Density functional theory-based simulations are applied to study the electronic structures, carrier masses, carrier mobility and carrier relaxation times in bulk and two-dimensional Zn ₂ (V,Nb,Ta)N ₃ ternary nitrides.

Stanene, composed of tin atoms, is a member of 2D-Xenes, two-dimensional single element materials. The properties of the stanene can be changed and improved by applying deformation, and it is important to know the range of in-plane deformation that the stanene can withstand. Using the Tersoff interatomic potential for calculation of phonon frequencies, the range of stability of planar stanene under uniform in-plane deformation is analyzed and compared with the known data for graphene. Unlike atomically flat graphene, stanene has a certain thickness (buckling height). It is shown that as the tensile strain increases, the thickness of the buckled stanene decreases, and when a certain tensile strain is reached, the stanene becomes absolutely flat, like graphene. Postcritical behaviour of stanene depends on the type of applied strain: critical tensile strain leads to breaking of interatomic bonds and critical in-plane compressive strain leads to rippling of stanene. It is demonstrated that application of shear strain reduces the range of stability of stanene. The existence of two energetically equivalent states of stanene is shown, and consequently, the possibility of the formation of domains separated by domain walls in the stanene is predicted.

The fullerene family, whose most popular members are the spherical C${}_{60}$ and C${}_{70}$ molecules, has recently added a new member, the cube-shaped carbon molecule C${}_8$ called a cubene. A molecular crystal based on fullerenes is called fullerite. In this work, based on relaxational molecular dynamics, two fullerites based on cubenes are described for the first time, one of which belongs to the cubic system, and the other to the triclinic system. Potential energy per atom, elastic constants, and mechanical stress components are calculated as functions of lattice strain. It has been established that the cubic cubene crystal is metastable, while the triclinic crystal is presumably the crystalline phase in the ground state (the potential energies per atom for these two structures are −0.0452 and −0.0480 eV, respectively).The cubic phase has a lower density than the monoclinic one (volumes per cubene are 101 and 97.7 Å${}^3$). The elastic constants for the monoclinic phase are approximately 4% higher than those for the cubic phase. The presented results are the first step in studying the physical and mechanical properties of C${}_8$ fullerite, which may have potential for hydrogen storage and other applications. In the future, the influence of temperature on the properties of cubenes will be analyzed.

Using the molecular dynamic simulations a new class of topological defects in silicene is investigated. Si atoms in silicene belong to two triangular sublattices shifted one with respect to the other by h along the direction normal to the sheet. Silicene can have two energetically equivalent structures when the first or second sublattice is above the other. Topological defects appear at the junctions of the domains of these two structures. Domain walls can be rectilinear or curvilinear. Such defects cannot disappear from the structure except as a result of the annihilation of defects with positive and negative topological charges. Structure and energy of the topological defects are calculated. The effect of temperature is shown. Similar defects inevitably exist in other group IVA elemental 2D materials with buckled structure, such as germanene, stanene, and plumbene. As a result of the work, the problem of experimental detection of such defects and the question of how they affect the physicochemical and mechanical properties of materials, in particular, toxicity or sensory properties, is posed.