The electronic structure and energetics of the tetragonal distortion for the fluorite-type dihydrides ${\text{TiH}}_2$, ${\text{ZrH}}_2$, and ${\text{HfH}}_2$ are studied by means of highly accurate first-principles total-energy calculations. For ${\text{HfH}}_2$, in addition to the calculations using the scalar relativistic (SR) approximation, calculations including the spin-orbit coupling have also been performed. The results show that ${\text{TiH}}_2$, ${\text{ZrH}}_2$, and ${\text{HfH}}_2$ in the cubic phase are unstable against tetragonal strain. For the three systems, the total energy shows two minima as a function of the $c/a$ ratio with the lowest-energy minimum at $c/a<1$ in agreement with the experimental observations. The band structure of ${\text{TiH}}_2$, ${\text{ZrH}}_2$, and ${\text{HfH}}_2$ (SR) around the Fermi level shows two common features along the two major symmetry directions of the Brillouin zone, $\Gamma -L$ and $\Gamma -K$, a nearly flat doubly degenerate band, and a van Hove singularity, respectively. In cubic ${\text{HfH}}_2$ the spin-orbit coupling lifts the degeneracy of the partially filled bands in the $\Gamma -L$ path, while the van Hove singularity in the $\Gamma -K$ path remains unchanged. The density of states of the three systems in the cubic phase shows a sharp peak at the Fermi level. We found that the tetragonal distortion produces a strong reduction in the density of states at the Fermi level resulting mainly from the splitting of the doubly-degenerate bands in the $\Gamma -L$ direction and the shift of the van Hove singularity to above the Fermi level. The validity of the Jahn-Teller model in explaining the tetragonal distortion in this group of dihydrides is discussed.

The energy change on each Occupied Molecular Orbital as a function of rotation about the C-C bond in ethane was studied using the B3LYP, mPWB95 functional and MP2 methods with different basis sets.Also, the effect of the ZPE on rotational barrier was analyzed. We have found that σ and π energies contribution stabilize a staggered conformation. The σ_s molecular orbital stabilizes the staggered conformation while the stabilizes the eclipsed conformation and destabilize the staggered conformation. The π_z and molecular orbitals stabilize both the eclipsed and staggered conformations, which are destabilized by the π_v and molecular orbitals. The results show that the method of calculation has the effect of changing the behavior of the energy change in each Occupied Molecular Orbital energy as a function of the angle of rotation about the C–C bond in ethane. Finally, we found that if the molecular orbital energy contribution is deleted from the rotational energy, an inversion in conformational preference occurs.

A series of seven 2-amino-4-arylthiazoles were prepared following Hantzsch’s modified method under microwave irradiation. A set of 50 derivatives was obtained and the in vitro activity against Giardia intestinalis was evaluated. The results on the biological activity revealed that, in general, the N-(5-bromo-4-aryl-thiazol-2-yl)-acetamide scaffold showed high bioactivity. In particular, compounds 6e (IC50 = 0.39 μM) and 6b (IC50 = 0.87 μM) were found to be more potent than the positive control metronidazole. Citoxicity and acute toxicity tests performed showed low toxicity and high selectivity of the most active compounds (6e SI = 139, 6b SI = 52.3). A QSAR analysis was applied to a data set of 37 obtained 2-amino-4-arylthiazoles derivatives and the best model described a strongly correlation between the anti-giardiasic activity and molecular descriptors as E2M, RDF115m, F10, MATS6v, and Hypnotic-80, with high statistical quality. This finding indicates that N-substituted aminothiazole scaffold should be investigated for the development of highly selective anti-giardial agent.

The IGM can isolate the n → π* interaction in δ g isosurfaces. The interaction is identified as a green flat disc in the middle of the interaction zone. However, is not able to reproduce the trends in the relative force found in NBO results.