In silico design of a new Zn-triazole based metal-organic framework for CO2 and H2O adsorption.

In search for future good adsorbents for CO2 capture, a nitrogen-rich triazole-type Metal-Organic Framework (MOF) is proposed based on the rational design and theoretical molecular simulations. The structure of the proposed MOF, named Zinc Triazolate based Framework (ZTF), is obtained by replacing the amine-organic linker of MAF-66 by a triazole, and its structural parameters are deduced. We used grand-canonical Monte Carlo (GCMC) simulations based on generic classical force fields to correctly predict the adsorption isotherms of CO2 and H2O. For water adsorption in MAF-66 and ZTF, simulations revealed that the strong hydrogen bonding interactions of water with the N atoms of triazole rings of the frameworks are the main driving forces for the high adsorption uptake of water. We also show that the proposed ZTF porous material exhibits exceptional high CO2 uptake capacity at low pressure, better than MAF-66. Moreover, the nature of the interactions between CO2 and the MAF-66 and ZTF surface cavities was examined at the microscopic level. Computations show that the interactions occur at two different sites, consisting of Lewis acid-Lewis base interactions and hydrogen bonding, together with obvious electrostatic interactions. In addition, we investigated the influence of the presence of H2O molecules on the CO2 adsorption on the ZTF MOF. GCMC simulations reveal that the addition of H2O molecules leads to an enhancement of the CO2 adsorption at very low pressures but a reduction of this CO2 adsorption at higher pressures.

Spin-Orbit Effects in the Spectroscopy of the X2Π and a4Σ- Electronic States of Carbon Iodide, CI.

Highly correlated ab initio calculations have been performed to describe the potential energy curves (PECs) and the spectroscopic properties of the X2Π state and of the first excited state of the CI radical. Multi Reference configuration interaction calculations with Davidson correction (MRCI+Q) and relativistic effective core potential for the iodine atom have been performed. It is found that the two lowest electronic states, the X2Π and the a4Σ- states, are stable against dissociation and well separated from the other electronic states. Spectroscopic constants of these two states have been evaluated using their calculated PECs. Because of the presence of the iodine atom in this molecular system, spin-orbit (SO) interactions are playing an important role in the molecular and in the dissociation regions. The excitation energy of the a4Σ- state is calculated 1.67 eV (MRCI) above the X2Π ground state and 1.70/1.62 eV (MRCI with SO correction) for the Ω = 1/2 and 3/2 transitions, respectively. The dissociation energy D0 of the X2Π ground state is evaluated 2.66 eV (MRCI calculation) without SO correction and 2.46/2.36 eV with SO correction for the Ω = 1/2 and 3/2 components, respectively. The dissociation energy D0 of the a4Σ- state is evaluated 0.99 eV (MRCI calculation) without SO correction and 0.83/0.72 eV with SO correction for the Ω = 1/2 and 3/2 components, respectively. This work should help for the identification of this radical in laboratory and in atmospheric media.

Energetic Diagrams and Structural Properties of Monohaloacetylenes HC≡CX (X = F, Cl, Br).

Highly correlated electronic wave functions within the Multi Reference Configuration Interaction (MRCI) approach are used to study the stability and the formation processes of the monohaloacetylenes HCCX and monohalovinylidenes C2HX (X = F, Cl, Br) in their electronic ground state. These tetra-atomics can be formed through the reaction of triatomic fragments C2F, C2Cl, and C2Br with a hydrogen atom or of C2H with halogen atoms via barrierless reactions, whereas the reactions between the diatomics [C2 + HX] need to overcome barriers of 1.70, 0.89, and 0.58 eV for X = F, Cl, and Br. It is found that the linear HCCX isomers, in singlet symmetry, are more stable than the singlet C2HX iso-forms by 1.995, 2.083, and 1.958 eV for X = F, Cl, and Br. The very small isomerization barriers from iso to linear forms are calculated 0.067, 0.044, and 0.100 eV for F, Cl, and Br systems. The dissociation energies of the HCCX systems (without ZPE corrections), resulting from the breaking of the CX bond, are calculated to be 5.647, 4.691, and 4.129 eV for X = F, Cl, Br, respectively. At the equilibrium geometry of the X(1)Σ(+) state of HCCX, the vertical excitation energies in singlet and triplet symmetries are all larger than the respective dissociation energies. Stable excited states are found only as (3)A', (3)A″, and (1)A″ monohalovinylidene structures.

Size-dependent mechanical properties of axial and radial mixed AlN/GaN nanostructure.

In this paper, continuum multiscale models are proposed to describe the size-dependent mechanical properties of two kinds of heterogeneous nanostructures: radially heterogeneous nanowires and longitudinally heterogeneous nanolaminates. In both cases, the continuum models involve additional surface/interface energies, which allow capturing size effects. Several models of imperfect interface models, like coherent and spring-layer ones, are shown to respectively capture the size effects, which are reported by first-principles calculations performed on heterogeneous nanostructures. In each case, a procedure is proposed to identify the parameters of the surface/interface model in the continuum framework, based on first-principles calculations performed on slab systems. The obtained continuum models allow avoiding full computations on atomistic models, which are not affordable for large sizes (diameters, layer thickness). An increase of the overall stiffness for both kinds of heterogeneous AlN/GaN nanostructures with the decrease of the dimensions is evidenced. The continuum models are then compared with full first-principles calculations to demonstrate their accuracy and their ability to capture size effects.

Reaction of CN(-) with F, Cl, O, and S Atoms: Attachment or Associative Detachment?

Highly correlated ab initio wave functions within the UCCSD(T)-F12 approach have been used to map the potential energy surfaces (PESs) describing the reactivity of the CN(-) (X(1)Σ(+)) anion with neutral atoms present in interstellar media (F, Cl, O, and S). With the H atom, for comparison, the reaction [CN(-)((1)Σ(+)) + H((2)S)] evolves along the PES of the X(2)Σ(+) electronic ground state of HCN(-) (or HNC(-)) until the crossing with the X(1)Σ(+) electronic ground state of HCN (or HNC), where electron detachment occurs. The process is rather similar to the two halogen atoms F and Cl, with some differences due to the larger electron affinity of the halogens, making possible the existence of ClCN(-) in a (2)Σ(+) state. The reaction of CN(-) with O and S atoms proceeds via a multistep mechanism. The lowest electronic state at long distance, the (3)Π state arising from the [CN(-)((1)Σ(+)) + O/S((3)P)] reaction channel, does not correlate with the X(1)Σ(+) ground state of the XCN(-) anion (X = O or S). This (3)Π state and its bent components cross at medium RXC (RXN) distances the X(1)Σ(+) ground state of XCN(-) or XNC(-), and at shorter distances the X(2)Π state of the neutral XCN or XNC where the extra electron can detach. With both O and S atoms, it is shown that the spin-orbit couplings can efficiently lead the [CN(-)((1)Σ(+)) + O/S((3)P)] reaction toward the stable X(1)Σ(+) ground state of XCN(-) and XNC(-).

Structure, Spectroscopy, and Bonding within the Zn(q+)-Imidazole(n) (q = 0, 1, 2; n = 1-4) Clusters and Implications for Zeolitic Imidazolate Frameworks and Zn-Enzymes.

Using density functional theory (DFT) with dispersion correction and ab initio post Hartree-Fock methods, we treat the bonding, the structure, the stability, and the spectroscopy of the complexes between Zn(q+) and imidazole (Im), Zn(q+)Imn (where q = 0, 1 and 2; n = 1-4). These entities are subunits of zeolitic imidazolate frameworks (ZIFs) and Zn-enzymes, which possess relevant roles in industrial and biological domains, respectively. We also investigate the Imn (n = 2-4) clusters for comparison. For each species, we determine several new structures that were not found previously. Our calculations show a competition between atomic metal solvation, by either σ-type interactions or π-stacking type interaction, and proton transfer through hydrogen bonding (H-bonding) in charged species. This results in several geometrical environments around the metal. These are connected with structural properties and the functional role of Zn cation within ZIFs and Zn-enzymes. Moreover, we show that the Zn(2+)Imn subunits do not absorb in the visible domain, which may be related to the photostability of ZIFs. Our findings are important for the development of new applications of ZIFs and metalloenzymes.

Nucleophilic or electrophilic interactions of C2 with HX systems (X = F, Cl, Br).

Highly correlated ab initio wave functions within the MRCI approach are used in a comparative study of the interactions between C2 and the three hydrogen halides HX (X = F, Cl, Br). Test calculations are also presented using the UCCSD(T)-F12 approach. The asymptotic regions are investigated for different relative orientations of the two moieties. It is shown that the three systems C2 + HX are bound, for intermolecular distances close to 3 Å, through nucleophilic interactions between C2 and HX for approaches perpendicular to the C-C axis, with decreasing interaction energies from HF to HBr. For HX approaching C2 along its axis, the interactions, governed by the electrophilic character of C2 are decreasing from HBr to HF. Even though the reactions toward the molecular systems HCCX or CCHX are exothermic, activation barriers (0.58 eV and more) are calculated at short distances, preventing the direct reactions toward the corresponding tetra-atomic systems.

Towards an elastic model of wurtzite AlN nanowires.

Starting with ab initio calculations of AlN wurtzite [0001] nanowires with diameters up to 4 nm, a finite element method is developed to deal with larger nanostructures/nanoparticles. The ab initio calculations show that the structure of the nanowires can be well represented by an internal part with AlN bulk elastic properties, and one atomic surface layer with its own elastic behavior. The proposed finite element method includes surface elements with their own elastic properties using surface elastic coefficients deduced from the ab initio calculations. The elastic properties obtained with the finite element model compare very well with those obtained with the full ab initio calculations.

New study of the stability and of the spectroscopy of the molecular anions NCO- and CNO-.

Using highly correlated wave functions, the ground and the low lying excited states of the molecular NCO(-) and CNO(-) anions have been reinvestigated. The stability of the electronic ground state of the two isomers with respect to dissociation and to electron detachment has been checked along the isomerization pathway. The regions of stability of the excited electronic states have been analyzed and identified and it is shown that only the ground state is stable and the corresponding potential energy surface presents three equilibrium positions. The rovibronic spectroscopy of the X (1)Σ(+) state of both NCO(-) and CNO(-) isomers has been determined by a variational approach leading to remarkable agreement with experimental data.

Carbazole derivatives containing chalcone analogues targeting topoisomerase II inhibition: First principles characterization and QSAR modelling.

Recently, a series of carbazole derivatives containing chalcone analogues (CDCAs) were synthetized as potent anticancer agents and apoptosis inducers. These compounds target the inhibition of topoisomerase II and present cytotoxic activities. After comparison to experiment, we validated the use of B3LYP, a density functional theory-based approach, to describe the structure and molecular properties of the carbazole subunit and CDCAs compounds of interest. Then, we derived relationships between the chemical descriptors and activity of these carbazole derivatives using multi-parameter optimization and quantitative structure activity relationships (QSAR) approaches. For the QSAR studies, we used multiple linear regression and artificial neural network statistical modelling. Our predicted activities are in good agreement with the experimental ones. We found that the most important parameter influencing the activity of the considered compounds is the octanol-water partition coefficient, highlighting the importance of flexibility as a key molecular parameter to favor cell membrane crossing and enhance the action of these CDCAs against topoisomerase II. Our results provide useful guidelines for designing new oral active CDCAs medicaments for cytotoxic inhibition.

Ab initio study of HZnF.

On the basis of highly correlated ab initio calculations, an accurate determination of the electronic structure and of the rovibrational spectroscopy has been performed for the electronic ground state of the HZnF system. Using effective core pseudopotentials for the Zn and F atoms and associated aug-cc-pVQZ basis sets, we have calculated, at the multireference configuration interaction level including the Davidson correction, the three-dimensional potential energy surface of the X(1)Sigma(+) ground state. The rovibrational energy levels have been obtained variationally, and the results have been discussed and compared with existing experimental data on the ground state of the close system HZnCl, which exhibits a complicated vibration-rotation spectrum. Our analysis shows that the nature of the H-ZnF bond is quite similar to that of the H-ZnCl bond, according to their bond lengths, harmonic frequencies of the H-Zn stretching mode, and dissociation energies into H and ZnF/ZnCl. The ab initio study of the electronic ground and excited states of ZnH and ZnH(+) are also presented using similar level of calculations. Characteristic constants are given for the first bounded electronic states correlating to the first two dissociation asymptotes of the neutral and ionic diatomics.

Ionic chemistry of tetravinylsilane cation (TVS+) formed by electron impact: theory and experiment.

We performed experimental and ab initio studies on tetravinylsilane cation (TVS(+)) and its ionic and neutral fragmentation products. The aim of the study is the assignment of the products formed in electron impact ionization reaction of TVS. The experimental data were compared with ab initio data calculated at the MP2/cc-pVDZ level of theory. We found good agreement between the calculated reaction enthalpies and experimental appearance energies of the ions. More generally, our calculations reveal that there is a competition between intramolecular isomerization and fragmentation processes occurring after ionization of TVS, leading to the formation of a multitude of neutral and ionic species important for characterizing the silicon-carbon-containing plasma and media. New routes for the synthesis of bearing silicon molecules are suggested.

Rotational excitation and de-excitation of C(2)(X 1Sigma(g)+) by para-H(2)(j = 0).

For the van der Waals C(2)(X (1)Sigma(g)(+))-H(2) molecular system, we generated a new ab initio potential energy surface (PES). We mapped this PES at the multireference internally contracted configuration-interaction method including the Davidson correction together with a large diffuse basis set. Then, we incorporated our PES into quantum scattering calculations at the close coupling and infinite order sudden approximation methods to cover collision energies ranging from 0.1 up to 4000 cm(-1). After Boltzmann thermal averaging, rate coefficients for temperatures of up to 1000 K are deduced. Discrepancies between our new rates and those computed previously are noticed. This should induce deviations in astrophysical modeling.

Electronic structure, reactivity, and spectroscopy of dihydrides of group-IB metals.

Atomic pseudopotentials and highly correlated wave functions, including spin-orbit interactions, have been used to evaluate the electronic structure, stability, and spectroscopy of triatomic molecule MH(2), with a metal M belonging to group IB (Cu, Ag, and Au). CuH(2) and AuH(2) have been recently observed by IR spectroscopy in solid hydrogen and bending anharmonic wave numbers have been assigned to these two systems. The AgH(2) molecule has not been detected nor experimentally characterized, despite several theoretical works arguing on its stability. Our results confirm that the MH(2) radicals have a metastable bent ground state separated from the dissociation into [M+H(2)] ground state by barriers which have been evaluated to 1.43, 0.78, and 0.80 eV, for Cu, Ag, and Au compounds, respectively. These barriers are calculated smaller than in previous determinations but still large enough to stabilize the MH(2) systems. Spectroscopic data are calculated for these radicals.