Arnab Majumdar | University of Calcutta (original) (raw)

Papers by Arnab Majumdar

Nature Communications, 2020

Transport properties like diffusivity and viscosity of melts dictated the evolution of the Earth’... more Transport properties like diffusivity and viscosity of melts dictated the evolution of the Earth’s early magma oceans. We report the structure, density, diffusivity, electrical conductivity and viscosity of a model basaltic (Ca11Mg7Al8Si22O74) melt from first-principles molecular dynamics calculations at temperatures of 2200 K (0 to 82 GPa) and 3000 K (40–70 GPa). A key finding is that, although the density and coordination numbers around Si and Al increase with pressure, the Si–O and Al–O bonds become more ionic and weaker. The temporal atomic interactions at high pressure are fluxional and fragile, making the atoms more mobile and reversing the trend in transport properties at pressures near 50 GPa. The reversed melt viscosity under lower mantle conditions allows new constraints on the timescales of the early Earth’s magma oceans and also provides the first tantalizing explanation for the horizontal deflections of superplumes at ~1000 km below the Earth’s surface.

Applied Physics A, 2021

Ab initio study of high-pressure phase transition and electronic structure of Fe-doped CeO2 with ... more Ab initio study of high-pressure phase transition and electronic structure of Fe-doped CeO2 with Fe concentrations of 3.125, 6.25, and 12.5 at% has been reported. At a constant-pressure consideration, the lattice constants and the volume of the supercell were decreased with an increasing concentration of Fe. The average bond length of Fe–O is lower than that of Ce–O. As a result, Fe doping induces the reduced volume of the cell, which is in good agreement with previous experiments. At high pressure (~ 30 GPa), it was found that the transition pressure from the fluorite to the cotunnite orthorhombic phase decreases at a higher concentration of Fe, indicating that the formation energy of the compound is induced by Fe-doping. Furthermore, compression leads to interesting electronic properties too. Under higher pressures, the bandgap increases in the cubic structure under compression and then suddenly plummets after the transition to the orthorhombic phase. The 3d states of Fe mainly in...

Journal of Magnetism and Magnetic Materials, 2017

The discovery of different two-dimensional (2D) materials both theoretically and experimentally, ... more The discovery of different two-dimensional (2D) materials both theoretically and experimentally, can change the scenario of the current electronic industry because of their intriguing properties. Among the 2D materials, the first one which was discovered experimentally was graphene. In this work we have studied the electronic and magnetic properties of a new allotrope of disordered graphene, which is not hexagonal, rather possesses tetragonal symmetry known as T-graphene (TG). Density functional theory (DFT) has been thoroughly employed to study the relevant electronic properties. In previous works, it has been reported that pristine TG is non-magnetic. It is also known that, introducing transition metal (TM) atoms is a feasible way to control the electronic and magnetic properties. Here we have reported the relevant properties of four TM atoms i.e. Sc, V, Cr and Mn doped TG. From the defect formation energy study, it has been noticed that all the structures are endothermic in nature. For each case, we have found appreciable amount of magnetic moment. With increasing atomic weight of the dopant atom, the magnitude of the magnetic moment also increases. We have tried to explain this magnetic ordering with the help of spin-polarized partial density of states (PDOS). Controlling spin degrees of freedom is important for building spintronic devices. From that point of view, we hope this study will be useful to build TG based spintronic devices.

Inorganic chemistry, 2016

The knowledge of stoichiometries of alkaline-earth metal nitrides, where nitrogen can exist in po... more The knowledge of stoichiometries of alkaline-earth metal nitrides, where nitrogen can exist in polynitrogen forms, is of significant interest for understanding nitrogen bonding and its applications in energy storage. For calcium nitrides, there were three known crystalline forms, CaN2, Ca2N, and Ca3N2, at ambient conditions. In the present study, we demonstrated that there are more stable forms of calcium nitrides than what is already known to exist at ambient and high pressures. Using a global structure searching method, we theoretically explored the phase diagram of CaNx and discovered a series of new compounds in this family. In particular, we found a new CaN phase that is thermodynamically stable at ambient conditions, which may be synthesized using CaN2 and Ca2N. Four other stoichiometries, namely, Ca2N3, CaN3, CaN4, and CaN5, were shown to be stable under high pressure. The predicted CaNx compounds contain a rich variety of polynitrogen forms ranging from small molecules (N2, ...

Physical Review B, 2021

An unprecedented graphyne allotrope with square symmetry and nodal line semimetallic behavior has... more An unprecedented graphyne allotrope with square symmetry and nodal line semimetallic behavior has been proposed in the two-dimensional (2D) realm. The emergence of the Dirac loop around the high-symmetry points in the presence of both the inversion and time-reversal symmetries is a predominant feature of the electronic band structure of this system. Besides, the structural stability in terms of the dynamic, thermal, and mechanical properties has been critically established for the system. Following the exact analytical model based on the realspace renormalization group scheme and tight-binding approach, we have inferred that the family of 2D nodal line semimetals with square symmetry can be reduced to a universal four-level system in the low-energy limit. This renormalized lattice indeed explains the underlying mechanism responsible for the fascinating emergence of 2D square nodal line semimetals. Besides, the analytical form of the generic dispersion relation of these systems is well supported by our density-functional theory results. Finally, the nontrivial topological properties have been explored for the predicted system without breaking the inversion and time-reversal symmetry of the lattice. We have obtained that the edge states are protected by the nonvanishing topological index, i.e., Zak phase.

Angewandte Chemie International Edition

Compression of hydrogen sulfide using first principles metadynamics and molecular dynamics calcul... more Compression of hydrogen sulfide using first principles metadynamics and molecular dynamics calculations revealed a modulated structure with high proton mobility which exhibits a diffraction pattern matching well with experiment. The structure consists of a sublattice of rectangular meandering SH(-) chains and molecular-like H3 S(+) stacked alternately in tetragonal and cubic slabs forming a long-period modulation. The novel structure offers a new perspective on the possible origin of the superconductivity at very high temperatures in which the conducting electrons in the SH chains are perturbed by the fluxional motions of the H3 S resulting in strong electron-phonon coupling.

The Journal of chemical physics, Jan 21, 2017

A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected ... more A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected to pressures up to 50 GPa reveals one structural phase transition near 10 GPa, detected by synchrotron powder x-ray diffraction, and metadynamics simulations. The ambient-pressure tetragonal phase of Li2PdD2 transforms into a monoclinic C2/m phase that is distinct from all known structures of alkali metal-transition metal hydrides/deuterides. The structure of the high-pressure phase was characterized using ab initio computational techniques and from refinement of the powder x-ray diffraction data. In the high-pressure phase, the PdD2 complexes lose molecular integrity and are fused to extended [PdD2]∞ chains. The discovered phase transition and new structure are relevant to the possible hydrogen storage application of Li2PdD2 and alkali metal-transition metal hydrides in general.

RSC Advances, 2014

ABSTRACT We study here the magnetic properties of two dimensional silicene using spin polarized d... more ABSTRACT We study here the magnetic properties of two dimensional silicene using spin polarized density functional theory. The magnetic properties were studied by introducing monovacancy and di-vacancy, as well as by doping phosphorous and aluminium into the pristine silicene. It is observed that there is no magnetism in the monovacancy system, while there is large significant magnetic moment present for the di-vacancy system. Besides, the numerical computation reveals that the magnitude of the magnetic moment is more when the system is doped with aluminium than phosphorous. All these theoretical predictions in this two dimensional system may shed light to open a new route to design silicon based nano-structures in spintronics.

RSC Adv., 2014

Various optical properties of two dimensional buckled silicene have been explored using spin unpo... more Various optical properties of two dimensional buckled silicene have been explored using spin unpolarized density functional theory by incorporating doping with phosphorous and aluminium atoms in the hexagonal network of pristine buckled silicene.

The recently synthesized FeH 5 at high pressure is calculated to be a superconductor with a criti... more The recently synthesized FeH 5 at high pressure is calculated to be a superconductor with a critical temperature (T c) of 51 K at 130 GPa. The crystal structure of this compound can be described as stacking bilayers of a puckered hexagonal honeycomb of H atoms sandwiched between slabs of atomic Fe and H atoms. The honeycomb layers resemble the predicted structure of a metallic and high T c Cmca phase of solid hydrogen. Electron-phonon interactions were mainly derived from coupling of the electronic bands with bending vibrations of the hydrogens in the puckered layers.

Compression of hydrogen sulfide using first principles metadynamics and molecular dynamics calcul... more Compression of hydrogen sulfide using first principles metadynamics and molecular dynamics calculations revealed a modulated structure with high proton mobility which exhibits a diffraction pattern matching well with experiment. The structure consists of a sublattice of rectangular meandering SH À chains and molecular-like H 3 S + stacked alternately in tetragonal and cubic slabs forming a long-period modulation. The novel structure offers a new perspective on the possible origin of the superconductivity at very high temperatures in which the conducting electrons in the SH chains are perturbed by the fluxional motions of the H 3 S resulting in strong electron-phonon coupling.

A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected ... more A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected to pressures up to 50 GPa reveals one structural phase transition near 10 GPa, detected by synchrotron
powder x-ray diffraction, and metadynamics simulations. The ambient-pressure tetragonal phase of Li2PdD2 transforms into a monoclinic C2/m phase that is distinct from all known structures of alkali metal–transition metal hydrides/deuterides. The structure of the high-pressure phase was characterized using ab initio computational techniques and from refinement of the powder x-ray diffraction data. In the high-pressure phase, the PdD2 complexes lose molecular integrity and are fused to extended [PdD2]∞ chains. The discovered phase transition and new structure are relevant to the possible hydrogen storage application of Li2PdD2 and alkali metal–transition metal hydrides in general.

The knowledge of stoichiometries of alkaline-earth metal nitrides, where nitrogen can exist in po... more The knowledge of stoichiometries of alkaline-earth metal nitrides, where nitrogen can exist in polynitrogen forms, is of significant interest for understanding nitrogen bonding and its applications in energy storage. For calcium nitrides, there were three known crystalline forms, CaN 2 , Ca 2 N, and Ca 3 N 2 , at ambient conditions. In the present study, we demonstrated that there are more stable forms of calcium nitrides than what is already known to exist at ambient and high pressures. Using a global structure searching method, we theoretically explored the phase diagram of CaN x and discovered a series of new compounds in this family. In particular, we found a new CaN phase that is thermodynamically stable at ambient conditions, which may be synthesized using CaN 2 and Ca 2 N. Four other stoichiometries, namely, Ca 2 N 3 , CaN 3 , CaN 4 , and CaN 5 , were shown to be stable under high pressure. The predicted CaN x compounds contain a rich variety of polynitrogen forms ranging from small molecules (N 2 , N 4 , N 5 , and N 6) to extended chains (N ∞). Because of the large energy difference between the single and triple nitrogen bonds, dissociation of the CaN x crystals with polynitrogens is expected to be highly exothermic, making them as potential high-energy-density materials.

The journal of physical chemistry. A, Jan 18, 2016

A new allotrope of nitrogen in which the atoms are connected to form a novel N6 molecule is predi... more A new allotrope of nitrogen in which the atoms are connected to form a novel N6 molecule is predicted to exist at ambient conditions. The N6 molecule has a charge-transfer complex with an open-chain structure containing both single and triple bonds. The charge transfer induces ionic characters in the intermolecular interactions and leads to a much greater cohesive energy for the predicted crystal compared to solid N2. The N6 solid is also more stable than a previously reported polymeric solid of nitrogen. Due to the kinetic stability of the molecules and strong intermolecular interactions, the N6 crystal is shown by metadynamics simulations to be dynamically stable around room temperature and to only dissociate to N2 molecules above 700 K. The N6 crystal can likely be synthesized under high-pressure high-temperature conditions, and the considerable metastability may allow for an ambient-pressure recovery of the crystal. Due to the large energy difference between the single and tripl...

The Journal of chemical physics, Jan 28, 2016

First principles calculations identified a phase transition in aluminium triiodide (AlI3) and pre... more First principles calculations identified a phase transition in aluminium triiodide (AlI3) and predicted its physical and spectroscopic properties under high pressure conditions. A high pressure monoclinic phase is predicted to exist above 1.3 GPa accompanied with a coordination change of aluminium resulting from a transformation from the ambient pressure 4-coordinated primitive monoclinic phase with space group P21/c to the monoclinic 6-coordinated structure with space group C2/m. Density functional phonon calculations predicted its dynamical and mechanical stability. Infrared effective charge intensities and Raman scattering tensors were obtained to characterize its spectroscopic properties. First-principles metadynamics simulations were employed to reconstruct this phase transition and provide the mechanism details for energetically favourable path from the ambient pressure P21/c structure to the predicted C2/m structure.

We study here the magnetic properties of two dimensional silicene using spin polarized density fu... more We study here the magnetic properties of two dimensional silicene using spin polarized density functional theory. The magnetic properties were studied by introducingm onovacancy and di-vacancy, as well as by doping phosphorous and aluminium into the pristine silicene. It is observed that there is no magnetism in the monovacancy system, while there is large significant magnetic moment present for the di-vacancy system. Besides, the numerical computation reveals that the magnitude of the magnetic moment is more when the system is doped with aluminium than phosphorous. All these theoretical predictions in this two dimensional system may shed light to open a new route to design silicon based nano-structures in spintronics.

Here we study the optical properties of two dimensional pure as well as doped buckled silicene na... more Here we study the optical properties of two dimensional pure as well as doped buckled silicene nanosheet using density functional theory in the long wavelength limit. Optical properties are studied by varying the concentration of substituted Aluminium (Al), Phosphorus (P) and Aluminium - Phosphorus (Al-P) atoms in silicene nanosheet. It has been observed that unlike graphene, no new electron energy loss spectra (EELS) peak occurs irrespective of doping type for parallel polarization. But for perpendicular polarization two new small yet significant EELS peak emerge for P doping. The origin of these new EELS peak may be
explained through the buckling effect of stable silicene. In addition, the calculations have revealed that the maximum values of the absorption coefficient of the doped system are higher than the pristine one. The study on reflectivity modulation with doping concentration has indicated the emergence of some strong peak having robust characteristic of doped reflective surface for both polarizations of electromagnetic field. Moreover, for all doped systems, the reflectivity modulation is restricted to low energy (< 4 eV) and high energy (> 8 eV) for parallel and perpendicular polarization respectively. Although no significant changes
are noticed in the maximum values of optical conductivity with doping concentration in perpendicular polarization, however, a sudden jump appears for Al-P co-doped system at 18.75% doping concentration. All these theoretical observations are expected to shed light in fabricating opto-electronic devices using silicene as the block material.

Nature Communications, 2020

Applied Physics A, 2021

Journal of Magnetism and Magnetic Materials, 2017

Inorganic chemistry, 2016

Physical Review B, 2021

Angewandte Chemie International Edition

The Journal of chemical physics, Jan 21, 2017

RSC Advances, 2014

RSC Adv., 2014

Compression of hydrogen sulfide using first principles metadynamics and molecular dynamics calcul... more Compression of hydrogen sulfide using first principles metadynamics and molecular dynamics calculations revealed a modulated structure with high proton mobility which exhibits a diffraction pattern matching well with experiment. The structure consists of a sublattice of rectangular meandering SH À chains and molecular-like H 3 S + stacked alternately in tetragonal and cubic slabs forming a long-period modulation. The novel structure offers a new perspective on the possible origin of the superconductivity at very high temperatures in which the conducting electrons in the SH chains are perturbed by the fluxional motions of the H 3 S resulting in strong electron-phonon coupling.

A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected ... more A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected to pressures up to 50 GPa reveals one structural phase transition near 10 GPa, detected by synchrotron
powder x-ray diffraction, and metadynamics simulations. The ambient-pressure tetragonal phase of Li2PdD2 transforms into a monoclinic C2/m phase that is distinct from all known structures of alkali metal–transition metal hydrides/deuterides. The structure of the high-pressure phase was characterized using ab initio computational techniques and from refinement of the powder x-ray diffraction data. In the high-pressure phase, the PdD2 complexes lose molecular integrity and are fused to extended [PdD2]∞ chains. The discovered phase transition and new structure are relevant to the possible hydrogen storage application of Li2PdD2 and alkali metal–transition metal hydrides in general.

The knowledge of stoichiometries of alkaline-earth metal nitrides, where nitrogen can exist in po... more The knowledge of stoichiometries of alkaline-earth metal nitrides, where nitrogen can exist in polynitrogen forms, is of significant interest for understanding nitrogen bonding and its applications in energy storage. For calcium nitrides, there were three known crystalline forms, CaN 2 , Ca 2 N, and Ca 3 N 2 , at ambient conditions. In the present study, we demonstrated that there are more stable forms of calcium nitrides than what is already known to exist at ambient and high pressures. Using a global structure searching method, we theoretically explored the phase diagram of CaN x and discovered a series of new compounds in this family. In particular, we found a new CaN phase that is thermodynamically stable at ambient conditions, which may be synthesized using CaN 2 and Ca 2 N. Four other stoichiometries, namely, Ca 2 N 3 , CaN 3 , CaN 4 , and CaN 5 , were shown to be stable under high pressure. The predicted CaN x compounds contain a rich variety of polynitrogen forms ranging from small molecules (N 2 , N 4 , N 5 , and N 6) to extended chains (N ∞). Because of the large energy difference between the single and triple nitrogen bonds, dissociation of the CaN x crystals with polynitrogens is expected to be highly exothermic, making them as potential high-energy-density materials.

The journal of physical chemistry. A, Jan 18, 2016

The Journal of chemical physics, Jan 28, 2016