• P Modak

Articles written in Bulletin of Materials Science

• Electronic structure and superconductivity of MgB2

Results of ab initio electronic structure calculations on the compound, MgB2, using the FPLAPW method employing GGA for the exchange–correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, 𝑐/𝑎 ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter by using our calculated, $D(E_F)$ and the experimental specific heat data. The $T_c$ is found to be 37 K. We use a parametrized description of the calculated band structure to obtain the 𝑇 = 0 K values of the London penetration depth and the superconducting coherence length. The penetration depth calculated by us is too small and the coherence length too large as compared to the experimentally determined values of these quantities. This indicates the limitations of a theory that relies only on electronic structure calculations in describing the superconducting state in this material and implies that impurity effects as well as mass renormalization effects need to be included.

• On the electronic structure and equation of state in high pressure studies of solids

We discuss the high pressure behaviour of zinc as an interesting example of controversy, and of extensive interplay between theory and experiment. We present its room temperature electronic structure calculations to study the temperature effect on the occurrence of its controversial axial ratio (𝑐/𝑎) anomaly under pressure, and the related electronic topological transition (ETT). We have employed a dense 63 × 63 × 29 k-point sampling of the Brillouin zone and find that the small (𝑐/𝑎) anomaly near 10 GPa pressure persists at room temperature. A weak signature of the anomaly can be seen in the pressure–volume curve, which gets enhanced in the universal equation of state, along with that of 𝐾-point ETTs. We attribute the change of slope in the universal equation of state near 10 GPa pressure, mainly to hybridization effects. The temperature effect in fact enhances the possibility of 𝐿-point ETT. We find that the 𝐿-point ETT is very sensitive to exchange correlation terms, and hence we suggest that further refinements in the theoretical techniques are needed to resolve the controversies on the ETT in Zn.

• Bulletin of Materials Science

Volume 43, 2020
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