Small Group IIa–VIa Clusters and Related Systems: A Theoretical Study of Physical Properties, Reactivity, and Electronic Spectra

Abstract

In the monomeric form, the title systems assume unexpected optical properties, and as oligomers they can serve as candidates for molecular devices. In bulk they are attractive in the area of material science. A broad set of quantum chemical methods ranging from density functional theory by the Hartree-Fock method and the Møller-Plesset perturbation theory to the coupled-cluster method, in connection with nonrelativistic Dunning's basis sets as well as with relativistic SDD basis sets were used. Electronic spectra were analyzed by means of time-dependent DFT, with the symmetryadapted cluster configuration interaction and with the internally contracted multireference configuration interaction. The Douglas-Kroll-Hess quasirelativistic Hamiltonian served as a basis for the estimation of the role of relativistic effects. All the diatomics representing 25 elements of a matrix formed by the combination of group IIa (Be, ..., Ba) with group VIa (O, ..., Po) atoms were characterized by calculated bond length, valence vibration, dipole moment, and the HartreeFock frontier orbital energies. Calculated characteristics were confronted with experimental data. The geometry of the oligomers (from dimers through hexamers) was investigated systematically, and the nature of the located stationary

Structural Diversity and Flexibility of MgO Gas‐Phase Clusters

“…15) have also given indications for cubic structures. [5] Up to now, computational studies have almost exclusively investigated neutral MgO clusters, without direct comparison to experiment, [3,[6][7][8][10][11][12][13][14][15][16][17] despite the fact that most experiments were performed on cationic clusters. The main conclusion from these studies has been that the most stable structures for a given value of n are cubelike, except for (MgO) 3n clusters, for which rings and stacks of rings are preferred.…”

Electronic structure and physical properties of MiXi clusters (M = B, Al; X = N, P; i = 1, 2, 3): Ab initio study

“…There is no apparent trend for these molecular properties; nevertheless calculated values indicate higher reactivity of the IIIa-Va species (higher A and lower I) than the IIa-VIa molecules. 43 The best Lewis acids among the studied systems are BN, 28,33 (8t) (BN) 2 , and (1s) (BP) 3 isomers. A lower I and a higher A of linear geometries of the dimers in comparison with rhombic structures reflect their higher reactivity, as was predicted by the NBO analysis.…”

“…43 In this work, the calculations are further complicated by multireferential characters of wavefunctions. Therefore, the study of monomers consisting of heavier atoms is not straightforward and screening for all 25 monomers of IIIa-Va systems cannot be expected to provide reliable information without utilizing both expensive methods and basis sets.…”

Strukturelle Vielfalt und Flexibilität von MgO‐Clustern in der Gasphase

“…15) deuteten ebenfalls auf kubische Strukturen hin. [5] Bisher wurden in Rechnungen fast ausschließlich neutrale MgO-Cluster untersucht, ohne direkten Vergleich zu Experimenten, [3,[6][7][8][10][11][12][13][14][15][16][17] obwohl die meisten Experimente an kationischen Clustern erfolgten. Die wesentliche Schlussfolgerung aus diesen Studien war, dass für einen bestimmten n-Wert die stabilsten Strukturen würfelartig sind, außer für (MgO) 3n , für das Ringe und deren Stapel bevorzugt werden.…”

“…Insbesondere wurden für alle Clustergrößen globale Strukturoptimierungen mithilfe der Dichtefunktionaltheorie (DFT) ausgeführt. Einige der hier gezeigten geometrischen Strukturen wurden zwar bereits früher mit verschiedenen Techniken für neutrale [3,7,[10][11][12][13][14][15][16][17] und anionische Cluster [18] berechnet, unsere Rechnungen identifizieren nun jedoch eindeutig die globalen Minima für alle diesen Anordnungen. Im Experiment werden Clusterkationen und deren schwach gebundene Komplexe mit Ar und O 2 im Molekularstrahl untersucht.…”