1) Density functional study of multiferroic Bi₂NiMnO₆

Adrian Ciucivara, Bhagawan Sahu, and Leonard Kleinman

Using both the generalized gradient approximation (GGA) and GGA+U density functionals and including the spin-orbit interaction while allowing for noncollinear spin orientations, we have calculated many of the properties of the multiferroic Bi₂NiMnO₆. The GGA and GGA+U results are in unexpectedly close agreement; in particular, their lattice constants are in excellent agreement with the measured values. The calculated GGA and GGA+U magnetizations per formula unit are 4.92 and 4.99 μ_B and the calculated ferroelectric polarizations are 16.84 and 16.63  μC  cm⁻². A discussion is given of the C2 space group of Bi₂NiMnO₆ and of the centrosymmetric C2∕m space group from which it can be generated with small atomic displacements.

Phys. Rev. B 76, 064412 (2007)

2) Density functional study of Ge_1−xMn_xTe

Adrian Ciucivara, Bhagawan R. Sahu, and Leonard Kleinman

Unlike GaAs, Mn impurities in GeTe do not create holes, making it possible to independently study the effect on the magnetization of the Mn and hole densities. Using a GGA+U density functional we found that the magnetization increases monotonically with hole density and that the magnetization peaks at about x=0.31 (per Mn) or x=0.47 (total magnetization). In every case the magnetic moment of any Mn atom was between 4.15μ_B and 4.27μ_B, so that the large variation found in the total magnetization (as a function of hole and Mn density) is due to variation in the collinearity of the Mn spins.

Phys. Rev. B 75, 241201 (2007)

3) Ab initio theory of gate induced gaps in graphene bilayers

Hongki Min, Bhagawan Sahu, Sanjay K. Banerjee, and A. H. MacDonald

We study the gate-voltage induced gap that occurs in graphene bilayers using ab initio density functional theory. Our calculations confirm the qualitative picture suggested by phenomenological tight-binding and continuum models. We discuss enhanced screening of the external interlayer potential at small gate voltages, which is more pronounced in the ab initio calculations, and quantify the role of crystalline inhomogeneity using a tight-binding model self-consistent Hartree calculation.

Phys. Rev. B 75, 155115 (2007)

4) Density functional study of Si(001)∕Si(110) and Si(100)∕Si(110) interfaces

Adrian Ciucivara, B. R. Sahu, Sachin Joshi, Sanjay K. Banerjee, and Leonard Kleinman,

Motivated by the non-Ohmic behavior of Si(001)∕Si(110) junctions recently discovered by us, we have performed density functional calculations using Si(001)∕Si(110) and Si(100)∕Si(110) superlattices containing 140 atoms in each layer. Approximate adhesion energies of 102 and 121 meV∕Ų were obtained for the two possible junction orientations. Figures showing covalent bonds across the interface are displayed. Interface bands span the Si(001)∕Si(110) energy band gap but not the Si(100)∕Si(110) gap. Valence band offsets of 86 and 93 meV were found; the former plays a role in the asymmetry of the I-V curves.

Phys. Rev. B 75, 113309 (2007)

5) Theoretical and experimental investigation of valence band offsets for direct silicon bond hybrid orientation technology

Sachin Joshi, Bhagawan Sahu, Sanjay. K. Banerjee, et al.  
APPLIED PHYSICS LETTERS 90 (4): Art. No. 043503 JAN 22 2007

6) Intrinsic and Rashba spin-orbit interactions in graphene sheets

Hongki Min, J. E. Hill, N. A. Sinitsyn, B. R. Sahu, Leonard Kleinman, and A. H. MacDonald

Starting from a microscopic tight-binding model and using second-order perturbation theory, we derive explicit expressions for the intrinsic and Rashba spin-orbit interaction induced gaps in the Dirac-like low-energy band structure of an isolated graphene sheet. The Rashba interaction parameter is first order in the atomic carbon spin-orbit coupling strength ξ and first order in the external electric field E perpendicular to the graphene plane, whereas the intrinsic spin-orbit interaction which survives at E=0 is second order in ξ. The spin-orbit terms in the low-energy effective Hamiltonian have the form proposed recently by Kane and Mele. Ab initio electronic structure calculations were performed as a partial check on the validity of the tight-binding model.

Phys. Rev. B 74, 165310 (2006)

7) Density functional study of the effect of pressure on the ferroelectric GeTe

Adrian Ciucivara, B. R. Sahu, and Leonard Kleinman

We compare local density approximation (LDA) and generalized gradient approximation (GGA) calculations of GeTe as a function of applied pressure. The LDA yields a fair result for the zero pressure trigonal angle but good to excellent results for the zero pressure lattice constant, energy gap, and relative positions of the two sublattices. More importantly, it yields results within the wide range of experimental values for the critical pressure at which the ferroelectric trigonal to rock salt transition takes place. We also obtain very reasonable results for the zero pressure cohesive energy, electric polarization, and Born effective charge, for which there are no experimental data. Except for the energy gap which is more than a factor of 2 too large, the GGA results are slightly better than the LDA.

Phys. Rev. B 73, 214105 (2006)

8) Effect of spin-orbit coupling on small platinum nanoclusters

M. N. Huda, Manish K. Niranjan, B. R. Sahu, and Leonard Kleinman

We have shown that spin-orbit coupling plays an important role in determining the structures of platinum nanoclusters. We have used spin-orbit coupling self-consistently with density functional theory to study the geometry of platinum clusters and their binding energy. It has been found that the relative energies of the isomers of a cluster of a given size can be changed due to the inclusion of spin-orbit coupling. Planar structures were found for Pt_n clusters with n≤5.

Phys. Rev. A 73, 053201 (2006)

9) Theoretical study of B diffusion with charged defects in strained Si

L. Lin, T. Kirichenko, B. R. Sahu, G. S. Hwang, and S. K. Banerjee

We investigate B diffusion in strained Si by using density functional theory calculations. We calculate the migration barriers and formation energies of the B-Si complexes at different charge states in the biaxial tensile strained {001} Si layer. The migration barriers and formation energies overall intend to decrease under strain at all charge states. For neutral and negatively charged B-Si complexes, the migration barrier reduces along the strain plane while the barrier in the direction perpendicular to strain plane remains unchanged, but there is no anisotropy in B diffusion for positively charged B-Si complexes.

Phys. Rev. B 72, 205206 (2005)

10) Osmium is not harder than diamond

B. R. Sahu and Leonard Kleinman

A recent measurement found Os has a larger bulk modulus than diamond, in agreement with an earlier calculation. We have made fully relativistic linear augmented plane-wave calculations of osmium and diamond and found diamond to have the larger bulk modulus, independent of whether the local-density- or generalized-gradient-approximation (GGA) exchange-correlation potentials are used. With the GGA our bulk modulus lies between two very recent and more accurate experimental values.

Phys. Rev. B 72, 113106 (2005)

11) PtN: A zinc-blende metallic transition-metal compound

B. R. Sahu and Leonard Kleinman

With fully relativistic full potential augmented plane wave calculations we confirm that the recently synthesized compound PtN is crystallized in the zinc-blende structure and is metallic. We find that the density of states consists of four pieces and discuss how each contributes to the bonding.

Phys. Rev. B 71, 041101 (2005)

12) Density functional determination of the magnetic state of β -MnAs

Manish K. Niranjan, B. R. Sahu, and Leonard Kleinman

Ferromagnetic hexagonal α-MnAs has a first-order phase transition to β-MnAs at about 40 °C. Because it shows no long-range antiferromagnetic order, most workers assume that it is paramagnetic in spite of the fact that it does not have a Curie-Weiss magnetic susceptibility. With the aid of density functional calculations, we show that it is antiferromagnetic and explain the lack of observed long-range order.

Phys. Rev. B 70, 180406 (2004)

13) Theoretical study of structural and electronic properties of δ -MoN

B. R. Sahu and Leonard Kleinman

Using density functional theory within the local density approximation and generalized gradient approximation, we compare the cohesive energy of molybdenum nitride in its hexagonal δ-phase with that in the NiAs structure from which it differs by small distortions. The energy bands and bulk modulus are calculated, the latter in good agreement with experiment. Although δ-MoN is a metal, we find a large ionic component to its bonding.

Phys. Rev. B 70, 073103 (2004)

14) Effect of atomic displacements on the ground state of α-TeO₂

B. R. Sahu and Leonard Kleinman

Using density-functional theory within the local-density approximation and generalized gradient approximation, we show that the distortion of oxygens and telluriums in the α-TeO₂ structure is crucial for obtaining the insulating state in conformity with an optical absorption experiment. The calculated value of the band gap is in reasonable agreement with the experimental value. Unexpectedly, we find the bonding to be almost completely ionic with a small covalent component.

Phys. Rev. B 69, 193101 (2004)

15) Theoretical study of structural and electronic properties of β-Ta₂O₅ and δ-Ta₂O₅

B. R. Sahu and Leonard Kleinman

Using density functional theory within the local density approximation (LDA) and generalized gradient approximation (GGA), we discuss the relative stability of the orthorhombic (or the β) phase and the hexagonal (or the δ) phase of tantalum pentoxide. We find that, both LDA and GGA pseudopotential calculations favor the δ phase, whereas spin-orbit all-electron calculations favor the β(δ) phase within the LDA (GGA); however, the all-electron energy differences are too small to be significant. The spin-orbit coupling has a significant effect on the band gaps and the band gap is indirect (direct) in the δ(β) phase. The chemical bonding between Ta and oxygen ions is of a mixed type (mainly ionic but partly covalent).

Phys. Rev. B 69, 165202 (2004)

16) Geometrical and electronic structure of the Pt-7 cluster: A density functional study

W. Q. Tian, Maofa Ge,   B. R. Sahu et al.
JOURNAL OF PHYSICAL CHEMISTRY A 108 (17): 3806-3812 APR 29 2004

17) Theoretical study of electronic and magnetic properties of MnN

B. R. Sahu and Leonard Kleinman

We present electronic structure calculations of manganese mononitride (MnN) in its tetragonally distorted NaCl structure using density-functional theory within the generalized gradient approximation. The structure with an antiferromagnetic arrangement of the spins on the Mn ions is found to be the energetically stable phase of the MnN compound. The chemical bonding between Mn and the N ion is of a mixed type (i.e., mainly ionic but partly metallic and covalent). The calculated spin magnetic moment on the Mn ion is close to the experimental value of 3.3μ_B.

Phys. Rev. B 68, 113101 (2003)

18) Density-functional study of palladium-doped small gold clusters

B. R. Sahu, Ge Maofa, and Leonard Kleinman

We have performed plane-wave pseudopotential calculations based on density-functional formalism with the generalized gradient approximation to study the atomic and electronic structure of neutral and charged palladium-doped gold clusters Au_nPd (n=1,4). We observe odd-even oscillations in highest occupied and lowest unoccupied molecular-orbital gaps and in the electron affinities, the latter in conformity with recent photoemission experiments of Koyasu et. al. The atomic structure and stability of these clusters are discussed.

Phys. Rev. B 67, 115420 (2003)

19) Geometrical and electronic structures of gold, silver, and gold-silver binary clusters: Origins of ductility of gold and gold-silver alloy formation 

H. M. Lee, Ge Maofa, B. R. Sahu et al.
JOURNAL OF PHYSICAL CHEMISTRY B 107 (37): 9994-10005 SEP 18 2003.

20) Non-enhancement of magnetic moments on transition metal impurities by alkali metal hosts

B. R. Sahu and Leonard Kleinman

Using 54-atom supercells, we calculate the spin magnetic moments of V impurities in Na and Co in Na and K. We conclude that the huge moments supposedly measured by Bergmann et al. are a consequence of those authors assuming that the anomalous Hall resistance is linearly related to the magnetic polarization.

Phys. Rev. B 67, 094424 (2003)

21) Large orbital magnetic moment and Coulomb correlation effects in FeBr₂

S. J. Youn, B. R. Sahu, and Kwang S. Kim

We have performed an all-electron fully relativistic density-functional calculation to study the magnetic properties of FeBr₂. We show that the correlation effect enhances the contribution from orbital degrees of freedom of d electrons to the total magnetic moment on Fe²⁺, as opposed to the common notion of a nearly total quenching of the orbital moment on the Fe²⁺ site. The insulating nature of the system is correctly predicted when the Hubbard parameter U is included. Energy bands around the gap are very narrow in width, and originate from the localized Fe-3d orbitals, which indicates that FeBr₂ is a typical example of a Mott insulator.

Phys. Rev. B 65, 052415 (2002)

22) Electronic structure and bonding in ultralight LiMg 

B. R. Sahu
MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY 49 (1): 74-78 SEP 5 1997

23) V. Sundararajan, B. R. Sahu, D. G.  KANHERE, et al.
COHESIVE, ELECTRONIC AND MAGNETIC-PROPERTIES OF THE TRANSITION-METAL ALUMINIDES FEAL, COAL AND NIAL 
JOURNAL OF PHYSICS-CONDENSED MATTER 7 (30): 6019-6034 JUL 24 1995