Searcharxiv⌕ Search

arXiv subjects

Kamal Krishna Saha

Publications and source records attributed to Kamal Krishna Saha.

9 recordsLinked to original sources
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↗
arXiv2004

Optical properties of random alloys : Application to Cu_{50}Au_{50} and Ni_{50}Pt_{50}

In an earlier paper [K. K. Saha and A. Mookerjee, Phys. Rev. B 70 (2004) (in press) or, cond-mat/0403456] we had presented a formulation for the calculation of the configuration-averaged optical conductivity in random alloys. Our formulation is based on the augmented-space theorem introduced by one of us [A. Mookerjee, J. Phys. C: Solid State Phys. 6, 1340 (1973)]. In this communication we shall combine our formulation with the tight-binding linear muffin-tin orbitals (TB-LMTO) technique to study the optical conductivities of two alloys Cu_{50}Au_{50} and Ni_{50}Pt_{50}.

cond-mat.mtrl-sci↗
arXiv2004

Optical properties of random alloys : A formulation

We present here a formulation for the calculation of the configuration-averaged optical conductivity in random alloys. Our formulation is based on the augmented-space theorem introduced by one of us [A. Mookerjee, J. Phys. C: Solid State Phys. 6, 1340 (1973)]. We show that disorder scattering renormalizes the electron and hole propagators as well as the transition amplitude. The corrections to the transition amplitude have been shown to be related to the self-energy of the propagators and vertex corrections.

cond-mat.mtrl-sci↗
arXiv2004

Block recursion and Green matrices

We present here generalization of the recursion method of Haydock et al [1] for the calculation of Green matrices (in angular momentum space). Earlier approaches concentrated on the diagonal elements, since the focus was on spectral densities. However, calculations of configuration averaged response functions or neutron scattering cross-sections require the entire Green matrices and self-energy matrices obtained from it. This necessitated the generalization of the recursion method presented here with examples.

cond-mat.mtrl-sci↗
arXiv2004

Electronic structure of random binary alloys : an augmented space formulation in reciprocal space

We present here a reciprocal space formulation of the Augmented space recursion (ASR) which uses the lattice translation symmetry in the full augmented space to produce configuration averaged quantities, such as spectral functions and complex band structures. Since the real space part is taken into account {\sl exactly} and there is no truncation of this in the recursion, the results are more accurate than recursions in real space. We have also described the Brillouin zone integration procedure to obtain the configuration averaged density of states. We apply the technique to Ni$_{50}$Pt$_{50}$ alloy in conjunction with the tight-binding linearized muffin-tin orbital basis. These developments in the theoretical basis were necessitated by our future application to obtain optical conductivity in random systems.

cond-mat.dis-nn↗
arXiv2003

Symmetry reduction in the augmented space recursion formalism for random binary alloys

We present here an efficient method which systematically reduces the rank of the augmented space and thereby helps to implement augmented space recursion for any real calculation. Our method is based on the symmetry of the Hamiltonian in the augmented space and keeping recursion basis vectors in the irreducible subspace of the Hilbert space.

cond-mat.mtrl-sci↗
arXiv2002

Electronic and Optical Properties of ZnIn$_2$Te$_4$

Band structure and optical properties of defect- Chalcopyrite type semiconductor ZnIn$_2$Te$_4$ have been studied by TB-LMTO first principle technique. The optical absorption calculation suggest that ZnIn$_2$Te$_4$ is a direct-gap semiconductor having a band gap of 1.40 eV., which confirms the experimentally measured value. The calculated complex dielectric-function $ε(E) = ε_1(E) + iε_2(E)$ reveal distinct structures at energies of the critical points in the Brillouin zone.

cond-mat.mtrl-sci↗
arXiv2002

Optical properties of perovskite alkaline earth titanates : a formulation

In this communication we suggest a formulation of the optical conductivity as a convolution of an energy resolved joint density of states and an energy-frequency labelled transition rate. Our final aim is to develop a scheme based on the augmented space recursion for random systems. In order to gain confidence in our formulation, we apply the formulation to three alkaline earth titanates CaTiO_3, SrTiO_3 and BaTiO_3 and compare our results with available data on optical properties of these systems.

cond-mat.mtrl-sci↗