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Abhijit Mookerjee

Publications and source records attributed to Abhijit Mookerjee.

At least 37 records · Page 2Linked to original sources
arXiv2011

Unusual Structure and Magnetism in MnO Nanoclusters

We report an unusual evolution of structure and magnetism in stoichiometric MnO clusters based on an extensive and unbiased search through the potential energy surface within density functional theory. The smaller clusters, containing up to five MnO units, adopt two-dimensional structures; and regardless of the size of the cluster, magnetic coupling is found to be antiferromagnetic in contrast to previous theoretical findings. Predicted structure and magnetism are strikingly different from the magnetic core of Mn-based molecular magnets, whereas they were previously argued to be similar. Both of these features are explained through the inherent electronic structures of the clusters.

cond-mat.mes-hall↗
arXiv2011

Thermal conductivity and diffusion-mediated localization in Fe_{1-x}Cr_{x} Alloys

We apply a new Kubo-Greenwood type formula combined with a generalized Feynman diagram- matic technique to report a first principles calculation of the thermal transport properties of disordered Fe_{1-x}Cr_{x} alloys. The diagrammatic approach simplifies the inclusion of disorder-induced scattering effects on the two particle correlation functions and hence renormalizes the heat current operator to calculate configuration averaged lattice thermal conductivity and diffusivity. The thermal conductivity K(T) in the present case shows an approximate quadratic T-dependence in the low temperature regime (T < 20 K), which subsequently rises smoothly to a T-independent saturated value at high T . A numerical estimate of mobility edge from the thermal diffusivity data yields the fraction of localized states. It is concluded that the complex disorder scattering processes, in force-constant dominated disorder alloys such as Fe-Cr, tend to localize the vibrational modes quite significantly.

cond-mat.mtrl-sci↗
arXiv2011

Engineering the magnetic properties of the Mn$_{13}$ cluster by doping

With a goal to produce giant magnetic moment in Mn$_{13}$ cluster which will be useful for practical applications, we have considered the structure and magnetic properties of pure Mn$_{13}$ cluster and substitutionally doped it with X = Ti, V, Cr, Fe, Co, Ni atom to produce Mn$_{12}$X clusters. We find that Ti and V substitutions in Mn$_{13}$ cluster are the most promising in terms of gaining substantial binding energy as well as achieving higher magnetic moment through ferromagnetic alignment of atom-centered magnetic moments. This has been demonstrated in terms of energetics and electronic properties of the clusters. For comparison, we have also studied the effect of N-capping of Mn$_{13}$ cluster, predicted in the earlier work [Phys. Rev. Lett. {\bf 89}, 185504 (2002)] as a means to produce stable giant magnetic moment in Mn clusters upto cluster size of 5 Mn atoms.

cond-mat.mes-hall↗
arXiv2011

Recursive approach to study transport properties of atomic wire

In this study, we propose a recursive approach to study the transport properties of atomic wires. It is based upon a real-space block-recursion technique with Landauer's formula being used to express the conductance as a scattering problem. To illustrate the method, we have applied it on a model system described by a single band tight-binding Hamiltonian. Results of our calculation therefore may be compared with the reported results on Na-atom wire. Upon tuning the tight-binding parameters, we can distinctly identify the controlling parameters responsible to decide the width as well as the phase of odd-even oscillations in the conductance.

cond-mat.mes-hall↗
arXiv2009

Augmented space recursion code and application in simple binary metallic alloy

We present here an optimized and parallelized version of the {\sl augmented space recursion code} for the calculation of the electronic and magnetic properties of bulk disordered alloys, surfaces and interfaces, either flat, corrugated or rough, and random networks. Applications have been made to bulk disordered alloys to benchmark our code.

cond-mat.mtrl-sci↗
arXiv2009

Structure, reactivity and electronic properties of V-doped Co clusters

Structures, physical and chemical properties of V doped Co$_{13}$ clusters have been studied in detail using density functional theory based first-principles method. We have found anomalous variation in stability of the doped clusters with increasing V concentration, which has been nicely demonstrated in terms of energetics and electronic properties of the clusters. Our study explains the nonmonotonic variation in reactivity of Co$_{13-m}$V$_m$ clusters towards H$_2$ molecules as reported experimentally [J. Phys. Chem. {\bf 94}, 2744 (1990)]. Moreover, it provides useful insight into the cluster geometry and chemically active sites on the cluster surface, which can help to design better catalytic processes.

physics.atm-clus↗
arXiv2008

Study of phase stability of MnCr using the augmented space recursion based orbital peeling technique

In an earlier communication we have developed a recursion based approach to the study of phase stability and transition of binary alloys. We had combined the recursion method introduced by Haydock, Heine and Kelly and the our augmented space approach with the orbital peeling technique proposed by Burke to determine the small energy differences involved in the discussion of phase stability. We extend that methodology for the study of MnCr alloys.

cond-mat.mtrl-sci↗
arXiv2008

A local-density approximation for the exchange energy functional for excited states : the band gap problem

We present excited states density functional theory (DFT) to calculate band gap for semiconductors and insulators. For the excited states exchange-correlation functional, we use a simple local density approximation (LDA) like functional and it gives the result which is very closed to experimental results. The linear muffin-tin potential is used to solve the self consistent Kohn-Sham equation

cond-mat.mtrl-sci↗
arXiv2008

Magnetism in small bimetallic Mn-Co clusters

Effects of alloying on the electronic and magnetic properties of Mn$_{x}$Co$_{y}$ ($x+y$=$n$=2-5; $x$=0-$n$) and Mn$_2$Co$_{11}$ nanoalloy clusters are investigated using the density functional theory (DFT). Unlike the bulk alloy, the Co-rich clusters are found to be ferromagnetic and the magnetic moment increases with Mn-concentration, and is larger than the moment of pure Co$_n$ clusters of same size. For a particular sized cluster the magnetic moment increases by 2 $μ_B$/Mn-substitution, which is found to be independent of the size and composition. All these results are in good agreement with recent Stern-Gerlach (SG) experiments [Phys. Rev. B {\bf 75}, 014401 (2007) and Phys. Rev. Lett. {\bf 98}, 113401 (2007)]. Likewise in bulk Mn$_x$Co$_{1-x}$ alloy, the local Co-moment decreases with increasing Mn-concentration.

physics.atm-clus↗
arXiv2007

Emergence of noncollinear magnetic ordering in small magnetic clusters: Mn$_n$ and As@Mn$_n$

Using first-principles density functional calculations, we have studied the magnetic ordering in pure Mn$_n$ ($n=2-$10, 13, 15, 19) and As@Mn$_n$ ($n=1-$10) clusters. Although, for both pure and doped manganese clusters, there exists many collinear and noncollinear isomers close in energy, the smaller clusters with $n\leqslant$5 have collinear magnetic ground state and the emergence of noncollinear ground states is seen for $n\geqslant$6 clusters. Due to strong $p-d$ hybridization in As@Mn$_n$ clusters, the binding energy is substantially enhanced and the magnetic moment is reduced compared to the corresponding pure Mn$_n$ clusters.

physics.atm-clus↗
arXiv2007

Electronic, magnetic and optical properties of random Fe-Cr alloys

In this communication we have studied the electronic structure, magnetic and optical properties of bcc \fecr alloys in the ferromagnetic phase. We have used the augmented space recursion technique coupled with tight-binding linearized muffin-tin orbital technique (TB-LMTO-ASR) as well as the coherent-potential approximation based on the Korringa-Kohn-Rostocker method (KKR-CPA). Also the plane wave projector augmented wave (PAW) method has been used with the disorder simulated by the special quasi-random structure method f or configuration averaging (SQS). This was to provide a comparison between the different methods in common use for random alloys. Moreover, using the self-consistent potential parameters from TB-LMTO-ASR ca lculations we obtained the spin resolved optical conductivity using the generalized recursion technique proposed by Müller and Vishwanathan.

cond-mat.dis-nn↗
arXiv2006

Phonons in disordered alloys : a multiple scattering approach

In this paper we shall discuss the effect of disorder induced configuration fluctuations on single particle and two-particle phonon Green functions in substitutional random binary alloys. The randomness of the system will be dealt within the augmented space theorem, introduced by one of us [J. Phys. C : Solid State Phys. 6, L205(1973)]. This will be combined with a generalized Edwards-Langer diagrammatic technique to extract various useful results in the form of mathematical expressions. The purpose of present manuscript will be to describe the scattering diagrams in full detail. This will form the basis of the calculational algorithms which we had used in an earlier paper on NiPd and NiPt alloys [J. Phys.: Condens. Matter 18, 4589-4608 (2006)]. We shall show the structure of all possible scattering diagrams up to the 4-th order and subsequently illustrate how to obtain Dyson's equation from a re-summation of the diagrammatic series. We shall also study how disorder scattering affects two-particle Green functions associated with thermal response. We shall show that disorder scattering renormalizes both the phonon propagators as well as the heat currents. These renormalized heat currents will be shown to be related to the self-energy of the propagators. We shall also study a different class of scattering diagrams which are not related to the self-energy but rather to the vertex corrections.

cond-mat.mtrl-sci↗
arXiv2006

An augmented space approach to the study of phonons in disordered alloys : comparison between the itinerant coherent-potential approximation and the augmented space recursion

A first principles density functional based linear response theory (the so called Density Functional Perturbation theory \cite{dfpt}) has been combined separately with two recently developed formalism for a systematic study of the lattice dynamics in disordered binary alloys. The two formalisms are the Augmented space recursion (ASR) and the Itinerant coherent potential approximation (ICPA). The two different theories (DFPT-ASR and DFPT-ICPA) systematically provides a hierarchy of improvements upon the earlier single site based theories (like CPA etc.) and includes non-local correlations in the disorder configurations. The formalisms explicitly take into account fluctuations in masses, force constants and scattering lengths. The combination of DFPT with these formulation helps in understanding the actual interplay of force constants in alloys. We illustrate the methods by applying to a fcc Fe$_{50}$Pd$_{50}$ alloy.

cond-mat.mtrl-sci↗
arXiv2006

Effect of short-range order on the electronic structure and optical properties of the CuZn alloy : an augmented space approach

In this work we have combined the generalized augmented space method introduced by one of us with the recursion method of Haydock et al (GASR), within the framework of the local density functional based linear muffin-tin orbitals basis (TB-LMTO). Using this we have studied the effect of short-range ordering and clustering on the density of states, optical conductivity and reflectivity of 50-50 CuZn alloys. Our results are in good agreement with alternative techniques. We argue that the TB-LMTO-GASR is a feasible, efficient and quantitatively accurate computational technique for the study of environmental effects in disordered binary alloys.

cond-mat.dis-nn↗
arXiv2006

Study of the one dimensional Holstein model using the augmented space approach

A new formalism using the ideas of the augmented space recursion (introduced by one of us) has been proposed to study the ground state properties of ordered and disordered one-dimensional Holstein model. For ordered case our method works equally well in all parametric regime and matches with the existing exact diagonalization and DMRG results. On the other hand the quenched substitutionally disordered model works in low and intermediate regime of electron phonon coupling. Effect of phononic and substitutional disorder are treated on equal footing.

cond-mat.dis-nn↗
arXiv2006

Structure, electronic properties and magnetic transition in manganese clusters

We systematically investigate the structural, electronic and magnetic properties of Mn$_n$ clusters ($n =$ 2$-$20) within the {\it ab-initio} pseudopotential plane wave method using generalized gradient approximation for the exchange-correlation energy. A new kind of icosahedral structural growth has been predicted in the intermediate size range. Calculated magnetic moments show an excellent agreement with the Stern-Gerlach experiment. A transition from ferromagnetic to ferrimagnetic Mn$-$Mn coupling takes place at $n=$ 5 and the ferrimagnetic states continue to be the ground states for the entire size range. Possible presence of multiple isomers in the experimental beam has been argued. No signature of non-metal to metal transition is observed in this size range and the coordination dependence of $d-$electron localization is discussed.

physics.atm-clus↗
arXiv2006

Lattice thermal conductivity of disordered NiPd and NiPt alloys

Numerical calculations of lattice thermal conductivity are reported for the binary alloys NiPd and NiPt. The present work is a continuation of an earlier paper by us [PRB, 72, 214207 (2005)]which had developed a theoretical framework for the calculation of configuration-averaged lattice thermal conductivity and thermal diffusivity in disordered alloys. The formulation was based on the augmented space theorem combined with a scattering diagram technique. In this paper we shall show dependence of the lattice thermal conductivity on a series of variables like phonon frequency, temperature and alloy composition. The temperature dependence of $κ(T)$ and its realtion to the measured thermal conductivity is discussed. The concentration dependence of $κ$ appears to justify the notion of a minimum thermal conductivity as discussed by Kittel, Slack and others. We also study the frequency and composition dependence of the thermal diffusivity averaged over modes. A numerical estimate of this quantity gives an idea about the location of mobility edge and the fraction of states in the frequency spectrum which is delocalized.

cond-mat.mtrl-sci↗