Tuning Excitonic Properties of Monochalcogenides via Design of Janus Structures.

Two-dimensional (2D) Janus structures offer a unique range of properties as a result of their symmetry breaking, resulting from the distinct chemical composition on each side of the monolayers. Here, we report a theoretical investigation of 2D Janus ''31 monochalcogenides from group IV ( and ' = Ge and Sn; , ' = S and Se) and 2D non-Janus 3̅1 counterparts. Our theoretical framework is based on density functional theory calculations combined with maximally localized Wannier functions and tight-binding parametrization to evaluate the excitonic properties.

Elucidating Black α-CsPbI Perovskite Stabilization via PPD Bication-Conjugated Molecule Surface Passivation: Ab Initio Simulations.

The cubic α-CsPbI phase stands out as one of the most promising perovskite compounds for solar cell applications due to its suitable electronic band gap of 1.7 eV. However, it exhibits structural instability under operational conditions, often transforming into the hexagonal non-perovskite δ-CsPbI phase, which is unsuitable for solar cell applications because of the large band gap (e.

Contrasting the stability, octahedral distortions, and optoelectronic properties of 3D MABX and 2D (BA)(MA)BX (B = Ge, Sn, Pb; X = Cl, Br, I) perovskites.

Efficient surface passivation and toxic lead (Pb) are known obstacles to the photovoltaic application of perovskite-based solar cells. A possible solution for these problems is to use thin-films of two-dimensional (2D) perovskite-based materials and the replacement of Pb with alternative divalent cations (B); however, our atomistic understanding of the differences between (3D) three-dimensional and 2D perovskite-based materials is far from satisfactory. Herein, we report a systematic theoretical investigation based on density functional theory (DFT) calculations for both 3D MABX and the Ruddlesden-Popper 2D (BA)(MA)BX (B = Ge, Sn, Pb, and X = Cl, Br, I) compounds to investigate the differences (contrasts) in selected physical-chemical properties, , structural parameters, energetic stability, electronic, and optical properties.

Decoding Van der Waals Impact on Chirality Transfer in Perovskite Structures: Density Functional Theory Insights.

Chiral organic-inorganic perovskites exhibit unique physicochemical properties driven by the symmetry of monovalent organic cations. However, an atomistic understanding of how chiral cations transfer their chirality to the inorganic framework and the role played by van der Waals (vdW) interactions in this process is still incomplete. In this work, we report a theoretical investigation, based on density functional theory calculations within the Perdew-Burke-Ernzerhof (PBE) formulation for the exchange-correlation functional, into the role of the vdW interactions in the chirality transfer process.

Ab initio investigation of topological phase transitions induced by pressure in trilayer van der Waals structures: the example of h-BN/SnTe/h-BN.

The combination of two-dimensional crystals through the formation of van der Waals bilayers, trilayers, and heterostructures has been considered a promising route to design new materials due to the possibility of tuning their properties through the control of the number of layers, alloying pressure, strain, and other tuning mechanisms. Here, we report a density functional theory study on the interlayer phonon coupling and electronic structure of the trilayer h-BN/SnTe/h-BN, and the effects of pressure on the encapsulation of this trilayer system. Our findings demonstrated the establishment of a type I junction in the system, with a trivial bandgap of 0.

The role played by the molecular geometry on the electronic transport through nanometric organic films.

The electronic transport properties in molecular heterojunctions are intimately connected with the molecular conformation between the electrodes, and the electronic structure of the molecule/electrode interface. In this work, we perform an ab initio density-functional-theory investigation of the structural and transport properties through self-assembled CuPc molecules sandwiched between gold contacts with (111) surfaces. We demonstrated (i) a tunneling regime ruled by the π orbitals of the aromatic rings of CuPc molecules; and (ii) a high variation (up to two orders of magnitude) of the current density with the orientation of the CuPc molecules relative to the gold surface.

Edge, size, and shape effects on WS, WSe, and WTe nanoflake stability: design principles from an ab initio investigation.

An improved atomistic understanding of the W-based two-dimensional transition-metal dichalcogenides (2D TMDs) is crucial for technological applications of 2D materials, since the presence of tungsten endows these materials with distinctive properties. However, our atomistic knowledge on the evolution of the structural, electronic, and energetic properties and on the nanoflake stability of such materials is not properly addressed hitherto. Thus, we present a density functional theory (DFT) study of stoichiometric (WQ2)n nanoflakes, with Q = S, Se, Te, and n = 1,…,16, 36, 66, and 105.

Spatial anisotropy of the quantum spin liquid system YbMgGaO revealed by ab initio calculations.

YbMgGaO was recently proposed as a promising quantum-spin-liquid candidate material. However, some details of its structure, such as those related to a spatial anisotropy, were not completely understood. In this work, we perform ab initio calculations based on density-functional-theory to investigate the structural, the electronic and the magnetic properties of YbMgGaO.

Electronic transport properties of MoS nanoribbons embedded in butadiene solvent.

Transition metal dichalcogenides (TMDCs) are promising materials for applications in nanoelectronics and correlated fields, where their metallic edge states play a fundamental role in the electronic transport. In this work, we investigate the transport properties of MoS zigzag nanoribbons under a butadiene (CH) atmosphere, as this compound has been used to obtain MoS flakes by exfoliation. We use density functional theory combined with non-equilibrium Green's function techniques, in a methodology contemplating disorder and different coverages.

Tuning the Magnetic Properties of FeCo Thin Films through the Magnetoelastic Effect Induced by the Au Underlayer Thickness.

Tuning the magnetic properties of materials is a demand of several technologies; however, our microscopic understanding of the process that drives the enhancement of those properties is still unsatisfactory. In this work, we combined experimental and theoretical techniques to investigate the handling of magnetic properties of FeCo thin films via the thickness-tuning of a gold film used as an underlayer. We grow the samples by the deposition of polycrystalline FeCo thin films on the Au underlayer at room temperature by a magnetron sputtering technique, demonstrating that the lattice parameter of the sub-20 nm thickness gold underlayer is dependent on its thickness, inducing a stress up to 3% in sub-5 nm FeCo thin films deposited over it.

Double-walled silicon nanotubes: an ab initio investigation.

The synthesis of silicon nanotubes realized in the last decade demonstrates multi-walled tubular structures consisting of Si atoms in [Formula: see text] and the [Formula: see text] hybridizations. However, most of the theoretical models were elaborated taking as the starting point [Formula: see text] structures analogous to carbon nanotubes. These structures are unfavorable due to the natural tendency of the Si atoms to undergo [Formula: see text].

Simple implementation of complex functionals: scaled self-consistency.

We explore and compare three approximate schemes allowing simple implementation of complex density functionals by making use of self-consistent implementation of simpler functionals: (i) post-local-density approximation (LDA) evaluation of complex functionals at the LDA densities (or those of other simple functionals) (ii) application of a global scaling factor to the potential of the simple functional, and (iii) application of a local scaling factor to that potential. Option (i) is a common choice in density-functional calculations. Option (ii) was recently proposed by Cafiero and Gonzalez [Phys.