Role of C in MgC_xNi_3 investigated from first principles

TL;DR

This study uses first-principles calculations to explore how vacancies in the carbon sub-lattice of MgCNi3 affect its structural, electronic, and magnetic properties, revealing changes in hybridization and electronic states.

Contribution

It provides a detailed first-principles analysis of vacancy effects on MgCNi3, including electronic structure and magnetic properties, using advanced computational methods.

Findings

Vacancies break C-Ni bonds, altering Ni 3d states and increasing itinerant character.

Charge redistribution is non-uniform across the Brillouin zone, with new states at the Gamma point.

Electronic structure changes suggest modified magnetic and conductive behavior.

Abstract

The influence of vacancies in the $C$ sub-lattice of $MgCNi_{3}$, on its structural, electronic and magnetic properties are studied by means of the density-functional based Korringa-Kohn-Rostoker Green's function method formulated in the atomic sphere approximation. Disorder is taken into account by means of coherent-potential approximation. Characterizations representing the change in the lattice properties include the variation in the equilibrium lattice constants, bulk modulus and pressure derivative of the bulk modulus, and that of electronic structure include the changes in the, total, partial and $\mathbf{k}$-resolved density of states. The incipient magnetic properties are studied by means of fixed-spin moment method of alloy theory, together in conjunction with the phenomenological Ginzburg-Landau equation for magnetic phase transition. The first-principles calculations reveal that due to the breaking of the $C$-$Ni$ bonds, some of the $Ni$ 3d states, which were lowered in energy due to strong hybridization, are transfered back to higher energies thereby increasing the itinerant character in the material. The Bloch spectral densities evaluated at the high symmetry points however reveal that the charge redistribution is not uniform over the cubic Brillouin zone, as new states are seen to be created at the $\Gamma$ point, while a shift in the states on the energy scale are seen at other high symmetry points.