## About

241

Publications

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Introduction

We are working on nanomaterials and designing new structures as well as materials for solar energy, solid state lighting, small clusters of metals and other systems, hard materials, surfaces and 2D materials using ab initio calculations.

Additional affiliations

August 2012 - present

January 1991 - October 1993

**International Center for Theoretical Physics, Trieste, Italy**

Position

- Research Expert, Staff Member

April 1985 - August 1999

Education

July 1972 - June 1977

July 1970 - May 1972

## Publications

Publications (241)

We study the structural stability and electronic properties of A3B (A = Cr, Mo, and W; B = Al, Ga, In, Si, Ge, Sn, and Be) compounds using ab initio pseudopotential method with Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) for the exchange-correlation functional. It is found that Cr3Be, Cr3Al, Cr3Ga, Cr3Si, Cr3Ge, Mo3Be, Mo3...

The β phase of tungsten has attracted great interest for spintronic applications due to its higher spin Hall angle compared to other elemental solids and large spin–orbit torque, but the stability of this phase is yet to be well understood as many different results are there in the literature mainly based on the film thickness, temperature, and ove...

The A15 β phase of tungsten has recently attracted great interest for spintronic applications due to the finding of giant spin-Hall effect. As β phase is stabilized by oxygen, we have studied the electronic structure of O-doped β-W from first principles calculations. It is found that 20 at.% O-doping makes β phase lower in energy than α-W. These re...

Prediction and experimental verification of silicon fullerenes and other polyhedral forms stabilized by metal atom encapsulation have led to the emergence of endohedral doping of clusters as a novel way to form strongly stable superatoms in macroscopic quantities. Assemblies of such superatoms have also been realized. This has opened up new opportu...

We present results of a state-of-the-art computational study of the atomic and electronic structure of Cs2n+2MnM’nX6n+2 (M = Cu, Ag; M’= In, Bi; X= Cl, Br, I) layers with up to three-unit-cell thickness (n = 3) as well as their bulk counterparts in the search for economical and stable halide double perovskites (HDP) with a direct band gap and stron...

Assemblies of clusters have been sought for a long time to synthesize new materials with unprecedented physical phenomena or to integrate desired functionalities for technological applications. However, except for some carbon fullerenes and ligated clusters, little progress has been made in achieving assemblies of other clusters due to their tenden...

Recent experiments on chemical tuning of spacer cations (phenyl-ethylammonium: PEA) with electronegative entities such as Cl or F in 2D−3D Ruddlesden−Popper (RP) perovskite layers show simultaneous improvement in their device performance and stability. In order to understand the role of such substitution on the properties and stability of 2D and 2D...

Sixteen atom Frank-Kasper golden cage with an endohedral atom that is favored by many endohedral clusters, such as Ti@Si16, Zr@Ge16, Zr@Sn16, [Y@Au16]+, and [Sc@Cu16]+, and a galaxy of representative endohedral clusters with different cages and different dopants.
The cover page is for the review article "Endohedrally Doped Cage Clusters" which app...

Thin films of β-W are the most interesting for manipulating magnetic moments using spin–orbit torques, and a clear understanding of α to β phase transition in W by doping impurity, especially oxygen, is needed. Here we present a combined experimental and theoretical study using grazing incidence X-ray diffraction, photoelectron spectroscopy, electr...

The discovery of carbon fullerene cages and their solids opened a new avenue to build materials from stable cage clusters as “artificial atoms” or “superatoms” instead of atoms. However, cage clusters of other elements are generally not stable. In 2001, ab initio calculations showed that endohedral doping of Zr and Ti atoms leads to highly stable Z...

A novel lead-free 2D perovskite, namely PEA2SnBr4, shows an impressive water-resistance by retaining its original crystal structure and optical properties when put in contact with water. Such key properties have been advantageously used in the fabrication of a novel co-catalytic system by coupling PEA2SnBr4 with graphitic carbon nitride. PEA2SnBr4@...

Recent experiments on Eu doped nanocrystals of CsPbX3 (X = Cl, Br) show that Eu exists in 3+ oxidation state even though it substitutes Pb which is in 2+ state in these perovskites. Therefore, the question arises, what is it that leads to the formation of Eu3+ in nanocrystals of these materials? In order to understand this, we have studied the dopi...

We report the results of density functional theory calculations on the atomic and electronic structure of solids formed by assembling A2B2PN (A = Ge and Sn, B = Cl, Br, and I) inorganic double helices. The calculations have been performed using a generalized gradient approximation for the exchange–correlation functional and including van der Waals...

We report results of the state-of-the-art ab initio calculations on two-dimensional (2D) hybrid halide perovskites capped with surface ligands to understand their effects on the stability with respect to bulk MASnBr3 (MA = CH3NH3). Considering the thinnest (one-unit-cell thick) layers R2SnBr4 with surface ligands of different lengths (R=MA, ethyl a...

Our recent research work on all-organic molecular ferroelectric has been published as an "Inside front cover" in the Issue 65 of Chemical Communication - Royal Society of Chemistry’s most cited journal.

Using density functional theory calculations, we study doping of a Cr, Mo, and W atom in boron clusters in the size range of 18-24 atoms and report the finding of metal atom encapsulated fullerene-like cage structures with 20 to 24 boron atoms in contrast to a fullerene-like structure of pure boron with 40 atoms. Our results show that bicapped drum...

Traditionally the lead and heavy metal containing inorganic oxides
dominate the area of ferroelectricity. Although, recently, the
lightweight non-toxic organic ferroelectrics have emerged as
excellent alternates but achieving higher temperature up to which
the ferroelectric phase can persist has been remained a challenge.
Moreover, only a few of th...

We study the stability of rare earth dopant, Eu, in metal halide perovskite CsPbBr3 with cubic and orthorhombic structures from first principles calculations. In these perovskites Eu is substitutionally doped on Pb sites due to their comparable ionic sizes which lead to only a small strain in the doped systems. Accordingly, our results show that th...

We have studied the stability of several borophene layers on Al(111) surface and found a structure called 9R from ab initio calculations. This layer competes with χ3 and β12 borophene layers and is made up of boron nonagons that form a network of hexagonal boron double chain. Remarkably it has no B6 hexagon unlike other borophene layers. All the th...

Although the nature of the chemical bond is at the heart of chemistry, chemists often work with several distinct conceptions of the chemical bond, which are not necessarily compatible with each other. The Lewis concept of the electron pair bond [1] is now over a century old, predating the quantum mechanical theory of bonding in molecules. We now re...

Thin layers of inorganic halide perovskites An+1MnX3n+1 (n = 1 – 6, A= Cs, M = Pb and Sn, and X = Cl, Br, and I) have been studied in orthorhombic and cubic phases along with layers of monoclinic CsSnCl3. It is found that one unit-cell-thick layers have low stability except monoclinic phase of CsSnCl3 where formation energy is slighly less than bul...

Thin layers of inorganic halide perovskites A n+1 M n X 3n+1 (n = 1-6, A= Cs, M = Pb and Sn, and X = Cl, Br, and I) have been studied in orthorhombic and cubic phases along with layers of monoclinic CsSnCl 3. It is found that one unit-cell-thick layers have low stability except monoclinic phase of CsSnCl 3 where formation energy is slighly less tha...

We study the structural stability and electronic properties of new classes of DNA-like inorganic double helices of the type A2B2XY (A = Si-Pb, B = Cl-I, and XY = PN and SiS) by employing first principles density functional theory (DFT) calculations including van der Waals interactions. In these quaternary double helices PN or SiS forms the inner he...

In this study, the evolution of C60F18 molecules on a Cu(001) surface was studied by means of scanning tunneling microscopy and density functional theory calculations. The results showed that fluorinated fullerenes (tortoise-shaped polar C60F18) decay on Cu(001) surfaces by a step-by-step detachment of F atoms from the C60 cage. The most favorable...

Carbon nanotubes have been extensively studied and been documented in literature. However, very little is known about their boron analogues. Pure boron clusters have been found to exist is myriad shapes and sizes: planar, quasi-planar, drum-shaped, and cage-like structures. Recently metal doped B14 and B16 tubular (drum shaped) structures have also...

Ab initio calculations on one, two, and three layers of SnS and SnSe compound semiconductors show that they all have indirect band gap similar to bulk and it varies in the range of ~0.5–1.6 eV within the generalized gradient approximation due to quantum confinement as well as structural relaxations. In two-dimensional structures, the difference bet...

We study the stability of drum-shaped transition metal (TM)-doped boron clusters, M@Bn with n = 14 and 16, and M = 3d, 4d, and 5d TM atom using ab initio calculations. Our results show that drum-shaped M@B14 clusters are favored for M = Cr, Mn, Fe, Co, and Ni, while in other cases, open conical or bowl shaped structures become more favorable. The i...

Results of ab initio pseudopotential calculations are presented concerning the atomic structure and magnetic properties of GaN doped with selected rare earth atoms. Effects of codoping these materials with Si are also discussed. It has been found that the doping of a Eu atom on a Ga site in bulk GaN creates significant local deformation and it cost...

Ab initio calculations on hard/soft (FePt)m/(FeCo)n, (m = 4, 6, 8 and n = 2-2m) magnetic superlattices show that the B2 type FeCo layers become anisotropic with varying interlayer spacing and enhanced magnetic moments. The average magnetic moment in superlattices is higher than in bulk FePt, resulting in high maximum energy product for (FePt)4/(FeC...

Boron atomic clusters show several interesting and unusual size-dependent features due to the small covalent radius, electron deficiency, and higher coordination number of boron as compared to carbon. These include aromaticity and a diverse array of structures such as quasi-planar, ring or tubular shaped, and fullerene-like. In the present work, we...

This paper develops a first principles atomistic model of single atom substitutions within boron suboxide to predict the effect of potential sintering aides (Al, Mg, Si, and Lu) and processing contaminants (C, N, F, S, P, Li, and Ti) on its cohesive energies and local bonding reconstruction. Our results indicate that metallic dopants strongly desta...

The atomic and electronic structure of both neutral and negatively charged ZrGen (n=1-21) clusters have been studied using ab initio calculations. The atomic structures have been identified by comparing the calculated results of the electronic spectra of the anion clusters with the available photoelectron spectroscopy data. We find that the atomic...

Atomic structure, alloying behavior, and magnetism in small Fe-Pt clusters
We report results of the atomic structure, alloying behaviour, and magnetism in FemPtn (m + n = 2-10) clusters using projector augmented wave (PAW) pseudopotential method and spin-polarized generalized gradient approximation (GGA) for the exchange-correlation energy. These r...

Ab initio calculations on CsSnX3
perovskites and mixed halides CsSn(XxY 1−x)3, X and Y = I, Cl, and Br, show that all of them have a direct
band gap of ∼1 eV which can be tuned by varying the compositions of X and Y. The optimized supercells are tetragonal, orthorhombic or monoclinic. The top of the valence band arises from hybridization of Sn 4s a...

Ab initio calculations on Eu doped
(GaN)
n (n = 12, 13, and 32) nanoparticles show that Eu doping in nanoparticles is favorable compared with bulk GaN as a large fraction of atoms lie on the surface where strain can be released compared with bulk where often Eu doping is associated with a N vacancy. Co-doping of Si further facilitates Eu doping as...

In this report, we use density functional theory to determine the effect of carbon (C) contamination on the electronic structure and elastic properties of boron suboxide (B6O. The electron localization surface identified 3 distinct bonding regions: 1) short, highly covalent, Bp - Bp bonds connecting 2 icosahedra; 2) ionic bonding between the equato...

Using ab initio calculations, we demonstrate strong in influence of valence electron concentration (VEC) on the local atomic structure and electronic properties of Mo6S9−xIx (x = 0−9) nanowires (NWs). We find new atomic models of the NWs with unique decoration of S/I atoms that are more stable than reported earlier. The electronic and mechanical pr...

The structural, electronic, and elastic properties of pristine and carbon-doped boron suboxide (B6O) are calculated using density functional theory. The results indicate that it is energetically preferable for a single carbon atom to substitute into an oxygen site rather than a boron site. The lattice parameters and cell volume increase to relieve...

We report results of a systematic study on atomic and electronic structure of 55-atom and 147-atom Fe-Pt nanoparticles with different compositions using ab initio calculations. Our results on 55-atom nanoparticles suggest icosahedral structure and segregation of Pt on the surface to be favourable. Also there is a tendency for Fe-Pt ordering on the...

We report the finding of a bowl-shaped quasi-planar structure of a B84 cluster with four hexagonal holes and a three-chain ring all around the edges using ab initio calculations. A large number of other isomers including those explored earlier such as an empty cage, a filled cage, and a disordered structure, have been found to lie in a significantl...

An atomistic model for the effect of carbon (C) doping on the structural reorganization of boron suboxide (B6O) was developed from first principles density functional theory. The results indicate that it is energetically preferable for a single C atom to substitute into an oxygen (O) site rather than a B site. The lattice parameters and cell volume...

The low-energy structures of PtnSnn (n = 1-10) and Pt3mSnm (m = 1-5) clusters have been determined using genetic algorithm incorporated with density functional theory. Platinum and tin atoms tend to mix with each other due to the energetically favorable Pt-Sn bonds. However, due to the larger atomic radius of Sn atoms, we find segregation of Sn ato...

Silicene, a graphene analogue of silicon, has been generating immense interest due to its potential for applications in miniaturized devices. Unlike planar graphene, silicene prefers a buckled structure. Here we explore the possibility of stabilizing the planar form of silicene by Ni doping using first principles density functional theory based cal...

Using ab initio calculations, we study Nbn and Tan clusters with n = 12, 15, and 17 and find superatoms made of transition metals. Nb12 and Ta12 have an empty cage icosahedral structure. Neutral Tan has icosahedral symmetry and 2 [LB magnetic moments while the cage for N1312 is slightly distorted and has no magnetic moment. These clusters behave li...

We present a brief account of the recent progress in the theoretical understanding of the electronic and structural properties of clusters of metals and semiconductors from ab initio calculations. The origin of the recently observed permanent electric dipoles in Nb clusters, the occurrence of magnetism in clusters of non-magnetic elements such as P...

We report results of ab initio calculations on Y-doped anion Sin clusters with n = 4–20. Our results suggest two growth behaviors in the intermediate range of n = 8 and 20: (1) There is the formation of linked clusters in which a metal atom links two subclusters and (2) where silicon atoms form a cage structure and the metal atom is inside the cage...

The structural, electronic, and magnetic properties of MoS2+x parallelogram shaped platelets having m and n Mo atoms on the adjoining edges have been studied using first principles calculations and by varying m and n from 1 to 6. These platelets have 100% S coverage on two adjoining edges while 50% S coverage on the other two edges. The structural...

We report results of ab initio calculations on yttrium oxide clusters using plane wave pseudopotential method within density functional theory. (Y2O3)n clusters in the size range of n = 1 - 10 prefer compact and symmetric globular configurations where preference for an octahedron unit of Y6O8 is seen. The evolution of the atomic structures show sim...

From first principles calculations, we show that (InN)32 nanoparticles favor rock salt structure compared with wurtzite structure in bulk. A phase transition from wurtzite to rock salt structure is known to occur in bulk InN at 12.1 GPa and higher values of pressure for AlN and GaN. However, at the nanoscale we show that this structural transition...

Ab initio calculations on interaction of a C atom on small Ptn clusters (n = 1–10) show strong carbidic bonding and a decrease in the magnetic moments of Pt clusters. The adsorption energy decreases in an oscillatory way with increasing size but suggests no graphitic phase on small Pt clusters. Ptn clusters (n < 7) remain nearly planar after C adso...

It has been reported that cage like hollow clusters of (ZnO)n
with n = 12 & 34 are stable and hence magic. Doping Mn impurity in
ZnO (ZnO:Mn) clusters is a well studied problem. In most of the studies,
single Mn doping has been achieved by substituting it on a surface Zn
site, leading to a stoichiometric configuration of
Znn-1MnOn and a large magne...

Undoped cages of (ZnO)n nanoclusters are magic with n = 12 and 34. However with Mn doping, our ab initio calculations show that O rich, nonstoichiometric Zn12MnO15 and Zn34MnO37 nanoclusters obtained from n = 13 and 35, become magic with 1μB magnetic moment. The Mn-doped nanoclusters can also be viewed as composite structures where a MnOx species (...

The growing need to understand factors that govern the properties of materials, rapid strides in theory, and the wide availability of scientific software and computing resources has lead to an explosion of theoretical and computational studies of materials. The chemistry of Kubas bonding, chemisorption, role of catalysts, and kinetic factors are ad...

The evolution of atomic and electronic structure of small Aun
(n = 1–16, and 55) clusters doped with a Gd atom has been investigated using density functional theory within generalized gradient approximation for the exchange–correlation energy. Pure gold neutral clusters with n up to 15 are planar. However, with the doping of a Gd atom, the atomic s...

This article reviews the fundamental aspects of the electronic structure of two-dimensional graphene and modification of the electronic structure at the Dirac point in order to create a band gap. We discuss how the states near the Dirac point are affected by confinement, adsorption and interaction with a substrate. The physical mechanism for contro...

Small nanoparticles of III-V compound semiconductors have often been considered to have open-cage structures. However, using first-principles calculations, we report the finding of a structural transition from empty-cage structures for (AlN)n and (GaN)n nanoparticles up to n = 34 that we studied, to a filled-cage structure for (InN)32. Further, pho...

Atomic structures and physical properties of Gd-doped alumina clusters—namely, GdAl2n–1O3n and Gd2Al2n–2O3n with n = 1–10—have been studied within the framework of spin-polarized density functional theory and the projector augmented wave pseudopotential method. We find that the atomic structures of the host clusters (Al2O3)n are not changed signifi...

First principles calculations using pseudopotentials and generalized gradient approximation (GGA) for the exchange–correlation energy show that addition of Si makes Eu doping in GaN energetically favorable. It breaks local symmetry around Eu ions and leads to shallow states below the conduction band that could facilitate intra-4f shell transitions....

The ground state structures of neutral and anionic clusters of Na(n)Si(m) (1 ≤ n ≤ 3, 1 ≤ m ≤ 11) have been determined using genetic algorithm incorporated in first principles total energy code. The size dependence of the structural and electronic properties is discussed in detail. It is found that the lowest-energy structures of Na(n)Si(m) cluster...

Ab-initio calculations on graphene doped with boron nitride (BN) nanoribbons and patches show opening of a band gap in all cases. The smallest width of graphene in these hybrid layers controls the band gap that varies slowly around ∼0.75 eV when the width of graphene region is in the range of 2 to 5 zigzag chains. Most interestingly the band gap is...

The atomic structures, growth behavior, and electronic properties of (Al2O3)n, n = 1–10, clusters have been studied within the framework of density functional pseudopotential theory and generalized gradient approximation for the exchange–correlation energy. The lowest energy isomers of these clusters show preference for 4-membered Al2O2 and 6-membe...

Ab initio calculations on ZnSe quantum dots (QDs) doped with one Mn atom predict a new nonstoichiometric magnetic magic Zn11MnSe13 structure in contrast to QDs of undoped ZnSe that are stoichiometric and exhibit magic behavior for ZnnSen with n = 13 and 34. Our results suggest that such doping would lead to a high abundance of only one specie (the...

In recent years gold clusters have been studied extensively due to their unusual properties and applications in cancer treatment and catalysis. Small gold clusters having up to 15 atoms are planar as shown in figure 1. Thereafter a transition occurs to 3D structures but the atomic structures continue to have high dispersion. Doping of these cluster...

We report the result of our study on magnetic properties of Mn doped ZnSe clusters within the pseudopotential based density functional theory (DFT). In the present work, we substituted one or two Mn atoms at different cationic sites of small ZnSe clusters and the corresponding stable geometrical configurations are obtained. In general, we find a la...

Properties of nanosilicon in the form of nanoparticles, nanowires, nanotubes, and as porous material are of great interest. They can be used in finding suitable components for future miniature devices, and for the more exciting possibilities of novel optoelectronic applications due to bright luminescence from porous silicon, nanoparticles and nanow...

Spatially resolved images of an individual C60F18 fluorofullerene molecule on Si(100) − 2 × 1 surface have been obtained using scanning tunneling microscopy. Scanning tunneling
microscopy results and ab initio calculations show that the fluorofullerene molecules interact with the Si(100) − 2 × 1 surface
with F atoms pointing down towards the surfac...

We report from ab initio calculations a magic magnetic cage cluster of gold, Gd @ Au-15, obtained by doping of a Gd atom in gold clusters. It has a highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.31 eV within the generalized gradient approximation that makes it a potential candidate for cancer therapy with an additio...

We report results of ab initio calculations on (GaN)n nanoclusters with n = 12, 16, 22, and 24 using generalized gradient approximation (GGA) for the exchange-correlation energy. We find cage structures of GaN clusters to be lower in energy as compared to bulk fragments which have been fully optimized. Selected cages have been doped with Gd and Nd...

The optical properties of bare and passivated ZnnSen (n=1–13) clusters have been studied within the framework of time-dependent local density approximation. The atomic structure of the clusters has been obtained using projector augmented wave pseudopotential method, with generalized gradient approximation for the exchange-correlation energy. The sm...

The geometric and electronic structures of NaN, CuN, and AgN metal clusters
are systematically studied based on the density functional theory over a wide
range of cluster sizes 2=<N=<75. A remarkable similarity is observed between
the optimized geometric structures of alkali and noble metal clusters over all
of the calculated cluster sizes N. The m...