The effect of shape and size in the stability of triangular Janus MoSSe quantum dots.

Asymmetric Janus transition metal dichalcogenide MoSSe is a promising catalytic material due to the intrinsic in-plane dipole of its opposite faces. The atomic description of the structures observed by experimental techniques is relevant to tuning and optimizing its surface reaction processes. Furthermore, the experimentally observed triangular morphologies in MoSSe suggest that an analysis of the chemical environment of its edges is vital to understand its reactivity. Here we analyze the size-shape stability among different triangular structures-quantum- dots proposed from the ideal S(-1010) and Mo(10-10) terminations. Our stability analysis evidenced that the S-Se termination is more stable than Mo; moreover, as the size of the quantum dot increases, its stability increases as well. Besides, a trend is observed, with the appearance of elongated Mo-S/Se bonds at symmetric positions of the edges. Tersoff-Hamann scanning tunneling microscopy images for both faces of the stablest models are presented. Electrostatic potential isosurfaces denote that the basal plane on the S face of both configurations remains the region with more electron density concentration. These results point toward the differentiated activity over both faces. Finally, our study denotes the exact atomic arrangement on the edges of MoSSe quantum dots corresponding with the formation of S/Se dimers who decorates the edges and their role along with the faces as catalytic sites.

A new family of copper-based MXenes.

In this work, we demonstrate, through first-principles calculations, the existence of a new family of copper-based MXenes. These add up new structures to the previously reported universe and span the interest of such 2D materials for applications in heterogeneous catalysis, ion-based batteries, sensors, biomedical applications, and so on. First, we propose the MXene-like structures: Cu2N, Cu2C, and Cu2O. Phonon spectra calculations confirmed their dynamical stability by showing just positive frequencies all through the 2D Brillouin zone. The new MXenes family displays metallic characteristics, mainly induced by the Cu-3d orbitals. Bader charge analysis and charge density differences depict bonds with ionic character in which Cu is positively charged, and the non-metal atom gets an anionic character. Also, we investigate the functionalization of the proposed structures with Cl, F, O, and OH groups. Results show that the H3 site is the most favorable for functionalization. In all cases, the non-magnetic nature and metallic properties of the pristine MXenes remain. Our results lay the foundations for the experimental realization of a new MXenes family.

Ab initio study of the cyclooctatetraenyl radical.

Ab initio calculations have been carried out on the 1,3,5,7- and 1,2,4,7-tetraene configurations of the cyclooctatetraenyl radical at UHF, ROHF, MCSCF, ROCISD, QCISD, and CCSD(T) levels of theory with 6-311G(d,p) and cc-pVDZ basis sets. Although spin contamination is present, the ROCISD calculations support the energies obtained from less intensive, UHF-based coupled cluster calculations over the energies obtained from MCSCF analysis of the pi-electron orbitals. The 1,3,5,7-form is a local minimum at the coupled cluster levels, higher in energy than the resonance-stabilized 1,2,4,7-form by 10-13 kJ/mol, but bounded by a barrier of less than 0.5 kJ/mol. The isomerization surface connecting these two structures is described and results reported from integration of the vibrational Schrödinger equation on that surface. Excited vibrational states at energies just above the isomerization barrier are dominated by the character of the 1,3,5,7-tetraenyl radical, which suggests that chemistry involving this intermediate at typical combustion temperatures may branch at this juncture.