• T Saha-Dasgupta

      Articles written in Bulletin of Materials Science

    • Third-generation muffin–tin orbitals

      O K Andersen T Saha-Dasgupta S Ezhov

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      By the example of $sp^3$-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: $sp^3d^{10}, sp^3$, 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.

    • Tight-binding model for carbon from the third-generation LMTO method: A study of transferability

      D Nguyen-Manh T Saha-Dasgupta O K Andersen

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      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 boundary condition defined in terms of a set of ‘hard’ sphere radii $a_{RL}$. Energy eigenvalues obtained from the singleparticle Schrödinger equation for MT potential is energetically accurate and very useful for predicting a reliable first-principles tight-binding (TB) model of widely different systems. In this study, we investigate a possibility 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, 𝜀𝜈. 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, 𝛾2, $\cdots$, 𝛾6) within an orthogonal representation 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 hexagonal graphite.

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