Ab initio density-functional calculations of the geometries, electronic structures, and magnetic moments of Ni-C clusters

We have performed ab initio molecular dynamics simulations of the clusters Ni₂, C₂, C₃, NiC_n (n = 1-6), and Ni₂C_n (n=4-6) using a fully self-consistent density-functional method that employs linear combinations of atomic orbitals as basis sets, standard norm-conserving pseudopotentials and the generalized gradient approximation to exchange and correlation. Our results for the pure clusters, which are compared with those obtained by other ab initio calculations, are in good agreement with available experimental data. Linear forms are energetically preferred for all the mixed clusters except NiC₂, NiC₆, and Ni₂C₆, which have cyclic structures. These latter findings differ markedly from results obtained recently using a tight-binding molecular dynamics method, which predict rhombic geometry for NiC₃ and three-dimensional structures for NiC₄, Ni₂C₄, NiC₅, and Ni₂C₆.