Theoretical studies of strongly correlated lanthanide intermetallics LnX3 (X=In, Sn)

Abstract

In this thesis the structural, elastic and electronic properties as well as electric field gradient of the strongly correlated intermetallics LnX3 (Ln = La-Gd, X = In, Sn) have been investigated by using the full potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method within the framework of density functional theory. The structural properties of these compounds are calculated by LDA, GGA, meta-GGA, WC, B3PW91, LDA+U and GGA+U schemes. The calculated lattice parameters are found consistent with the available experimental results. Our results show contrac- tion of lattice constant along the series and the divalent state of Eu is also verified. The itinerant and localized behavior of electrons in f -states of these compounds is also discussed. These compounds have 4f orbitals and hence strong electron-electron correlation effect is expected, therefore, the electronic properties are also calculated with the Hubbard potential U (GGA + U and LDA + U) and the effect of Hubbard potential on the density of states is discussed in details. The relativistic effects are also considered by including the spin-orbit coupling (SOC). The spin-orbit coupling predict the correct electronic properties and also reveals the splitting of 4f states of the rare-earth elements. It affects the band structures of the compounds and induces non-degeneracies in some degenerate states in the vicinity of the Fermi level. Furthermore, the SOC effect increases from left to right in the lanthanide series in the LnIn3 and LnSn3 , which shows interesting nature of SOC effect in the periodic table. The elastic constants of these compounds are also calculated. Our calcu- lated values for the elastic constants of the compounds are closer with the available experimental values as compared to the other theoretical results. The mechanical properties for the compounds under studies such as shear iii modulus, bulk modulus, Young’s modulus, Kleinman parameters, anisotropic ratio, Poisson’s ratio, Lame’s coefficients are also determined . The Cauchy pressure and B/G ratio are also investigated to evaluated the ductile and brittle nature of LnIn3 and LnSn3 compounds. The Sound velocities for shear and longitudinal waves, and Debye temperature also explored on the basis of mechanical properties. The Electric field gradients (EFG) are also calculated for the rare-earth intermetallics LnIn3 and LnSn3 (Ln = La, Ce, Pr and Nd) using the GGA, GGA + U, as well as GGA + SOC. Our results show that the EFGs calculated by GGA+U approach are in better agreement with the available experimental values of the M ̈ssbauer spectroscopy as compared to the other theoretical

schemes. Our results show nonzero EFGs at rare-earth sites in the AFM phase. The present research will add some theoretical understanding of these materials and will also fill the gap about some of the physical properties of these compounds in literature.