Utilisation des méthodes de localisation multi-référence pour les systèmes quasi-dégénérés

La structure électronique et les propriétés de transfert de charge intramoléculaire de certains composés à valence mixte ont été étudiés au niveau ab-initio multi-référence, en utilisant des orbitales moléculaires canoniques et localisées. Les composés chimiques étudiés sont : un cation de spiro pi-sigma-pi : 5,5'(4H,4H')-spirobi-[cyclopenta[c]pyrrole]2,2',6,6'tetrahydro cation, ("Spiro" dans le texte suivant); une série des chaînes cationiques linéaires composées d'atomes de béryllium : BeN, (avec N = 6, ..., 12); et deux molécules bis-triarylamines : N,N,N',N'-Tetra(4-méthoxyphényl)-1,4phénylènediamine cation, et bis{4-[N,N-di(4-méthoxyphnyl)amino]phényl}butadiyne cation. Les modèles théoriques et les méthodes de calcul utilisées dans ce travail sont les suivants : CAS-SCF, CAS+S, CAS+SD (MRCI), et CAS+SD en utilisant des orbitales localisées. Des différents bases contractées ont été utilisés. Les surfaces d'énergie potentielles adiabatiques de l'état électronique fondamentale et les trois états excités les plus bas du cation de Spiro, ont été calculés, au sein d'un modèle à deux états, et un potentiel de double-puits a été obtenu pour l'état électronique fondamental. En suivant la localisation/délocalisation de charge dans le système p de valence du Spiro à travers la coordonnée de réaction du transfert de charge intramoléculaire, nous avons montré un faible couplage électronique entre les deux moitiés d'oxydoréduction de ce cation moléculaire. L'effet de la corrélation dynamique, en utilisant des orbitales localisées ou canoniques, a été jugé cruciale pour une description quantitative de la structure électronique et les autres paramètres importantes de transfert d'électron de ce système modèle à valence mixte. Les résultats des chaînes linéaires de béryllium montrent une évolution progressive de classe III (couplage électronique fort) envers classe II (couplage électronique faible) en fonction de nombre d'atomes de béryllium. En effet, dans les cas où (N > 10), les chaînes cationiques ont été trouvés se rapprocher de la classe I, où le couplage disparaît. Les paramètres de transfert d'électrons intramoléculaire Vab, Ea, et Eopt ont été calculés pour chaque chaîne atomique. Il à été montré que la baisse des valeurs de Vab avec l'augmentation de N suit une courbe exponentielle.The electronic structure and the intramolecular charge transfer properties of a selected number of mixed valence compounds were investigated at multireference ab-initio level, using both canonical and localized molecular orbitals. The chemical compounds studied are: a spiro p-s-p molecular cation: 5,5_(4H,4H_)- spirobi[cyclopenta[c]pyrrole]2,2',6,6'tetrahydro cation (the "Spiro" molecule in the following); a series of cationic linear chains composed of beryllium atoms: BeN, (with N = 6, ..., 12); and two bis-Triaryl amines molecules: namely N,N,N',N'-Tetra(4-methoxyphenyl)-1,4-phenylenediamine cation, and bis{4-[N,N-di(4-methoxyphenyl)amino]phenyl}butadiyne cation. The theoretical models and computational methods used in this work are: CAS-SCF, CAS+S, CAS+SD (MRCI), and CAS+SD using localized orbitals. Different basis sets contractions were used. For Spiro cation, The potential energy surfaces of the adiabatic ground and the lowest three excited electronic states have been computed, within a two-state model, and a double-well potential has been obtained for the ground electronic state. We have demonstrated a low coupling interaction between the two redox moieties of this molecular cation by following the charge localization/delocalization in the valence _ system through the reaction coordinate of the intramolecular charge transfer. The effect of dynamical correlation, using either localized or canonical orbitals, was found to be crucial for a quantitative description of the electronic structure and some important electron transfer parameters of this model mixed-valence system. The results of the linear beryllium chains show a consistent gradual shift between different classes of mixed-valence compounds as the number of beryllium atoms increases, from class-III strong coupling toward class-II valence trapped. Indeed, in the largest cases (N > 10), the cationic chains were found to be closer to class I, where the coupling vanishes. The intramolecular electron transfer parameters Vab, Ea, and Eopt were calculated for each atomic chain. It is shown that the decrease of Vab with increasing N follows an exponential pattern

Utilisation des méthodes de localisation multi-référence pour les systèmes quasi-dégénérés

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Rearrangement of Diferrocenyl 3,4-Thiophene Dicarboxylate

Treatment of 3,4-(ClC(O))2-cC4H2S (1) with [FcCH2OLi] (2-Li) (Fc = Fe(η5-C5H5)(η5-C5H4)) in a 1:2 ratio gave 3,4-(FcCH2OC(O))2-cC4H2S (3). Compound 3 decomposes in solution during crystallization to produce FcCH2OH (2) along with 3,4-thiophenedicarboxylic anhydride (4). The cyclic voltammogram of 3 exhibits a reversible ferrocene-related redox couple (E1/2 = 108 mV, vs. Cp2Fe/Cp2Fe+) using [NnBu4] [B(C6F5)4] as the supporting electrolyte. DFT calculations reveal that the energy values of the LUMO orbitals of 3 (3,4-thiophene core) show 1 eV higher energies than that one of 2,5-(FcCH2OC(O))2-cC4H2S (5), both compounds’ HOMO orbitals are close to each other. Compound 4 was characterized by single X-ray structure analysis. It forms a band-type structure based on intermolecular O1···S1 interactions being parallel to (110) and (1–10) in the solid state, while electrostatic C···O interactions between the C=O functionalities of adjacent molecules connect both 3D-networks. Hirshfeld surface analysis was used to gain more insight into the intermolecular interactions in 4, the enrichment ratios (E) suggest that O···H, S···S, and O···C are the most favored intermolecular interactions, as shown by E values above 1.20. The relevance of the weak O···H, O···O, and O···C contacts in stabilizing the molecular structure of 4 was highlighted by the interaction energies between molecular pairs

Rearrangement of Diferrocenyl 3,4-Thiophene Dicarboxylate

Treatment of 3,4-(ClC(O))2-cC4H2S (1) with [FcCH2OLi] (2-Li) (Fc = Fe(η5-C5H5)(η5-C5H4)) in a 1:2 ratio gave 3,4-(FcCH2OC(O))2-cC4H2S (3). Compound 3 decomposes in solution during crystallization to produce FcCH2OH (2) along with 3,4-thiophenedicarboxylic anhydride (4). The cyclic voltammogram of 3 exhibits a reversible ferrocene-related redox couple (E1/2 = 108 mV, vs. Cp2Fe/Cp2Fe+) using [NnBu4] [B(C6F5)4] as the supporting electrolyte. DFT calculations reveal that the energy values of the LUMO orbitals of 3 (3,4-thiophene core) show 1 eV higher energies than that one of 2,5-(FcCH2OC(O))2-cC4H2S (5), both compounds’ HOMO orbitals are close to each other. Compound 4 was characterized by single X-ray structure analysis. It forms a band-type structure based on intermolecular O1···S1 interactions being parallel to (110) and (1–10) in the solid state, while electrostatic C···O interactions between the C=O functionalities of adjacent molecules connect both 3D-networks. Hirshfeld surface analysis was used to gain more insight into the intermolecular interactions in 4, the enrichment ratios (E) suggest that O···H, S···S, and O···C are the most favored intermolecular interactions, as shown by E values above 1.20. The relevance of the weak O···H, O···O, and O···C contacts in stabilizing the molecular structure of 4 was highlighted by the interaction energies between molecular pairs

Beryllium Dimer: A Bond Based on Non-Dynamical Correlation

The bond nature in beryllium dimer has been theoretically investigated using high-level <i>ab initio</i> methods. A series of ANO basis sets of increasing quality, going from sp to spdf ghi contractions, has been employed, combined with HF, CAS-SCF, CISD, and MRCI calculations with several different active spaces. The quality of these calculations has been checked by comparing the results with valence Full-CI calculations, performed with the same basis sets. It is shown that two quasi-degenerated partly occupied orbitals play a crucial role to give a qualitatively correct description of the bond. Their nature is similar to that of the edge orbitals that give rise to the quasi-degenerated singlet–triplet states in longer beryllium chains

A Novel Approach by Needles in the Payzone of Heterogeneous Tight Carbonate: A Case Study for Offshore Marginal Field

The new Fish-bones Completion &amp; Stimulation approach by needles in the pay stack aims at addressing heterogeneous tight carbonate by increasing flow area in the lower permeable streaks, which is efficient as hundreds of tunnels drain connecting the borewell to the body of the reservoir to increase well productivity and oil recovery. The initial plan includes selecting the best ones from Stair step horizontal well, Dual Lateral well, five lateral fish-bone drilling, and horizontal drilling along with hydraulic fracture. Considering the lessons of failure to clean internal tubes, the modified 4-1/2” Liner is installed in the lower two sub-layer by jetting subs combing with production subs for matrix acidizing in the upper one sub-layer as per modified Fish-bones Completion Design. In addition, special acid-releasing float shoes and new fishing baskets are applied to avoid those previous problems with this well technique. The candidate well shows good oil test and production, which improved by three times at 2000bbl/d with respect to the initial plan in the B field. This paper describes the technology background and characteristics, design factors, modified design, execution, well test, and lessons learned during implementation

Beryllium-Dimer: a Bond Based on Non-Dynamical Correlation

The bond nature in beryllium dimer has been theoretically investigated using high-level ab initio methods. A series of ANO basis sets of increasing quality, going from sp to spdfghi contractions, has been employed, combined with HF, CAS-SCF, CISD and MRCI calculations with several different active spaces. The quality of these calculations has been checked by comparing the results with valence Full-CI calculations, performed with the same basis sets. It is shown that two quasi-degenerated partly-occupied orbitals play a crucial role in order to give a qualitatively correct description of the bond. Their nature is similar to the edge orbitals that give rise to the quasi-degenerated singlet-triplet states in longer beryllium chains