Hybrid density functional study on lattice vibration,thermodynamic properties,and chemical bonding of plutonium monocarbide

Hybrid density functional theory is employed to systematically investigate the structural,magnetic,vibrational,thermodynamic properties of plutonium monocarbide（Pu C and Pu C0.75）.For comparison,the results obtained by DFT,DFT ＋ U are also given.For Pu C and Pu C0.75,Fock-0.25 hybrid functional gives the best lattice constants and predicts the correct ground states of antiferromagnetic（AFM） structure.The calculated phonon spectra suggest that Pu C and Pu C0.75 are dynamically stable.Values of the Helmholtz free energy ？F,internal energy ？E,entropy S,and constant-volume specific heat Cv of Pu C and Pu C0.75 are given.The results are in good agreement with available experimental or theoretical data.As for the chemical bonding nature,the difference charge densities,the partial densities of states and the Bader charge analysis suggest that the Pu–C bonds of Pu C and Pu C0.75 have a mixture of covalent character and ionic character.The effect of carbon vacancy on the chemical bonding is also discussed in detail.We expect that our study can provide some useful reference for further experimental research on the phonon density of states,thermodynamic properties of the plutonium monocarbide.