Showing papers by "Tanusri Saha-Dasgupta published in 2003"
TL;DR: In this paper, 3rd generation muffin-tin orbitals (MTOs) are downfolded to smaller and smaller basis sets: sp3d10,sp3, and bond orbitals.
Abstract: By the example of sp3-bonded semiconductors, we illustrate what 3rd-generation muffin-tin orbitals (MTOs) are. We demonstrate that they can be downfolded to smaller and smaller basis sets: sp3d10,sp3, and bond orbitals. For isolated bands, it is possible to generate Wannier functions a priori. Also for bands, which overlap other bands, Wannier-like MTOs can be generated a priori. Hence, MTOs have a unique capability for providing chemical understanding.
46 citations
TL;DR: In this article, the problem of phase stability in NiPt alloy systems was studied using the augmented space recursion based on the tight binding-linearized muffin-tin orbital as the method for studying the electronic structure of the alloys.
Abstract: We have studied the problem of phase stability in NiPt alloy systems We have used the augmented space recursion based on the tight binding-linearized muffin-tin orbital as the method for studying the electronic structure of the alloys In particular, we have used the relativistic generalization of our earlier technique We note that, in order to predict the proper ground state structures and energetics, in addition to relativistic effects, we have to take into account charge transfer effects with precision
17 citations
TL;DR: In this paper, the authors show that there are other hopping integrals which are equally important for the band shape as the integral for hopping between the partners of the pair, which is the common interpretation of the local density approximation (LDA) band structure of the vertical V-V pair.
Abstract: The common interpretation of the local-density approximation (LDA) band structure of ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ is that the apparent splitting of the ${a}_{1g}$ band into a low intensity structure deep below the Fermi energy and a high intensity feature above it is due to the bonding-antibonding coupling of the vertical V-V pair. Using tight-binding fitting to\char22{}as well as first-principles Nth order muffin-tin orbital (NMTO) downfolding of\char22{}the spin-up $\mathrm{LDA}+U$ ${a}_{1g}$ band, we show that there are other hopping integrals which are equally important for the band shape as the integral for hopping between the partners of the pair.
16 citations
TL;DR: In this paper, the authors proposed a new wave function basis set in which the energy dependence of the interstitial region and inside muffin-tin (MT) spheres is treated on an equal footing.
Abstract: The third-generation LMTO method provides a new wave function basis set in which the energy dependence of the interstitial region and inside muffin -tin (MT) spheres is treated on an equal footing. Within the improved method, basis functions in the interstitial are the screened spherical waves (SSWs) with bound- ary condition defined in terms of a set of 'hard' sphere radii aRL. Energy eigenvalues obtained from the single- particle Schrodinger equation for MT potential is energetically accurate and very usefu l for predicting a reli- able first-principles tight-binding (TB) model of widely different systems. In this study, we investigate a possi - bility of the new basis sets transferability to different environment which could be crucial for TB applications to very large and complicated systems in realistic materials modelling. For the case of C where the issue of sp 2 vs sp 3 bonding description is primarily important, we have found that by downfolding the unwanted channels in the basis, the TB electronic structure calculations in both hexagonal graphite and diamond structures are well compared with those obtained from the full LDA schemes if we use the same choice of hard sphere radii, aRL and a fixed, arbitrary energy, e e ν. Moreover, the choice is robust and transferable to various situations, from different forms of graphite to a wide range of coordination. Using the obtained minimal basis set, we have been investigating the TB Hamiltonian and overlap matrices for different structure types for carbon, in particular we have predicted the on-site and hopping parameters ( γ1, γ γ2, … …, γ γ6) within an orthogonal represen- tation for Slonczewski-Weiss-McClure (SWMcC) model of the Bernal structure. Our theoretical values are in excellent agreement with experimental ones from magnetoreflection measurements of Fermi surfaces for hex- agonal graphite.
11 citations
TL;DR: In this article, the electronic structure of VOSeO was investigated via density-functional calculations, which indicated that the system is better thought of as an alternating spin-½ chain with moderate interchain interactions, an analog of (VO) 2 P 2 O 7.
Abstract: Motivated by an early experimental study of VOSeO 3 , which suggested that it is a quasi-two-dimensional system of weakly coupled spin dimers with a small spin gap, we have investigated the electronic structure of this material via density-functional calculations. These ab initio results indicate that the system is better thought of as an alternating spin-½ chain with moderate interchain interactions, an analog of (VO) 2 P 2 O 7 . The potential interest of this system for studies in high magnetic field given the presumably small value of the spin gap is emphasized.
7 citations
TL;DR: In this article, the authors review the augmented space based approaches to thermodynamics and ordering of binary alloys, and give several examples of metallic alloys to illustrate their methodology, and discuss the application of augmented space in the design of alloys.
Abstract: The communication reviews the augmented space based approaches to thermodynamics and ordering of binary alloys. We give several examples of metallic alloys to illustrate our methodology.
6 citations
TL;DR: In this paper, an efficient method which systematically reduces the rank of the augmented space and thereby helps to implement augmented space recursion for any real calculation is presented. And this method is based on the symmetry of the Hamiltonian in the augmented spaces and keeping recursion basis vectors in the irreducible subspace of the Hilbert space.
Abstract: 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.
4 citations
TL;DR: In this article, a downfolding technique within the newly developed muffin-tin orbital-based method is used to analyse the density-functional band structure obtained in the local spin density approximation.
Abstract: We study the electronic band structure of CaMnO3, in order to understand the origin of the dispersion of the Mn(eg) bands, which is in contrast with the predicted dispersionless bands within the Anderson–Hasegawa double-exchange model with infinite Hund's-rule coupling. A downfolding technique within the newly developed muffin-tin orbital-based method is used to analyse the density-functional band structure obtained in the local spin density approximation. The finite Hund's coupling parameter in realistic situations allows the same-spin bands on the two manganese sublattices to mix producing a large dispersion. The calculated Wannier functions for the Mn(eg) bands also show large oxygen character at sites further away from nearest oxygen sites causing long-ranged Mn–Mn hopping processes.
3 citations