Research Interests:

(a) Development of Electronic Structure Method:

This work involves the improvement of the DFT-based linear electronic structure method for the development of a generally applicable electronic-structure method which is intelligible, fast and accurate. The new basis set has been aimed to have desired flexibility of being simplified to make a useful compromise between being short-ranged, minimal and accurate. This led to first-principles approach of deriving model Hamiltonians and direct generation of Wannier-like functions giving rise to an unique scheme of material modeling.

  • Phys. Rev. B 62, R16219 (2000)
  • Bull. of Mater. Sci. 26 27 (2003)

(b) Electronic Structure of Strongly Correlated Electron Systems:

An important example of complex materials, are materials with strong electron-electron correlations. The modern many-body approach, namely the Dynamical Mean Field theory (DMFT) has turned out to be a major advancement in the electronic structure calculation of correlated electron material in general. LDA+DMFT approach which merges local density approximation (LDA) with DMFT has proved to be a major breakthrough for the realistic modeling of correlated materials. The activity of the group in this context, involves coupling of the effective Wannier-like description of the one-electron Hamiltonian with that of DMFT calculations. This showed the crucial role of chemistry in a many-body calculation. The developed methodology has been applied to the problem of metal-insulator transition in V2O3 and description of electronic structure of spin-peierls system TiOCl. The combined LDA+DMFT calculations have been applied in understanding High-Tc cuprates as well as in the understanding differential behavior of Sr and Ca based ruthenates.

  • Nature Comm. 1, 105 (2010), Phys Rev Lett 104 047401 (2010), Phys. Rev. B 76, 085127 (2007), New J Phys 9, 380 (2007), Phys. Rev. B 71, 153108 (2005).
  • Phys. Rev. B 78, 035132 (2008), Phys. Rev. B 79, 134522 (2009).
  • Phys. Rev. B Rapid Commn, 83, 041103 (2011).

(c) Low dimensional Quantum Spin Systems:

In recent years a major challenge to materials physics has been posed by a class of low dimensional spin-systems that are essentially highly quantum in nature and they lead to novel physical properties and new phases. We have applied the first-principles derived Wannier function technique to identify the underlying spin model, often coupled with the quantum Monte Carlo or exact diagonalization technique for the investigation of magnetic properties in number of these compounds like spin systems of general formal A3BB'O6, spin dimer system CuTe2O5, spin tube system Na2V3O7, spin-tetrahedron-based Cu4Te5O12X4 system.

  • Phys. Rev. B 82, 235122 (2010)
  • Phys. Rev. B 77, 224437 (2008) (Editors Choice)
  • Phys. Rev. Lett. 95, 107201 (2005)
  • Phys. Rev. B 75, 024404 (2007)

(d) Double perovskites:

In recent years the field of double perovskite oxides posed major challenges in their understanding that it cannot be an extension of simple 3D perovskite oxides. The challenge is fundamental. The analysis of electronic structure of double perovskite compound La2NiMnO6, showed that the ferromagnetism in this compound is governed by the super-exchange interaction, giving rise to a nearly room-tempeature Tc of 280 K in an insulating material, which is rare in nature. Further, the study showed presence of soft IR-active phonon modes exhibiting strong coupling with spin which explained the observed dielectric anomaly governed by exchange-striction driven spin-phonon coupling. The work on double perovskites based on 3d-5d transition metals showed presence of large magneto-optic signals opening up the possibility of device applications and also explained the Tc trend. The hybridization driven antiferromagnetism has been suggested for La doped double perovskite compound Sr2FeMoO6.

  • Phys. Rev. Lett. 100, 186402 (2008); Phys. Rev. B 79, 144403 (2009).
  • Appl. Phys. Lett. 92, 201912 (2008); Phys. Rev. B 83, 104418 (2011).
  • Phys. Rev. B 80, 224412 (2009).

(e) Spinels: Interplay between charge, orbital and spin:

The spinel compounds with their geometrically frustrated configuration have been discussed in great detail in recent time. Based on density functional calculations, we proposed a possible orbital ordering in MnV2O4 which consists of orbital chains running along crystallographic a and b directions with orbitals rotated alternatively by about 45o within each chain. We also carried out studies on spinel compounds with orbitally active A sites, as is the case of FeCr2S4 and FeSc2S4. In FeCr2S4, the B cation is magnetic while for FeSc2S4, the B cation is non-magnetic. FeCr2S4 orders magnetically in a ferrimagnetic spin arrangement between Fe and Cr moments with a transition temperature7 of 167K, while FeSc2S4 does not order magnetically down to a measured temperature of 50 mK . FeCr2S4 shows long range orbital order in polycrystalline samples while a glassy freezing has been observed in single crystal. FeSc2S4, in contrast, has been reported as an orbital liquid. We explored the microscopic origin of this differential behavior and also discuss the possible origin of the insulating behavior of these compounds at low temperature.

  • Phys. Rev. Lett. 102, 216405 (2009).
  • Phys. Rev. B Rapid Commun. 80, 201101 (2009); Phys. Rev. B Rapid Commun. 82, 041105 (2010)

(f) Nano-materials:

We have studied problems related of structural stability CdS nanoclusters, structure, bonding, and magnetism of Co clusters, exhibiting an unusual growth pattern and V doped Co clusters. We further investigated the interplay of magnetism and hybridization effects in structure of small transition metal clusters.

  • J. Phys. Chem. C 112, 8206 (2008); J. Phys. C 20, 445217 (2008)
  • Phys. Rev. B 76, 014429 (2007); Phys. Rev. B 80, 085418 (2009)
  • Phys. Rev. B 83, 075425 (2011); Phys. Rev. B (in press)