arXiv subjects

Vikram Mahamiya

Publications and source records attributed to Vikram Mahamiya.

13 recordsLinked to original sources

arXiv2025

Mechanical Force-Driven Charge Redistribution for Hydrogen Release at Ambient Conditions in Transition Metal-Intercalated Bilayer Graphene

Transition-metal (TM) atom-functionalized nanomaterials are promising candidates for hydrogen storage due to their ability to adsorb multiple hydrogen molecules through Kubas interactions. However, achieving efficient hydrogen desorption at ambient conditions remains a critical challenge for practical use. Here, we present a novel approach to modulate the desorption temperature of hydrogen in TM-intercalated bilayer graphene (BLG) using external mechanical forces. By employing first-principles density functional theory (DFT) and thermodynamic occupancy probability calculations, we demonstrate that adjusting the interlayer distance allows for precise control over the interaction energy of H2, thereby facilitating its desorption at ambient conditions. Complete hydrogen desorption occurs when the interlayer distance is reduced below 4.7 {\AA}, 5.3 {\AA}, and 5.1 {\AA} for Sc-, Ti-, and V-intercalated BLG, respectively. Our findings suggest that external mechanical forces can effectively bring hydrogen occupancy to zero by minimizing charge transfer from the TM d-orbitals to H2 antibonding orbitals. Notably, while the total charge transferred from the TM atoms remains nearly constant at varying interlayer distances, its redistribution between the graphene layers and H2 fine-tunes the interaction strength. This approach can be extended to large interlayer distances, as supported by recent experiments on graphene oxide membranes [ACS Nano 12, 9309 (2018)]. Furthermore, recent experimental advances in noble gas and alkali metal intercalation in BLG highlight the potential of this approach to overcome the long-standing challenge of high desorption temperatures in TM-functionalized layered nanomaterials.

cond-mat.mtrl-sci↗

arXiv2024

Characterization of Silicon Carbide Biphenylene Network through G0W0-BSE Calculations

Two-dimensional silicon carbide stands out among 2D materials, primarily due to its notable band gap, unlike its carbon-based counterparts. However, the binary nature and non-layered structure of bulk SiC present challenges in fabricating its 2D counterpart. Recent advancements in technology have led to the successful synthesis of atomically thin, large-scale epitaxial monolayers of hexagonal-SiC and Si9C15 , marking a significant milestone in semiconductor research. Inspired by these advancements, we have computationally designed another stable phase of 2D-SiC in the popular biphenylene network, termed SiC-biphenylene. This structure is characterized by interconnected polygons of octagons, hexagons, and tetragons arranged periodically. The dynamical and thermal stability has been confirmed through ab initio phonon dispersion and molecular dynamics simulations. The structure demonstrates a high melting point of approximately 3475 K and a direct band gap of 2.16 eV using the HSE06 functional. Upon considering many-body effects, the quasiparticle band gap widens to 2.89 eV at the G0W0 level, indicating pronounced electron correlation effects within the material. The optical spectrum obtained from solving the Bethe-Salpeter equation (G0W0+BSE) identifies the first optically active exciton peak at 2.07 eV, corresponding to a strongly bound exciton with a binding energy of 0.82 eV. Furthermore, the investigation into stable bilayer structures across various stacking configurations highlights the impact of stacking patterns on excitonic binding energies. Our investigation extends to identifying the stable bulk phase of SiC-biphenylene, revealing lower self-energy corrections compared to monolayer and bilayer structures, attributed to increased electron delocalization in bulk structures.

cond-mat.mtrl-sci↗

arXiv2023

Defect-driven tunable electronic and optical properties of two-dimensional silicon carbide

Recently, an atomic-scale two-dimensional silicon carbide monolayer has been synthesized {[}Polley \emph{et al., }Phys. Rev. Lett. \textbf{130},076203 (2023){]} which opens up new possibilities for developing next-generation electronic and optoelectronic devices. Our study predicts the pristine SiC monolayer to have an ``indirect'' band gap of 3.38 eV $(K\rightarrow M)$ and a ``direct'' band gap of 3.43 eV $(K\rightarrow K)$ calculated using the HSE06 functional. We performed a detailed investigation of the various possible defects (i.e., vacancies, foreign impurities, antisites, and their various combinations) on the structural stability, electronic, and optical properties of the SiC monolayer using a first-principles based density-functional theory (DFT) and molecular dynamics (MD) simulations. A number of physical quantities such as the formation energy, electronic band gap, and the effective masses of charge carriers, have been calculated. We report that the SiC monolayer has a very low formation energy of 0.57 eV and can be stabilized on TaC \{111\} film by performing the surface slab energy and interfacial adhesion energy calculations. Nitrogen doping is predicted to be the most favorable defect in silicon carbide monolayer due to its very low formation energy, indicating high thermodynamic stability. An interesting transition from semiconducting to metallic state is observed for $N_{C}$ and $Al_{Si}$ defective systems. For the pristine SiC monolayer, we find that the conduction band is nearly flat in the $M\rightarrow K$ direction, leading to a high effective mass of $3.48m_{o}$. A significant red shift in the absorption edge, as well as the occurrence of additional absorption peaks due to the defects, have been observed in the lower energy range of the spectrum.

cond-mat.mtrl-sci↗

arXiv2023

Potential reversible hydrogen storage in Li-decorated carbon allotrope PAI-Graphene: A first-principles study

Two-dimensional porous carbon nanomaterials are proven to be promising hydrogen storage substrates as they possess high surface area, large number of active sites, low molecular mass, and hydrogen molecules can be adsorbed on both sides of these materials. By performing first-principles density functional theory-based calculations, we report ultrahigh reversible hydrogen uptake in lithium decorated 2D carbon allotrope PAI-graphene, which is formed of a regular pattern of polymerized as-indacenes (PAI). We found that a single unit cell of PAI-graphene can be decorated by 8 Li atoms, in which each Li atom can reversibly adsorb 4 hydrogen molecules, leading to 15.7 % of H uptake, remarkably higher than the DOE demand of 6.5 %. Li atom donates its valence 2s-electron to PAI-graphene and gets ionized. The adsorption energies of the various H2 attached to Li-atom are found to be suitable for reversible use during practical applications. Hydrogen molecules get attached to the ionized metal atom by electrostatic interactions. An energy barrier of 1.48 eV is present for the diffusion of Li atoms between the two most stable adsorption sites which justifies the absence of the clustering of Li atoms.

cond-mat.mtrl-sci↗

arXiv2023

Benchmarking Gaussian Basis Sets in Quantum-Chemical Calculations of Photoabsorption Spectra of Light Atomic Clusters

The choice of Gaussian basis functions for computing the ground-state properties of molecules, and clusters, employing wave-function-based electron-correlated approaches, is a well-studied subject. However, the same cannot be said when it comes to the excited-state properties of such systems, in general, and optical properties, in particular. The aim of the present study is to understand how the choice of basis functions affects the calculations of linear optical absorption in clusters, qualitatively, and quantitatively. For this purpose, we have calculated linear optical absorption spectra of several small charged and neutral clusters, namely, Li$_{2}$, Li$_{3}$, Li$_{4}$, B$_{2}^{+}$, B$_{3}^{+}$, Be$_{2}^{+}$, and Be$_{3}^{+}$, using a variety of Gaussian basis sets. The calculations were performed within the frozen-core approximation, and a rigorous account of electron correlation effects in the valence sector was taken by employing various levels of configuration interaction (CI) approach both for the ground and excited states. Our results on the peak locations in the absorption spectra of Li$_{3}$ and Li$_{4}$ are in very good agreement with the experiments. Our general recommendation is that for excited-state calculations, it is very important to utilize those basis sets which contain augmented functions. Relatively smaller aug-cc-pVDZ basis sets also yield high-quality results for photoabsorption spectra, and are recommended for such calculations if the computational resources are limited.

physics.chem-ph↗

arXiv2022

Influence of Defects on the Valley Polarization Properties of Monolayer MoS$_{2}$ Grown by Chemical Vapor Deposition

Here, the underlying mechanisms behind valley de-polarization is investigated in chemical vapor deposited 1L-MoS$_{2}$. Temperature dependent polarization resolved photoluminescence spectroscopy was carried out on as-grown, transferred and capped samples. It has been found that the momentum scattering of the excitons due to the sulfur-vacancies attached with air-molecule defects has a strong influence on the valley de-polarization process. Our study reveals that at sufficiently low densities of such defects and temperatures, long range electron-hole exchange mediated intervalley transfer due to momentum scattering via Maialle-Silva-Sham (MSS) mechanism of excitons is indeed the most dominant spin-flip process as suggested by T. Yu et al. The rate of momentum scattering of the excitons due to these defects is found to be proportional to the cube root of the density of the defects. Intervalley transfer process of excitons involving $Γ$-valley also has significance in the valley de-polarization process specially when the layer has tensile strain or high density of $V_S$ defects as these perturbations reduce $K$ to $Γ$-energy separation. Band-structural calculations carried out within the density functional theory framework validate this finding. Experimental results further suggest that exchange interactions with the physisorbed air molecules can also result in the intervalley spin-flip scattering of the excitons, and this process gives an important contribution to valley depolarization, specially at the strong scattering regime.

physics.optics↗

arXiv2022

Remarkable enhancement in catechol sensing by the decoration of selective transition metals in biphenylene sheet: A systematic first-principles study

Motivated by the recent successful synthesis of biphenylene structure [Science 372, (2021), 852], we have explored the sensing properties of this material towards the catechol biomolecule by performing the first-principles density functional theory and molecular dynamics simulations. Pristine biphenylene sheet adsorbs catechol molecule with a binding energy of -0.35 eV, which can be systematically improved by decorating the transition metals (Ag, Au, Pd, and Ti) at various possible sites of biphenylene. It is observed that the catechol molecule is adsorbed on Pd and Ti-decorated biphenylene sheets with strong adsorption energies of -1.00 eV and -2.54 eV, respectively. The interaction of the catechol molecule with biphenylene and metal-decorated biphenylene is due to the charge transfer from the O-2p orbitals of the catechol molecule to the C-2p orbitals of biphenylene and d-orbitals of metals in metal-decorated biphenylene, respectively. From the Bader charge calculation, we found that 0.05e amount of charge is transferred from the catechol molecule to pristine biphenylene, which gets almost double (~0.1e) for the Ti-decorated biphenylene sheet. The diffusion energy barrier for the clustering of the Pd and Ti atoms comes out to be 2.39 eV and 4.29 eV, computed by performing the climbing-image nudged elastic band calculations. We found that the catechol molecule gets desorbed from the pristine biphenylene sheet even at 100 K but remains attached to metal (Pd, Ti) decorated biphenylene sheets at room temperature by performing the ab-initio molecular dynamics simulations. The Ti-decorated biphenylene sheet has more sensitivity toward catechol adsorption while the Pd-decorated biphenylene sheet has a suitable recovery time at 500 K. The results suggest that the Pd and Ti-decorated biphenylene sheets are promising materials for catechol detection.

cond-mat.mtrl-sci↗

arXiv2022

Influence of compressive strain on the hydrogen storage capabilities of graphene: A density functional theory study

Pristine graphene is not suitable for hydrogen storage at ambient conditions since it binds the hydrogen molecules only by van der Waals interactions. However, the adsorption energy of the hydrogen molecules can be improved by doping or decorating metal atoms on the graphene monolayer. The doping and decoration processes are challenging due to the oxygen interference in hydrogen adsorption and the clustering issue of metal atoms. To improve the hydrogen adsorption energy in pristine graphene, we have explored the hydrogen storage capabilities of graphene monolayer in the presence of compressive strain. We found that at 6 % of biaxial compressive strain, a 4*4*1 supercell of graphene can adsorb 10 H$_2$ molecules above the graphene surface. The average binding energy of H$_2$ for this configuration is found to be -0.42 eV/H$_2$, which is very suitable for reversible hydrogen adsorption. We propose that a 4*4*1 supercell of graphene can adsorb a total number of 20 H$_2$ molecules leading to a high hydrogen uptake of 9.4 %. The interaction between orbitals of carbon and hydrogen atoms and the charge transfer process have been studied by plotting the partial density of states and surface charge density plots. The electronic density around the C-C bonds of graphene increases in the presence of compressive strain, due to which hydrogen molecules are strongly adsorbed.

cond-mat.mtrl-sci↗

arXiv2022

Prediction of a Novel 2D Porous Boron Nitride Material with Excellent Electronic, Optical and Catalytic Properties

Holey graphyne (HGY) is a recently synthesized two-dimensional semiconducting allotrope of carbon composed of a regular pattern of six and eight-vertex carbon rings. In this study, based on first-principles density functional theory and molecular dynamics simulations, we predict a similar stable porous boron nitride holey graphyne-like structure that we call BN-holey-graphyne (BN-HGY). The dynamical and thermal stability of the structure at room temperature is confirmed by performing calculations of the phonon dispersion relations, and also ab-initio molecular dynamics simulations. BN-HGY structure has a wide direct bandgap of 5.18 eV, which can be controllably tuned by substituting carbon, aluminum, silicon, and phosphorus atom in place of sp and sp$^2$ hybridized boron and nitrogen atoms of BN-HGY. We have also calculated the optical properties of the HGY and BN-HGY structures for the first time and found that the optical absorption spectra of these structures span full visible and a wide range of ultraviolet regions. We have found that the Gibbs free energy of the BN-HGY structure for the hydrogen adsorption process is very close to zero (-0.04 eV) and, therefore, the BN-HGY structure can be utilized as a potential catalyst for HER. Therefore, we propose that the boron nitride analog of holey graphyne can be synthesized and that it has a wide range of applications in nanoelectronics, optoelectronics, spintronics, ultraviolet laser, and solar cell devices.

cond-mat.mtrl-sci↗

arXiv2022

Ultrahigh reversible hydrogen storage in K and Ca decorated 4-6-8 biphenylene sheet

By applying density functional theory (DFT) and ab-initio molecular dynamics (AIMD) simulations, we predict the ultrahigh hydrogen storage capacity of K and Ca decorated single-layer biphenylene sheet (BPS). We have kept various alkali and alkali earth metals, including Na, Be, Mg, K, Ca, at different sites of BPS and found that K and Ca atoms prefer to bind individually on the BPS instead of forming clusters. It was found that 2x2x1 supercell of biphenylene sheet can adsorb eight K, or eight Ca atoms, and each K or Ca atom can adsorb 5 H$_2$, leading to 11.90 % or 11.63 % of hydrogen uptake, respectively, which is significantly higher than the DOE-US demands of 6.5 %. The average adsorption energy of H$_2$ for K and Ca decorated BPS is -0.24 eV and -0.33 eV, respectively, in the suitable range for reversible H$_2$ storage. Hydrogen molecules get polarized in the vicinity of ionized metal atoms hence get attached to the metal atoms through electrostatic and van der Waals interactions. We have estimated the desorption temperatures of H$_2$ and found that the adsorbed H$_2$ can be utilized for reversible use. We have found that a sufficient energy barrier of 2.52 eV exists for the movement of Ca atoms, calculated using the climbing-image nudged elastic band (CI-NEB) method. This energy barrier can prevent the clustering issue of Ca atoms. The solidity of K and Ca decorated BPS structures were investigated using AIMD simulations.

cond-mat.mtrl-sci↗

arXiv2022

High-capacity reversible hydrogen storage in scandium decorated holey graphyne: Theoretical perspectives

We have investigated the hydrogen storage capabilities of scandium decorated holey graphyne, a recently synthesized carbon allotrope, by applying density functional theory and molecular dynamics simulations. We have observed that one unit cell of holey graphyne can adsorb 6 Sc atoms, and each Sc atom can adsorb up to 5 H$_2$ molecules with an average binding energy and average desorption temperature of -0.36 eV/H$_2$ and 464 K, respectively. The gravimetric weight percentage of hydrogen is 9.80 %, which is considerably higher than the Department of Energy, United-States requirements of 6.5 %. We have found that a total amount of 1.9e charge transfers from the 3d and 4s orbitals of Sc atom to the C-2p orbitals of holey graphyne by performing the Bader charge analysis. Hydrogen molecules are bonded with the scandium atom by Kubas interactions. The ab-initio molecular dynamics simulations confirm the structural integrity of scandium decorated holey graphyne system at the high desorption temperatures. The presence of sufficient diffusion energy barriers for the Sc atom ensure the avoidance of metal-metal clustering in the system.

cond-mat.mtrl-sci↗

arXiv2022

Exploring yttrium doped C$_{24}$ fullerene as a high-capacity reversible hydrogen storage material: DFT investigations

By employing the state-of-the-art density functional theory, we report the hydrogen storage capability of yttrium decorated C$_{24}$ fullerene. Single Y atom attached on C$_{24}$ fullerene can reversibly adsorb a maximum number of 6 H$_2$ molecules with average adsorption energy -0.37 eV and average desorption temperature 477 K, suitable for fuel cell applications. The gravimetric weight content of hydrogen is 8.84 %, which exceeds the target value of 6.5 wt % H by the department of energy (DoE) of the United States. Y atom is strongly bonded to C$_{24}$ fullerene with a binding energy of -3.4 eV due to a charge transfer from Y-4d and Y-5s orbitals to the C-2p orbitals of C$_{24}$ fullerene. The interaction of H$_2$ molecules with the Y atom is due to the Kubas type interaction involving a charge donation from the metal d orbital to H 1s orbital, and back donation causing slight elongation of H-H bond length. The stability of the system at the highest desorption temperature is confirmed by ab-initio molecular dynamics simulations, and the metal-metal clustering formation has been investigated by computing the diffusion energy barrier for the movement of Y atoms. We have corrected all the calculated energies for the van der Waals (vdW) interactions by applying the dispersion energy corrections, in addition to the contribution of the GGA exchange-correlation functional. The C$_{24}$+Y system is stable at room temperature, and at the highest desorption temperature, the presence of a sufficient diffusion energy barrier prevents metal-metal clustering. Furthermore, binding energies of H$_2$ are within the target value by DoE (-0.2-0.7 eV/H$_2$ ), while H$_2$ uptake (8.84 % H) is higher than DoE's criteria. Therefore, we propose that Y decorated C$_{24}$ fullerene can be tailored as a practically viable potential hydrogen storage candidate.

cond-mat.mtrl-sci↗

arXiv2021

Scandium decorated C$_{24}$ fullerene as high capacity reversible hydrogen storage material: Insights from density functional theory simulations

Using first-principles density functional theory simulations, we have observed that the scandium decorated C$_{24}$ fullerene can adsorb up to six hydrogen molecules with an average adsorption energy of -0.35 eV per H$_2$ and average desorption temperature of 451 K. The gravimetric wt % of hydrogen for the scandium decorated C$_{24}$ fullerene system is 13.02%, which is sufficiently higher than the Department of Energy, United States demand. Electronic structure, orbital interactions, and charge transfer mechanisms are explained using the density of states, spatial charge density difference plots, and Bader charge analysis. A total amount of 1.44e charge transfer from the 3d and 4s orbitals of scandium to the 2p carbon orbitals of C$_{24}$ fullerene. Hydrogen molecules are attached to scandium decorated C$_{24}$ fullerene by Kubas type of interactions. Diffusion energy barrier calculations predict that the existence of a sufficient energy barrier will prevent metal-metal clustering. Ab-initio molecular dynamics (A.I.M.D.) simulations confirm the solidity of the structure at the highest desorption temperature. Therefore, we believe that the scandium decorated C$_{24}$ fullerene system is a thermodynamically stable, promising reversible high-capacity hydrogen storage device.

cond-mat.mtrl-sci↗