First-Principles Study On The Structural,Electronic,and Thermodynamic Properties Of Curium Dioxide

Due to energy shortage,the development of nuclear energy has important meaning for alleviating energy shortage and protecting the environment.Actinides and their compounds have attracted the attention of people in the application of nuclear energy and curium dioxide?CmO₂?plays an important role in the nuclear fuel cycle.The first-principles method,based on the density functional theory,is one of the most popular methods for studying material properties.In this paper,the ground-state properties of CmO₂ are studied by the first-principles method.The main work is as follows:We present a systematic investigation of the ground-state structural,electronic,mechanical,and thermodynamic properties of CmO₂ with the local density approximation?LDA?+U and the generalized gradient approximation?GGA?+U approaches.Firstly,with considering the different values of the Coulomb repulsion parameter U,we find that the FM state is more energetically stable than the AFM state.Secondly,The ferromagnetic configuration with half-metallic character is predicted to be energetically stable while a charge-transfer semiconductor is predicted for the antiferromagnetic configuration.Thirdly,the elastic constants and phonon spectra show that CmO₂ mechanically and dynamically stable.Based on the first-principles phonon density of states,thermal expansion coefficient,specific heat and entropy are calculated by using the quasiharmonic approximation and compared with experimental data.The mode Grüneisen parameters are presented to analyze the anharmonic properties,we can obtain that the anharmonic effect of CmO₂ is comparable with UO₂ but is weaker than that of PuO₂.We deduce the phonon group velocities?_j of FM and AFM states by utilizing the phonon spectra data?_j?q?.The Slack relation is applied to obtain the lattice thermal conductivity in temperature range of 300–1600 K.The spin-orbit coupling?SOC?effects on the lattice structures,electronic density of states and band gaps are also carefully studied,and compared with other AO₂?A=U,Np,Pu,and Am?.After including the SOC effects,the lattice parameter has little changes.Within LDA+U method,the AFM state of CmO₂ is predicted to be a metal,while within LDA+U+SOC method,it turns to a charge-transfer semiconductor with a band gap of 113 meV.For the band gap of AFM state of AO₂,the LDA+U+SOC method has a better prediction than the LDA+U method when compared with the corresponding experimental results,but the trend agree.