The structural, electronic, dynamical, and optical properties of a group of 2D germanium-based compounds, including GeC, GeN, GeO, GeSi, GeS, GeSe, and germanene, are investigated by employing first-principles calculations. The most stable structure of each of these systems is identified after considering the most probable configurations and performing accurate phonon calculations. We introduce a new phase of germanene, which we name the tile germanene, which is significantly more stable than the known hexagonal germanene. We apply the modern modified Becke–Johnson and DFT1/2 schemes to obtain an accurate band structure for the selected 2D materials. It is seen that GeO and GeC exhibit the highest bandgaps of >3 eV in this group of nanomaterials. Moreover, we argue that, in contrast to the semi-metallic nature of hexagonal germanene, tile germanene is a very good conductor. The band edges of our semiconducting 2D materials are accurately aligned to the vacuum level to address the potential photocatalytic application of these systems for water splitting and carbon dioxide reduction. The optical properties, including dielectric functions, refractive index, reflectivity, and loss function of the samples, in the presence of excitonic effects, are investigated in the framework of the Bethe–Salpeter approach.

The electronic and optical features of some potential single-photon sources in two-dimensional silicon carbide monolayers is studied via ab initio calculations and group theory analyses. A few point defects in three charge states (negative, positive, and neutral) are considered. By applying performance criteria, Stone-Wales defects without and with combination of antisite defects are studied in detail. The formation energy calculations reveal that neutral and positive charge states of these defects are stable. We compute the zero-phonon-line energy, the Huang-Rhys (HR) factor, and the photoluminescence spectrum for the available transitions in different charge states. The calculated HR values and the related Debye-Waller factors guarantee that the Stone-Wales defects have a high potential of performing as a promising single-photon emitter.

We propose an electromechanical scheme where the electronic degrees of freedom of boron vacancy color centers hosted by a hexagonal boron nitride (hBN) nanoribbon are coupled for quantum information processing. The mutual coupling of color centers is provided via their coupling to the mechanical motion of the ribbon, which in turn stems from the local strain. The coupling strengths are computed by performing ab initio calculations. The density functional theory results for boron vacancy centers on boron nitride monolayers reveal a huge strain susceptibility. In our analysis, we take into account the effect of all flexural modes and show that despite the thermal noise introduced through the vibrations one can achieve steady-state entanglement between two and more number of qubits that survives even at room temperature. Moreover, the entanglement is robust against mis-positioning of the color centers. The effective coupling of color centers is engineered by positioning them in the proper positions. Hence, one is able to tailor stationary graph states. Furthermore, we study the quantum simulation of the Dicke-Ising model and show that the phonon non-equilibrium phase transition occurs even for a finite number of color centers. Given the steady-state nature of the proposed scheme and accessibility of the electronic states through optical fields, our work paves the way for the realization of steady-state quantum information processing with color centers in hBN membranes.