Thermodynamic properties of neptunium nitride; A First principles study

Shibata, Hiroki ; Tsuru, Tomohito   ; Nishi, Tsuyoshi; Hirata, Masaru ; Kaji, Yoshiyuki  

The thermal and mechanical properties of neptunium nitride (NpN) were investigated by first principles calculations. From the Helmholtz free energy equilibrium lattice constants, thermal expansion coefficients, bulk moduli and specific heat capacities were calculated for temperatures up to 1500 K. The electronic specific heat capacity was also calculated from the electronic density of states (DOS) at the Fermi energy. The obtained specific heat capacity reproduced the experimental data well. It was thus clarified that the specific heat capacity of NpN consists of the lattice and electronic specific heat capacities and the contribution of the lattice dilatation to the specific heat capacity.