  In this study, we employ the Wien2k code to conduct ab-initio study of a
novel potential all-d-metal Heusler alloy Co$_2$MnNb. The analysis utilizes the
comparison of local spin density approximations (LDA) with Perdew-Burke-Ernzerh
parameterized Generalized Gradient Approximation (PBE-GGA) for structural
optimization while modified Becke-Jones potential (mBJ) exchange-correlation
potentials to examine various characteristic properties of the alloy under
study. Employing Birch-Murnaghan equation of state, we construct the
energy-versus-volume curve, facilitating the determination of stable phases and
structural parameters of the investigated alloys. Structural optimization in
both non-magnetic (NM) and spin-polarized (FM) states reveals the stability of
the alloy in the FM state. The compound exhibits metallic behavior in bulk,
with notable anisotropic semiconducting behavior for down spin while pure
metallic behavior for up spin electrons. Partial density of states of each
element of the composition is also analysed to compare their respective
contribution towards the observed band structure. The anisotropic behavior of
Co$_2$MnNb for a specific spin state could be of importance in future
spintronic and other thin films device applications.
