPGCl2) was synthesized in the solid phase and characterized previously. The Fourier transform infrared and Raman spectra of (CdDPGCl2) in the solid state were recorded and analyzed. Emphasis was placed on the vibrational assignment of the [(O2P=O-[CdCl2]-HN=C) fragment of the complete molecular structure. With the aim of assisting the vibrational assignment of the experimental spectra, a comparison with the spectra of N-di-isopropylphosphorylguanidine ligand was carried out and ab initio calculations have been performed with several effective core potentials and valence basis sets (Hay-Wadt (HW) and Stevens-Basch-Krauss (SBK)). Due to our limited computational resources, hydrogen atoms replaced the isopropyl groups. The calculated geometrical parameters showed excellent agreement with the experimental, as well as the RHF/MP2 calculated infrared wave numbers, when compared to the IR/Raman experimental wave numbers.

Predictive QSPR analysis of corrosion inhibitors for super 13% Cr steel in hydrochloric acid

An experimental and theoretical study on the inhibition corrosion efficiencies of twenty three compounds in hydrochloric acid (15% w/v) on 13% Cr modified stainless steel (martensitic) has been carried out. This inhibitor set includes amines, thiourea derivatives and acetylenic alcohols. Experimental weight losses at 60oC were correlated with group and quantum AM1 descriptors obtained from QSPR analysis. Such data, for a large set of molecules, offer a unique opportunity for searching for correlations between inhibition corrosion efficiency and molecular properties. Calculations based on three different statistical methodologies were carried out. The first method, using calibration procedures, employs an ordinary least squares (OLS) methodology with a simple descriptor selection based on R2 values. From this procedure, we obtained a model, Y15, having a R2 value of 0,979 and a Q2 value of 0.786. The second method employs a descriptor selection based on the second-order cross-validation OLS procedure (SOCV-OLS). In this process, the variables are chosen according to their ability to predict molecular inhibition efficiencies. The best model obtained using this methodology, Q5, had R2 and Q2 values of 0.859 and 0.785, respectively. The third method, based on regular partial least squares (PLS), resulted in R2 and Q2 values of 0.859 and 0.754, respectively. All calculations were carried out for the weight isoesteric Langmuir adsorption function (WILA function), ln(qM/(1-q )) or ln Kads. A careful comparison between the calibration and the cross-validation descriptor selection indicated that they had very few descriptors in common. This article presents some key equations and the most relevant descriptors. We are unaware of any similar QSPR study on super 13% Cr stainless steel in the literature.

Valence electronic excitation of the SiF4 molecule: generalized oscillator strength for the 5t2 ? 6a1 transition and ab initio calculation

The electronic excitation of the silicon tetrafluoride (SiF4) molecule has been studied using the angle-resolved electron energy-loss technique, at 1.0 keV incident electron energy, in the 0-50 eV energy range with an angular range of 1.5°-20.0°. The absolute generalized oscillator strength (GOS) for the 5t2→6a1 electronic transition, located at 13.0 eV, has been determined. A minimum has been observed in the GOS for this transition at K2 = 1.4 au. We have also determined the absolute elastic and inelastic differential cross sections at 1 keV. In order to help in the interpretation of the experimental results, ab initio calculations have been performed for the vertical valence transitions and ionization energies for the SiF4 molecule. Configuration-interaction calculations, including single and double excitations (CI-SD) and the symmetry-adapted-cluster expansion (SAC) were used. The CI-SD approach was also employed to obtain the optical oscillator strength for the 5t2→6a1 transition.

Configuration interaction simulation of the NEXAFS photoabsorption spectrum of naphthalene

The near-edge X-ray absorption fine structure (NEXAFS) spectrum of naphthalene was analysed theoratically using the final state approximation rule. ROHF/SCF calculations were carried out for a localized core-hole cationic state under the Bagus-Schaffer scheme for each channel of inequivalent excitations. CI calculations were performed allowing single and double excitations from carbon 1s electrons to the first ten virtual orbitals. The energies and oscillator strengths were calculated. The final spectrum was generated by convolution of Gaussian peaks with 0.5 eV as FWHM of the statistically-averaged calculated transitions. The theoretical result shows remarkable agreement with the experimental high-resolution NEXAFS data measured at BESSY II. Work is in progress to get better control of the variational wave function collapse problem at CI level through the use of symmetry breaking core-hole excited states (MEG-CI). This methodology might offer a clear and transparent way to take into account the relaxational and correlation energy, the virtual orbital specificity and the required restricted configuration interaction needed to the NEXAFS prediction problem.

Density functional theory study of the Fourier transform infrared and Raman spectra of dichloro-bis(2,4-pentanedionate)tin(IV)

Fourier transform infrared and Fourier transform Raman spectra of dichloro-bis(2,4-pentanedionate)tin(IV) have been obtained. Density functional theory (DFT) BLYP calculations, have been carried out with the purpose of understanding the metal-ligand region spectra of this compound. Vibrational wavenumbers calculated by BLYP/6-31G* force fields are closed with the experimental results. The percentage of deviation of the bond lengths and bond angles gives a good picture of the normal modes, and serves as a basis for the assignment of the wavenumbers. The calculated geometrical parameters show slight differences compared with the experimental ones, and these differences can be explained by the different physical state of Sn(acac)2Cl2. The DFT-BLYP calculations assumed a free molecule in the gas phase. The experimental wavenumbers are obtained from the spectra of solid samples.