Enhanced Elastocaloric Effects in γ-Graphyne.

The global emphasis on sustainable technologies has become a paramount concern for nations worldwide. Specifically, numerous sustainable methods are being explored as promising alternatives to the well-established vapor-compression technologies in cooling and heating devices. One such avenue gaining traction within the scientific community is the elastocaloric (eC) effect. This phenomenon holds promise for efficient cooling and heating processes without causing environmental harm. Studies carried out at the nanoscale have demonstrated the efficiency of the eC effect, proving to be comparable to that of state-of-the-art macroscopic systems. In this study, we used classical molecular dynamics simulations to investigate the elastocaloric effect for the recently synthesized γ-graphyne. Our analysis goes beyond obtaining changes in eC temperature and the coefficient of performance (COP) for two species of γ-graphyne nanoribbons (armchair and zigzag). We also explore their dependence on various conditions, including whether they are deposited on a substrate or prestrained. Our findings reveal a substantial enhancement in the elastocaloric effect for γ-graphyne nanoribbons when subjected to prestrain, amplifying it by at least 1 order of magnitude. Under certain conditions, the changes in the eC temperature and the COP of the structures reach expressive values as high as 224 K and 14, respectively. We discuss the implications of these results by examining the shape and behavior of the carbon-carbon bond lengths within the structures.

On the CO[Formula: see text] adsorption in a boron nitride analog for the recently synthesized biphenylene network: a DFT study.

CONTEXT: Recent advances in nanomaterial synthesis and characterization have led to exploring novel 2D materials. The biphenylene network (BPN) is a notable achievement in current fabrication efforts. Numerical studies have indicated the stability of its boron nitride counterpart, known as BN-BPN. In this study, we employ computational simulations to investigate the electronic and structural properties of pristine and doped BN-BPN monolayers upon CO[Formula: see text] adsorption. Our findings demonstrate that pristine BN-BPN layers exhibit moderate adsorption energies for CO[Formula: see text] molecules, approximately [Formula: see text]0.16 eV, indicating physisorption. However, introducing one-atom doping with silver, germanium, nickel, palladium, platinum, or silicon significantly enhances CO[Formula: see text] adsorption, leading to adsorption energies ranging from [Formula: see text]0.13 to [Formula: see text]0.65 eV. This enhancement indicates the presence of both physisorption and chemisorption mechanisms. BN-BPN does not show precise CO[Formula: see text] sensing and selectivity. Furthermore, our investigation of the recovery time for adsorbed CO[Formula: see text] molecules suggests that the interaction between BN-BPN and CO[Formula: see text] cannot modify the electronic properties of BN-BPN before the CO[Formula: see text] molecules escape. METHODS: We performed density functional theory (DFT) simulations using the DMol3 code in the Biovia Materials Studio software. We incorporated Van der Waals corrections (DFT-D) within the Grimme scheme for an accurate representation. The exchange and correlation functions were treated using the Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA). We used a double-zeta plus polarization (DZP) basis set to describe the electronic structure. Additionally, we accounted for the basis set superposition error (BSSE) through the counterpoise method. We included semicore DFT pseudopotentials to accurately model the interactions between the nuclei and valence electrons.

Elastocaloric Effect in Graphene Kirigami.

Kirigami, a traditional Japanese art of paper cutting, has recently been explored for its elastocaloric effect (ECE) in kirigami-based materials (KMs), where an applied strain induces temperature changes. Importantly, the feasibility of a nanoscale graphene kirigami monolayer was experimentally demonstrated. Here, we investigate the ECE in GK representing the thinnest possible KM to better understand this phenomenon. Through molecular dynamics simulations, we analyze the temperature change and coefficient of performance (COP) of GK. Our findings reveal that while GKs lack the intricate temperature changes observed in macroscopic KMs, they exhibit a substantial temperature change of approximately 9.32 K (23 times higher than that of macroscopic KMs, which is about 0.4 K) for heating and -3.50 K for cooling. Furthermore, they demonstrate reasonable COP values of approximately 1.57 and 0.62, respectively. It is noteworthy that the one-atom-thick graphene configuration prevents the occurrence of the complex temperature distribution observed in macroscopic KMs.

On the adsorption mechanism of caffeine on MAPbI3 perovskite surfaces: a combined UMC-DFT study.

Recently, it was experimentally shown that the performance and thermal stability of the perovskite MAPbI3 were improved upon the adsorption of a molecular layer of caffeine. In this work, we used a hybrid methodology that combines uncoupled monte carlo (UMC) and density functional theory (DFT) simulations to carry out a detailed and comprehensive study of the adsorption mechanism of a caffeine molecule on the surface of MAPbI3. Our results showed that the adsorption distance and energy of a caffeine molecule on the MAPbI3 surface are 2.0 Å and -0.3 eV, respectively. The caffeine/MAPbI3 complex presents a direct bandgap of 2.38 eV with two flat intragap bands distanced 1.15 and 2.18 eV from the top of valence bands. Although the energy band levels are not significantly shifted by the presence of caffeine, the interaction MAPbI3/perovskite is enough to affect the bands' dispersion, particularly the conduction bands.

Temperature Effects on the Fracture Dynamics and Elastic Properties of Popgraphene Membranes.

Popgraphene (PopG) is a new 2D planar carbon allotrope which is composed of 5-8-5 carbon rings. PopG is intrinsically metallic and possesses excellent thermal and mechanical stability. In this work, we report a detailed study of the thermal effects on the mechanical properties of PopG membranes using fully-atomistic reactive (ReaxFF) molecular dynamics simulations. Our results showed that PopG presents very distinct fracture mechanisms depending on the temperature and direction of the applied stretching. The main fracture dynamics trends are temperature independent and exhibit an abrupt rupture followed by fast crack propagation. The reason for this anisotropy is due to the fact that y-direction stretching leads to a deformation in the shape of the rings that cause the breaking of bonds in the pentagon-octagon and pentagon-pentagon ring connections, which is not observed for the x-direction. PopG is less stiff than graphene membranes, but the Young's modulus value is only 15 % smaller.

Bosonic Charge Carriers in Necklace-like Graphene Nanoribbons.

Motivated by the success of graphene in flat optoelectronics, several carbon allotropes have recently been proposed. One of these allotropes, graphene nanoribbons (GNRs) with a singular "necklace-like" atomic structure, was recently synthesized through a bottom-up chemical approach. The absorption spectrum exhibited a band gap of 1.4 eV for this novel GNR geometry. Guided by its exciting electronic and structural properties, investigations should be performed to outline the major features of this material focused on expanding organic-based energy conversion and storage applications. In particular, the formation and dynamics of charge carriers are crucial in defining the material's performance. Here we describe the formation and transport of charge carriers in necklace-like graphene nanoribbons (NGNRs). A 2D tight-binding Hamiltonian endowed with lattice relaxation effects constitutes the basis of the theoretical approach employed to examine the carrier formation and dynamics in these lattices. Results demonstrate that polarons and effective boson species are spontaneously generated in NGNRs by the addition of holes or electrons to the system. Both types of generated quasiparticles are dynamically stable and can move at surprisingly low electric-field regimes. Remarkably, the formation of effective bosons is a process triggered by a higher density of added charges. The understanding of the carriers' formation and transport in NGNRs can pave the way for their broad usage in producing novel optoelectronic applications, added to the possibility of Bose-Einstein condensate phenomena.