Search query: Ab-initio study of ReCN in the bulk and as a new two dimensional material

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abstract: First principles total energy calculations have been applied to describe the ReCN bulk structure and the formation of ReCN monolayers and bilayers. Results demonstrate a strong structural rearrangement in the monolayer due to a reduced dimension effect: an increase in the lattice parameter, accompanied with the contraction of the distance between the C and N planes. On the other hand, a ReCN bilayer has structural parameters similar to those of the bulk. Surface formation energies show that the monolayer is more stable than bilayer geometries. Although bulk ReCN shows a semiconductor behavior, the monolayer ReCN presents a metallic behavior. This metallic character of the ReCN monolayer is mainly due to the d orbitals of Re atoms.
author_names: Jonathan Guerrero-Sanchez

Noboru Takeuchi

Armando Reyes-Serrato
title: Ab initio study of ReCN in the bulk and as a new two dimensional material
venue: Scientific Reports
year: 2017

abstract: MAX phases, which are widely studied experimentally and theoretically, have general formula of M(n+1)AXn, where M is transition metals, A is A group element and X is C and N. In this study, the structural, mechanical and electronic properties have been researched for hypothetical MAX phase TiMSiB, where M is Cr and Mn by applying ab initio calculations. Initially, structural optimizations have been completed and the outcomes crosschecked with the studies of Ti2SiB in literatures [1] After optimization process have been achieved, the mechanical stability has been proved. Moreover, Young, Bulk, Shear modules and Poisson ratio for the compounds have been estimated by using elastic constants. Also, to understand the anisotropic behavior of the materials, directional dependent two and three dimensional mechanical properties have been plotted. Finally, electronic band structures and corresponding density of state (DOS) have been plotted.
author_names: Bugra Yildiz

Gokhan Surucu

Aytac Erkisi
title: An ab initio Study of Cr and Mn Doped MAX Phase TiMSiB
venue: 2019 3rd International Symposium on Multidisciplinary Studies and Innovative Technologies (ISMSIT)
year: 2019

abstract: Janus transition metal dichalcogenides (TMDs) have recently emerged as a new class of two dimensional materials with a vertical dipole moment. Here, using time domain ab initio simulations, we show that electron hole recombination can be substantially suppressed via different stacking orientations of bilayer MoSSe. Despite having a larger net dipole moment, S Se/S Se oriented MoSSe bilayer has a shorter carrier lifetime due to a strong non adiabatic coupling and a small band gap. The electron hole recombination is coupled to the interlayer out of plane motion. In contrast, the opposite vertical dipoles weaken interlayer interactions in symmetric oriented MoSSe bilayers. Consequently, initial and final states are localized within different layers and this significantly suppresses carrier recombination, resulting in an order of magnitude longer in the excited carrier lifetime in Se S/S Se oriented MoSSe bilayers. Our simulations provide theoretical insights into the carrier dynamics and suggest a way for enhancing carrier lifetime in Janus TMDs for efficient energy harvesting.
author_names: Bin Song

Li-Min Liu

Chiyung Yam
title: Suppressed Carrier Recombination in Janus MoSSe Bilayer Stacks: A Time Domain Ab Initio Study.
venue: The journal of physical chemistry letters
year: 2019

abstract: One of the fundamental properties of semiconductors is their ability to support highly tunable electric currents in the presence of electric fields or carrier concentration gradients. These properties are described by transport coefficients such as electron and hole mobilities. Over the last decades, our understanding of carrier mobilities has largely been shaped by experimental investigations and empirical models. Recently, advances in electronic structure methods for real materials have made it possible to study these properties with predictive accuracy and without resorting to empirical parameters. In this article, we review the most recent developments in the area of ab initio calculations of carrier mobilities of semiconductors. In the first part, we offer a brief historical overview of approaches to the calculation of carrier mobilities, and we establish the conceptual framework underlying modern ab initio approaches. We summarize the Boltzmann theory of carrier transport and we discuss its scope of applicability, merits, and limitations in the broader context of many body Green's function approaches. We discuss recent implementations of the Boltzmann formalism within the context of density functional theory and many body perturbation theory calculations, placing an emphasis on the key computational challenges and suggested solutions. In the second part of the article, we review applications of these methods to materials of current interest, from three dimensional semiconductors to layered and two dimensional materials. In particular, we discuss in detail recent investigations of classic materials such as silicon, diamond, GaAs, GaN, Ga2O3, and lead halide perovskites as well as low dimensional semiconductors such as graphene, silicene, phosphorene, MoS2, and InSe. We also review recent efforts toward high throughput calculations of carrier transport. In the last part, we discuss the extension of the methodology to study spintronics and topological materials and we comment on the possibility of incorporating Berry phase effects and many body correlations beyond the standard Boltzmann formalism.
author_names: Samuel Ponce

Wenbin Li

Sven Reichardt

Feliciano Giustino
title: First principles calculations of charge carrier mobility and conductivity in bulk semiconductors and two dimensional materials.
venue: Reports on progress in physics. Physical Society
year: 2020

abstract: Mono or few layer black phosphorus (BP) emerges as promising photovoltaic and optoelectronic materials with realistic applications subjected to instability and short charge carrier lifetime. Experiments show that covalent functionalization can improve the stability but the underlying mechanism for the prolonged lifetime remains elusive. By performing spin polarized time domain density functional theory combined with nonadiabatic (NA) molecular dynamics simulations, we demonstrate that BP passivated with both phenyl and nitrophenyl can suppress the nonradiative electron hole recombination by a factor of 2 and 3, respectively, relative to the pristine system. The slow recombination is due to the interplay between energy gap, NA coupling, and decoherence time, which happens through either hole trap assisted process or in a direct way between free electron and hole in the spin up channel. The observations hold in the spin down channel. The study suggests that the passivating strategy should work for BP and other two dimensional materials.
author_names: Yaqing Wei

Weihai Fang

Run Long
title: Covalent Functionalized Black Phosphorus Greatly Inhibits Nonradiative Charge Recombination: A Time Domain ab Initio Study.
venue: The journal of physical chemistry letters
year: 2019

abstract: Summary form only given. Phosphorene [1,2] is a new family member of two dimensional materials. We observed strong and highly layer dependent photoluminescence in few layer phosphorene (two to five layers) (Fig. 1) The results confirmed the theoretical prediction that few layer phosphorene has a direct and layer sensitive band gap. We also demonstrated that few layer phosphorene is more sensitive to temperature modulation than graphene and MoS2 in Raman scattering. The anisotropic Raman response in few layer phosphorene has enabled us to use an optical method to quickly determine the crystalline orientation without tunneling electron microscopy or scanning tunneling microscopy. Our results provide much needed experimental information about the band structures and exciton nature in few layer phosphorene [3] Two dimensional (2D) layered materials, including semi metallic graphene, semiconducting transition metal dichalcogenides (TMDs) and insulating hexagonal boron nitride (hBN) have been heavily investigated in past decade. Compared with the gapless graphene, most recently investigated TMD semiconductor MoS2 has energy gap in the range of 1.3 eV (bulk) to 1.8 eV (monolayer) MoS2, an indirect band gap material in its bulk form, becomes a direct band gap semiconductor when thinned to a monolayer, enabling significantly enhanced photoluminescence in monolayer MoS2. Black phosphorous (termed as phosphorene) has become a new class of 2D layered material, with predicted layer dependent band gap ranging from 0.3 eV (bulk) to 1.5 eV (monolayer) Particularly, few layer phosphorene with narrow band gaps ranging from mid infrared to near infrared wavelengths can fill the space between the gapless graphene and the comparably large gap TMD semiconductors. The predicted direct band gap nature in few layer phosphorene will also enable high performance optoelectronic devices, compared with the indirect band gap behavior in most few layer TMD semiconductors. However, so far there has been very little experimental data to confirm the theoretical prediction in few layer phosphorene.
author_names: Yuerui Lu
title: A new two dimensional material: Phosphorene
venue: 2015 IEEE MTT S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS AMP)
year: 2015

abstract: Silicon dioxide or silica, normally existing in various bulk crystalline and amorphous forms, was recently found to possess a two dimensional structure. In this work, we use ab initio calculation and evolutionary algorithm to unveil three new two dimensional (2D) silica structures whose thermal, dynamical, and mechanical stabilities are compared with many typical bulk silica. In particular, we find that all three of these 2D silica structures have large in plane negative Poisson's ratios with the largest one being double of penta graphene and three times of borophenes. The negative Poisson's ratio originates from the interplay of lattice symmetry and Si O tetrahedron symmetry. Slab silica is also an insulating 2D material with the highest electronic band gap >7 eV) among reported 2D structures. These exotic 2D silica with in plane negative Poisson's ratios and widest band gaps are expected to have great potential applications in nanomechanics and nanoelectronics.
author_names: Zhibin Gao

Xiao Dong

Nianbei Li

Jie Ren
title: Novel Two Dimensional Silicon Dioxide with in Plane Negative Poisson's Ratio.
venue: Nano letters
year: 2017

abstract: The dynamics of proton transfer (PT) through hydrogen bonds in a two dimensional water layer confined between two graphene sheets at room temperature are investigated through ab initio and quantum classical simulations. The excess proton is found to be mostly solvated as an Eigen cation where the hydronium ion donates three hydrogen bonds to the neighboring water molecules. In the solvation shell of the hydronium ion, the three coordinated water molecules with two donor hydrogen bonds are found to be properly presolvated to accept a proton. Although no hydrogen bond needs to be broken for transfer of a proton to such presolvated water molecules from the hydronium ion, the PT rate is still found to be not as fast as it is for one dimensional chains. Here, the PT is slowed down as the probability of finding a water with two donor hydrogen bonds in the solvation shell of the hydronium ion is found to be only 25% 30% The hydroxide ion is found to be solvated mainly as a complex anion where it accepts four H bonds through its oxygen atom and the hydrogen atom of the hydroxide ion remains free all the time. Here, the presolvation of the hydroxide ion to accept a proton requires that one of its hydrogen bonds is broken and the proton comes from a neighboring water molecule with two acceptor and one donor hydrogen bonds. The coordination number reduction by breaking of a hydrogen bond is a slow process, and also the population of water molecules with two acceptor and one donor hydrogen bonds is only 20% 25% of the total number of water molecules. All these factors together tend to slow down the hydroxide ion migration rate in two dimensional water layers compared to that in three dimensional bulk water.
author_names: Arindam Bankura

Amalendu Chandra
title: Proton transfer through hydrogen bonds in two dimensional water layers: a theoretical study based on ab initio and quantum classical simulations.
venue: The Journal of chemical physics
year: 2015

abstract: Two dimensional (2D) materials have shown extraordinary performances as photocatalysts compared to their bulk counterparts. Simulations have made a great contribution to the deep understanding and design of novel 2D photocatalysts. Ab initio simulations based on density functional theory (DFT) not only show efficiency and reliability in new structure searching, but also can provide a reliable, efficient, and economic way for screening the photocatalytic property space. In this review, we summarize the recent developments in the field of water splitting using 2D materials from a theoretical perspective. We address that DFT based simulations can fast screen the potential spaces of photocatalytic properties with the accuracy comparable to experiments, by investigating the effects of various physical/chemical perturbations. This, at last, will lead to the enhanced photocatalytic activities of 2D materials, and promote the development of photocatalysis.
author_names: Yunguo Li

Yan-Ling Li

Baisheng Sa

Rajeev Ahuja
title: Review of two dimensional materials for photocatalytic water splitting from a theoretical perspective
year: 2017

abstract: Two dimensional materials offer a unique platform where both bulk and atomic HHG can be investigated. The generation of high order harmonics from atomic and molecular gases enables the production of high energy photons and ultrashort isolated pulses. Obtaining efficiently similar photon energy from solid state systems could lead, for instance, to more compact extreme ultraviolet and soft x ray sources. We demonstrate from ab initio simulations that it is possible to generate high order harmonics from free standing monolayer materials, with an energy cutoff similar to that of atomic and molecular gases. In the limit in which electrons are driven by the pump laser perpendicularly to the monolayer, they behave qualitatively the same as the electrons responsible for high harmonic generation (HHG) in atoms, where their trajectories are described by the widely used semiclassical model, and exhibit real space trajectories similar to those of the atomic case. Despite the similarities, the first and last steps of the well established three step model for atomic HHG are remarkably different in the two dimensional materials from gases. Moreover, we show that the electron electron interaction plays an important role in harmonic generation from monolayer materials because of strong local field effects, which modify how the material is ionized. The recombination of the accelerated electron wave packet is also found to be modified because of the infinite extension of the material in the monolayer plane, thus leading to a more favorable wavelength scaling of the harmonic yield than in atomic HHG. Our results establish a novel and efficient way of generating high order harmonics based on a solid state device, with an energy cutoff and a more favorable wavelength scaling of the harmonic yield similar to those of atomic and molecular gases. Two dimensional materials offer a unique platform where both bulk and atomic HHG can be investigated, depending on the angle of incidence. Devices based on two dimensional materials can extend the limit of existing sources.
author_names: Nicolas Tancogne-Dejean

Angel Rubio
title: Atomic like high harmonic generation from two dimensional materials
venue: Science Advances
year: 2018