Pd speciation on black phosphorene in a CO and C2H4 atmosphere: a first-principles investigation.

Deposited transition metal clusters and nanoparticles are widely used as catalysts and have long been thought stable in reaction conditions. We investigated the electronic structure and stability of freestanding and black phosphorene supported small Pd clusters containing 1 to 6 atoms in a CO or C2H4 atmosphere by extensive first-principles based calculations. We showed that, driven by the thermodynamics, subnanometric Pd clusters and single Pd atom on phosphorene may evolve for a better balance among metal-metal, metal-support and metal-adsorbate interactions, etc., resulting in atomic dispersion of Pd in reaction conditions. The strong interfacial Pd-P interactions would deform preformed Pd clusters into atomic strips of various lengths with enhanced stability comparable to bulk Pd. The diffusion barriers of terminal Pd atoms in the zigzag direction on phosphorene are small (<0.3 eV) and vary within ∼0.1 eV with the length of these atomic strips. Further adsorption of CO or C2H4 alters the Pd-P and Pd-Pd interactions and forms thermodynamically stable surface Pd species with decreased diffusion barriers, suggesting that atomic dispersion of Pd can be achieved on phosphorene, especially in a CO or C2H4 atmosphere. The current work may help to understand the superior catalytic performance of supported subnanometric transition metal catalysts in reaction conditions and pave the way for fabrication of single atom catalysts with the desired performance.

S2O2q+ (q = 0, 1, and 2) Molecular Systems: Characterization and Atmospheric Planetary Implications.

We use accurate ab initio methodologies at the coupled cluster level ((R)CCSD(T)) and its explicitly correlated version ((R)CCSD(T)-F12) to investigate the electronic structure, relative stability, and spectroscopy of the stable isomers of the [S2O2] system and of some of its cations and dications, with a special focus on the most relevant isomers that could be involved in terrestrial and planetary atmospheres. This work identifies several stable isomers (10 neutral, 8 cationic, and 5 dicationic), including trigonal-OSSO, cis-OSSO, and cyc-OSSO. For all these isomers, we calculated geometric parameters, fragmentation energies, and simple and double ionization energies of the neutral species. Several structures are identified for the first time, especially for the ionic species. Computations show that in addition to cis-OSSO and trans-OSSO proposed for the absorption in the near-UV spectrum of the Venusian atmosphere other S2O2, S2O2+, and S2O22+ species may contribute. Moreover, the characterization of the stability of singly and doubly charged S2O2 entities can also be used for their identification by mass spectrometry and UV spectroscopy in the laboratory or in planetary atmospheres. In sum, the quest for the main UV absorber in Venus' atmosphere is not over, since the physical chemistry of sulfur oxides in Venus' atmosphere is far from being understood.

Neutral and Multicharged Ions of Small Aluminum Oxides: Structures, Spectroscopy, and Energetics.

We use accurate ab initio methodologies at the Coupled Cluster level to compute the stable forms of AlxOyq+ (x = 1, 2; y = 1, 2; q = 0-3) species for which we derive an accurate set of geometrical and vibrational spectroscopic data. We also determine their adiabatic single, double, and triple ionization energies. These spectroscopic and thermodynamical data may help for identifying these species in laboratory, in astrophysical media, and in plasma and confirm previous observations of multi-charged AlxOy clusters by Atom Probe Tomography (ATP) coupled to mass spectrometry. They should help for identifying and understanding the complex chemical processes occurring during the Al2O3 growth in laboratory and in astrophysical media and those taking place at the degradation of Al-containing materials by high temperature corrosion/oxidation.

Identification of Key Intermediates during the NO and H2S Crosstalk Signaling Pathways.

The stable isomers and electronic states of [S,S,N,O]- species are investigated with a special focus on the most relevant isomers that could be involved in the NO/H2S cross-talk pathways in biological media. This work identifies eight stable anions, among which are the already known cis-SSNO- and trans-SSNO- molecules and a new NO3--like anionic species, NS2O-. Our computations show that the previously determined structure in lab experiment is trans-SSNO-, which is not relevant for biological activity in vivo. Instead, NS2O- is proposed as the most likely key intermediate in vivo during important biological processes. This result alleviates the corresponding controversy in the literature.

Electronic and Vibrational Spectroscopy of CsS.

Using multi configurational ab initio methodologies, we compute the potential energy curves (PECs) of the lowest electronic states of the diatomic CsS. These computations are performed using internally contracted multireference interaction configuration including Davidson correction (MRCI+Q) with and without considering spin-orbit effects. The shapes of the PECs are governed by the interactions between the two ionic states, 2Σ+ and 2Π, correlating at large internuclear separations ( RCsS) to the first ionic dissociation limit and the other electronic states correlating to the three lowest neutral dissociation limits. Computations show the importance of considering a large amount of electron correlation for the accurate description of the PECs and spectroscopy of this molecular system. As expected, these PECs are also strongly affected by the spin-orbit interaction. For the bound states, we report a set of spectroscopic parameters including equilibrium distances, dissociation energies, and vibrational and rotational constants. The effects of spin-orbit-induced changes on these parameters are also discussed. Moreover, we show that the 22Π state presents a "bowl" potential with a rather flat region extending to large RCsS distances. After being promoted to this state, wavepackets should undergo strong oscillations, similar to those observed by Zewail and co-workers for the NaI molecule. These should provide information on the shape of the PEC for the 22Π state and also on the couplings between this and the neighboring states.

Driving Chemistry and Europe.

"… Mobility that favors individual exchanges between researchers is extremely important for the scientific community. The merging of scientific publications within a consortium of European journals and the creation of the European Chemistry Congresses have been major successes …" Read more in the Guest Editorial by Gilberte Chambaud.

Physisorbed H2@Cu(100) surface: potential and spectroscopy.

Using an embedding approach, a 2-D potential energy function has been calculated to describe the physisorption interaction of H2 with a Cu(100) surface. For this purpose, a cluster model of the system calculated with highly correlated wavefunctions is combined with a periodic Density-Functional-Theory method using van der Waals-DF2 functional. Rotational and vibrational energy levels of physisorbed H2, as well as D2 and HD, are calculated using the 2D embedding corrected potential energy function. The calculated transitions are in a very good agreement with Electron-Energy-Loss-Spectroscopy observations.

Carbon dioxide interaction with isolated imidazole or attached on gold clusters and surface: competition between σ H-bond and π stacking interaction.

Using first principle methodologies, we investigate the subtle competition between σ H-bond and π stacking interaction between CO2 and imidazole either isolated, adsorbed on a gold cluster or adsorbed on a gold surface. These computations are performed using MP2 as well as dispersion corrected density functional theory (DFT) techniques. Our results show that the CO2 interaction goes from π-type stacking into σ-type when CO2 interacts with isolated imidazole and Au clusters or surface. The balance between both types of interactions is found when an imidazole is attached to a Au20 gold cluster. Thus, the present study has great significance in understanding and controlling the structures of weakly-bound molecular systems and materials, where hydrogen bonding and van der Waals interactions are competing. The applications are in the fields of the control of CO2 capture and scattering, catalysis and bio- and nanotechnologies.

Electronic structure and magnetic properties of naphthalene- and stilbene-diimide-bridged diuranium(V) complexes: a theoretical study.

The magnetic exchange coupling between two diuranium(V) ions exhibiting the 5f1-5f1 configuration in diimide-bridged complexes [Cp3UV]2(µ-L) (L = stilbene-, naphthalene-diimide) has been investigated theoretically using relativistic ZORA/DFT calculations. Using two different hybrid PBE0 and B3LYP functionals, combined with the broken symmetry (BS) approach, we found that the BS states of both naphthalene and stilbene complexes have lower energy than the corresponding high-spin (HS) triplet ones. The B3LYP/BS estimated exchange coupling J constants (- 16.1 vs. - 9.0 cm-1 respectively for the naphthalene and stilbene complexes) corroborate well with those obtained previously for other pentavalent diuranium(V) diimide-bridged systems. The computed J value is found to be sensitive to π-network linking the two magnetic U(V) centers. The natural spin density distributions and molecular orbital analyses explain well the antiferromagnetic character of these compounds and clarify the crucial role of the π aromatic spacer in promoting spin polarization and delocalization favoring the magnetic coupling. Furthermore, the effective involvement of the 6d/5f metal orbitals in metal-ligand bonding plays an important role for the magnetic communication between the two active U(V) 5f electrons. Graphical abstract.

Ab initio study of the low lying electronic states of ZnF and ZnF-.

Highly correlated ab initio calculations have been performed for an accurate determination of the electronic structure and of the spectroscopy of the low lying electronic states of the ZnF system. Using effective core pseudopotentials and aug-cc-pVQZ basis sets for both atoms, the potential curves, the dipole moment functions, and the transition dipole moments between relevant electronic states have been calculated at the multireference-configuration-interaction level. The spectroscopic constants calculated for the X(2)Sigma(+) ground state are in good agreement with the most recent theoretical and experimental values. It is shown that, besides the X(2)Sigma(+) ground state, the B(2)Sigma(+), the C(2)Pi, and the D(2)Sigma(+) states are bound. The A(2)Pi state, which has been mentioned in previous works, is not bound but its potential presents a shoulder in the Franck-Condon region of the X(2)Sigma(+) ground state. All of the low lying quartet states are found to be repulsive. The absorption transitions from the v=0 level of the X(2)Sigma(+) ground state toward the three bound states have been evaluated and the spectra are presented. The potential energy of the ZnF(-) molecular anion has been determined in the vicinity of its equilibrium geometry and the electronic affinity of ZnF (EA=1.843 eV with the zero energy point correction) has been calculated in agreement with the photoelectron spectroscopy experiments.

Adsorption of Hydrophobic and Hydrophilic Ionic Liquids at the Au(111) Surface.

Electrode-electrolyte microscopic interfacial studies are of great interest for the design and development of functional materials for energy storage and catalysis applications. First-principles-based simulation methods are used here to understand the structure, stability, energetics, and microscopic adsorption mechanism of various hydrophilic and hydrophobic ionic liquids (ILs; 1-butyl 3-methylimidazolium [BMIm]+[X]-, where X = Cl, DCA, HCOO, BF4, PF6, CH3SO3, OTF, and TFSA) interacting with a metallic surface. We have selected the Au(111) surface as a potential electrode model, and our computations show that ILs (anions and cations) adsorb specifically at some selective adsorption sites. Indeed, hydrophilic anions of ILs are strongly adsorbed on the gold surface (via Au-Cl and Au-N bonds at Au(111)), whereas hydrophobic anions are weakly bonded. The [BMIm]+ is always found to be stabilized parallel to the metal surface, irrespective of the nature of the anion, through various kinds of noncovalent interactions. Mulliken, Löwdin, and Hirshfeld charge analyses reveal that there is significant charge transfer between ILs and the surface that may enhance the charge transfer mechanism between the surface and electrolytes for electrochemical applications. Our study shows that the electrostatic and van der Waals interactions are in action at these interfaces. Moreover, we show that there are several covalent and noncovalent interactions between ILs and the metal surface. These interactions play an essential role to maintain the electrostatic behaviors at the solid-liquid interface. The present findings can be helpful to predict specific selectivity and subsequent design of materials for energy harvesting and catalysis applications.

Role of size and shape selectivity in interaction between gold nanoclusters and imidazole: a theoretical study.

We present a theoretical study on the structure, stability, spectra and electronic properties of imidazole (Im) adsorbed on gold nanoclusters (Aun, n = 2, 4, 6, 8, 10, and 20). These computations were performed using various density functional theories with and without inclusion of Grimme's (D3) dispersion correction. For small clusters, we also carried out wavefunction-based ab initio (MP2 and SCS-MP2) computations for comparison. Vibrational, atoms in molecules (AIM) and natural bond orbital (NBO) analyses clearly reveal the occurrence of charge transfer (CT) through covalent (N1-Au) and noncovalent interactions that play important roles in the stability of the Im@Aun complexes with anchor assisted H-bonds (Cα-H · Au). Therefore, gold clusters can act as H-bond acceptors with biomolecules for development of new materials and applications. Our study establishes also the ability and reliability of PBE0 and M05-2X functionals compared to B3LYP and PBE for an accurate description of covalent and noncovalent interactions between Im and gold clusters since they lead to close agreement with MP2. Finally, we show that the Au8 cluster may be viewed as large enough to mimic the 3D gold surface.