Abstract. We discuss the application of the Agapito Curtarolo and Buongiorno Nardelli (ACBN0) pseudo-hybrid Hubbard density functional to several transition metal oxides. ACBN0 is a fast, accurate and parameter-free alternative to traditional DFT+U and hybrid exact exchange methods. In ACBN0, the Hubbard energy of DFT+U is calculated via the direct evaluation of the local Coulomb and exchange integrals in which the screening of the bare Coulomb potential is accounted for by a renormalization of the density matrix. We demonstrate the success of the ACBN0 approach for the electronic properties of a series technologically relevant mono-oxides (MnO, CoO, NiO, FeO, both at equilibrium and under pressure). We also present results on two mixed valence compounds, Co 3 O 4 and Mn 3 O 4 . Our results, obtained at the computational cost of a standard LDA/PBE calculation, are in excellent agreement with hybrid functionals, the GW approximation and experimental measurements.

Serpentine clay minerals are found in many geological settings. The rich diversity, both in chemical composition and crystal structure, alters the elastic behavior of clay rocks significantly, thus modifying seismic and sonic responses to shaley sequences. Computation of the elastic properties is a useful tool to characterize this diversity. In this paper we use first principles methods to compare the mechanical properties of lizardite Mg3(Si2O5)(OH)4, a polymorph of serpentine family, with the new compounds derived by substituting Mg ions with isovalent elements from different chemical groups. New compounds are first selected according to chemical and geometrical stability criteria, then full elastic tensors, bulk and shear modulii, and acoustic velocities are obtained. Overall, the new compounds have a lower anisotropy and are less resistant to mechanical deformation compared to the prototype, thus providing valuable information regarding chemical composition and mechanical properties in these systems.

The pressure‐induced phase transitions in nanostructured SnSe were investigated using angle‐dispersive X‐ray diffraction in a synchrotron source along with first‐principles density functional theory (DFT) calculations. The variation of the cell parameters along with enthalpy calculations for pressures up to 18 GPa have been considered. Both the experimental and the theoretical approaches demonstrate a phase transition at around 4 GPa. Below 8.2 GPa the X‐ray diffraction patterns were fitted using the Rietveld method with space group Pnma (No. 62). The lattice parameters and atomic positions for the above‐mentioned symmetry were used in DFT calculations of thermodynamic parameters. The enthalpy calculations with the computationally optimized structure and the proposed Pnma structure of SnSe were compatible. The variations of the cell volume for the high‐pressure phases are described by a third‐order Birch–Murnaghan equation of state.

Graphene-like ZnX (X=O, S, Se, Te) structures are studied using the DFT+U method to address in detail the questions regarding the dynamical stability and also their utility in optoelectronic devices. The layer modulus, the Young's modulus, the shear modulus, and the Poisson coefficient demonstrate the stability of all ZnX in the presence of the Hubbard parameter U. Cohesion energy calculations show ZnO to be the most stable one and ZnSe to be the least stable one among the four systems. The presence of a direct bandgap in all the systems makes them suitable for use in optoelectronic devices. The gap values range between 2.13 eV in ZnTe and 3.50 eV in ZnO. U values tend to increase the bandgap in all the systems. This increase is seen to be as high as 100% in ZnO. A detailed study of the band structure and partial density of states is carried out. The electronic, optical, and thermoelectric properties of the ZnX monolayers are exhibited. The superior limit of the figure of merit increases with temperature and the highest value is found to be of the order of 0.6 in ZnO at 900 °C. Overall, the inclusion of the Hubbard parameter demonstrates better stability and also its importance in technological applications.